"Pacific Seeds Grain Sorghum agronomy Guide 200809"
Pacific Seeds Grain Sorghum agronomy Guide 2008/09 CONTENTS Grain sorghum in Australia.............................................................................2 Growth stages of grain sorghum ...................................................................2 Irrigated grain sorghum ................................................................................ 13 Pacific Seeds Yearbook 2008/2009 - Grain Sorghum 1 GraiN SOrGhuM ThE GrOWTh iN auSTraLia STaGES OF Grain sorghum is Australia’s most important summer grain crop both in terms of area sown and quantity GraiN SOrGhuM of grain produced. Australia’s grain sorghum There have been nine growth stages identified in the industry has seen spectacular growth over the past development of grain sorghum. For simplicity and the 40-50 years with the area utilised increasing from purposes of this Grain Sorghum Agronomy Guide, we less than 2000 hectares just after World War II to will condense the growth and development of three peak at around 800-900,000 hectares in the early major growth stages. to mid eighties. The area sown to grain sorghum This guide will look at the development that occurs in has now consolidated to around 600-700,000ha the sorghum plant at each growth stage. Agronomic despite droughts, with around two thirds produced and management guide lines are outlined for each in Queensland and one third in New South Wales. of the three growth stages to assist with enhancing The Northern Territory and Western Australia also sorghum crop production. produce small areas of grain sorghum. Each of the three growth stages is shown below. The aim of the Grain Sorghum Agronomy Guide is to provide growers, agents, advisers and other interested parties with information on maximising returns from the grain sorghum crop. In order to grow optimum yielding crops many things have to be considered and this is best explained by relating the crop growth stage to enhanced management of the plant. The term “physiology of yield” refers to all the physical and biochemical processes that occur in or to the plant that have an effect on the final yield. These factors range from soil moisture, temperature and nutrition to the effect of weeds, insects and disease at each growth stage of the grain sorghum crop. In the Grain Sorghum Agronomy Guide we will look at the each of the three major growth stages and once understood we can use our best management, cultural Bud initiation in grain sorghum and agronomic practices to optimise a grain sorghum (The bud or head is initiated at the point of the knife) crop return. MajOr GrOWTh STaGES OF GraiN SOrGhuM G1. G2. G3. VEGETaTiVE FLOraL GraiN FiLLiNG Emergence to bud initiation To commencement of flowering To physiological maturity Range days Range days Range days 28 Average 38 45 25 Average 31 39 21 Average 26 32 2 Pacific Seeds Yearbook 2008/2009 - Grain Sorghum GrOWTh STaGE ONE This is the period from germination to floral or bud initiation which occurs around the six leaf stage in grain sorghum. This period has the greatest impact on yield as head size is directly proportional to the length of this period and the area of leaf developed during this time. Since the maximum yield potential is set at the time of floral initiation, it is important that the plant have optimal growing conditions at this stage. This is the foundation upon which the final yield of the crop will be based and requires good early crop husbandry, in particular a good seed bed and good planting techniques are a priority for maximising yields. a) Seed bed preparation For furrow irrigation, well prepared hills and beds are essential to a successful crop. Poor bed preparation can result in: 4 poor seed depth taken at planting depth and should be taken over a 4 poor seed distribution number of days prior to planting to ensure that soil 4 seeds planted on sides of hills temperature is rising. Low soil temperature slows 4 poor root development the germination process. At 17°C seedlings will take 4 inability to run water efficiently seven days to emerge. However, at 15°C seedling 4 problems with cultivating and side dressing. emergence time will extend out to 12 days. The longer it takes a seedling to emerge, the greater the b) Optimum temperature for risk of that seedling being attacked by soil borne sorghum establishment insects or diseases. The key to reliable sorghum crop establishment is Soil borne diseases adequate seedbed or soil temperature along with Death of seedlings post and pre-germination sufficient but not excessive soil moisture. associated with cool soil temperature is generally Planting times vary depending on the location. In caused by either soil borne fungi or soil dwelling Central Queensland sorghum can be sown as early as insects. Generally speaking, seeds will germinate at late August and can finish in late February in northern temperatures as low as 10°C, however growth is very areas of the Central Highlands. In Northern New slow and the stress imposed on the seedlings leave South Wales and the Darling Downs planting has them weak and vulnerable to attack. traditionally commenced from late September/early October and the last crops are generally planted by A number of normally harmless fungi in the soil can early to mid January. attached sorghum, the most common are With this range of planting times and areas comes a 4 Pythium wide variation in soil temperature. The optimum soil 4 Fusarium temperature range for seedling establishment is 21 to 4 Rhizoctonia. 33°C. Soil temperatures outside this range can result in slower seedling establishment or in extreme cases, Identification of seedling disease can be difficult as pre inhibiting germination completely. and post germination disease symptoms are similar. Effects on seedling establishment by lower Symptoms include gappy stands, rotten seed, brown than optimum temperatures to red discolouration of the primary and secondary roots, damping off of the seedling, chlorosis of the When planting rain occurs in early spring, a final cold leaf and stunting. Seedling growth and biomass can snap for the year often follows. This could seriously be severely affected. affect the germination and establishment rates of the grain sorghum seedlings planted at this time. The Pythium can be identified by gently pulling on recommended minimum soil temperature for the affected roots, if the outer layer easily comes adequate germination and establishment is free, leaving the white inner core it is most likely 17°C taken at 8am. This temperature should be Pythium spp. Pacific Seeds Yearbook 2008/2009 - Grain Sorghum 3 Factors and conditions that favour seedling/seed Points to note are: diseases: 4 Three to four days prior to planting, take soil 4 pH < 6 temperature readings at 8am at planting depth. 4 temperatures < 21°C 4 Ensure that soil temperature is at least 4 waterlogged conditions/poor drainage 16°C and rising. 4 soil compaction 4 Sowing with discs in wet soil can cause soil smearing and reduce emergence of secondary 4 soil crusting/low aeration root development. 4 poor placement of fertilisers and herbicides 4 Ensure that adequate soil moisture is available. 4 poor seed quality/damage 4 Slower emergence will result and higher seedling 4 deep planting, poor seed distribution mortality at soil temperatures below the optimum. 4 poor weed control. 4 If rain falls after planting and before emergence, the temperature generally drops and the incidence 15 days after sowing 100 of soil borne diseases will be much greater. Cool Soil Tolerant Warm Soil Responsive 90 4 Planting is best delayed until adequate seedbed 80 10 to 12 degrees temperature has been achieved. Generally, early 12 to 14 degrees 70 14 to 16 degrees plantings mature at the same time as planting 60 two to three weeks later when the seedbed has 50 warmed up. 40 Seedling establishment effects from higher 30 than optimum temperatures 20 10 While a lot of work has been done on the effects of 0 lower soil temperature on seedling establishment, poor emergence due to high soil temperature can MR-STRIKER MR-BUSTER MR-MAXI PAC 2423 BONUS MR Pacific MR43 be a serious problem in some areas. In the middle of summer in areas such as Central Queensland, the Western Darling Downs and North West New Factors for managing diseases: South Wales soil temperatures of well over 40°C are regularly experienced. 4 plant good quality seed 4 plant treated seed Points to note are: 4 plant into warm soil 4 Soil temperature above 40°C can reduce seedling establishment and over 45°C expect a significant 4 avoid practices that impose stress upon seedlings reduction. e.g. excessive fertiliser with the seed. 4 When planting during hot conditions, soil moisture 4 accurate seedling – depth and distribution can disappear rapidly – faster than the secondary 4 maintain good soil structure roots can grow. 4 good weed control. 4 Zero or minimal till where there is a good cover The table below highlights the effect of soil of stubble can help in maintaining soil moisture temperature on seedling emergence. and keeping the soil cooler. Expected time Temperature Effect on seed Effect on seedling emergence to emergence 12°C Slow germination providing Poor emergence coupled with 14 days > time for soil borne pests increased incidence of soil diseases and disease to attack (Pythium, Fusarium etc.) 15°C Satisfactory germination 50% emergence to be expected. 7 - 12 days Similar disease expectations as at 12°C 16°C Good germination Adequate for good emergence 18°C Good germination Good, quick emergence 5 - 7 days 20°C Ideal Ideal 4 Pacific Seeds Yearbook 2008/2009 - Grain Sorghum 4 If applying fertiliser with the seed, ensure the safe recommended rate is not exceeded and if conditions are particularly hot, consider reducing the fertiliser rate or applying away from the seed. 4 Be careful in very hot conditions if planting deep to find the soil moisture. 4 Ensure adequate soil moisture prior to planting. c) Plant nutrition High yielding crops of sorghum require adequate nutrition and should any nutrient be found lacking, appropriate fertilisers need to be applied. Rates of fertiliser will vary depending on locality, soil type, previous crop and fertiliser history. Generally, the main nutrients that will be required are nitrogen and phosphorus. Sulphur, potassium and zinc may also be deficient in some areas. Soil moisture profile and N may influence N timing decisions. The timing of the fertiliser application is most important. The application of fertilisers, particularly nitrogen, before floral initiation begins (GS1) d) Seed characteristics will increase yield potential whereas fertilisers The other major factor in optimum plant establishment applied after this period (around 30 - 35 days after is the seed itself. In ideal conditions most seed will emergence) will help to maintain yield potential. Thus germinate and establish adequately. However in the bulk of nitrogen should be applied prior to, or marginal conditions the quality and germination of the at sowing. Side dressing, if a split application is used, seed will affect seedling vigour and establishment. should occur no later than 30 days after sowing. Seed with a germination of over 90% is the optimum Phosphorus is best applied as a band at sowing. and it will have the best possibility of establishing in Drilling fertiliser with the seed is more efficient than marginal conditions. Seed between 80-90% can still be broadcasting however check that you don’t exceed good seed depending on its vigour and density. Even the recommended rates of products such as seed as low as 70% (minimum germination) can still be MAP and DAP by referring to the table below. good seed if the vigour is high. However planting rates should be increased and plant establishment could be In general, it is advisable to place nitrogen fertiliser less even in these lower germination lines. away from the seed. It is best to pre-apply or use alternate non seeding runs during sowing for Seed density has been found to affect germination nitrogen fertiliser application. The table below gives percentage. Trials have shown that with sorghum, an indication of the tolerance of sorghum to different seed of a higher density will have a higher percentage forms of nitrogen and phosphorus mixtures applied and rate of germination and in general produce more with the seed. vigorous seedlings. However, if a precision planter with fertiliser box To ensure that seed is of the highest density (and so attachments is used, the fertiliser can be placed to enhance the vigour) the final processing step at Pacific the side and below the seed without endangering the Seeds’ grading plant is over the gravity table. Any germinating seedling. light seed which is low in specific gravity separates to SuGGESTEd MaXiMuM FErTiLiSEr raTES WiTh ThE SEEd row spacing KG Product kg/ha Cm ins N/ha urea CK700 daP MaP 18 7 25.0 54 75 130 200 36 14 12.5 27 37 65 100 53 21 8.3 18 25 43 66 71 28 6.3 13 18 32 50 90 35 5.0 11 15 26 40 Source: Incitec/Pivot Fertiliser Guide Pacific Seeds Yearbook 2008/2009 - Grain Sorghum 5 the bottom of the table where it is discarded as offals. Grain Sorghum head number per metre Regardless of seed size, only seed of high specific of row under different plant populations 18 gravity finds its way into Pacific Seeds’ bags. 40 000 60 000 120 000 16 Head Number per Meter 14 e) Plant populations 12 In Australia dryland plant populations range 10 from 30-90,000 plants/ha. Populations above 8 100,000 plants/ha even in the most favourable 6 environments in Australia are rare. Normal 4 2 recommendations fall into the range as follows: 0 Pac 2423 MR-Striker Pac 2437 MR-Buster Pac 2434 Pacific MR43 MR-Maxi Pac 2436 Pac 2418 Pac 2435 Lower rainfall 30-60,000 plants/ha Higher rainfall 55-70,000 plants/ha + limited irrigation Irrigation 70-150,000 plants/ha Tillers per Plant Spring Plant Gatton Farm 2007 6.00 For irrigated crops 100-150,000 plants/ha is Plant spacing 50cm the most common. Refer to the Irrigated Grain 5.00 Sorghum Agronomy Notes for more information 4.00 on growing irrigated sorghum. Tillers 3.00 Because plant populations vary so much from district 2.00 to district, and also between varieties, Pacific Seeds has developed an optimum plant population for each 1.00 area and for each variety. 0.00 Pac 2437 MR-Buster Pac 2423 MR-Striker Pacific MR43 MR-Maxi Pacific MR32 Pac 2418 Pac 2436 Pac 2434 Pac 2435 Tillering in Sorghum The tillering habit of grain sorghum has been a valuable contributor to the final yield of most At this stage, lower tillering hybrids don’t put on crops. Tillering allows for significant compensation, some of the excess tillers that high ability varieties particularly where poor plant establishment occurs, do. However, these rarely contribute anyway. and/or the growing season is better than expected. Population trials on the Liverpool Plains All commercially available sorghum varieties have the demonstrated that populations as low as ability to tiller. Tiller number is generally dictated by 25,000 plants/ha can yield greater than 2.5 t/ha. four major factors: HERBICIDE APPLICATION - GRAIN SORGHUM Vegetative phase Grain filling phase Stage 0 1 2 3 4 5 6 7 8 9 Emergence 3 leaves 5 leaves Head Flag leaf Boot Flowering Soft Hard Physiological fully fully initiation visible dough dough maturity emerged emerged Planting Height (cm) 0 10 20 35 110 120 Days -10 -3 0 9 12 24 35 45 50 55 65 75 90 100 application Post-sowing pre-emergent Pre-plant application Post-emergent application Avoid Avoid Desiccation, spraying spraying harvest aid Potentially damaging stage for post emergent herbicides Source: NSW DPI Grain Sorgum Ag Facts 6 Pacific Seeds Yearbook 2008/2009 - Grain Sorghum 4 genetics beneficial to yield; however yields of over 10t/ha are 4 good supply of carbon regularly achieved with one metre rows. 4 Pacific Seeds have developed specific protocols to Wider row spacing or skip-row configuration has test tillering ability so growers and consultants can become popular in areas where moisture may be make good planting decisions a limiting factor. This also helps to reduce the risk 4 night time temperatures <18°C during the of crop failure due to inefficient use of available soil 4-6 week stage. moisture. As a rule of thumb, skip row or wide row Inter-plant spacing also influences tiller production by configuration can be advantageous where yields are increasing competition for carbon, but under common lower than 3 t/ha. Single skip can be with row spacing row spacings, plant population needs to be too high from 75cm to 1m and involves planting two rows and to affect any real reduction. missing the next. Double skip has two rows planted and then two rows missed. Wide row is commonly Early plantings at low plant populations will encourage used when planting single rows 1.5 to 2.0 m apart. tillering, whilst later plantings will tend to tiller less. Although later plantings tiller less, good conditions It is important when planting in these configurations can still produce high vegetative production. This that the desired plant population remains the same. generally manifests itself as extra leaves, extra leaf In other words, the seeds that would have been sown area and taller plants. in the skipped rows are evenly distributed into the planted rows. There has been a call to the seed industry to produce non to low tillering hybrids, mainly in response to Over the last five years, Pacific Seeds has done poor seasons, and the need to expand the industry numerous trials on row configuration and plant to meet growing demand. At this stage, lower populations. Through these trials, two Pacific Seeds tillering hybrids don’t put on some of the excess hybrids have proved to suit skip row farming. These tillers that high ability varieties do. However, these are MR-Maxi and Pacific MR43. rarely contribute anyway. Low tillering sorghums need to be combined with much smaller plants, which g) Weed control doesn’t occur as of yet and will only be suited to Weeds can be a major problem in this growth stage environments which produce less than 2.5t/ha. as they compete with the developing seedling for f) Row Spacing/Row Configuration moisture nutrients and space. Spraying herbicides Sorghum has been grown with row spacing to control weeds before planting is one option and varying from 15cm to 2m and various configurations growers practicing zero or minimal till operations of row arrangement. With higher yielding areas and often use this method. irrigation, narrower row spacing has proved to be At planting, it is common to use a pre-emergent Solid vs Single Skip herbicide. Atrazine is the major herbicide used Side by Side comparison - All years for the control of most annual grasses and 9000 8000 broad-leafed weeds and can also be used as a Average yield difference kg/ha 7000 382 kg/ha. post-emergent herbicide but is not effective on 6000 grass weeds. 5000 kg/ha 4000 h) Soil borne insects 3000 2000 Soil dwelling insects have always been a major pest 1000 of crops and pastures, seedling losses of over 70% Solid Single Skip 0 have been attributed to soil insects. In recent times, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Trials changes in crop management, primarily stubble retention and zero till have encouraged the build up Yield comparision: Grain Sorghum, of certain soil insects, in particular, false wireworm, Single Skip vs 150cm Solid. 2005-2008 which is very common in all areas and is one of the 8000 Average difference 50 kg/ha most damaging soil insects. 7000 increase in yield for 6000 150 cm row spacing The push to plant early to avoid heat at flowering yield kg/ha 5000 has increased the vulnerability of sorghum seedlings 4000 to insect attack. Cooler soil temperatures slow the 3000 2000 rate of emergence and growth of secondary roots, 1000 giving soil insects more time to damage seeds and Single Skip Solid 150cm 0 seedlings. Early planting dates coincide with peak 1 2 3 4 5 6 7 8 9 10 11 12 13 Trials larvae development of the false wire worm. Pacific Seeds Yearbook 2008/2009 - Grain Sorghum 7 Management of soil insects in stubble retention/zero till management systems are limited; however options Sorghum heads suffering heat stress include: 4 Plant only treated seed, as in-furrow sprays are seedling root supports the sorghum plant for 5-6 ineffective, and surface applied sprays will not weeks, poor secondary root development can lead to affect false wire worm. plant death and reduced yields. Inter-row cultivation 4 If possible avoid summer crop stubble on the early in conventionally tilled fields can aid in development plant, as numbers will likely be higher on crop of secondary and stabilising roots. However, should stubble such as sorghum, maize and mungbean. the secondary roots be well established, the effect of a heatwave at this stage will be withered leaves and 4 Use high quality seed and accurate seeding depth. a burnt appearance but the plants should recover 4 Plant into warm soils (greater than 17°C) following a return to more favourable conditions. 4 Use press wheels, good seed/soil contact hides the If moisture stress is combined with heat stress seed. at this stage, the number of grains per head is reduced Although these strategies greatly improve the which can have a severe effect on grain yield. establishment of sorghum, significant loss can still occur if insect pressure is high. GrOWTh STaGE TWO In cases where replants are required due to false This is the period from floral or bud initiation to wire worm, planting after Spring, from mid-October flowering when the plant stops making leaves and onwards can be successful as wireworm larvae switches over to making the head. At the beginning generally have pupated by then. of this stage not all the leaves are visible. i) The effect of heat and moisture stress a) Pre-flowering heat and moisture stress on growth stage one Stress during this stage can result in floral abortion. The stress factors could include low soil fertility, The effects of heat and moisture stress or heatwave moisture stress and heat stress. Stress at this stage conditions can have a number of effects on a grain can seriously affect grain sorghum crops and can sorghum crop. often be seen in hot dry seasons. Should heat and/ Heatwave conditions at growth stage one (the or moisture stress occur at this stage, yield can be vegetative stage) probably have least impact, provided severely affected. If the heads are in the boot stage sub-soil moisture is sufficient and follow-up rain the stress can physically damage the head to a level occurs. If secondary root development has not fully that they will not set seed. The crop may still be taken place, the plant will have difficulty coping and green but brown empty heads emerge from the boot secondary root development will not proceed. Initial with variable to nil seed set. 8 Pacific Seeds Yearbook 2008/2009 - Grain Sorghum The symptoms of pre-flowering moisture During G.S. 3 the top four leaves and the head itself stress include: contribute 93% of the photosynthesis for the final 4 leaf rolling and exaggerated leaf erectness yield, although these leaves make up only 60% of the total leaf area at this time. Because of this fact 4 bleaching and burning of the leaf tips and margins anything that affects the leaf area must be important. 4 delayed flowering The leaf eating insects are again a problem during this 4 poor head exertion stage and these have been dealt with earlier in the 4 head blasting and floral abortion. agronomy notes. b) Insect control a) Post flowering heat and moisture stress The main insects affecting sorghum in this growth The effects can be equally as damaging to yield stage are the leaf eaters and sucking pests. These as pre-flowering heatwave conditions but in a include Helicoverpa spp., grasshoppers, cutworms different form. The physical effect on the plant and also aphids. can be to induce such severe moisture stress that the sorghum plant shuts down, the Control of these insects is not economical unless in supporting structure of the stem reduces and very high numbers. The economics of controlling the the plants can lodge. population should be carefully considered before any attempt is made. There are no stem boring insects in Symptoms of post-flowering moisture stress include: Australia which are of economic significance. 4 premature leaf and stem death or plant senescence c) Plant disease 4 stalk collapse and lodging There are a number of diseases which affect the 4 stalk rot sorghum plant during this growth stage. Root rots and stalk rots are the most important. The 4 sometimes a significant reduction in seed size. development of root rot is usually due to poor b) Leaf diseases aeration, waterlogging and hard pans, and can occur in soils where high yielding crops are grown. This leads Leaf diseases which will affect photosynthesis to a shallow root system and extensive root decay. can cause major yield losses. Such diseases include Stalk rot hastens the death of the plant, weakens the leaf rust, leaf blights, bacterial stripes and spots and stalk and may cause the plant to lodge. Control of sugarcane mosaic - Johnson Grass strain. It must stalk and root rots is through good agronomy and be remembered that to be significant the disease management. Balanced soil fertility is also important, symptoms must be fairly well established on the top high levels of nitrogen, and low levels of potassium four leaves. Leaf diseases which affect the lower should be avoided. leaves late in the season are not very significant. GrOWTh STaGE ThrEE Most hybrids have very good tolerance to the major leaf diseases and only rarely do these diseases Growth stage two finishes after the head has become a problem and affect yield. Prolonged damp emerged from the boot and the first yellow pollen and humid weather can occasionally cause major leaf sacks (anthers) are exerted. Growth stage three disease issues. in grain sorghum is the final stage of growth and is completed when the seed has reached physiological c) Sorghum midge maturity (black layer). This stage is of great The major insect pest of grain importance as it influences the grain weight and the sorghum is the sorghum midge longer the period in this stage, the higher the grain which is a small, fragile orange weight. Lack of nutrients, heat and moisture stress fly about the size of a small or loss of leaf area will result in low grain filling and mosquito. therefore low grain weight. A midge damaged head has the appearance that it has The total leaf area present before floral initiation failed to set seed. The female midge lays her eggs in will determine the size of the head developed. The the developing florets and when the eggs hatch, the function of these early leaves is to feed the head up larvae feed on the developing seed. until the time of flowering. The midge life cycle and how midge resistant In the sorghum plant, photosynthesis occurring varieties impact on it during G.S. 1 and G.S. 2 contributes only 12% of The Midge Tested Rating (MTR) is a management the final yield. Most of the grain growth comes tool. The rating puts the relative resistance of from photosynthesis that occurs in G.S. 3 (88%). sorghum hybrids to midge into perspective. Pacific Seeds Yearbook 2008/2009 - Grain Sorghum 9 d) Other sorghum head insect control MIDGE LIFE CYCLE The Helicoverpa and the Sorghum Head Caterpillar EGG can be a problem from time to time when feeding on the sorghum head in sufficient numbers. 2 helicoverpa spp. DA R OU YS 1H The adult moths are nocturnal, resting during the day on the undersides of the leaves. The female generally LARVA starts to lay eggs two or three days after emergence from the pupal case in the soil. The eggs hatch after three to five days. The sorghum head caterpillar This pest is present in most parts of Southern and ADULT Central Queensland sorghum growing areas. It attacks only the sorghum head and starts at the flowering 4D YS DA stage but it is usually two to three weeks before AY S 10 severe damage occurs. 1-5 S The young larvae just feed on the pollen sacks PUPA R YEA and as they grow, attack the developing grain. RESTING They web clusters of seed together and the whole STAGE head can become covered and matted with webbing in which there are small particles of excreta. The most A product with an MTR of 6, for example, has six severe damage occurs during the milky soft dough times more resistance than a susceptible variety. The stage as the larvae damage the developing grains by resistance level is directly related to the amount of feeding on them, eroding the surface or by chewing grain lost per day per egg laying midge. away whole portions of them. The MTR is a powerful management tool to help Control of helicoverpa and sorghum decide which variety to plant. At flowering, if head caterpillar sorghum midge are present, the decision whether Populations of these pests can be controlled or not to spray will be clearer. Farmers should realise there are different levels of midge resistance to some extent by natural mortality agents. The in sorghum and scouting for midge is still required most useful of these is the cannibalistic behaviour of as the numbers will influence the decision on the larvae and the presence of naturally occurring control measures. viruses and predators. Control of Helicoverpa and all other pests is through an integrated crop management New thresholds for heliothis program and this should be discussed with the 2.4 grams/grub/day increased from 1.5 grams/grub/day chemical supplier, agronomist or crop advisor. – an estimated damage increase of 60%. rutherglen Bugs Recent QDPI&F research has discovered that the damage caused by a single heliothis larvae is 60% In recent years, there have been reports from many greater than once thought. Higher damage levels grain sorghum growing areas of large numbers of combined with high grain prices have significantly Rutherglen Bugs infesting sorghum heads. Yield lowered spray thresholds. Nucleopolyhedrovirus loss, higher screening percentage and lighter grain or NPV is the product of choice for controlling problems have been occurring due to high heliothis, but timing is everything. We strongly populations of these bugs. They will commonly advise growers to seek professional insect occur on crops following hot dry weather and feed checking services. by sucking sap from the leaves, stem and head. A midge and sorghum loss calculator is available Research is continuing on threshold numbers but online at download at http://www.pacificseeds. com. control is warranted if the population is over 50 to au/tools/AgronomyTopicsV2.htm. 100 bugs per head. The introduction of midge resistance into sorghum Nymphs and adults both feed on the crop so and the use of the MTR formula has been a significant scouting and detecting mature bugs and controlling advance in the sorghum industry. Growers, industry early is recommended to reduce the risk of rapid and environment all benefit. population increase. 10 Pacific Seeds Yearbook 2008/2009 - Grain Sorghum e) Lodging in grain sorghum Under tough conditions where grain sorghum plants often experience stress in one form or another, lodging can result to varying levels. There are a number of different categories of lodging in grain sorghum and one or more of these can occur at any stage of the plant’s growth stage. Lodging can result when the sorghum plant undergoes severe stress from: 4 moisture stress soon after flowering 4 heat 4 disease 4 agricultural chemicals. If lodging in grain sorghum is a possibility, early harvest is necessary to maximise yield but with the penalty that harvesting is often slower and there is the added expense of drying the grain. Pre- harvest spraying with herbicides such as glyphosate has proven to be highly beneficial and should be considered as an essential management tool for growing successful grain sorghum crops. Crops infected with charcoal rot should not be sprayed out as this may increase the rate of lodging. Ergot in sorghum f) Managing heat and moisture stress To minimise the risk of ergot infection, the Queensland Department of Primary Industries and The effect of heat and moisture stress on the grain Fisheries (QDPI&F) has developed a strategy that sorghum plant can be managed and minimised with aims to avoid sorghum flowering at times when there adequate agronomic practices although you can’t plan could be a reasonable chance of cool, wet or humid for unexpected heat wave conditions. conditions. In Southern Queensland and Northern To help guard against the damage caused by moisture New South Wales, the QDPI&F crop and weather and heat stress the best method is to try and avoid models show sorghum crops flowering between it. Optimising soil moisture levels can do this, as can January and mid March are at low risk from ergot, planting at times so that flowering is less likely to unless there is unseasonably cool weather. In Central occur when heatwaves are expected. Varieties, which Queensland crops flowering before mid April are at a have the “staygreen” character, can also help. lower risk. Soil moisture levels can be optimised in a If a stressed crop receives late rain and a late crop of tillers emerge, growers should consider spraying out number of ways: with herbicides such as glyphosate. This should be 4 start with a full profile adopted particularly when the tillers are very late and 4 avoid excessive plant populations the weather has turned cool and showery. 4 control weeds which contribute to moisture From QDPI&F information, Pacific Seeds has stress and compete for nutrients developed a chart indicating the optimum time to 4 zero till or conserving stubble cover can assist in plant each hybrid. Growers are urged to obtain the maintaining sub-soil moisture. QDPI&F information leaflet on sorghum ergot for further information. g) Ergot in grain sorghum Sorghum ergot was first reported in Queensland at h) Pre-harvest spraying/desiccation Gatton in April 1996. Some years have seen some Spraying out a sorghum crop as a harvest aid has high levels of infection in localised areas particularly in become common practice in most areas. Glyphosate later planted crops that have been flowering through is the most common herbicide used and the benefits wet, humid weather. Rain and high humidity at are: quicker crop dry down, earlier harvest, knocks flowering accompanied by temperatures of out immature tillers and heads, stops the crop 20–24oC are ideal conditions for ergot infection. growing and taking away more moisture from the soil. 12 Pacific Seeds Yearbook 2008/2009 - Grain Sorghum irriGaTEd GraiN SOrGhuM Irrigated grain sorghum is produced under two main systems – flood irrigation or overhead sprinkler system. Flood irrigation can be in essentially two systems – furrow or bays where the water is administered by syphons, gated pipe or various types of check valve systems. Overhead sprinklers / irrigators range from the large centre pivot and lateral move irrigators to hand shift pipes and travelling irrigators. All have their advantages and disadvantages and certain soil types are more suitable to one system over another. However, when looking at setting Crops should not be sprayed too early as pinched up an irrigation system such things as topography, grain can result and crops should be relatively green soil types, water supply, water infiltration rate, and have at least 30 to 50% green leaf for effective evaporation rate, potential crop types and of course uptake of the herbicide. cost all have to be examined. A rule of thumb for spray out timing is when at least When using furrow irrigation, the duration of 80 to 90% of the heads in the field have reached black each watering or the time of inundation can have a major impact on yield. If watering time is prolonged layer (physiological maturity). At this stage, the grain and water logged conditions result for more than 24 moisture will be between 25 and 30%. hours at each irrigation, yield losses of up to 50% have i) Grain maturity, harvesting been recorded compared to non water logged areas. Rule of thumb is 0.2t/ha/day lost. Once the grain is mature (see picture below), harvesting must be Be careful using time as a measure of an irrigation’s done and several situations should efficacy, as soil type, length of the field, the slope, the be taken into account. Correct flow rate and the deficit of each field is different. header drum settings and speeds When the soil becomes water logged following long must be used to ensure there is no periods of flood irrigation, nitrogen uptake by the damage to the grain. The moisture content of grain to plant is reduced and nitrogen is lost from the soil be stored is also critical with 13% being the maximum through leaching and denitrification. To minimise allowed for acceptance at receival depots. The grain yield losses when flood irrigating, the crop should be may be at a higher moisture content when harvested irrigated quickly and evenly and then drained rapidly but must be dried in a grain drier before being stored. to reduce the duration and severity of the water logged (anaerobic) soil condition. Once in storage, weevils and other stored grain insects must be controlled. These insects are Field layout and irrigation management are main regarded as some of the most serious pests of grain. causes of water logging of irrigated crops. Most of Their feeding not only results in direct damage to the irrigation in Australia occurs on medium to heavy the grain but also allows secondary pests to invade clay soils with slopes less than 2%. Generally these the storage areas and do further damage. Grain soils have a very good water holding capacity, but storage insects can enter the silo from a preliminary have slow infiltration rates and slow drainage rates. infestation starting in the sorghum paddock, or they These soil types water log easily under the wrong may already be present from left over grain from type of management. Generally clay soils with slopes previous crops. of less than one percent should not exceed furrow lengths greater than 500m. Hygiene is a basic requirement and growers should ensure that left over grain is not exposed and However, through good bed/row preparation, head should be treated with an appropriate chemical. ditch layout, and the use of lower soil water deficits, This means that all grain handling equipment, flat paddocks can be managed effectively. headers, augers, trucks, silos, etc should be hosed Furrow irrigation efficiency is maximised where fields down at the end of the harvest and sprayed with an are professionally levelled. Single slope fields perform appropriate insecticide. best, but this not always possible. Pacific Seeds Yearbook 2008/2009 - Grain Sorghum 13 Planting times With flood irrigation in furrows, the situation is slightly different. In trials conducted at Emerald Typical optimum early sowing times in cotton growing comparing single rows one metre apart at 120,000 districts are late September, early October. Soil plants per hectare and twin rows 40cm apart on one temperatures at this time are normally rising (taken metre beds, the single rows yielded 7.0 t/ha while the at 8am at planting depth) and temperatures of 16 twin rows yielded 9.2 t/ha. to 18°C are ideal for spring plantings. In Central Queensland, sorghum has been planted successfully Narrow rows at populations of 80,000-150,000 in August, provided soil temperature levels are allow for higher rates of tillering, which allows for adequate. compensation and yield increase if seasonal conditions are better than expected. In situations where stress Planting as early as agronomically possible will provide pre-flowering reduces viable tiller numbers, higher a number of benefits: populations will yield more if water supply is adequate 4 increased water use efficiency, by avoiding yield through flowering and grain fill. loss from heat If the flood irrigation system allows and the soil type 4 maximise tillering and leaf production is suitable, two metre beds with four to six rows 4 lessen the risk of yield loss from sorghum midge on the bed have proved very successful with plant populations up to 150,000/ha. 4 reduce the influence of heat at flowering Higher populations yield more if stress occurs 4 higher yields compared to later plant. post flowering. Recent trial work demonstrates a Late plantings in summer should be timed to very flat response curve under full irrigation and complete flowering before diurnal temperatures optimum populations would be 120,000 1m rows fall below 18°C (day) and 13°C (night) as and 140,000 at 75cm rows. temperatures below these may result in reduced seed set. Recommended established plant populations A general range between 100,000 and 150,000 plants Sorghum is sensitive to frosts so grain fill should per hectare are often used. However populations on be completed before the first severe frost. the lower end have been shown to produce excellent yields. Plant populations on the higher end may be an Row spacing and plant populations advantage for management with detail to high water Overhead sprinkler irrigation lends itself to any and nutrition inputs. combination of row spacing from narrow rows 15 to 20cm apart to wider rows up to one metre Some hybrids have reputations as low apart. Wider rows can allow inter row cultivation for population hybrids. better weed control, however experience and trial An interpretation for this hybrid’s ability to tiller work has shown that evenly spaced narrow rows have and varieties with tillering ability can be planted at a yield advantage over wider rows. lower densities. 14 Pacific Seeds Yearbook 2008/2009 - Grain Sorghum Pacific Seeds’ summer crop sowing chart gives a NITROGEN UPTAKE AT A YIELD OF 7t/ha recommendation of plant populations for each hybrid. 250 Soil and plant nutrition 215 The following information on irrigated grain sorghum 200 182 nutrition is taken from an ‘Incitec’ brochure on 151 Kg N / ha 150 sorghum nutrition. 100 81 Sorghum is potentially a very productive crop and as such can place high demands on soil nutrient supplies. 50 10 For instance, studies have shown that a sorghum 0 crop yielding 7t/ha would take from the soil around 20 40 60 85 95 215kg of nitrogen, 25kg of phosphorus, 170kg of DAYS potassium and a balance of trace elements. Adequate supplies of nutrients in the correct proportion Split applications may be preferable if there are are essential for normal crop development and reservations as to the future water supply or maturation. A nutritional deficiency or imbalance substantial rates are to be used. invariably increases the duration of sorghum growth, thus increasing susceptibility to midge attack and Side dressings applied at the boot stage have increasing moisture usage. produced significant yield and protein increases when insufficient nitrogen has been applied at planting. Studies have shown that N, P, K uptake by sorghum is greatest during the rapid vegetative (G.S.1) growth It has been suggested that less total nitrogen is period and during the grain formation stage (G.S.3). needed with side dressings if two thirds is applied at The period from emergence to floral initiation has the planting and one third at the boot stage. greatest influence on potential grain yield as head size Irrigated sorghum will access between 70-80% of its tiller number is established during this period. Since total nitrogen requirement from the top 60cm. the potential yield is set at the time of floral initiation, Soil testing and nitrogen recommendations should it is essential that the plant has optimum growing be based on subsoil results concentrating on the top conditions during this first growth stage. 60cm. Dryland crops will access deeper nitrogen as Maintenance of adequate nutrition after floral they chase water if available. initiation is essential to maintain the potential grain number already determined and to increase the Phosphorus (P) protein content of the grain. Phosphorus is vital for the early development of young sorghum. It is an essential component of Nitrogen substances which manufacture sugars and proteins in Sorghum takes up 40% of its nitrogen requirement the plant. The uptake of phosphorus peaks at early in the vegetative period prior to floral initiation. A flowering, 45% of the total phosphorus demand being shortage of nitrogen during this period significantly taken up during booting and flowering. A phosphorus reduces growth in stems and leaves and consequently deficiency in sorghum, leads to restricted root in the number of flowers produced and so leads development and delayed flowering and maturity. to a reduction in yield. For the remaining nitrogen Phosphorus is best applied as a band at planting demand, that taken up between flowering and so that seedlings have immediate access to maturity is most important, for a shortage of plant the element. available nitrogen during this period results in large reductions in the protein content of the grain. Sorghum crops will only respond fully to applied nitrogen if the soil phosphate is adequate Nitrogen fertilisers are best drilled into the beds and readily available. prior to planting as germination is severely reduced if nitrogen is in direct contact with the seed. Early planted spring crops, growing in cool conditions Applications with seed contact are limited. will often respond to phosphorus even if soil phosphate tests are good. Recent studies into Nitrogen efficiency improves with yield phosphorus and sorghum have identified that sorghum is susceptible to long fallow disorder. yield Target (t/ha) Nitrogen (kg/ha) Due to enforced long fallows, yield responses to 7 210 phosphorus fertilisers are becoming more common. 10 250 Another side effect of utilising stored soil moisture is the possible redistribution of nutrient to the surface, 12 300 were its remains unavailable for much of the season. Pacific Seeds Yearbook 2008/2009 - Grain Sorghum 15 PHOSPHORUS UPTAKE AT A YIELD OF 7t/ha POTASSIUM UPTAKE AT A YIELD OF 7t/ha 40 180 170 35 161 160 35 136 30 140 30 120 Kg K / ha Kg P / ha 25 100 21 20 80 80 15 60 10 9 40 5 20 12 1 0 0 20 40 60 85 95 20 40 60 85 95 DAYS DAYS Average yield responses to seed applied Phosphorus Soil tests give some indications as to soil zinc status have been around 400kg/ha. This is probably best but best judgements are from visual symptoms and applied by an ammonium phosphate (DAP, MAP or a or leaf analysis. Zinc can be applied as a foliar when proprietary Starter). the problem is noticed but by the time the yield depression is under way the treatment is really The ‘pop-up’ effect on sorghum, the fast start given to only a correction. Zinc applications as foliar sprays seedlings in cool conditions, does not appear as clear should be applied within four weeks of emergence. cut as the corn ‘pop-up’. Prevention is better than cure and any suspicion on Phosphorus responses are likely when soil P levels are zinc deficiency should be counteracted by one of the less than 15 p.p.m. various soil applied zinc formulations. The oxide and sulphate monohydrate forms should be applied twelve Potassium (K) weeks before planting if the crop is to derive any Potassium is taken up in large quantities by the benefit from it. sorghum plant. Potassium plays a major role in the Nutrition information references: ‘Incitec Sorghum water relations within the plant and increases vigour, Nutrition Bulletin’. disease resistance and grain quality. Sorghum takes up 50% of its potassium requirements during the Plant water use vegetative period prior to floral initiation. Adequate Sorghum of different maturities requires different supplies of potassium are therefore essential in the amounts of water for optimum production. A full establishment of a healthy stand of grain sorghum. season late maturing hybrid will use more water and Zinc (Zn) nutrients than a quick season hybrid but longer season hybrids may have higher yield potential. Zinc, although required in relatively small amounts, is essential during the development of the young The amount of water required to produce a sorghum sorghum plant. A zinc deficiency which most crop with maximum yield is not a fixed value as commonly occurs on alkaline soils can greatly delay temperature and relative humidity during the growing flowering and maturity. Yield potential is also period along with wind and soil moisture all determine depressed by zinc deficiency. the rate of evaporation from the soil and transpiration GRAIN SORGHUM WATER USE PATTERN AND CRITICAL GROWTH STAGES Vegetative phase Grain filling phase Stage 0 1 2 3 4 5 6 7 8 9 10mm/day Emergence 3 leaves 5 leaves Head Flag leaf Boot Flowering Soft Hard Physiological fully fully initiation visible dough dough maturity emerged emerged 0mm/day Planting Height (cm) 0 10 20 40 80 110 120 120 Days -10 -3 0 9 12 24 35 45 50 55 65 75 90 100 16 Pacific Seeds Yearbook 2008/2009 - Grain Sorghum from the plant. In favourable seasons the water When irrigation water is in limited supply, the requirement may be as low as 400 to 450 mm whereas preplant application should be followed by one in a hot dry year this requirement could be up to 700 watering applied just as the sorghum starts to boot. to 850 mm to produce maximum yields. Should rainfall be favourable to the boot stage, this one The graph opposite shows the daily water use in grain watering should be delayed as late as possible so it will sorghum which peaks during the late boot to early carry the crop well into the grain development stage. flowering stage. Moisture availability at this stage is Should you have a moderate water supply, enough critical to the yield of the crop. Moisture stress for for a preplant application plus two waterings, the more than a few days during this period will result first irrigation would be applied a few days prior to in lower grain yield, quality and standability can be boot and the second a few days after flowering has affected where severe moisture stress is encountered been completed. If significant rainfall occurs prior in the 2 weeks after flowering. to booting, application of water may be delayed with good results. Irrigation management If you have enough water for preplant plus three Grain sorghum is a very water efficient crop and irrigations, your best irrigation schedule would be to is more tolerant to stress than maize. Sorghum is apply the first irrigation five to seven days prior to capable of very high water use efficiency, but under boot, the second at boot, and the third 10 days later cooler environments with good water supply, maize or by milk stage. will produce more grain/mm. Sorghum WU ranges Should you plan to apply four or five irrigations, apply between 10-25kg/mm depending on stress levels and the first seven to nine days prior to boot and one management. With careful management and today’s every 10 days thereafter. hybrids, 25kg/mm is possible. Total water required during the maturation stage For maximum yields the available water in the active is small but moisture is essential during this stage root zone should not drop below 50% storage to ensure full grain fill and to maintain plant quality. capacity. At peak use, sorghum will use about Irrigators sometimes encounter the question of 80-95mm of water in a 12 day period. when to stop irrigating grain sorghum so as to permit proper grain fill but leave the soil moisture There are a number of ways to determine reservoir depleted to allow room for storing the proper time to irrigate – soil moisture off-season precipitation. In sorghum, the crop is said instruments, taking soil samples, keeping records by to be physiologically mature when the grain reaches logging water use and supply, and by stage of plant the hard dough stage. Experience and research growth. Most likely the best system would be a indicate soil moisture availability measurements of combination of two or more of these, but the most 50 to 60% of field capacity are adequate to carry the practical method for many growers is to go by stage crop once it has reached physiological maturity. In of plant growth. most cases this is around 30 days after flowering. In summary: Timing for irrigation management Limited irrigation available Full Irrigation COOL arEa - MEdiuM TO hiGh raiNFaLL irrigation scheduling Established plants irrigation scheduling Established plants Post emergence (4 - 6 leaves) 100 - 150 000 / ha Vegetation stage (6 - 8 leaves) 60 - 100 000 / ha Mid vegetative (8 - 10 leaves) Pre-flowering / Late boot Late boot / Pre-flowering 60 - 65 000 / ha Early grain fill Early grain fill 72 - 75 000 / ha Mid grain fill 82 - 85 000 / ha hOT arEa - LOW TO MEdiuM raiNFaLL irrigation scheduling Established plants Vegetation stage (6 - 8 leaves) 40 - 70 000 / ha Pre-flowering / Late boot 60 - 65 000 / ha Early grain fill 75 - 80 000 / ha Based on a medium maturity variety. All of the information in this document is subject to copyright. No part of this document may in any form or by any means (whether electronic, mechanical, or otherwise) be copied, reproduced, stored in a retrieval system, transmitted or provided to any other person without the prior written permission of Pacific Seeds Pty Ltd, who owns the copyright. The information provided in this brochure is intended as a guide only. Various factors, including planting times and environmental conditions may alter the characteristics of plants. Pacific Seeds Yearbook 2008/2009 - Grain Sorghum 17 NOTES 18 Pacific Seeds Yearbook 2008/2009 - Grain Sorghum