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Phosphorus Nelson

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Phosphorus  Nelson Powered By Docstoc
					    Phosphorus Sources and
Management in Organic Production
           Systems


     Nathan O. Nelson1 and Rhonda Janke2
    1Kansas  State University Department of Agronomy
    2Kansas State University Department of Horticulture,
            Forestry, and Recreation Resources
Is P Fertility Inherently Different in
Organic Agriculture?
 “The aim of nutrient management within organic farming
  systems is to work, as far as possible, within a closed
  system” Stockdale et al., 2001.

 “Dependence on external inputs, whether chemical or
  organic, is reduced as far as possible.” Elmaz et al.,
  2004.

 “Organic farming systems rely on the management of
  soil organic matter to enhance the chemical, biological,
  and physical properties of the soil, in order to optimize
  crop production.” Watson et al., 2002.
Is P Fertility Inherently Different in
Organic Agriculture?
                                  45                                                         110
                                                                       Soil-test P           105
                                  40
                                                                       Corn Yield
                                                                                             100
      Bray Soil-test P (mg kg )




                                                                                                   Relative Corn Yield (%)
                                  35
      -1




                                                                       y = -1.08x + 2235
                                                                            r2 = 0.62        95
                                  30
                                                                                             90
                                  25
                                                                                             85
                                  20
                                                                                             80
                                  15
                                                                                             75
                                  10                                                         70
                                          y = -1.09x + 2174
                                   5                                                         65
                                               r2 = 0.71
                                   0                                                      60
                                   1975               1985           1995              2005
                                                              Year
                                                                      Data from Dodd and Mallarino, 2005
Is P Fertility Inherently Different in
Organic Agriculture?
 Organically produced crops still need P
 Soil properties affected by management/ cropping
  systems can alter P availability and cycling
    •   Arbuscular mycorrizal fungi
    •   Organic carbon
Arbuscular Mycorrhizal Fungi (AMF)
 Symbiotic association between fungus and root
    •   Root provides food (carbon source)
    •   Fungus increases root exploration and nutrient uptake.
 Organic Agriculture tends to increase AMF
    •   Will sometimes increase P uptake/crop growth (Kahiluoto
        and Vestberg, 1998).
    •   …and sometimes not
        (Scullion et al., 1998)
 Even with AMF, organically
  grown crops still respond
  to P additions
  (Dann et al., 1996).               Credit: Randy Molina, Oregon State University, Corvallis
Is P Fertility Inherently Different in
Organic Agriculture?
 Organically produced crops still need P
 Soil properties affected by management/ cropping
  systems can alter P availability and cycling
    •   Arbuscular mycorrizal fungi
    •   Organic carbon
    •   Organic production does not produce consistent effects
        for these properties/processes
    •   Other agricultural practices will increase OC and
        positively affect AMF.
 Phosphorus Sources 
N Source Effects on P Management –
Feast or Famine
 Fresh plant biomass has N:P ratio of ~ 8:1
 Organic N sources supplying ample P
    • Manures – dairy, beef, swine, poultry litter (~4:1)
         Composted manures – increases P concentration (~2:1)
    • Plant composts – N:P varies
         Avg. 6:1with a high 11:1 and low of 1:1
 Organic N sources supplying little or no P
    • Green Manures
    • Blood Meal
Phosphorus Sources for Organic
Agriculture
 Inorganic P Sources
   • Rock Phosphate
   • Bone Meal
 Organic-based P sources
   • Green Manures - ?
   • Manures
   • Composts
        Composted Manures
        Composted Plant Biomass
Rock Phosphate as a P Source
 Rock phosphate (RP) is a slowly soluble P source
  from mined phosphate (calcium phosphates).
 Solubility is highly dependant on several factors
    • Soil type
        Low pH
        Low Ca
        Low P fixing Capacity
                                 Rock phosphate
                                 mine in India
    • RP source
        Sedimentary RP Reactive/soft (North Carolina, Gafsa)
        Igneous and Metamorphic
Rock Phosphate as a P Source
 Phosphorus availability – relative response
  approaches 1:1
    • Optimum soil                          30

      and RP source                   Corn 25
                                    Biomass
                                     (g/pot) 20


                                            15


                                            10

                                                                   Triple Super Phosphate
                                             5
                                                                   Gafsa RP

                                             0
                                                  0   50     100         150       200      250
     Source: Correa et al., 2005.
                                                      Phosphorus Rate (mg dm-3)
     Sci. Agric. 62:159-164
Rock Phosphate as a P Source
 Phosphorus availability – relative response does
  not approach 1:1
      • 6-yr field study



                                       Cumulative 6-yr Dry Matter Yield (t ha )
                                                                            -1
                                                                                  45
      • Low pH soil
                                                                                           Triple Super Phosphate
                                                                                           Gafsa RP

      • Lime application
                                                                                  40
        before year 1

                                                                                  35




                                                                                  30
                                                                                       0           10               20           30
 Source: Scholefield et al., 1999                                                            Phosphorus Application (kg ha-1 yr-1)
 Nutr. Cycl. Agroecosyst. 53:147-155
Rock Phosphate as a P Source
 Green manures can increase RP efficacy
                              • 200 kg P ha-1
                              3.5
                                                                                                                   No Green Manure
                               3                                                                                   With Green Manure
   Dry Matter Yield (g/pot)




                              2.5

                               2

                              1.5

                               1

                              0.5

                               0
                                    Control   Triple Super   Algerian          North            Tunisian        Christmas            China
                                               Phosphate                      Carolina           (Gafsa)         Island
                                                              ------------------------------ Rock Phosphates ------------------------------

 Source: Zaharah and Bah. 1997. Nutr. Cycl. Agroecosyst. 48:247-255
Green Manures as a P Source - ?

 Green Manures – legume crops grown and tilled
  in to soil (not harvested).
   • Some species can extract soil P that is unavailable
     to other crops (e.g., white lupin, faba bean, nitro
     alfalfa).
   • Decomposition releases P
   • Some green manures may decrease P uptake of
     succeeding crop (e.g., white lupin).
 Green manures may increase P availability, but
  are not a P source
Green Manures as a P Source - ?
Change in Soil Test P
during Green manure –
Sorghum rotation
Source: Cavigelli and Thien, 2003.
Soil Sci. Soc. Am. J. 76:1186-1194


                                                5
                                                4
                                                23
                                                1




“…[green manures] cannot substitute for maintenance P
fertilizer application.” (Horst et al., 2001)
Manures and Composts as P Sources

 Majority of P in manures and composts is
  inorganic P
  Source                                      % Organic P % Inorganic P
  Feedlot manure                                       25           75
  Composted manure                                     16           84
  Dairy                                                25           75
  Poultry litter                                       10           90
  Swine                                                 9           91
 Source: Eghball et al., 2002. J. Soil Water Conserv. 57:470-473.
P Availability in Manures and Compost

 P availability ranges from 70 to 100 %
  available.
 Use 70% for
  low P soils
 Use 100% for
  high P soils or
  maintenance
  applications

Source: Sikora and Enkiri, 2005
Agron. J. 97:668-673.
P Availability in Manures and Compost

 High variability between manure types
Changes in Mehlich 3 P for 80 d following    Relationship between the C/P ratio
 application of 4 manures and fertilizer        and the Olsen P in three soils




Source: Griffin et al., 2003
Soil Sci. Soc. Am. J. 67:645-653.           Source: Leytem et al., 2005.
                                            Soil Sci. Soc. Amer. J. 69:1516-1524.
When P is in Excess
 P inputs to surface waters promote
  eutrophication and degrade water quality
When P is in Excess
 Continual use of Manures and composts to supply
  N can increase soil test P far beyond crop
  requirements
   • Organic farming with poultry litter as the sole N
     source raised soil test P to 800 to 1000 mg P kg-1
     (Mikkelsen, 2000)
When P is in Excess
 High soil test P results
  in higher runoff P
  losses.




Source: Tarkelson and Mikkelsen, 2004
Comm. Soil Sci. Plant Anal. 35:2987-3007.
When P in in Excess
 Surface application of
  broiler litter resulted in
  high runoff P concn.
  regardless of soil P
  concentration.
 High litter rate = 200
  kg N ha-1


Source: Tarkelson and Mikkelsen, 2004
J. Environ. Qual. 33:1424–1430.
Best Management Practices to Reduce P
Losses
 No-till/Cover Crops
   • Reduces runoff volume and erosion
 Grass Buffer Strips
   • Trap sediment and increase infiltration
 Incorporation of manure/compost prior to
  rainfall
   • Reduces interaction of manure/compost with runoff
     water.
In Summary…
 Inorganic P Sources
   • Rock Phosphate – only acidic soils
   • Bone Meal – acidic soils
 Organic-based P sources
   • Manures – good P source 70-100% available
   • Composts
        Composted Manures – similar to manures
        Composted Plant Biomass – higher C:P ratio, may be
         less available than other composts
 Use BMPs to reduce erosion and runoff when
  applying manures and composts

				
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