Organic Waste N and P Dynamics Under Dryland Agroecosystems Jim Ippolito and Ken Barbarick USDA-ARS-NWISRL & Colorado State University

Organic Waste Land Application Approach: Agronomic rates based on crop N requirements Excess P addition/accumulation

P-based vs N-based approach: P-based vs N-based approach: Utilizing long-term N-based data to make future P-based decisions   Approach Account for all P added with organic waste (i.e. biosolids) application. Account for all P removed with grain or straw. Determine total soil P at the end of the project. From the above, can we predict total P present? What fraction(s) dominate P in this system? Determine environmental risk based on the Colorado P Index Risk Assessment (Sharkoff et al., 2005).

Site Information  Littleton/Englewood – CSU land application program Dryland wheat-fallow agroecosystem Dryland wheat-fallow agroecosystem 1982 through through , 6.7 (“agronomic rate”), 13, 27 Mg ha -1 biosolids0, 6.7 (“agronomic rate”), 13, 27 Mg ha -1 biosolids Applied every other year, except 1998Applied every other year, except x 16.8 m plots; 4 replicates; RCB design3.6 x 16.8 m plots; 4 replicates; RCB design Incorporated to 20 cmIncorporated to 20 cm 40 Mg ha -1 biosolids plots history:40 Mg ha -1 biosolids plots history: 6.7 Mg ha -1 in 1982, then 40 Mg ha -1 from Mg ha -1 in 1982, then 40 Mg ha -1 from

Phosphorus Accountability   Biosolids P analysis completed for every application year.   Total grain and straw P determined at every harvest.   Total soil P (4M HNO 3 ) determined at July 2003 harvest.   Composite soil samples from plot center (July 2003). 0-20cm and 20-60cm depths. Near plot center to avoid potential biosolids redistribution due to years of tillage (Yingming and Corey, 1993). Air dried, sieved, weighed for analysis.

predicted kg biosolids-borne P accumulated in soil (2003) Cumulative ( ) kg grain and straw P removed Cumulative ( ) kg biosolids-borne P appliedBiosolids Application Rate (Mg ha -1 )

% kg P in the 0-60-cm depth Mg ha -1 Adjusted Percent Recovery Adjusted Actual Increase Predicted Increase (from previous table) Actual Increase Harvest Soil 1982 BackgroundBiosolids Application Rate To adjust, we used the control plots: 5.41 – (-0.49) = 5.90 kg P added overall. Therefore, subtract 5.90 kg P from actual. Prediction of Soil P Content What soil fraction dominates P?

P Fractionation (Kuo, 1996) < Probability Level (P) a779 bc104 b † b1110 c200 d a525 ab144 c a400 ab83.3 b a154 a16.7 a mg kg -1 ; 0-20-cm depth Mg ha -1 Ca-bound POccluded PFe-Bound PAl-Bound PSoluble/ Loosely Bound P Biosolids Rate

Risk interpretations: Net score Potential for Off-Site P Movement <8Low Organic nutrient application based on crop N requirements. 8 to 11Medium Organic nutrient application based on crop N requirements. Some management changes may be needed. 12 to 15High Organic nutrient application based on crop P requirements. >15Very High Do not apply organic nutrients. Colorado P Index Risk Assessment Colorado P Index Risk Assessment Sharkoff et al. (2005): efotg.nrcs.usda.gov/references/public/CO/COATN_95v3.pdf

FactorsClassBiosolids Rate (Mg ha -1 ) rating Runoff class Soil permeability class Slope Slow 0-1% 1 (low) AB-DTPA soil test (0- to 20-cm depth) 3 (high; 38 mg kg -1 )4 (very high; 47 mg kg -1 ) P application rate4 (very high; > 370 kg P 2 O 5 ha -1 ) P application method Summer applied- incorporated 3 (high) Best Management Practice Net Score Risk Level None0 (none) 11 Medium 0 (none) 12 High

What happens if you receive a “high” P risk index rating?   Apply base on crop P requirements. Will significantly alter application approach Supplemental N fertilizer addition   Consider using other BMPs   No alternative?... You can wait Our 40 Mg ha -1 application rate took 3 wheat-fallow cropping cycles (6 years) for P concentrations to be lowered below the limitation.

Site Information: Data range: 1993 to 2004 Biosolids and N fertilizer rates bracketed the agronomic N rate for dryland wheat: 0 to 11 Mg ha -1 biosolids 0 to 110 kg N ha -1 Switching Gears to Nitrogen

Questions Asked:   What is the long-term estimated N equivalency under organic waste (i.e. biosolids) application?   What is the first-year N mineralization rate from organic waste application: Overall? “Wet” years? “Dry” years?

Approach   N or B (grain uptake) = N or B (grain conc) *Grain Yield*1000 (Linear regression was performed over biosolids rate, over N rate)   Biosolids N (equivalency) = B (slope) /N (slope)   Biosolids (plant-available N) = [N NO3 + Kv(N NH4 ) (N o )] + residual   Biosolids (1st-year mineralization rate) = [Biosolids N (equivalency) *0.20] Biosolids (plant-available N)

Overall Results   Biosolids N fertilizer equivalency: 9 kg N Mg -1 biosolids   Biosolids 1 st year mineralization rate: 27 to 33%

Comparison of vs Increased ppt.   Biosolids N equivalency: 8.2 kg N Mg -1   Biosolids 1 st year mineralization rate: 25-32% (J. Environ. Qual., 2000; 29: ) Drought   Biosolids N equivalency: 7.7 kg N Mg -1   Biosolids 1 st year mineralization rate: 21-27% (Agronomy J., 2007; 99: )

Implications for Idaho Agriculture   Future reductions in water availability will shift irrigated agriculture: Dryland or reduced irrigation cropping systems   Production can be increased, input costs reduced, and environmental quality improved with good knowledge of: Crop growth Water use efficiency and timing Nutrient management and dynamics

Questions? Jim Ippolito Research Soil Scientist USDA-ARS-Northwest Irrigation and Soils Research Laboratory Kimberly, ID Phone: (208) References: Barbarick, K.A., and J.A. Ippolito Dryland wheat nutrient assessment for 12 years of biosolids applications. Agron. J. 99: Ippolito, J.A., K.A. Barbarick, and K.L. Norvell Biosolids impact soil phosphorus recovery, fractionation, and potential environmental risk. J. Environ. Qual. 36: Kuo, S Phosphorus. pp In D.L. Sparks (ed.). Methods of Soil Analysis, Part 3 - Chemical Methods. Soil Science Society of America. Madison, WI. Sharkoff, J.L., R.M. Waskom, and J.G. Davis Colorado Phosphorus Index risk assessment. Agronomy Technical Note No. 95 (revised). United States Department of Agriculture-Natural Resources Conservation Service and State of Colorado. Yingming, L., and R.B. Corey Redistribution of sludge-borne cadmium, copper, and zinc in a cultivated plot. J. Environ. Qual. 22:1-8.