Phosphorus Update. Addy Elliott Colorado State University Department of Soil and Crop Sciences

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1 Phosphorus Update Addy Elliott Colorado State University Department of Soil and Crop Sciences

2 Phosphorus Application Considerations In order to provide sufficient nutrients to crops while preserving water quality: Soil Testing Amendment Testing + Field Environment Assessment USDA-NRCS P- Index Risk Assessment

3 Regulatory Requirements for Colorado P-IndexP Effective June 30, 2004 Requires CAFOs to do risk assessment for P runoff potential Purpose: to determine if producer should apply manure on N or P basis. USDA-NRCS requires completion of a P- Index to be eligible for federal funding assistance in livestock systems.

4 CO P-Index P Risk Assessment Developed by USDA-NRCS and CSU Ranks the relative potential for phosphorus movement from agricultural fields to surface water resources

5 N:P Ratios Imbalance in manure and compost N:P ratios compared to plant N and P uptake If manure or compost is applied to provide adequate N for a crop, the amount of P added to the soil with this manure or compost is 2 to 3 times greater than P needs of that crop

6 N:P uptake ratio of some crops and N:P ratios of different manures and compost Crop Yield (bu/acre) N:P uptake ratio Manure N:P ratio range Barley :1 Cattle feedlot 2:1 to 3:1 Corn :1 Dairy 5:1 to 7:1 Oats :1 Swine 1.5:1 to 4:1 Rye :1 Chicken 2:1 to 4:1 Sorghum :1 Broiler 2:1 to 6:1 Wheat :1 Compost 2:1 to 4:1 Sugar beets (tons/ac) :1 Eghball, B. Manure Matters. Vol. 2. No. 9.

7 When to Use P-Index? P A risk assessment is required when: manure, effluent, or other organic by-products will be land applied Should amendment be applied based on crop nitrogen (N) or phosphorus (P) requirements?

8 Preliminary P Risk Screening Tool Will animal manures or other organic nutrients be applied to this field? YES Is soil test P greater than: 10 ppm AB-DTPA; 30 ppm Bray P1; 30 ppm Mehlich 3, or; 20 ppm Olsen (NaCOH 3 )? YES Can storm water runoff or irrigation tailwater reach a surface water body? (continuous or intermittent stream, irrigation ditch, lake, or wetland, etc.) YES Complete a Colorado Phosphorus Index Risk Assessment for this field. NO NO NO A Colorado Phosphorus Index Risk Assessment is not needed for this field. A Colorado Phosphorus Index Risk Assessment is not needed for this field. Base organic nutrient application rates on crop nitrogen requirements. A Colorado Phosphorus Index Risk Assessment is not needed for this field. Base organic nutrient application rates on crop nitrogen requirements.

9 CO P-Index P Risk Factors All 4 site and management factor scores (1-4) are added together to determine relative risk of P movement off-site RISK FACTORS Runoff Class Soil Test P P Application Rate P Application Method

10 Risk Factor Components Runoff Class Field slope Least permeable soil layer in top 3 feet Soil Test P Sample from top 2 to 3 inches for continuous no-till cropland, hayland and pastures Sample from top 8 to 12 inches for tilled cropland

11 Risk Factor Components P Application Rate Average annual application rate calculated for the current crop rotation: Organic sources (manure, compost, residue, soil) Inorganic sources (fertilizer) P Application Method Use the highest risk applicable for multiple phosphorus applications Longer surface exposure has greater chance of runoff

12 BMP Credits For each BMP practiced, subtract 1 point: Contour buffer strip Cover crops Filter strips Furrow diking Grassed waterways Polyacrylamide (PAM) Residue management Terraces

13 P-Index Summary Site specific information required Use preliminary P risk screening tool Assess and score risk factors Apply BMP credits Make interpretations Apply nutrients accordingly!!

14 CSU Current P Research Two primary research questions: 1) Does P source affect P runoff concentrations? 2) Do soil calcium carbonate (lime) levels affect P runoff?

15 Source Project Treatments Dyecrest Dairy manure treatments: Raw manure Windrow composted manure Vermicomposted manure Rock P treatment: Soft rock P (<0.02 mm 2 )

16 Methods: Field The same rainfall simulation method was followed for both research projects.

17 Does source matter? Treatment Soil P Runoff P Petiole P Yield* ppm ppm ppm lb/a Control 6.4 c 3.22 b 1,767 b 17,860 c Raw Manure 80 lb P 2 O 5 /A 7.7 c 3.24 b 1,779 b 20,038 bc 160 lb P 2 O 5 /A 15.9 a 4.72 a 2,149 a 27,443 ab Composted Manure 80 lb P 2 O 5 /A 8.0 c 2.88 b 1,672 b 31,799 a 160 lb P 2 O 5 /A 11.6 b 2.71 b 1,821 b 30,056 a Vermicompost 80 lb P 2 O 5 /A 11.1 b 2.60 b 1,798 b 23,522 bc 160 lb P 2 O 5 /A 9.7 bc 2.57 b 2,102 a 31,799 a Means with a common letter within a column are not significantly different (p< 0.10) by least significant difference. * To convert to smaller area, lb/a * = lb/ 1,000 ft 2.

18 CSU Source Research Results P source matters!! Olsen P is a good indicator of both plant available P and mobile P forms in this soil. Compost and vermicompost applied at the same P 2 O 5 rate as raw manure have: Significantly less runoff P available Sufficient plant P levels Comparable yield Rock P is NOT SOLUBLE in alkaline soils

19 Soil CaCO 3 Level Project: Treatments 8 plots per location CO- 9% CaCO 3 ; fresh wet manure KS- 4% CaCO 3 ; aged, aerated manure NE- 1% CaCO 3 ; aged, aerated manure Treatment Application Rates: kg P 2 O 5 / ha CO- 0, 67, 135, 269, 538, 807, 1211, 1614 KS- 0, 112, 224, 448, 897, 1345, 2018, 2690 NE- 0, 123, 247, 493, 986, 1480, 2219, 2959

20 Are P Absorption Sites Saturated? P Saturation by CaCO 3 Levels % Saturation 8% 7% 6% 5% 4% 3% 2% 1% 0% Lbs P2O5/Ac Added 9% CaCO3 - CO 4% CaCO3 - KS 1% CaCO3 - NE

21 Runoff Total Dissolved P (ppm) Does CaCO 3 Content Predict NEBRASKA 1% CaCO 3 KANSAS 4% CaCO 3 COLORADO 9% CaCO 3 Runoff P? Mehlich - 3 Sol Test P (ppm)