Updated Strategies when Using Poultry Litter as Fertilizer
A White Paper on this website provides details about using poultry litter as fertilizer for crops, as well as how to properly store this material so that it retains its optimum fertility value. The preponderance of research cited in that paper produced results that affirm the value of poultry litter as an alternative and/or supplement to commercial fertilizer for corn and soybean production in the Midsouth.
Results from recent research projects conducted on a Blackland Prairie soil in northeast Mississippi provide information that can be used to refine how and when poultry litter can be used as a fertilizer for Midsouth crops, especially soybeans. Summaries of those research projects follow.
An article by Feng et al. titled “Soil physical and hydrological properties as affected by a five-year history of poultry litter applied to a cotton-corn-soybean rotation system” appears in Soil Sci. Soc. Am. J. 85:1-14 (2021). The reported results are from a field study that was conducted on a Leeper fine sandy loam soil for 8 years in corn, cotton, and soybean rotations at Verona, Miss. Details of and results from that study follow.
• The nonirrigated field study was conducted to determine the potential influence of poultry litter (PL) application on soil physical and hydrological properties.
• The study consisted of four crop rotations that involved continuous cotton and three rotations schemes with cotton, corn, and soybeans for 5 years (2010-2014). All plots were planted with soybeans from 2015 through 2017.
• Fertility treatments consisted of 1) no fertilizer, 2) a standard fertilizer treatment with conventional synthetic fertilizers applied to meet the nutrient needs of each crop in the rotation, and 3) uncomposted PL applied in an amount to meet the full N requirements of the cotton crop. No synthetic N fertilizer was applied to the cotton or soybean crops, but corn received synthetic N above that supplied by PL to meet its higher demand for N. P and K fertilizers were applied to soybeans based on soil test recommendations.
• The consequences of the 5 years of fertility treatments on soybeans were measured in the sixth (2015) and eighth (2017) years of the study. Soil properties measured in these years were bulk density (BD), penetration resistance (PR), saturated hydraulic conductivity, soil water content at field capacity (FC) and permanent wilting point (PWP), infiltration rate, and water stable aggregates.
• Yearly PL application in the 2010-2014 period reduced BD by 6% in 2015 and 4% in 2017 compared to that of soil that received synthetic fertilizers.
• PR did not differ between the PL and fertilized treatments in 2015 and 2017.
• PL addition in the 2010-2014 period resulted in a significant increase in FC and PWP water content of 20 and 41% in 2015 and 8 and 13% in 2017 compared to that following no added fertilizer and the addition of commercial inorganic fertilizer, respectively.
• Saturated hydraulic conductivity of soil amended with PL was about three times greater than that of soil amended with inorganic fertilizer.
• PL addition from 2010-2014 improved soil aggregate stability by 17 and 31% in 2015 compared to that of the other two fertility treatments, respectively. There ware no differences in soil aggregate stability among treatments in 2017.
• Soybean yields from the plots that received PL vs. those that received inorganic fertilizer were a significant 8% more in 2015 (68.2 vs. 63.2 bu/acre) and 11% more in 2017 (67.9 vs. 61.3 bu/acre), thus suggesting that the improvement in soil properties following the addition of PL was associated with a soybean yield increase.
• Crop rotation did not significantly affect soil physical and hydrological properties.
• These results suggest that the addition of PL as a fertilizer is an effective management practice for improving soil health that will in turn contribute to increased soybean yield.
• (Note: This research was financially supported by MSPB for a Project titled “Stabilizing dryland soybean yield and profit in dominant soils across Mississippi”).
An article by Tewolde et al. titled “Managing soil nutrient buildup by rotating crops and fertilizers following repeated poultry litter applications” appears in Soil Sci. Soc. Am. J. 85:340-352 (2021). The reported results are from a field study that was conducted on a Leeper fine sandy loam soil for 5 years (2010-2014) in cotton, corn, and soybean rotations at Verona, Miss. Details of and results from that study follow.
• The nonirrigated field study was conducted to determine whether or not buildup of nutrients resulting from repeated application of poultry litter (PL) to the same site can be managed by rotating PL and synthetic N fertilizers and rotating cotton, corn, and soybean crops in the southeastern US.
• The study consisted of two factors–four levels of crop rotation involving cotton, corn, and soybeans, and five fertility strategies that were 1) an unfertilized control (UTC), 2) a standard fertilization with synthetic fertilizers applied to meet the requirements of each crop (STD), 3) a phosphorus (P)-based PL fertilizer application every year for 5 years (PL5P), 4) a nitrogen (N)-based PL application every 5 years (PL5N), and 5) an N-based PL application in the first 2 years and synthetic N fertilizer applied at the same rate as in 2 above in the last 3 years of the study (PL2N). Fertilizers applied in treatments 2 (STD), 4 (PL5N), and 5 (PL2N) above were based on the N requirement of cotton, while the fertilizer applied in treatment 3 (PL5P) above was applied in an amount to meet the expected P removal by cotton. When corn was planted in the rotation, synthetic N fertilizer was applied to supplement N supplied by PL in order to meet the higher N demand by corn. Applications of P and potassium (K) fertilizers in treatment 2 (STD) above were made according to soil test recommendations for each crop grown in the rotation.
• Extractable nutrients were measured in soil samples taken after crop harvest each year. Both fertility and rotation treatments affected nutrient levels, but the fertility by rotation interaction was never significant.
• P is the element that most accumulates in the soil following repeated PL applications, and it was elevated more than three times that of the STD when PL was applied to meet cotton’s N requirement (treatment 4–PL5N) in this study. When PL was applied as in treatment 3 above (PL5P), this excess accumulation of P did not occur; however, synthetic N fertilizer had to be applied to meet the N requirement of the cotton and corn crops. Thus, the authors concluded that the P-based PL application (PL5P) is an effective method for managing PL application. However, this method will require the addition of synthetic N each year to cotton and corn crops.
• Results from this research showed that K depletion is a concern when fertilizing crops with PL, especially when soybeans are grown in a rotation scheme. Thus, extractable K in the soil should be monitored when PL is used as a fertilizer.
• Results from the study showed that magnesium buildup in the soil did not occur with the P-based application strategy. Extractable calcium was not affected by the fertility treatments.
• Extractable zinc and copper accumulated in the soil regardless of PL management strategy, but the authors did not attach concern to this since their documented toxicity is not widespread. Extractable iron also accumulated in the soil in response to the PL applications, but its magnitude was small and was not a concern. Extractable manganese was not affected by the PL treatments.
• In this study, crop rotation did not clearly and consistently affect residual soil nutrients.
• From these results, the authors concluded that 1) when excess nutrients accumulate in the soil as a result of repeated PL applications, rotating fertilizers where PL application is suspended for 2-3 years during which only N fertilizer is added will return soil nutrient status to near initial levels and may be more efficient; 2) applying PL based on the P and/or N need of the crop will likely result in soil K depletion, which will be problematic when soybeans are grown in the rotation; and 3) crop rotation will aid in reducing P and K buildup in the soil, but may not be as effective as rotating PL with synthetic fertilizers to manage soil nutrient buildup that may result from repeated PL application.
The results from the above two studies show that 1) using PL as a fertilizer will improve soil health attributes, 2) PL should be rotated with synthetic fertilizers to ensure a stable soil nutrient status, and 3) PL application strategy should be managed to ensure that major nutrients such as P and K that are needed for crop development are at the proper level in the soil. This will require monitoring their level in the soil when PL is applied as a fertilizer to ensure proper adjustment of fertilization strategy involving PL and inorganic fertilizers.
Composed by Larry G. Heatherly, May 2021, larryh91746@gmail.com