Use of precision farming to improve applications of feedlot waste to increase nutrient use efficiency and protect water quality

Spatial variability in crop yields can be caused by many factors, which mak es it difficult to determine the most limiting factors. Application of anim al wastes to relatively infertile areas offers the potential to supply need ed nutrients and improve soil physical properties. The objectives of this s tudy were to test a manure application strategy to reduce spatial variabili ty in corn (Zea mays L) yield and to identify the most limiting nutrients i n relatively low yielding areas in a field. Fresh solid beef feedlot manure was applied in 1997 to a strip across areas with variable fertility status . No fertilizer was applied with the manure in 1997. Uniform N fertilizer, but no manure, was applied in 1998. Leaf tissue samples and chlorophyll met er readings were collected along the strips during the growing season and f rom adjacent strips without manure application. Grain yield was determined at plant maturity. In 1997, chlorophyll meter readings indicated season lon g N deficiency (< 95% sufficiency index) in no-manure plots with sufficienc y indices of 93, 88, 85, and 88% for the V10, V17, R2, and R3 growth stages , respectively. Only an early season N deficiency was detected in a few of the no-manure plots in 1998. Leaf tissue analyses indicated N and P were gr owth limiting factors in 1997, with leaf N concentrations of 25, 26, and 27 mg g(-1) for non-manure plots and 30, 33, and 31 irig g(-1) for manure plo ts at V12, R1, and R3 growth stages, respectively. Leaf P concentrations we re 2.0, 2.0, and 1.9 mg g(-1) for no-manure plots versus 2.5, 2.7, and 2.3 mg g(-1) for manure plots, respectively. In 1998, neither N or P were ident ified as limiting factors. Grain yields in 1997 were 10.2 and 12.2 Mg ha(-1 ), which increased to 11.9 and 12.8 Mg ha(-1) in 1998 for no-manure and man ure plots, respectively.