Changes In Nitrogen Use Efficiency And Soil Quality After Five Years Of Managing For High Yield Corn And Soybean

Average corn grain yields in the USA have increased linearly at a rate of 1.7
bu/acre over the past 35 years with a national yield average of 140 bu/acre. Corn yield
contest winners and simulation models, however, indicate there is ~100 bu/a in
exploitable corn yield gap. Four years (1999-2002) of plant development, grain yield and
nutrient uptake were compared in intensive irrigated maize systems representing (a)
recommended best management practices for a yield goal of 200 bu/acre (M1) and (b)
intensive management aiming at a yield goal of 300 bu/acre (M2). For each management
level, three levels of plant density (30000-P1, 37000-P2 and 44000-P3 seed/acre) were
compared in a continuous corn and corn- soybean rotation. Over five years, the grain
yields increased 11% as a function of management and this effect was manifest under
higher plant densities. A high yield of 285 bu/acre was achieved at the M2, P2 treatment
in 2003. Higher population resulted in greater demand for N and K per unit grain yield.
Over the past five years, nitrogen use efficiency has steadily improved in the M2
treatment due to improvements in soil quality. Intensive management and population
levels significantly increased residue carbon inputs with disproportionately lower soil
respiration. Closing the yield gap requires higher plant population and improved nutrient
management to maintain efficient and profitable improvement in maize production. Soil
quality improvements and higher residue inputs under intensive management should
make this task easier with time.
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