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1. Changes in Nitrogen use Efficiency and Soil Quality After Five Years of Managing for High Yield Corn and SoybeanAverage corn gain yields in the USA have increased linearly at a rate of 1.7 bulacre over the past 35 years with a national yield average of 130 bdacre. Corn yield contest winners and simulation models, ho ~ever, indicate there is -100 bda in exploitable corn yield gap. Six years (1999-2004) of plant development, grain yield and nutrient uptake \yere compared in intensive irrigated maize systems representing (a) recommended best management practices for a yield goal of 200 bdacre (Ml) and (b) intensive... |
2. Response Surface Models Of Subsoil K Concentration For Loess Over Till Soils In MissouriCrop uptake of potassium (K) has demonstrated sensitivity to subsoil variation in K content. This fact has not been sufficiently considered in K management strategies in part due to logistical difficulties in sampling spatially variable subsoil K. We propose a simplified soil factorial model, a response surface, to enable site-specific accounting of whole root zone K supply for loess over till soils. We compared the performance of two peak functions and a non-parametric local regression procedure... |