John (Jack) Meisinger and Dennis Timlin. BARC-East - 10300 Baltimore Ave, USDA-ARS, Bldg 163F Room 6, Beltsville, MD 20705-2350
Last year we examined a common observation in multi-year or multi-location N-response studies, which is the capacity of the soil-plant system to vary plant available N with growing conditions, this characteristic is termed soil-plant N resiliency. The soil-plant N resiliency concept will continue to be examined by reviewing its properties and examining various hypotheses that could produce it. Nitrogen resiliency is a general biological characteristic of the soil-plant N cycle that is thought to be caused by soil and crop factors that interact with each other, and the weather, to produce higher grain yields on N-stressed plots in years with high- yield potentials and lower yields on the same plots in low-yield potential years. Some possible soil factors contributing to N resiliency are higher organic-N mineralization rates in good years, and/or higher N recovery efficiencies resulting from lower leaching and/or lower denitrification losses. Potential crop factors contributing to resiliency include a higher percentage distribution of fixed C into the grain compared to the roots in good years, or simply a greater total production of dry matter. The weather in high-yield years also interacts with N resiliency components with high solar radiation and ample rainfall contributing to higher photosynthesis vs. respiration rates, and/or higher transpiration rates that would transport more nitrates to the crop root surfaces. A crop-soil simulation model will be utilized to examine several of these hypotheses and their interaction with weather. The above hypotheses are necessarily speculative, because soil-plant N resiliency has not been systematically studied. Our examination of soil-plant N resiliency will hopefully encourage future research studies that should expand our understanding of this characteristic, should identify management practices to enhance resiliency, and should permit improved communication of this characteristic to producers.