McSwiney, C.P., S.S. Snapp, L.E. Gentry, and G.P. Robertson
Presented at the All Scientist and GLBRC Sustainability Meeting (2009-05-05 to 2009-05-07 )
Synchrony requires that substantial nutrient pulses added to agroecosystems be applied when and where crop uptake is maximized in order to avoid losses to the environment. For rainfed systems, sufficient soil water is essential to move carefully placed/timed nutrients into plants and something that growers cannot control over the short-term. We report yields from a multi-year N rate study under a range of rainfall regimes at the W. K. Kellogg Biological Station in Michigan and examine N synchrony for two growing seasons, one sufficient and one deficient in rainfall. We measured soil N availability with ion exchange resin strips in conjunction with destructive maize plant harvests to monitor N uptake in maize fields fertilized at different N rates. Growing season rainfall (June-July) ranged from 6.5 to 16.1 cm for all of the years presented. Grain yields reached an asymptote at similar N rates each year, approximately 101 kg N ha-1. In 2007, a year when rainfall was not sufficient, less N accumulated in aboveground maize biomass, crop residues had lower C:N ratios, and greater quantities of N remained in the soil compared to 2006, when rainfall was sufficient. Effects of insufficient rainfall on the agroecosystem left the system susceptible to N loss. In rainfed systems, N synchrony could be an attainable goal when soil organic matter has been built up to provide soil water and N buffering to crops.
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