Improving Synchrony of Nitrogen Turnover and Crop Demand Through Zonal Management.

Conventional tillage systems, such as chisel plow, may not be optimal for synchronizing the supply of nitrogen (N) from biological sources with crop demand as they typically involve extensive soil disturbance that mineralizes N at times when crop demand is low and in locations where plant roots may not be present. There is emerging evidence that zonal management can influence mineralization and nitrification processes through direct and indirect means. The impact of ridge tillage systems and cover crop management were explored at the sub-meter spatial scale in a field study, to quantify N supply and demand over space and time. Ridge tillage was hypothesized to protect soil organic matter and concentrate readily mineralizable materials around plants at re-ridging.   

Field sites were established at Michigan State University and University of Illinois Champaign-Urbana in 2011 in a split-plot design with main tillage treatments of ridge tillage vs. chisel plow, and a split-plot treatment of winter rye cover vs. winter fallow. Throughout the 2012 growing season we monitored inorganic N and potentially mineralizable nitrogen (PMN) in zero-fertilizer subplots at three positions:  in-row, shoulder (7.5 in from row), and furrow (15 in from row). Additionally, plant response was assessed using a SPAD meter to measure chlorophyll content, end-of-season tissue N content, and per plant yield. 

At growth stage V6, PMN levels were higher at the in-row position of ridge tillage treatments than in corresponding chisel plow treatments. Ion exchange resins indicated that the production of NO₃- was higher overall in ridge tillage treatments following the re-ridging event, especially at the in-row position. End-of-season grain N content and per plant yield was also higher in ridge tillage treatments. Overall, ridge tillage exhibited greater synchrony of N turnover with plant demand by relocating residues around plants and stimulating N turnover.