Tillage and previous crop effects on dynamics of nitrogen in a wheat-soil system

The effects of tillage and preceding legume crops on N flux in the soil-plant system require quantification For developing sustainable cropping systems. We measured changes in soil and plant N under the influence of tillage [no till (NT) vs, conventional tillage (CT)] and previous crops [spring wheat (Triticum aestivum L.), red clover (Trifolium pratense L.) green manure, and field pea (Pisum sativum L.)]. The study was conducted from 1994 through 1996 on a well-drained sandy loam soil (coarse-loamy, mixed, frigid, Typic Cryoboralf) near Fort Vermilion, Alberta (58 degrees 23'N, 116 degrees2'W). Nitrogen uptake by wheat was increased by NT and legume crops, At seeding, CT soil had 28 kg ha(-1) more NO3-N to 100-cm depth than NT soil. Apparent net N mineralization in the growing season was 71 and 22 kg N ha(-1), respectively, for the NT and CT systems. Previous crop effect on net N mineralization (kg N ha(-1)) was red clover (56) > field pea (51) > wheat (34). Approximately 18 kg N ha(-1) was net-mineralized from red clover residues compared with insignificant amounts from pea and wheat residues. Microbial biomass turnover's contribution to net N mineralization (28 to 40 kg N ha(-1)) was increased by NT and previous legume crop, Soluble organic N decreased by 7 kg ha(-1) between seeding and maturity for all experimental treatments. The results indicate that N fertilizer recommendations should allow for greater mineralization of organic N ender NT than CT and following a legume green manure.