Tillage method and soil fertilization effects on crop yield and nitrate leaching

Effects of tillage (T), i.e., rotary tilling to 25 cm depth, reduced tillag e (RT), rotary tilling to 5-6 cm depth and application of farmyard manure ( M), chemical fertilizer (F), and mixed application of manure-chemical ferti lizer (MF) on crop yield and some soil characteristics were investigated du ring two years of upland cropping (with a rotation of oat - soybean and whe at - field corn) in an Andosol field. Regardless of the tillage method applied, MF resulted in higher yields of o at, wheat and field corn than M or F. Soybean yield was not influenced sign ificantly by either treatments, although the highest yield occurred in the RTM plot. The tillage treatment did not significantly affect soil pH, total nitrogen and microbial biomass nitrogen, but the application of farmyard m anure increased these parameters in the soil surface layer (0-20 cm). Amoun ts of soil organic matter changed in accordance with the amount of crop res idues reincorporated, especially in the surface layer. During wheat and field corn cropping, RTM plots resulted in larger amounts of leached nitrate than the other plots. This was caused by continuous mine ralization of organic nitrogen from the manure and increased water permeabi lity of soil in these plots.