Efects of Conservation tillage and crop residues on soil nutrient contents

The experimental results showed that the nutrient contents of loamy soil under two crops a year(winter wheat+maize) was increasing with the decrease of tillage practices to the soil．The contents of organic matter,tota1 N and available P of surface soi1(0～10cm) under zer0 tillage were significantly higher(P<0．05)than those under conventional tillage (shallow tillage),and available K was the highest among all the treatments．The increasing of available P and K for the zer0 tillage is significantly related to the increasing of organic matter and decrease of pH value resulting from the organic matter increasing．There was a linear relationship existing among those factors．Straw mulch is favorable to the nutrient accumulation at surface soil，but itsingnificant different efects have nat found compared with othercrop residue retention measures．