| A field expereriment was conudeted with a maize-wheat-soybean rotation in the western Loess Plateau. There were four tillage treatments, namely conventional tillage (t), conventional tillage with stubble retention (ts), no-till (nt) and no-till with stubble retention (nts). The dynamic of crop yield, soil water stable aggregate, water use efficience, soil total carbon, organic carbon, total nitrogen and mineralized nitrogen content were observed from 2001 to 2007. The results are as follows:1. After three rotation cycles, the highest total grain yield and stubble yield for ten harvestings among four treatments were found under ts treatment, there were 3.63 t/ha (P<0.05) and 2.36 t/ha (P>0.05) higher than those under t treatment. The second highest yeild was found under nts treatment, with 2.48 t/ha and 1.95 t/ha higher than both under t treatment respectively. There was no significant difference on crop yield among four treatments in the first two implementation years, no-till and stubble retention showed significant effects on crop yield after seven years of tillage treatment. The results indicated that there was a delayed yield response to the conservation tillage.2. There were no siginificant treatment effects on WUEs of grain and stubble from 2001 to 2007, although the WUE from stubble retention treatment wes ovservaed higher than than that from no-stubbel retention.3. After seven years treatment implementation, the rank of >0.25 mm size water stable aggregate content in 0-5cm layer for four treatments was as following: nts (34.9%) > nt (32.3%) > t (27.4%) > ts (24.37%), tillage had significant effect on water stable aggregate content, the highest value in 5-10 cm soil layer was obatained under ts treatment and the lowest under t treatment. There was a significant correlation between aggregate content and easily oxidized organic carbon.4. After three rotation cycles, the highest soil total carbon for 0-10cm layer was found under nts treatment. The total organic carbon under ts, nt and nts were greater by 13.1%, 11.5% and 36.1% than that under t, no-till and stubble retention had significant positive effect on soil organic carbon content. The percent of organic carbon in total carbon decreased by 1.2% under t treatment, however,, increased by 3.1%, 2.7% and 18.2% under ts, nt and nts treatment compared with treatment started. The easily oxidized organic carbon among four treatments showed following rank: nts (7.72g/kg) > nt (6.50g/kg) > ts (6.49g/kg) > t (5.59g/kg), no-till and stubble retention had significant effect on increasing the easily oxidized organic carbon content. The Carbon pool management index (CPMI) was greater by 12.6%, 20.1% and 46.6% under ts, nt and nts than that under t treatment.5. In 2007, the soil total nitrogen for 0-10cm layer under ts, nt and nts treatment was greater by 9.6%,3.6% and 26.5% than t teatment(P<0.05). Total nitrogen under t, ts, nt and nts treatments increased by 15.4%, 30%, 16.2% and 49.5% compared with in 2001. No significant difference on mineral nitrogen was found among the four treatments The results indicated that stubble retention provided additional source of organic nitrogen and increased the organic N use efficiency.6. The C/N ratio under t, ts, nt and nts was greater by 12.75%, 15.97%, 6.87% and 24.16% in 2007 than that in 2001. Stubble retention increased the nitrogen content dramaticly.The results could be used to promote and extend conservation tillage practice in the Loess plateau for better resource utilization and sustainable develepment.
|
PDF Full Text Request