| The importance of conservation tillage to sustainable agriculture development has been widely recognized at present. A field experiment was conducted 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, soil oxidizable organic carbon, organic carbon and phosphorous were observed during 2001 to 2005.1. Conservation tillage treatment had positive effects on crop yield and total biomass over time. After two cycles of rotation, the total biomass and total yield for seven harvestings were the highest under TS treatment (72.23 and 35.51 t/hm~2) and lowest under T treatment (67.58 and 33.48 t/hm~2). Stubble retention significantly increased the soybean and maize crop yields (P<0.05) in 2004 and 2005. Soybean yield under NTS treatment increased by 0.88 t/hm~2 in 2004 compared with that in 2002. Maize crop under TS treatment in 2005 was increased by 3.56t/hm~2 compared with that in 2001, indicating that both no-till and stubble retention had effect on promoting maize and soybean growth. However, the treatment effect on grain quality was less than that on biomass and yield.2. There was no significant treatment effect on surface soil water stable aggregate content after first cycle of rotation. However, there was significant difference in >0.25 mm size water stable aggregate content between the treatments (P<0.05) . The highest water stable aggregate content for 0-5 cm soil layer was measured under NT treatment, which was 3.43%, 2.67% and 3.13% higher than that under TS, NTS and T treatments, respectively. No relationship was found between aggregate and organic carbon in the aggregate.3. The easily oxidized organic carbon in the 0 to 5 cm soil layer were the highest under NTS and the lowest under T treatment although there was no significant diiference after first cycle of rotation. The highest easily oxidized organic carbon was found under NTS treatment and lowest under T treatment. The easily oxidized organic carbon was 19.69%, 12.92% and 38.67% lower under T treatment than TS, NT and NTS treatments in 2004, respectively. A positive linear regression was found between easily oxidized organic carbon and total N content (P=0.01) . Total organic carbon increased over time under three conservation tillage treatments. Under NTS treatment, total organic carbon was increased by 21.5% whereas total organic carbon increased by 9.0 % only under T treatment. The easily oxidized organic carbon accounted for 75.9% and 79.5% of total organic carbon under T and NTS treatment in 2005, indicating easily oxidized organic carbon could be considered as a sensitive indicator to response of tillage practice.4. After two rotation cycles, there were some nitrogen surplus in 0-200 cm soil profile, indicating that annual crops could not fully use the soil nitrogen in the deep soil layer which might result in nitrate leaching.5. After five years rotation, soil available P at 0-10 cm layer increased under three conservation treatments. The highest available P concentration was found under TS treatment. There was a positive relationship between available P and organic matter, indicating that increasing organic matter could improve the P use efficiency.In summary, conservation tillage improved soil chemical and physical properties after 5 years implementation in a maize-wheat-soybean rotation in the Qingyang Loess Plateau, hence increased crop productivity in longer term.
|
PDF Full Text Request