| From year2008to2011, typical maize hybrid chuandan418was used to study the regulation of soil fertility variation and characteristics of nutrient absorption, utilization, dynamic growth and yield differences of maize under maize/soybean and maize/sweet potato relay intercropping systems in two main maize producing areas in Sichuan, Shehong in the middle and Ya’an in the west, and the effects of nitrogen fertilizer application and nitrogen strategies on the yield, nitrogen absorption, utilization and their mechanism of maize under two systems were e studied under field experiment. The main results were as follows:1. Regulation of soil fertility variation and differences of maize yield and nutrient uptake in two relay intercropping systemsAfter a year of planting, there was significant differences in soil fertility contents of cultivate layer in different crop strips. The residuals of nitrate nitrogen, available nitrogen and available potassium in the soybean strip were significantly higher than those in the sweet potato strip, however, the residuals of ammonium nitrogen and available phosphorus in the sweet potato strip were higher than those in the soybean strip, and soil fertility contents of cultivate layer in maize strip were of no significance in the two relay intercropping systems. After two or three-year’s strip rotation, the differences of nutrient absorption were great as the preceding crops were soybean or sweet potato, and the accumulation of nitrogen and potassium were higher in maize/soybean than that in maize/sweet potato, while the accumulation of phosphorus was opposite. There was a decreasing in soil fertility content of cultivate layer after crop rotation with maize. The results showed that maize had a better equilibrium effect on nutrient absorption, which would mainly be nitrate nitrogen, available nitrogen and phosphorus.Maize yield in maize/soybean was higher than that in maize/sweet potato with no significant difference after one year planting. This indicated that interspecies reciprocity benefited to maize yield production, but the yield-increasing effect were not significant. After two or three-year’s strip rotation, the maize yield of maize/soybean was considerably higher than that of maize/sweet potato. The two year’s productions were more than those of the previous year with679.5kg/ha and839.1kg/ha on average and with the increases of9.4%and12.6%in the two experimental sites, which reflected a more significant productivity in Shehong than that in Ya’an, the increased productivity may mainly due to the significantly increasing of kernels per ear in Shehong.2. The differences of N Management effects in two relay intercropping systems Two-year’s results in the two experimental sites showed that planting patterns, nitrogen application rates, and nitrogen strategies all had an significant effect on maize yield and there was a significant interactions among them. The results demonstrated that maize yield in maize/soybean was higher than that of maize/sweet potato significantly. In maize/soybean intercropping system; maize yield at treatment N180was significantly higher than other treatments in Ya’an, but that in Shehong was of no significance. In maize/sweet potato intercropping system, maize yield under treatment N270was the highest. Based on the appropriate nitrogen application level established at the previous year, the experiment focused on nitrogen strategies was conducted in Shehong from year2010to2011. The results showed that the two relay intercropping systems both achieved high yield when the nitrogen application amount was between180and270kg/ha, the maize yield in maize/soybean was highest, reaching7710.67kg/ha with the assigning proportion (basic N:jointing N:huge bellbottom N)3:2:5, but maize yield was highest in maize/sweet potato when the assigning proportion was5:0:5, and it reached6648.42kg/hm2.The content of crude protein and lysine were significantly higher in maize/soybean than those in maize/sweet potato, and those remained higher in Ya’an compared to Shehong; The content of crude fat and starch which were insignificantly higher in maize/sweet potato than those in maize/soybean remained higher in Shehong compared to Ya’an. With the increasing of nitrogen application level, the content of crude protein in both the relay intercropping systems increased significantly, and reached their peaks under treatment N360. The amount of lysine increased significantly with the increasing of nitrogen application when the amount of nitrogen was under270kg/ha, however, there was a decreasing trend under the treatment N360, while starch content decreased significantly with increasing of nitrogen fertilizer. The effects of different nitrogen assigning proportions on crude protein and lysine was significant, which indicated that increasing jointing nitrogen application increased crude protein and better effects were obtained by multiple fertilizing method.3. Effects of nitrogen fertilizer on the growing of maize in two relay intercropping systemsStudies found that different planting patterns with different nitrogen levels and nitrogen strategies affected the growth of maize, the accumulation and distribution of dry matters, reflecting significant or extremely significant interaction effects. In the early growth stage, medium-to-high nitrogen levels restrained maize growth. In the middle growth, medium nitrogen application level showed advantages. In maize/soybean intercropping system, plant height, stem diameter, LAI index and SPAD values inceased fastly under the treatment of N180, with30%basic N:20%jointing N:50%huge bellbottom N, however, those indexes were higher in maize/sweet potato relay intercropping when applied N270,50%basic N:50%huge bellbottom N. N360restrained maize growth; Those was mainly because forward nitrogen application led to nitrogen deficiency in Mid-grain-filling stage, decline of LAI index and SPAD values rapidly, which went against the formation of yield. As a result, slower deceasing of LAI index and SPAD values under two systems at suitable nitrogen application level and suitable nitrogen strategie would help to avoid the senescence of leaves.4. Effects of nitrogen fertilizer on maize photosynthesis and accumulation distribution of dry matter in the two relay intercropping systemsAfter successive years of research, results in two experimental sites were concluded that planting patterns, nitrogen application level and nitrogen strategies had a significant effect on photosynthetic rate, stomatal conductance, PS II maximum photochemical efficiency and EQY in every growth stage. The Pn and stomatal conductance of ear leaves in maize/soybean intercropping system were higher than that in maize/sweet potato intercropping system during silking stage and filling stage, but was decreased slowly in filling stage. Maize/soybean improved PS II maximum photochemical efficiency, EQY of ear leaves and the accumulation of photosynthetic products when nitrogen fertilizer was between90and180kg/ha and assigning proportion was30%basic N:20%jointing N:50%huge bellbottom N, meanwhile it helped increase dry matter output rate from leaves and stems to grains, avoiding the senescence of leaves, therefore, and the maximum speed of growth and average growth rate increased, which also helped extend the grain-filing days. All of these benefited the improvement of photosynthetic capacity and the accumulation of photo synthate in Mid-grain-filling stage, ensured that ear length increased appropriately, kernels per ear also improved, and then the whole group storage capacity increased, maize yield potential improved. but for maize/sweet potato there was significant advantage when applied nitrogen fertilizer between180and270kg/ha at assigning proportion was50%basic N:50%huge bellbottom N At silking stage various photosynthetic characteristics indexes were higher when applied nitrogen forward, but was decreased faster at filling stage, because of nitrogen stress, PS II maximum photochemical efficiency and EQY were lower which was against the accumulation of photosynthetic products.5. Effects of nitrogen fertilizer on maize nitrogen metabolism, absorption, utilization and soil nitrate nitrogen accumulation and their interrelation.Plant patterns, nitrogen fertilizer levels and nitrogen application strategies had a significant effect on enzymes activity involved in Nitrogen metabolism, absorption, utilization and soil nitrate nitrogen accumulation. The nitrogen accumulation in maize/soybean was higher than that in maize/sweet potato significantly. N harvest index and N use efficiency were also improved. In maize/soybean intercropping system, there was47.29%to55.48%of nitrogen coming from nutritive organs before blooming,44.52%to52.71%coming from assimilation after flowering. In maize/sweet potato intercropping system, there was51.88%to61.75%of nitrogen coming from nutritive organs before blooming，38.25%to48.12%coming from assimilation after flowering. The accumulation of nitrate nitrogen after maize harvest in maize/soybean which was mainly concentrated from0to60cm layer was significantly higher than that in maize/sweet potato; however, it was slightly higher in maize/sweet potato than that in maize/soybean from60to120cm layer. Proper nitrogen application level and application time helped improve nitrogen absorption and utilization, and promote nitrogen metabolism, and reduce nitrate nitrogen loss effectively. The nitrogen absorption of maize and nitrogen agricultural production efficiency were increased applied180to270kg/ha nitrogen fertilizer to both planting patterns compared to other nitrogen application levels. Maize/soybean relay intercropping system along with3:2:5and maize/sweet potato relay intercropping system along with5:0:5could increase enzymes activity involved in N metabolism and nitrogen use efficiency.Forward nitrogen application would decrease the accumulation of nitrate nitrogen in soil under two systems was mainly due to less fertilizer requirement for maize in the early growing stage, most nitrogen lost caused by leaching which along with the way water flew to below60cm and denitrification, causing a great loss of nitrogen. The accumulation of nitrate nitrogen increased significantly with the increasing of nitrogen application level, especially excessive high level with forward nitrogen applied was not good for improving the activities of nitrate reductase (NR), glutamine synthetase(GS) and sucrose phosphate synthetase(SPS) during the later period of maize growth, and would reduce nitrogen use efficiency... |
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