| In order to explore the farming system of the long-term straw return,reducing the amount of nitrogen fertilizer based on the conventional nitrogen amount of farmers can significantly optimize the agronomic traits of maize.To improved the photosynthetic performance of maize,delay leaf senescence,improve root architecture,increase yield and grain nitrogen.It can increase the economic benefit of nitrogen fertilizer.In this test,the variety was the main factor and the nitrogen topdressing amount during jointing was the secondary factor.It use split plot design,and repeated three times.It were used nine spring-sown mid-late maturing compact maize varieties(3 of which are market-leading varieties and 6 of similar varieties cultivated in the laboratory),and four different nitrogen fertilizers were applied at the jointing stage.Four different nitrogen fertilizers were B1: 0 kg/ha(control treatment);B2: 300 kg/ha(equivalent to pure nitrogen 138 kg/ha);B3: 450 kg/ha(equivalent to pure nitrogen 207 kg/ha);B4: 600 kg/ha(conventional treatment,equivalent to pure nitrogen 276 kg/ha).And the top dressing is urea(46% nitrogen).The results show:1.The plant height,ear height,and leaf area of the three leaves of the maize all showed a single-peak change trend with the increase of the amount of nitrogen chasing,and reached the highest value under B3 treatment.Under B3 treatment,the plant height,ear height,and bar clover leaf area were significantly higher than that of B1 treatment,which were 7.1%,5.8%,and 16.1%,respectively.2.The biomass of maize stalks,leaves,roots and female spikes showed a single-peak change trend with the increase of nitrogen chasing amount,and reached the highest value under B3 treatment,and the leaf sheath biomass reached the highest value under B2 treatment.B4 treatment reached the lowest value.Reflecting the inhibitory effect of high nitrogen on various parts of biomass.The biomass of stalks,leaves,roots and female spikes under B3 treatment was significantly higher than that under B4 treatment,which weree 50.1%,20.9%,44.5%,and 60.2% higher,respectively.The above-ground biomass of B3 treatment was significantly higher than that of B4 treatment,and was 41.4% higher.3.The photosynthetic rate and transpiration rate of panicle leaves have been increasing with the increase of the amount of nitrogen chasing,and the SPAD value has a single-peak change trend with the increase of the amount of nitrogen chasing.Under B4 treatment,the photosynthetic rate and transpiration rate of maize ear leaves were significantly higher than that of B1 treatment,which were 38.6% and 55.1% higher,respectively.Under the B3 treatment,the SPAD value of the maize ear leaves was significantly higher than that of the B1 treatment,which was 24.1% higher.4.The characteristic values of light intensity and light quality distribution at the ear and the bottom.It all showed a trend of decreasing first and then increasing with the increase of nitrogen chasing amount,and reached the lowest value under B3 treatment.Under B1 treatment,the average inclination angle of maize ear and bottom leaves were significantly higher than that of B3 treatment,which were 167 % and 70.5%higher,respectively.Under B1 treatment,the transmittance of scattered radiation of maize ear and bottom leaves were significantly higher than that of B3 treatment,which was 80.1% and 100% higher,respectively.5.The POD and SOD enzyme activities in the ear leaves have been increasing with the increase of the amount of nitrogen chasing.The POD and SOD enzyme activities in the ear leaves under B4 treatment were significantly higher than those in the B1 treatment,which were 104% and 56.9% higher.The MDA enzyme activity of the leaves in the panicle showed a trend of decreasing first and then increasing with the increase of the amount of nitrogen chasing,and reached the lowest value under B3 treatment,which was significantly lower than that of B1 treatment,and was 42.7% lower.6.The surface root structure index values of the surface layer all showed a single-peak change trend with the increase of the amount of nitrogen chasing.Under B3 treatment,the root length,root surface area,root average diameter,root volume,and number of root tips were significantly higher than those of the B1 treatment.They were 39.0%,63.0%,17.4%,35.7% and 34.3% higher,respectively.7.The yield of maize grains showed a single-peak change trend with the increase in the amount of nitrogen chasing.Under B3 treatment,the yield was significantly higher than that of B1 treatment,which was 18.5% higher.When screening yield-related indicators,it was found that the correlation between plant height,surface root architecture,photosynthetic performance of ear leaves,distribution of light intensity and light quality at ear and bottom,and the activity of leaf protective enzymes at ear positions reached a significant level.And the coefficient of determination R2 = 0.87.The nitrogen content of maize kernels has been increasing with the increase of nitrogen content.But with the increase of nitrogen content,the increase of nitrogen content in grains has become smaller.The nitrogen content of grains under B4 treatment was significantly higher than that of B1 treatment,and it was 39.5% higher.When screening the relevant indexes of grain nitrogen content,it was found that plant traits,stalk biomass,photosynthetic performance of panicle leaves,distribution characteristics of light intensity and light quality at panicle and bottom,protective enzyme activities of panicle leaves and leaf root topography and grain nitrogen content The correlation of the quantity reached a significant level.And the determination coefficient R2 = 0.87.Under the long-term straw returning farming system in the middle-late maize planting area in Shanxi,it can be optimized to reduce the amount of nitrogen fertilizer by 25%(that is,to apply nitrogen fertilizer 450 kg / ha during the jointing period)on the basis of the conventional nitrogen amount(600 kg / ha).It can optimization agronomic traits,and enhance the photosynthetic performance of the ear leaves,and optimize the distribution of light intensity and light quality at the ear and bottom,and delay the senescence of the leaves at the ear,and improve the surface root system configuration,and increase the amount of nitrogencontaining nutrients transferred to the grain,and benefit the economic benefits of nitrogen fertilizer.It also can reduce the impact of nitrogen leaching on soil ecology,thereby increasing the economic,social and ecological benefits of maize. |
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