| The purpose of this experiment is to clarify a suitable combination of tillage methodand nitrogen rate to improve wheat yield and protein content in Shajiang black soil. Underthe field experiment conditions, three tillage methods (subsoiling tillage, rotary tillage, andconventional tillage) was used as the main area, four nitrogen application rates (0,120,225and330kg·hm-2) was used as deputy district. From this experiment, physical, chemical andbiological characteristics of Shajiang black soil, nitrogen assimilation after jointing stage,nitrogen accumulation, distribution, transport and utilization efficiency, grain yield andprotein content were determined to study the effects of different tillage methods andnitrogen application rate on the soil nitrogen transformation, nitrogen utilization andphysiological mechanism of wheat in Shajiang black soil region. The results of this studyare as follows:Soil bulk density was reduced, soil moisture content and total porosity was increasedand root biomass was extended by subsoiling tillage in10-40cm soil layer. Soil bulk densityof surface layer (0-10cm) was reduced by rotary tillage and root biomass was higher on thissoil layer. Conventional tillage changed the original soil with clay shifting and the bulkdensity of the surface soil was increased. Rotary tillage and conventional tillage cann’timprove the heavy state on rhizospheric layer of Shajiang black soil. Rotary tillage evenincreased soil bulk density of10-20cm soil layer, resulting in a decrease of root volume.Visible, subsoiling tillage can break the plough layer, improve rhizospheric soil conditionsand promote the growth of wheat root downward.NO3-N supply of surface layer (0-20cm) can be improved during earlier stage of wheatby rotary tillage. Soil nitrogen on root growth layer (0-40cm) of subsoiling can continue tosupply root growth in the whole growth period. In addition to conventional tillage andsubsoiling tillage which showed NO3-N content of N225treatment was significant highest in0-20cm layer in flowering stage. Other stages NO3-N content, NH4+-N content and totalnitrogen content were increased with the increasing of nitrogen application rate in0-20cmand20-40cm layer under three kinds of tillage method. With the increasing of nitrogenapplication rate, NO3-N content was significantly enhanced, but NH4+-N content and totalnitrogen content were relatively stable. Ammonifying bacteria and nitrifying bacteria were more active in the flowering stageand middle filling stage. The activity of denitrifying bacteria in soil was contrary toammoniated bacteria and nitrifying bacteria. The activity of denitrifying bacteria in jointingstage and mature stage were higher. Urease and protease activity in rhizospheric soil werehigher in jointing and flowering stage, urease activity was far greater than othermicroorganisms and enzyme activity. Ammonifying bacteria, urease and protease activity ofsubsoiling in rhizospheric soil were the highest in each period, except the peak ofammonifying bacteria activity in rotary tillage is higher than conventional tillage, the restshowed that conventional tillage was higher than rotary tillage. Nitrifying bacteria activity ofrotary tillage in rhizospheric soil was the highest in jointing and flowering stage. Nitrifyingbacteria activity of subsoiling tillage was the highest20days after flowering and maturity.The higher soil nitrogen levels of subsoiling way can meet the nitrogen absorbing of roots,so the inhibition of denitrifying bacteria was not obvious. Ammonifying bacteria, nitrifyingbacteria, denitrifying bacteria, urease and protease activity of high nitrogen application rate(N225and N330) were significantly higher than low nitrogen application rate (N120) andN0in three tillage methods. Denitrifying bacteria activity of N225treatment was the highestunder the three kinds of tillage method. Ammonifying bacteria, nitrifying bacteria, ureaseand protease activity of subsoiling increased significantly and N330treatment was thehighest in each stage. But for conventional and rotary tillage, with the increase of nitrogenapplication rate, the improvement of soil nitrogen transformation microorganisms activityand enzymatic activity was not significant, and sometimes when the nitrogen fertilizer over225kg· hm-2, there were lower trend.The effects of tillage methods on the size and the duration of GS activity weresignificant. There were different responses of GS activity on nitrogen application rate underdifferent tillage. The peaks of GS activity, free amino acid content and soluble proteincontent were found10days after flowering in subsoiling way with225or330kg·hm-2nitrogen application rate, other treatment combinations were found in flowering stage. Freeamino acids and soluble protein content of leaf is consistent with the GS activity in responseto a combination of tillage method and nitrogen application rate. Chlorophyll content, leafarea index of functional leaf and GS activity, free amino acids, soluble protein, total nitrogencontent of grain were the highest by subsoiling way. Subsoiling tillage not only improvedthe ability of nitrogen assimilation in wheat, but also for the duration and the content ofnitrogen assimilation, and the function was significant. With the increase of nitrogenapplication rate, the ability of leaf nitrogen assimilation in subsoiling was enhancedsignificantly and N330treatment was the highest. But for conventional and rotary tillage, when the nitrogen fertilizer over225kg·hm-2, there were lower trend in some stage. GSactivity and free amino acid content of grain increased with the increasing of nitrogenapplication rate under three tillage systems. Soluble protein content and total nitrogencontent of grain with N330treatment were the highest in subsoiling10days and20daysafter flowering and N225treatment were the highest30days after flowering. Conventionaland rotary tillage were the highest with N225treatment throughout the whole filling stage.Nitrogen accumulation in various organs and total nitrogen accumulation in floweringstage, subsoiling tillage was the highest, rotary tillage was the lowest. Leaf nitrogendistribution rate of rotary tillage was the highest, spike and stem nitrogen distribution rate ofsubsoiling tillage was the highest. Subsoiling tillage had higher translocation nitrogen fromvegetative organs to grain, higher absorption nitrogen after flowering and highercontribution from absorption nitrogen after flowering to grain than the other two tillagemethods. So the nitrogen accumulation and distribution rate of grain were the highest. Theamount of translocation nitrogen, translocation efficiency and absorption nitrogen afterflowering were the lowest in two years experiment. So the nitrogen accumulation anddistribution rate of grain were the lowest. The distribution rates of stem, spike-stalk andshell were the highest. Total nitrogen accumulation and nitrogen accumulation and thedistribution ratio (except grain) in various organs were increased with the increase ofnitrogen application rate, nitrogen accumulation in grain, N225treatment was the highest.Compared with the other two tillage methods, positive promotion on grain nitrogenaccumulation of subsoiling tillage were more significant with the increase of nitrogenapplication rate. With the increase of nitrogen application rate, translocation nitrogen fromvegetative organs to grain was increased. With the increase of nitrogen application rate, thechange trend of translocation efficiency, contribution rate from translocation nitrogen tograin, absorption nitrogen after flowering and contribution rate from absorption nitrogenafter flowering were different.Tillage method and nitrogen application rate had a significant impact on grain yield andprotein content. Grain yield and protein content of subsoiling were the highest, rotary tillagewas the lowest. Under the three kinds of tillage method, wheat yield and protein contentwere increased with the increase of nitrogen application rate. The spikes, kernels per spike,103grain weight and grain yield in subsoiling way with330kg hm-2nitrogen applicationrate is the highest, and the outputs of conventional tillage and rotary tillage were maximumin nitrogen application rate for225kg·hm-2. The grain protein content was highest with225kg·hm-2nitrogen application rate under three kinds of tillage.Due to the high nitrogen absorption of roots, the high assimilation ability of leaf and grain and the high translocation nitrogen from vegetative organs to grain in subsoiling, soilnitrogen contribution rate, nitrogen recovery efficiency, partial factor productivity fromapplied nitrogen, nitrogen harvest index and nitrogen input-output ratio were effectivelyimproved. Nitrogen uptake of wheat is limited in rotary tillage, but the utilization efficiencyof absorbed nitrogen was high in the plant. Under those three kinds of tillage method, theresponses of nitrogen uptake efficiency, nitrogen utilization efficiency, soil nitrogencontribution rate, nitrogen recovery efficiency, nitrogen physiological efficiency, partialfactor productivity from applied nitrogen, nitrogen harvest index and nitrogen input-outputratio on nitrogen application rate were consistency. With the increase of nitrogen applicationrate, nitrogen efficiencies were decreased. Mainly because that the distribution rate ofnitrogen at grain decreased relatively, and the distribution rate in stem increased with theincrease of nitrogen application rate causing nitrogen utilization efficiency decreased. |
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