N Characteristics Of Crop-soil-fertilizer Continuums Of Different Rotation Systems

Field experiment was conducted to determine N uptake, distribution and its fate in variouscrop rotation systems by using15N-labeled technique, which based on a long-term fieldexperiment conducted in QuZhou, North China Plain. In this study, we indicated theimpacts of optimizing nitrogen and water management, increasing soil carbon restitutionand planting nitrogen-fixing crops on “N uptake–soil residues–losses”, explore thenitrogen accumulation and transport at anthesis and maturity stages, and identify the N fateand residual efficiency and evaluate the sustainability of new-established rotation systems.The purpose of this study was to find a cropping system which should be considered foreconomic and sustainable agricultural development in the NCP. The main results were asfollows:(1) The content of accumulated nitrogen in crop aboveground organs and the content oftransferred nitrogen to the grain volume of soil nitrogen are significantly higher than thatof fertilizer nitrogen. So soil nitrogen is the main nitrogen source of the crop. In this study,the accumulation of soil nitrogen in wheat、summer maize、soybeans and spring maizeaccounted for74%、70%、90%and80%. The nitrogen content of wheat in seed mostlycame from the accumulation before flowering. About half of nitrogen content of maize inseed came from the accumulation after flowering. The transport contribution rate by organof summer and spring maize ranged from34.63%to57.74%. The transport contributionrate by organ of soybeans only accounted for16.80%.(2) Nitrate of Con.W/M system with soil depth performance increased for the first and thendecreased, conventional treatment40-140cm soil nitrate was significantly higher thanoptimal treatment. Nitrate accumulated in the soil surface and gradually decreased withsoil depth in the Opt.W/M system. In summer maize and soybeans season nitrogen leachedwith water down strongly. Less nitrogen and more times of fertilization in M system, lessnitrogen leached with water down. Excessive application of nitrogen fertilizer led to soilnitrogen accumulation, in plenty of water conditions with water downward migration.After the whole cropping system, conventional treatment40-100cm15N content wassignificantly higher than optimal treatment,40-60cm was accumulation peak. The15Ncontent of the optimal treatment with soil depth performance decreases with less nitrogen leaching.(3) Under the experimental conditions, the fate of fertilizer in various crop rotation systemsperformed as follows: soil residual> crop uptake> loss. After crop was harvest, apparent Nlosses and soil residues increased with N rate increasing. As to the conventional treatment,the proportion of crop uptake、soil residues and loss were2:6:2. The proportion in the Msystem were3:6:1, the three others are about3:5:2. Less nitrogen and more times offertilization raised the efficiency of nitrogen fertilizer.(4) Compared with other crop rotations, soil nitrogen pool of W/M-M stayed at a lowerlevel state surplus, surplus of21.22kgN/hm2. When the soil nitrogen pool was in thebalance, N fertilization of spring maize、wheat and summer maize should be controlled atabout100、150and170kgN/hm2. W/M-M system not only increased food production butalso balanced the soil nitrogen pool.(5) For comparison with the2-year system grain yields in the five systems were calculatedevery2years as one rotation from2010-2012. The grain yield was the highest in theW/M-M system, followed by Opt.W/M and Con.W/M, and then W/B-M and M. Over thefour rotations, the yield for W/M-M achevied32249kg/hm2, which was1.7%higher thanthat of Opt.W/M. Grain yield in the M system was the lowest among the five croppingsystems, at only65%of the yield in W/M-M. The grain yield of Con.W/M and W/B-Mwere respectively22%and49%lower than that of W/M-M system. Maize showed greaterpotential than wheat in the water and N application decreaseing. The W/M-M systemshould be considered for sustainable agriculture development in the NCP.