Modelling Studies On Maize Growth And Soil C And N Cycling In The Black Soil

Black soil(Mollisols) is a typical soil and maize (Zea mays L.) is the main crop in Jilin province. In recent year, soil degradation increased with over application of fertilizers and improper tillage and this consequently increase the risk of environmental pollution. It is regarded a feasible method to study crop growth and soil C and N cycling using modeling approach.Decision Support Systems for Agro-technology Transfer (DSSAT) is one of the most widely applied models globally, but there was no report that the DSSAT model has been applied in the Black soil region in China, especially there was no report on using the calibrated crop model and cultivar parameters to simulate soil C N cycling in China. Therefore, this thesis arm at simulating maize growth and soil C and N cycling in the Black soil field in Jilin province using the DSSAT 4.5 model with specially designed field and long term experiments. Through the sensitivity analysis of main output variables (crop growth, yield, crop N uptake, and soil mineral N), sensitive parameters was found effectively. At the same time, the effects of crop managements, climate and different fertilizer N application levels on yield and soil C N dynamics were studied. The best management practices were selected to maintain high yield and soil fertility, and to reduce environmental pollution risk. The research results will provided useful methods for agricultural development, decision making, land use policy and cropping adjustment in the future. The evaluation and sensitivity methods for the DSSAT 4.5 CERES-Maize model can be applied to other crop, soil and region. The methods can also be used to forecast long term yield potential by agricultural extension sectors. Meanwhile, our researches provide useful dataset to support DSSAT 4.5 application. The main research fruits can be summarized as below.Understanding the DSSAT model and its working principle is the key step for parameter calibration. Designing a good field experiment and using a correct lab analysis method are the key step for obtaining model evaluation dataset; effectively collecting long term field experimental data is a pre-condition for applying DSSAT model in sequence/rotation analysis of the long term field experiment. Applying the DSSAT crop system model to simulate field crop growth and soil C N cycling is the key step for regional simulation. Sensitivity analysis and evaluation methods are mostly used method for model application and evaluation. After literature review, systematically learn the two methods are necessary to successfully evaluate a model. Learning quantitative theory of crop growth, soil C N dynamics and soil water balance lay the foundation of model evaluation and modification.When applying the DSSAT model to a new system, a key step is to determine model output sensitivity to input parameters because some sensitive parameter in some region may not be sensitive in other region. For this reason, this study carried out a systematically sensitivity analysis to the main crop management parameters of 4 main dry land crops (Maize, soybean, spring wheat and potato). The results showed agreements for all crops; crop growths and soil mineral N were sensitive to sowing date, density, fertilizer N application rates and times. These results were in agreement with field experimental results.DSSAT CERES-Maize model was applied to our 2008 field experiment with Maize in Black soil to simulate crop growth (LAI, aboveground dry weight and grain yield). Maize cultivar parameters were calibrated using average field data, and the simulation results follow. Planting 8 to 10 days earlier resulted in maize yield reductions of 10%. Yields increased curveilinearly with the increases in plant density in the low to mid range (<5 plants m-2), and levelled off when the density reached 5 plants m-2. Yield and fertilizer N rate followed a diminishing yield pattern with the maximum yield being obtained at a fertilizer N rate of 200-250 kg N hm-2. The optimum fertilizer dress date was June 15-28. The research results also showed that DSSAT model can be used to simulate maize growth in other region of China and the sensitivity method that was established in this research can be applied to other crops, such as rice and wheat.Using 2009 field experiment, DSSAT CERES-Maize model and DSSAT CENTURY soil model were used to simulate crop N uptake and soil C and N dynamics to crop management parameters (sowing date, density and fertilizer N application rates and dates). The results showed that maize targeted yield of 12000-15000 kg hm-2 can be achieved by applying 200 to 240 N kg hm-2. Under this fertilization., the simulated N uptake (aboveground) ranged 250 to 290 N kg hm-2, including 120 to 140 N kg hm-2 from soil N and 130 to 150 N kg hm-2 from fertilizer N. Higher fertilizer N rates of 250 to 420 N kg hm-2 resulted in the increased residual soil N of 63 to 183 N kg hm-2 at harvest. Delaying dress date of N fertilizer (after June 28) also resulted in the increases of residual soil mineral N. When applying up to 6000 kg hm-2 crop residue to the field, simulated soil active organic C and N maintained supply/demand balance during growing season. The study recommended that 200 to 240 kg N hm-2 fertilizer N and up to 6000 kg hm-2 crop residue should be applied to maize field to achieve the targeted maize yield and maintain soil organic C and N balance in black soil zone of Jilin province, China.DSSAT Sequence model was used to simulate 17 years long term maize continuous field experiments (1990-2007) in Gongzhuling, Jilin China. Three N levels (treatments) were used in the simulation; no fertilizer N (NO),165 kg fertilizer N hm-2 (N165) and Organic N(112 kg N hm-2) plus fertilizer N 165 kg N hm-2) (M112+N165). Both measured and simulated results showed that maize yields, soil C and N changed with time, and the trends reflect climate changes (i.e., yields was lower in drought years). This proved that vater, temperature and solar radiation are key factors for crop growth. There was a significant correlation between the simulated and the measured maize yield (R2=0.69). Simulated soil organic C and N showed that under single fertilizer N165 kg N hm-2, soil N leaching increased up to 150 kg N hm-2 at harvest. It was also found that under N165 treatment,100% crop residual return can maintain soil active organic C and N balance during 17 year period. Under M112+N165 treatment,100% crop residual return can increase soil active organic C and N significantly and reduce soil mineral N leaching.