| Guanzhong region with fertile soil, abundant light, heat and water resources, is the major area for grain production in Shaanxi Province. Statistics during recent 15 to 20 years show that the gap of grain yield per hectare between Shaanxi Province and the whole country is widen. So it is urgent and pressing to increase grain yield per hectare for grain security in Shaanxi Province. Wheat-summer rotation is the main crop production system in Guanzhong region. Reasonable fertilizer application is the focus of plant nutrition researchers. In recent years, there are many problems about the application of nitrogen, phosphorus and potassium fertilizers in the rotation system. Grain yield in wheat-summer rotation system is closely related to status of nitrogen, phosphorus and potassium nutrients in soil. Scientific management of the three nutrients resources plays a very important role in improving wheat and maize yields. Therefore, through field experiments and laboratory analysis, using optimized cultivation and management measures of water, fertilizer, crop varieties and planting density, this research aims to explore production potential of land in Guanzhong area under wheat-maize rotation system, and clarify the absorption and accumulation status of nutrient resources such as nitrogen, phosphorus and potassium in high-yield condition. Meanwhile this study is purposed to find the optimization ratio of nitrogen, phosphorus and potassium fertilizer to provide theory basis for rational fertilization and nutrient resources management, and to provide technical supports for steadily increasing grain yield. The main results were showed in the following:1. Fertilizer Application Status Evaluation of Wheat and Maize in Guanzhong Plain of Shaanxi ProvinceTo fully clarify nutrient resources management status and existing problems of fertilizer application of wheat and maize in Guanzhong plain of Shanxi Province, 220 households in Gaoling county, Wugong county and Yangling agricultural demonstration district were randomly selected by the end of 2008 to investigate household management, field management and fertilization status of wheat and maize. The investigation results showed that the application amount of nitrogen fertilizer for maize was 47.6% higher than for wheat. The ratio of households who applied reasonable amount of nitrogen and phosphate fertilizer for wheat production was 36.8% and 27.4% respectively. Households inputting more N fertilizer for maize accounted for more than 70% of all the surveyed households. More than 80% of N and P fertilizer and all the K fertilizer were applied as base fertilizer for wheat, and 72.6% of N fertilizer and more than 95% P and K fertilizer were applied as base fertilizer for maize. The input ratio of nitrogen, phosphorus and potassium nutrients for wheat production was 52.4%, 35.9% and 11.7% respectively. Maize mainly was applied N fertilizer, followed by P and K fertilizer. Nutrient inputs of nitrogen, phosphorus and potassium for maize production accounted for 77.6%, 15.3% and 7.1% respectively.2. Effect of Optimized NPK Fertilizer Application on Wheat Yield and Nutrients Absorption and AccumulationField experiment from 2007 to 2008 in Dianbei wan village of Fufeng county Shaanxi Province was conducted to study the effect of optimized NPK fertilizer application on wheat yield and nutrients absorption and accumulation. The results show that the optimized NPK fertilizer application significantly increased grain yield and biomass of wheat. Nitrogen fertilizer had the most obvious effect on increasing grain yield, which increased grain yield from 5974 kg/ha to 8218 kg/ha. Phosphorus and potassium fertilizer had the same effect on grain yield increase. Balanced NPK fertilization could significantly improve wheat spikelet number and 1000-grain weight. The order of wheat spikelet number was the same as that of yield. Optimized NPK fertilizer application could greatly improve nitrogen absorption amount of wheat grain and straw. Nitrogen fertilizer efficiency in the NPK treatment was 35.3%, which was the highest one compared to other treatments with the nitrogen fertilizer efficiency ranged from 12.2% to 18.7%. Approximate 72.3% to 77.8% of nitrogenous fertilizer was not utilized by crops. The consumption amount of N, P and K nutrients for 100 kg grain yield was 2.74, 0.42 and 2.17 kg respectively. More nitrogen fertilizer promoted uptake of nitrogen, reduced uptake of potassium, but had no effect on phosphorus uptake. Overall, the nitrogen consumption increased, whereas phosphorus and potassium consumption decreased for production of 100 kg wheat grain in the NPK treatment.3. Study on Nitrogen Uptake, Transformation and Accumulation of Winter Wheat under Different FertilizationOne-year field experiment from 2008 to 2009 was conducted to study nitrogen uptake, transformation and accumulation of winter wheat (Xiaoyan 22) under different fertilization, which aimed to provide a theory for N application of winter wheat in Guanzhong area of Shaanxi Province. The results showed that wheat grain yield increased significantly when nitrogen, phosphorous and potassium were applied with organic fertilizer. When organic N rate was 150 kg/ha and chemical N rate ranged from 150 to 225 kg/ha, wheat grain yield reached 9000 kg/ha, which was higher than that of conventional fertilization. When N rate was between 270 and 300 kg/ha without organic fertilizer, the difference of wheat grain yield was not significant compared with conventional fertilization, which indicated that organic fertilizer had great effect on the increase of yield. Fertilization had significant effects on N accumulation. N accumulation amount increased significantly when N, P and K were applied to wheat compared with conventional fertilization. N accumulation amount ranged from 249.3 to 283.0 kg/ha when N, P and K were incorporated with organic fertilizer. N accumulation amount in the middle and later growth stages and N transformation amount of nutritional organ after anthesis increased when N, P and K were applied to wheat compared with conventional fertilization. In conclusion, in order to get high wheat grain yield, the recommended N application rate in Guanzhong area of Shaanxi Province was from 150 to 225 kg/ha, which should be applied with P, K and organic fertilizer.4. Effect of Different Fertilizer Application Patterns on Yield and Nutrients Balance of MaizeField experiment in 2009 was conducted to study the effect of different fertilizer application patterns on maize yield, nutrients absorption and balance. The results showed that organic fertilizer with nitrogen, phosphorus and potassium fertilizer could significantly improve the grain yield of maize. Maize ear number and rate of empty culms increased gradually with the increase of planting density. More spikelets decreased the influence of empty culms on grain yield in high-planting-density condition. The rate of dry matter accumulation accelerated at the former growth stage, and then slowed down at the later growth stage. The main phases for biomass accumulation were from seedling to jointing stage and from floret to filling stage. Total nitrogen uptake amount of maize increased as application rate of nitrogen fertilizer increased. The increased amount of nitrogen absorbed was mainly because grain took up more nitrogen. The highest amount of nitrogen, phosphorus and potassium absorbed in all the treatments were 223.3, 26.0 and 216.4 kg/ha respectively. High-yield treatment could improve harvest index nitrogen fertilizer, but reduced harvest index of phosphorus and potassium fertilizer to some extent. The highest harvest index of nitrogen, phosphorus and potassium fertilizer in all the treatments were 78.2%, 82.8% and 33.8% respectively. Harvest index of phosphorus fertilizer was the highest, followed by nitrogen and potassium in the same fertilizer application pattern.5. Tentative Research on Super-high-yield of Summer Maize in Guanzhong Region of Shaanxi ProvinceUsing Zhengdan 958 as research material, field experiment was carried out in 2008 to study the effect of planting density on grain yield of summer maize, which aimed to explore production potential of summer maize in Guanzhong area Shaanxi Province. The results showed that the regression equation of planting density and yield is in the following: y = 5E-07x2 + 0.138x + 279.46(R2 = 0.8406). Grain yield and biomass of summer increased significantly along with the increase of planting density, and high-density treatment could greatly improve grain yield. Grain yield reached 1172 kg/mu in the 6500 plants/mu planting density treatment, which was 31.3% higher than that of 4500 plants/mu planting density treatment. High-density displayed obvious yield increase. Row number and grain number per panicle increased, and then decreased and 100-grain weight decreased as the plant density increased. Row number and grain number per panicle was the highest when planting density was 5500 plants/mu, and 100-grain weight was the highest in the 4,500 plants/mu treatment. Planting density increased plant height and ear height, and reduced stem diameter, which was bad for lodging-resistance.
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