| Paddy rice-upland crop rotation system is a major cropping system which distributed widely along the Yangtze River basin in China. A unique character of this system is the annual conversion of soil from aerobic to anaerobic and then back to aerobic condition (i.e. alternative changes in soil moisture and temperature), which can result in changes of soil physical, chemical, and biological prosperities among seasons, and difference from the upland or wetland ecosystem, as a special agroecosystem. However, there are some practical problems in this rotation ecosystem, such as unclear soil fertility quality, limiting factors of soil nutrients, lack of fertilization guidelines, decrease of fertilization efficiency and output-input ratio and so on. So, it is important to reveal the figures of nutrition cycling, nutrient-limiting factors and status of soil fertility quality, and to fertilize for crops, which can increase the yield of crops and fertilization efficiency, reduce the loss of fertilizers and the risk of over-fertilization, and also ensure the safety of food and environmental and promote the Chinese sustainable agricultural development.In this study, soil investigation, pot and field experiments were conducted to reveal the figures of nutrition cycling, nutrient-limiting factors and status of soil fertility quality, and study the effects of nitrogen (N), phosphorus (P), potassium (K) fertilizers on rapeseed and rice and their efficiency. The computer language of Visual Basic and web technology of Active Server Pages (ASP) were employed to design the software of Soil Fertility Quality Evaluation and Fertilization Decision System for Paddy rice-upland Rotation System. The main results were as follows.1. A soil investigation was conducted to study on the soil fertility variation in Jingzhou county of Hubei province from 1981 to 2006. The results showed that, from 1981 to 2006, soil pH and organic matter decreased by 3.35% and 32.2%, while total nitrogen (TN), available N (alkali-hydrolysable N, AN), available phosphorus (AP) and available potassium (AK) increased by 0.4 g kg-1,21 mg kg-1,8 mg kg-1 and 32 mg kg-1, respectively. That should be presumably resulted from more application of inorganic fertilizers (especially acid and/or physiologically-acid fertilizers), less application of organic fertilizers, little growing of green manure and removal of crop residues and straws. Balanced application of organic and inorganic fertilizers is urgent to improve soil organic matter, pH and soil fertility in this area.2. A soil investigation was conducted to anlysis the status of soil nutrients in the paddy rice-upland rotation regions of Hubei province and some methods were employed to evaluate the soil fertility quality. The results showed that the average pH in paddy rice-upland rotation regions was 6.01, and part of the region was very acid. Average soil organic matter concentration was 21.6 g kg-1 with a very great difference among soils, which indicated that the soil organic matter in paddy-rice rotation system region was not sufficient. Average soil available N was 120.3 mg kg-1, and the concentrations of most of soils were over 90 mg kg-1, which suggested that soil available N in this region was moderately abundant. Average soil available P (Olsen P) was 12.6 mg kg-1, and the concentrations of most of soils were less than 10 mg kg-1, which suggested that soil available P in this region was moderately deficient. Average soil available K was 86.2 mg kg-1, and 20.8% of soils available K was less than 60 mg kg-1, which indicated that soil available K in this region was deficient. Soil available calcium (Ca), magnesium (Mg), silicon (Si), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn) was abundant, of whose average concentrations were 2680,244,176,117,25,3.2,1.9 and 42 mg kg-1, respectively. The average concentrations of molybdenum (Mo) and boron (B) were 0.48 and 0.068mg kg-1, respectively, which indicated that soil available Mo and B in this region were deficient.The soils in the regions of paddy rice-upland rotation in Hubei province could absorb and fix the elements of P, K and B, with the absorption ratio of 59.9%,31.6% and 32.1%, respectively, while sulfur (S), Cu, Mn and Zn were not absorbed and fixated by the soils. In addition, the elements of N, P and K were the main limiting factors of crop growth in the regions.Based on fuzzy logic and the total data set (TDS) of soil quality indicators (pH, OM, available N, P and K, total N, P and K, available Fe, Mn, Cu, Zn, B, Mo and CEC), the results of soil fertility quality assessment showed that the average integrated score of soil fertility quality was 0.509. Soil fertility quality in Macheng and Jingzhou county was mainly grade III, that in Chibi and Shayang county was mainly grade II and III, and in Honghu county was grade II. There were no grade I (very good) and grade V (very bad) in this region of five counties.Soil organic matter, available N, P, K, B, Zn and Mo were chosen by principal components analysis and correlation analysis to form the minimum data set (MDS) for evaluating the soil fertility quality. The results of soil fertility quality evaluated basing on the MDS showed that the average integrated score of soil quality was 0.441. Soil fertility quality in Macheng, Chibi, Shayang, Jingzhou and Honghu county was mainly grade III, followed by grade IV.3. A field experiments of nitrogen, phosphorus and potassium fertilizers were conducted to study the fertilization efficiency and the recommendable fertilization rates of N, P, K for rice and rapeseed. The results showed that applications of N, P and K fertilizers promoted the yield and the yield component factors of rice and rapeseed, of which, N and P fertilizers significantly increased the yield of rapeseed. What's more, the yield of rice and rapeseed increased by N fertilizer was much greater than that of P and K fertilizers, which suggested that N fertilizer was the main factor of the yield. Application of N, P fertilizer increased the economic output of rice and rapeseed, while K did not increased the economic output, and K even lead to loss in rice. In addition, application of P, K fertilizer could get more economic output in rapeseed than that of in rice. In rapeseed and rice, partial factor productivity (PFP) and agronomic efficiency (AE) of N fertilizer increased by the elevated N fertilizer application rates and that of recovery efficiency (RE) increased first and then decreased. However, PFP, AE and RE of P, K fertilizer significantly decreased by the elevated P, K fertilizer application rates, respectively. The use efficiency of P and K fertilizer was better than that of N fertilizer in rapeseed, while the use efficiency of N and K fertilizer was better than that of P fertilizer in rice. The use efficiency (PFP, AE and RE) of N, P and K fertilizer in rice and rapeseed was different, i.e. the use efficiency of N fertilizer in rice was better than that in rapeseed, the use efficiency of P, K fertilizer in rice was worse than that in rapeseed.The regression of quadratic equation (one factor (y=a+bx+cx2) and three factors (Y=bo+b,N+b2P+b3K+b4NP+b5NK+b6PK+b7N2+b8P2+b9K2)) of N, P and K fertilizers showed that the optimum fertilization rates for rapeseed were:N 165-270 kg ha-1 with the average of 216 kg ha-1; P2O5 68-110 kg ha-1 with the average of 93 kg ha-1; K 42-147 kg ha-1 with the average of 100 kg ha-1, and the ratio of N:P2O5:K2O was 1:0.43:0.46. While, the optimum fertilization rates for rice were:N 89-220 kg ha-1 with the average of 170 kg ha-1; P2O5 39-97.5 kg ha-1 with the average of 67 kg ha-1; K 59-232 kg ha-1 with the average of 121 kg ha-1, and the ratio of N:P2O5:K2O was 1:0.39:0.71.Field experiment demonstrated that the recommendable fertilization of N, P and K for rapeseed and rice increased the economical output compared with the conventional fertilization by framers, i.e. the yield of rapeseed increased by 462 kg ha-1, and the economical output increased by 1570 Yuan ha-1, with an increase of 16.9%. For rice, the yield and economical output increased by 1058 kg ha-1,1693 Yuan ha-1, respectively.4. The computer language of Visual Basic and web technology of Active Server Pages (ASP) were employed to design the software of Soil Fertility Quality Evaluation and Fertilization Decision System for Paddy rice-upland Rotation System. Based on the mathematic method of fuzzy logic, Soil Fertility Quality Evaluation System provides the total data set (TDS) and minimum data set (MDS) for assessing the soil fertility quality of the paddy rice-upland rotation system region of Hubei province. Based on the field experiment, Fertilization Decision System could recommend the application rates of N, P and K fertilizers for rapeseed and rice according to the soil nutrient status and the nutrient demand of rapeseed and rice. The system also provided the knowledge of balance fertilization, nutrient demand of rapeseed and rice, pests and weeds of rapeseed and rice, fertilization guideline of rapeseed and rice.5. A pot experiment of winter wheat-rice and rapeseed-rice rotation was conducted to study the changes of soil nutrtions and the balance of N, P and K in the paddy rice-upland rotation system. The results showed fertilization (with N, P and K fertilizers) and non-fertilization (control) treatment had no effect on soil pH in the two years'experiment. The fertilization treatment did affect the soil nutrients, i.e. increase the concentration of soil N, P and organic matter (OM), while non-fertilization treatment decreased the concentration of soil N, P and K, thus, it reduced the soil fertility.The balance of N and P in this two rotation systems were surplus, with the value of 1380,561 mg pot-1 (rapeseed-rice) and 1899,582 mg pot-1 (wheat-rice), respectively, but the balance of K was deficit, with the value of 27 mg pot-1 (rapeseed-rice) and 156 mg pot-1 (wheat-rice), respectively. The surplus of N, P and the deficit of K in rapeseed-rice rotation system were less than those in wheat-rice rotation system. In addition, the N, P, K balance of rapeseed-rice pot experiment was different from that in rapeseed-rice field experiment, i.e. in the pot experiment, N and P were in surplus and K was in deficit, while, in field experiment, N was in surplus, P was in balance and K was in deficit.
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