Study On Evaluation Of Farmland Fertility And Its Application In Hubei Province

Farmland is the most important resource of agricultural production and the prime of land, fertility of which has a direct influence on food security and sustainable development of agriculture. Therefore, it is fundamental work of improving quality of farmland and properly making use of it to evaluate farmland fertility grade and analysis the factors and their change conditions affecting on soil fertility.Adopting traditional method of soil survey and geological information system (GIS), geological position system (GPS), remote system (RS) techniques, choosing 4 counties (or cities) in 3 agricultural areas, including Ezhou City in Edong hilly area along Yangtze River located at eastern Hubei province, Zhongxiang City in central area of Hubei province, both Jiangling County and Jingzhou District in Jianghan Plain located at south Hubei province, investigate and study farmland fertility and its variation characters with time and space within period of 1980-1981 and 2003-2005. Using farmland fertility evaluation achievements, it is also to carry out special study to such research hotspots as soil nitrogen testing and fertilizer recommendation, indexes of abundance and shortage of soil available P, models of precision farming in south China, improvement and utility of middle-and-low-yield cropland, food security, compare soil nutrient interpolation with different sampling density. Conclusions were as follows:1. The evaluating units of farmland fertility established by overlapping soil maps and soil utilizing maps with GIS, index system and evaluation model were set up respectively according to the physiognomy of three areas above, and the farmland fertility grade was comprehensively evaluated. The result showed that farmland in Ezhou City could be divided into one to six grades, in which grade one to grade two (high-yield farmhmd) accounted for 22.57% and grade four or below (low-yield farmland)38.22% in area. The farmland in Jiangling County (including Jingzhou District) and Zhongxiang City could be divided into one to four grades, in which mid-and high-yielding farmland took up 77.75% and 72.12%, and mid- and low-yielding farmland 22.25% and 27.88%. However, in near twenty years, farmland in different areas had an obvious change that the amount and quality of farmland in hill district decreased obviously, while the area in plain district had a little bit decrease, and the quantity and quality were almost stable.2. Soil physico-chemical properties and variability in space and time in tillaged-layer of paddy, dry field and vegetable field in different physiognomic areas were analyzed. The variation characteristics for various soil nutrient elements in the three different types of farmland before and after twenty years were explored and compared. It were revealed that content of soil OM, total N, available K showed a decline in paddy fields, soil available P increase obviously, that contents of soil OM, total N, fast K exhibited an increase in dry fields. And the same trend of soil acidification was showed in both paddy and dry fields. For vegetable field, the distribution properties of soil nutrients in both tillaged-layer(0-20cm) and sub-tillaged-layer (20-40cm) were studied. The research discovered that contents of OM, alkali-hydrolyzable N, available P and K, and available B,Zn,Fe,Mn,Mo took on vertical distribution (tillaged-layer＞sub-tillaged-layer), while pH value showed reverse development (tillaged-layer＜sub-tillaged-layer)-pH6.65 in tillaged-layerand and pH7.14 in sub-tillaged-layer. So, the above results indicated that soil nutrient elements accumulated in tillaged-layer and acidification developed into under-layer. According to the various types of soil classification, the main variation rules of chemic.-physical properties of them were gained at the same time.3. By using interpolation methods of Kriging, spline function, distance-and-weight-countdown, comparing interpolation effects for contents of soil nutrient in different space, and analyzing proper sampling density in line with soil properties, the research found out that interpolation methods of Kriging and distance-and-weight-countdown was more precise than method of spline function, the dispersion degree of interpolation results lower than actually, that of method of spline function higher, proper sampling density had relation to soil utility types and variability of contents of soil nutrient elements, and that soil texture had influence on interpolation error—the interpolation error of dry farmland was larger than of paddy field, and that of soil available P was the largest, that of pH the smallest, and that of NH₄⁺—N and available K in middle. The interpolation error of available P and pH had little change with the increase of soil sampling density and that of NH₄⁺—N and available K decreased as sampling density increasing in the study area.4. In light of fact that content of available P in farmland soil rose to a great extent, twenty-seven rape applying P experiments were carried out in year 2003-2005 in the main rape plantation area of Hubei province to examine grading standard for current soil available P. The results showed that application of P to rape could markedly increase its production, 92.6% experiments for fertilizing P got 5% increase of production, each kilogram of P₂O₅ could produce 6.2 kg of rapeseed and output/input ratio reach 3.10 in average. If taking 50%, 75% and 90% of CK production (no application of P) as standard for P deficiency, the indexes of extreme lack, serious lack and lack were 9.9 mg/kg, 14.3 mg/kgå’Œ20.2 mg/kg, respectively, which showed the new indexes could be taken as a guidance for present rape production.5. Nutrition status of N in soil and rice plant was quickly obtained from plot trial for N-fertilizer treatment. By membrane of ion-exchange resin and digital camera, the data of leaf color index and vegetation Index were collected and studied with the help of image manipulation technique, which indicated that indexes for both leaf color and vegetation had significant correlation with amount of fertilization and so did soil available nutrients obtained by method of ion-exchange resin with the maximum number of tillering. Furthermore, diagnosing model for N-nutrient was preliminarily established, which laid foundation for establishing precision farming model in Edong hilly area along Yangtze River by making use of GIS software to manage these information dynamically.