Study On Spatial Variability And Site-specific Management Of Soil Nutrients Within Fields

Spatial unsynchronization of nutrient supply and demand was one of the most important factors influencing high yield of crops and efficient use of nutrients. At present, little information is available on spatial variability and site-specific management of soil nutrients in main grain production areas from the viewpoint of grid-sampling scales, soil nutrients, crop yield and nutrient uptake being systematically considered. In this research, a rice production area (collective contract management system) of Jiangchuan farm in Heilongjiang province, a winter wheat - summer corn production area (family responsibility management system) of Hengshui in Hebei province, and a spring corn production area (family responsibility management system, rain-fed condition) of Taojia in Jilin province were selected as three experimental areas. Soil nutrient spatial variability characteristics under three grid-sampling scales (50 m×50 m, 100 m×100 m and 150 m×150 m ) in the three study areas, spatial relationship among soil nutrient contents, total nutrient uptake rates and crop yields, and crop response to site-specific balanced fertilization were studied using information technology, such as GIS and GPS, and geo-statistics. This will give scientific bases to develop site-specific nutrient management techniques within fields suitable to Chinese status of collective contract and family responsibility management systems. The main results obtained are summarized as follows:1. Spatial variability of soil nutrientsSpatial variability of soil nutrients in the three study areas were evaluated using traditional statistics and geo-statistics. In the rice production area of Jiangchuan farm under the collective contract management system, soil nutrient limiting factors were N, P, K and Zn. Significant differences in contents of soil nutrients among 9 fields were found in the study area under three grid-sampling scales. Whereas insignificant differences in contents of each nutrient in soils were observed under the three grid-sampling scales. Distinct spatial distribution similarity for each soil nutrient under the three grid-sampling scales was found with relatively high contents in some areas of the study area and relatively low contents in other areas. These showed that status of main soil nutrients under the collective contract management system can be evaluated on 150×150-m grid-sampling scale, and it was technically feasible to develop regionalized N, P, K and Zn nutrient management at the level of the field in the study area.In the winter wheat - summer corn production area of Hengshui under family responsibility management system, the emphasis on soil nutrient management was focused on N, P and K, and the management of Zn should also be given some attention. Insignificant differences in status (average content and C.V.) of each nutrient in soils were found in the study area under three grid-sampling scales. Distinct spatial distribution similarity for each soil nutrient under the three grid-sampling scales was observed with relatively high contents in some areas of the study area and relatively low contents in other areas. These indicated that status of main soil nutrients under family responsibility management system can be evaluated on 150×150-m grid-sampling scale, with the costs of soil sampling, soil testing, etc. decreasing significantly as sampling density decreasing.In the spring corn production area of Taojia under family responsibility management system, soil nutrient limiting factors were N, P, K and Zn. Insignificant differences of each nutrient in soils were generally found in the study area under three grid-sampling scales. Whereas significant differences in contents of soil P and Zn among three production groups were observed under 50×50-m and 100×100-m grid-sampling scales. Distinct spatial distribution similarity for each soil nutrient under the three grid-sampling scales were found, with relatively high contents in some areas of the study area and relatively low contents in other areas. These showed that the status of soil OM and K under family responsibility management system can be evaluated on 150×150-m grid-sampling scales, but the status of soil available P was undervalued and the status of soil available K was overvalued. It was technically feasible to develop regionalized OM and K management at the level of production group, and for soil available P and Zn, each production group could be regionalized into 2 management units, with each unit consisted of connected farmer plots.The moderate collective contract production management in main grain production regions of Northeastern Plain and North-central Plain has a broad prospect from 12th five-year plan. The results indicated that it was technically feasible to develop moderate collective production management of soil nutrients in Taojia of Jinlin study area and Hengshui of Hebei study area under family responsibility management system (Each production group could be regionalized into 1-2 management units for the main soil nutrients, with each unit consisted of connected farmer plots. The area of moderate collective production management is generally more than 6.7 ha ), which is helpful for extending balanced fertilization and enhancing economic income.2. Spatial relationship between soil nutrient contents and crop yieldsBased on the determined yields of crop grain and straw and the collected samples on a 100 m×100 m grid in the three study areas, spatial variability of crop grain yields and the spatial relationship among grain yields, total nutrient uptake rates and soil nutrient contents were analyzed. The results showed that significant spatial variability of crop grain yields and total nutrient uptake rates was found under different management systems (the collective contract management system and the family responsibility management system), and different conditions of agricultural production, with respective C.V. of crop grain yields and total nutrient uptake rates ranging from 9.7% to 15.8% and from 8.2% to 21.1%. Spatial variability of crop grain yields was closely correlated with total uptake rates of nitrogen, phosphorus (P2O5) and potassium (K2O) during growth period of crop, with respective correlation coefficients being 0.76-0.87, 0.68-0.90 and 0.35-0.65.Soil available nutrient was identified as significant sources of crop nutrient uptake. Spatial variability of total uptake rates of nitrogen and phosphorus during growth period of rice, winter wheat, summer corn and spring corn was closely and positively correlated with soil OM contents or corresponding available N or P contents in soils prior to crop seeding. Whereas spatial variability of total potassium uptake rates during growth period of winter wheat was significantly and positively correlated with soil available K contents.Soil nutrient status was one of the most important factors affecting crop yield potentials. Spatial variability of crop grain yields was positively correlated with contents of soil OM and available nutrients. Rice grain yields in Jiangchuan farm study area was closely and positively correlated with contents of OM and available N in soils. Grain yields of winter wheat in Hengshui study area was closely and positively correlated with soil OM contents, and a positive correlation relationship between grain yields and contents of soil available P and Zn was not significant at p < 0.05, respectively. Whereas grain yields of summer corn was closely and positively correlated with soil NH4+-N contents in Hengshui study area. Grain yields of spring corn in Taojia study area was closely and positively correlated with contents of OM, NO3--N and available Zn in soils.3. Proper nitrogen and phosphorus application rates and crop response to the site-specific balanced fertilizationField experiments were conducted to determined proper nitrogen and phosphorus application rates under medium soil fertility in Hengshui and Taojia study areas. The results showed that respective proper N and P2O5 application rates under medium soil fertility in Hengshui study area ranged from 220 to 260 and from 90 to 110 kg/ha for winter wheat, and from 220 to 280 and from 95 to 115 kg/ha for summer corn. Proper N and P2O5 application rates of spring corn under medium soil fertility in Taojia study area ranged from 170 to190 and from 60 to 75 kg/ha, respectively.Site-specific balanced fertilization techniques for high yield and high quality crop production in the three study areas were developed based on the regionalized soil nutrient GIS maps and a computerized fertilizer recommendation system. The results from field experiments showed that significant increase of grain yield, economic income and recovery rate of applied N were observed for the site-specific balanced fertilization. In Jiangchuan farm study area of Heilongjiang, site-specific balanced fertilization techniques increased rice yield, income and nitrogen recovery rate by 4.3%-11.2%, 778.70-1532.00 RMB Yuan/ha and 12.6-14.0 percentage point, respectively. In Hengshui study area of Hebei, yield, income and nitrogen recovery rate by site-specific balanced fertilization techniques respectively increased by 6.7%, 992.5 RMB Yuan/ha and 15.2 percentage point for winter wheat, and by 5.3%-9.0%, 454.19-464.92 RMB Yuan/ha and 8.4-10.7 percentage point for summer corn. In Taojia study area of Jilin, site-specific balanced fertilization techniques increased spring corn yield and income by 7.3%-8.9% and 1280.94-1647.78 RMB Yuan/ha, respectively.