Site specific nutrient management in China

1. Introduction
The large and ever increasing population in China continues to put pressure on its limited agricultural land resource. This problem will become increasingly serious in the future. It is estimated that the population of China will increase to 1.6 billion and 0.7 billion tons of grain for food will be needed by 2030. The solution of this problem will depend on the application of advanced scientific technology to realize the rational allocation and efficient use of natural resources. How to manage soil nutrients and allocate efficiently organic and inorganic resources of nutrients is the key for sustainable development of crop production in China. Since the 1970s substantial progress has been made in soil testing and improvement of fertilizer application, but a uniform rate of application of fertilizer is usually recommended for a 15-20 ha field regardless of soil nutrient variability within the field. Therefore, some regions of the fields receive too much fertilizer, but others too little.

As a result, land and nutrient resources are wasted with loss of opportunities and benefit. Little work has been done in China to understand the spatial variability of soil nutrients, which affect the sustainable development of agriculture. The precision agriculture approach has been successfully applied in some developed countries with advanced mechanization and large scale operation. The basic principle of variable rate technology (VRT) and site-specific nutrient management (SSNM), which adjusts each agricultural input precisely on the basis of the specific condition of each operation unit of the field should be adaptable to any crop production system, with necessary adjustment of the specific techniques. In this way, with the development of modern technology, precision agriculture can exercise a great influence on technological evolution of agriculture of China.

2. Spatial variability of soil nutrients and crop yield under different management systems
A key requirement for precision agriculture development is to understand comprehensively the spatial variability of soil nutrients. Precision agriculture in developed countries is based on large scale agriculture production with an advanced level of mechanization. However, under the small scale operation in the family responsibility system in China, in which each farmer’s family operate small field plots separately, it is difficult to study the spatial variability of soil nutrients and to develop the variable rate technique (Jin, 1998).

The results from the developed countries show that soil variability can occur on any scale including area, field, regions within the field and even between some millimeter spaces. Bouma and Finke (1993) divided the variability of soil properties into several categories. The first is the static variability, such as soil texture and organic matter. The second is the dynamic variability, such as soil moisture and temperature. The variability of these properties has a direct relationship with the specific condition in the field, but the variability of physical-chemical properties is more important for researchers because it is the main reason for the variability of crop yield. With support from the Ministry of Agriculture, Monsanto and IMC Global, a study on soil fertility variability within a 50 hectare cotton field in Handan county of Hebei province, one of the main cotton production regions, was conducted by the Soil and Fertilizer Institute (SFI) of the Chinese Academy of Agricultural Seiences (CAAS) in 1998/1999. Results indicated that after about 20 years of small scale separate operation, remarkable variability in available soil nutrient content was found for most soil nutrients studied. Soil available P, K and Boron (B) had C.V.s of more than 30% (Jiang, 2000). A similar study was done for a 20 hectare field in Changyang state Farm in a suburb of Beijing, where for about 20 years, the field was managed as a single operational unit (large scale operation). Notable variability in soil fertility was also found under this large scale with a C.V. of more than 15% for most soil nutrients tested. The spatial variability of soil nutrients under the small scale operation was greater than that under the large scale operation. The spatial distribution of different nutrients was affected differently by regional or random factors. Under the small scale operation with each farmer’s family operating on separate field plots, the spatial distribution of soil nutrients had a close relationship with farmers’ history of fertilization, crop variety and field management.

In 1998 the variability of crop yields within fields was investigated at both of the previously mentioned sites. The results showed that under the large scale operation in the Changyang State Farm, wheat yield, kernel/ear and spike number all differed spatially. The wheat yield differences among various zones within the field were generally in the range from several 100 to over 2000 kg/ha. In some extreme cases the difference was over 4000 kg/ha, with the highest yield 5403 kg/ha in one site, and the lowest yield 1325 kg/ha in another site. The crop yield showed a different homogeneity for each field and the macro-nutrients had smaller C.V.s than of micro-nutrients. Moreover the content of nutrients extracted from the seeds correlated significantly with the crop yield, thereby emphasizing that the soil nutrients had a great influence on the spatial variability of crop yield (Jiang, 2000).

Since understanding of the spatial variability of soil physical-/chemical properties is essential for optimizing fertilizer use, the nature of spatial variability of soil condition and crop growth under various conditions in China is being studied further.

3. Site-specific soil nutrient management systems
The SFI of the Chinese Academy of Agricultural Sciences (CAAS), in cooperation with the International Plant Nutrition Institute (IPNI), has studied soil nutrient variation and SSNM for different management systems in China. The outcome is summarized below.

3.1. Technological system for soil nutrients test and information management
It is essential to have a reliable soil testing system for the development of precision agriculture. In 1990, the SFI introduced a systematic technique for soil testing and fertilizer recommendation, and established the CAAS-IPNI Soil and Plant Analysis Laboratory. Rapid services in soil testing and nutrient status evaluation for available macro, secondary and micro elements in soil have come into effect and database and management systems have been developed (Jin, 1995). In the CAAS-IPNI Soil and Plant Analysis Laboratory, multi-nutrients extraction solutions (ASI extraction solution) and systematic approach have been used to improve the soil testing efficiency (Portch and Hunter, 2002). Greenhouse and field trials were conducted and fertilizer recommendation models for various plant nutrients developed based on the field experiment results.

Recognizing the effectiveness and reliability of the soil testing and fertilizer recommendation system used in the CAAS-IPNI Soil and Plant Analysis Laboratory, the lab was named by as the National Laboratory for Soil Testing and Fertilizer Recommendation of Chinese Academy of Agricultural Sciences in August, 2005, and will be used as technical supporting and training basis for national soil testing and fertilizer recommendation program in program.

In addition, national and regional soil and fertilizer information systems have been developing and a soil and fertilizer research network has been established to link to the provincial research institutions across China, thereby treating network management of information (Jin et al., 1999).

3.2. Site specific nutrient management system at village/field scale
In the previously mentioned site in Handan county of Hebei province with the small scale field operation system, the soil nutrient status for each farmer’s small field plot was obtained by overlaying the contour map of soil nutrients with the distribution map of the farmer’s fields on a geographical information system (Jiang, 2000). By using the soil testing and fertilizer recommendation procedure developed with the systematic approach technology (Jin, 1995, 1997) it was possible to move the recommendations for a l5-20 ha field to smaller defined plots assigned to individual farmers’ families within the field. A fertilizer recommendation was made for each plot for each farmer, and variable fertilization was realized by the farmers by hand. The results showed that higher yields were obtained with recommendations according to the specific farmer’s plots and the yield differences among farmers were less than those treated according to traditional recommendations. The result indicated that at this specific site, the recommended site specific fertilization increased yield by 19.8% and resulted in increase of net income of 5314 Yuan/ha (or 643 US$/ha) (Yang et al., 1999).

Under the large scale operation system, the soil nutrient management unit was based on the spatial variability of soil nutrients in the field. Results indicated that the wheat yield map shown in Figure 1 was in a good agreement of the soil available P map, indicating that wheat yield was affected by soil available P level in the soil (Jiang, 2000).

3.3 Site specific nutrient management at county/township scale
The SSNM approach has been tested in county/township scale in Yutian county of Hebei province and Ling county of Shandong Province in 1998-2000. Soil samples were taken from selected sites from main grain crop production fields using guidance of a GPS system. Complete soil analysis for available level for all plant essential nutrients was done in the CAAS-IPNI Cooperative Soil and Plant Analysis Laboratory. Soil nutrients maps were developed by using a GIS system, and the entire experimental area (county and/or township) was regionalized based on the developed contour maps of soil nutrients. Fertilizer recommendations for each nutrient for wheat and corn for each region were made based on the soil nutrient status in the region and nutrient requirement for the targeted yield (Fig 1).


Fig. 1 Regionalized balance fertilization for wheat in Yutian county

Field experiments were conducted to compare the effect of the regionalized SSNM fertilization and the farmer’s practice on crop yield and N recovery in wheat and corn. Results indicated that compared with farmers’ practice, on average, SSNM increased wheat yield by 12.5% with net benefit of 784 Yuan/ha (95 US$/ha), corn yield by 16.8% with net benefit of 1053 Yuan/ha (127 US$/ha)(Table 1). Nitrogen recovery was also improved, from 30.3% in farmers’ practice to 40.1% in the SSNM treatment for wheat, and from 19.1% in farmers’ practice to 32.3% in the SSNM treatment for corn (Table 2).

Table 1. Crop yield increase and profit from regionalized SSNM fertilization



Table 2. N recovery influenced by regionalized SSNM fertilization


4. SSNM in related research projects
Future study of the nature of soil fertility variation, and to develop correct fertilizer management program based on the local condition, under the cooperative research between China (MOA/CAAS) and Canada (IPNI), 45 soil fertility monitored villages have been established in selected locations in 30 provinces of China. In each village, soil samples were taken by grid sampling with 50 x 50 or 100 x 100 grids. Soil samples were analyzed in the CAAS-IPNI Cooperative Soil and Plant Analysis Laboratory. Soil nutrient maps were developed by using the Arc-GIS system. At the same time, 10 fields were selected from each village to monitor balance of nutrient input and output, cycling of nutrients in the soil-plant system, and changes of soil fertility with time. A data base was developed for each village with all information from soil testing, field trails, and related survey information input. Soil fertility and fertilizer management programs have been developed in the village and will be used to guide soil fertility management and fertilization in the village and surrounding areas.

With this program, all nutrients were applied in each farmer’s small field in a balanced manner, based on the understanding of the soil fertility, and fertilizer input being optimized and net benefit being maximized. In the soil nutrient monitored village in Ershilipo village in Xinzhou city of Shanxi province, for example, results from the 10 monitored farmer’s plots indicated that the optimized SSNM fertilization increased wheat average yield in 4 years from 2000 to 2004 by 8% to 22%.

Tab 3. Wheat yields with SSNM and fermers’ practice in Ershilipu village in Shanxi Province, 2001-2004