A case study from China - Zhejiang Province
Problem to be solved: To reduce fertiliser application and increase biodiversity and rice yield
Heavy fertilizer application is one of the principal causes of biodiversity loss in soil ecosystems. In China, average N application (mainly in the form of Urea) in paddy field is much higher than that in other major rice growing countries. In Zhejiang Province, rice farmers apply 150-250 kg ha-1 fertilizer N to maintain yield levels of 5.5-8.0 t ha-1. Consequently, the fertilizer-N use efficiency is quite low (normally lower than 20%), and the subsequent environmental impacts from rice field such as nitrate leaching to groundwater and release of greenhouse gases into the atmosphere have become serious concerns in China. Heavy fertilizer application has also led to soils that are low in soil microbial biomass, microbial community diversity and activity. Since soil microorganisms play a crucial role in the cycling of almost all major plant nutrients and the energy flow of soils, the changed microbial community by heavy fertilizer application can affect the turnover of soil organic matter, the supply of indigenous N and crop yield.
Objectives: To provide farmers with options for high yield and environmental friendly options, the site-specific nutrient management (SSNM) for rice was developed at Zhejiang University in collaboration with the International Rice Research Institute (IRRI). SSNM aims at dynamic field-specific management of N, P, and K fertilizer to optimize the balance between supply and demand of nutrients. On site in Jinhua district, Zhejiang Province was used to compare the site-specific nutrient management (SSNM) and the farmers’ fertilizer practice (FFP) in terms of fertilizer-N use efficiency, rice yield and economic profit from 1998-2005. In order to understand the changes of soil microbial population size and community structure to heavy fertilizer application, at the same time, several experiments were also conduct to analyse soil microbial characterization.
The work was mainly undertaken by researchers of Zhejiang University, China. Dr Huaiying Yao and Dr Qichun Zhang participated soil microbial analyses, and Prof Guanghuo Wang arranged the field experiment and evaluated the agronomic performance of SSNM in farmers’ fields. Several visiting researchers (Witt C. and Buresh R.J.) and local farmers participated this research.
Application of the ecosystem approach to soil biodiversity management:
In this case study, the comparison of agronomic performance associated SSNM and FFP practices, as well as their effects on soil microbial community, demonstrates Principals 4 and 5 of the ecosystem approach. Principal 4 addresses that the need to manage ecosystems in an economic context. Principal 5 recognizes that the sustained functioning and resilience of ecosystems depend on conserving relationships among diverse and interacting species.
Results revealed that SSNM systems generally improved the agronomic performance and was more environmental friendly than FFP. Based on the data from 1998-2005, average grain yield of SSNM increased by 0.5 t ha-1 over FFP. The N use efficiency increased significantly, the N agronomic efficiency in the SSNM practice increased about 5 kg grain kg fertilizer-N-1 compared to the FFP practice. About 30% of fertilizer N, 25% of fertilizer P, and 10% of fertilizer K could be reduced through adoption of SSNM in the site, which would effectively eliminate an unnecessary source of pollution in the rice ecosystem. The economic profit increase by SSNM over that in FFP was 8-14%.
SSNM practice also improved soil microbial biomass, community diversity and activity (Table 1). Plate counts of culturable microbes and 16S rRNA gene denaturing gradient gel electrophoresis (DGGE) analysis revealed that soil microbial community diversity increased significantly in the SSNM practice compared to the practice FFP. Phospholipid fatty acid (PLFA) analysis suggested that soil microbial biomass increased significantly.
Table 1 Some microbial parameters of adopting SSNM practices
Parameter measured | Effect of adopting SSNM over FFP |
Culturable bacteria | Generally higher number and more species |
Culturable fungi | Equal or higher number |
Actinomycete | Equal or higher number |
Soil microbial biomass C | Generally higher |
Total-PLFA | Generally increased |
Shannon index (DGGE) | Generally increased |
Microbial biomass N turnover | Faster |
The authors of this case study felt that more detailed research was necessary to understand the relationship between the increase in microbial diversity and the improvement of the agronomic performance.
Relevance to the Programme of Work on agricultural Biological Diversity:
The site-specific nutrient management was evaluated in about 200 irrigated rice farms in Asia. It is an approach that is worthy of replication in other high-fertilized agricultural areas.
Outcomes of activities:
The site-specific nutrient management (SSNM) is biologically and functionally more diverse than the farmers’ fertilizer practice (FFP), and that soil microbes play an important role in soil N turnover.
Lessons Learnt:
Higher species diversity, larger population sizes and enhanced microbial activities in SSNM systems may be linked to better agronomic performance levels of SSNM compared to FFP.
The good balance between supply and demand of nutrients can promote soil microbial activity, and the rapid microbial N turnover can increase soil indigenous N (organic matter) supply and improve N fertilizer use efficiency.
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