While inorganic fertilizers combined with high-yielding varieties, mechanization, irrigation, and other inputs have contributed to sustained increases in crop yield and food security in the 20th century, relying on blanket applications of fertilizer is inefficient and can cause excessive nutrient losses to the environment. A new paradigm for plant nutrition needs to result in robust co-benefits for these seemingly contradicting goals, and it also needs to improve the nutritional quality of agricultural products.
Global needs to meet the growing food demand appear to conflict with pressures on land, biodiversity, environmental pollution and the changing climate. A new paradigm for plant nutrition needs to result in robust co-benefits for these seemingly contradicting goals, and it also needs to improve the nutritional quality of agricultural products.
While inorganic fertilizers combined with high-yielding varieties, mechanization, irrigation, and other inputs have contributed to sustained increases in crop yield and food security in the 20th century, relying on blanket applications of fertilizer is inefficient and can cause excessive nutrient losses to the environment.
Crop yield growth has been particularly slow in Sub-Saharan Africa and it has also slowed down in other world regions, suggesting that recent yield trends in agri-food systems are insufficient to meet the anticipated food demand from existing cropland. Plant nutrition plays a central role in producing sufficient and nutritious food, lessen rural poverty, and reducing the environmental footprint in the context of increasing competition for land and water, and under more extreme weather conditions associated with climate change.
One of the forward looking solutions to that is the Site-Specific Nutrient Management (SSNM) approach developed in the 1990s for smallholder cereal production systems in Asia, which seeks to address large variability among farms and fields in their seasonal plant nutrient needs.
The science behind SSNM was initially based on a stepwise model that allows calculating the required nitrogen (N), phosphorus (P), and potassium (K) amounts to attain a targeted yield, with additional rules for the timing and in-season adjustment of fertilizer applications. SSNM thereby provided concrete decision advice to farmers on the rate, sources and time of fertilizer applications.
Over 25 years and through numerous national and international partnerships, SSNM evolved further in its underlying science, field methods and workflows, decision support tools and dissemination approaches, covering a growing number of crops, cropping systems, and countries in Asia and Africa. Growth stage or real-time approaches for in-season N management were developed, including optional use of diagnostic tools such as leaf color charts or chlorophyll meters.
Algorithms for P and K were improved. Advances in information technology and mobile communications made it possible to generate tailored recommendations by using weband smartphone-based apps such as Nutrient Expert, Rice Crop Manager, and RiceAdvice.
These tools were aimed at breaking the pervasive information and service asymmetry that is common in smallholder farming systems in the developing world, where there is a very low extension-to-farmer ratio, and where professional agricultural services such as soil testing are either not available, not affordable or not reliable. Crops for which specific SSNM solutions have been developed so far include maize, rice, wheat, soybean, cassava, potatoes, and several others.
In China, the Nutrient Expert platform currently provides SSNM-based advice for 23 different crops, including fruits and vegetables. Many studies on SSNM were conducted in Asia, where fertilizer use is common in intensive farming, but SSNM was also introduced in Africa during the past 15 years, where low input cropping systems are still predominant, often with low yield, specific soil constraints, or degradation of soil health due to nutrient mining.
While the benefits of SSNM in cereal production systems have been demonstrated in numerous studies for rice and wheat in both Asia and Africa, previous studies have been limited to specific locations and conditions. A comprehensive and systematic synthesis across different crops and regions is lacking.
Meta-analysis is a quantitative systematic review with statistical power to objectively synthesize results from multiple studies. However, critiques have cited flaws with their implementation, among them is publication bias, which emanates from selective publication of studies that reject the null hypothesis. This can lead to misleading conclusions, if analytical techniques to overcome publication bias are not used.
Here we present the first global quantitative synthesis of the performance of SSNM and discuss the major lessons learned for maize, rice and wheat, which account for about 43% of the world’s food calorie supply and consume about 51, 41 and 33% of global N, P and K fertilizers, respectively.
Results from our meta-analysis clearly show that SSNM creates cobenefits, with greater yields, profit, and N use efficiency when compared with the farmer fertilizer practice for maize, rice and wheat. SSNM reduces N and P fertilizer rates in most cases, except in situations where nutrients are mined such as in Africa, and is essential component of agronomic solutions for sustainable crop production.
These benefits were realized across geographies and under variable conditions, indicating a very robust performance in widely varying environments and management options, although rigorous testing and continuous improvement is needed.
Digital tools have been developed for widespread dissemination of SSNM recommendations, but uptake by farmers has remained low. Reaching millions of farmers can be achieved through integration of policy incentives, financial and input supply services, and improved knowledge exchange among extension, public, and private partners.
Read the study:
Chivenge P, Saito K, Bunquin MA, Sharma S, Dobermann A. (2021) Co-benefits of nutrient management tailored to smallholder agriculture. Global Food Security, Vol 30.
