Can the advisory system Nutrient Expert® balance productivity, profitability and sustainability for rice production systems in China?

Highlights

• Smallholder rice growers in China apply too much nitrogen (N) fertilizer, given their realized yields.

• Using Nutrient Expert® (NE) as advisory system for scientific fertilization helps reduce economic loss and ecological risk.

• NE maintained rice yields, increased net profit while decreasing N loss.

• Sustainable N application rates were 122–214 kg ha⁻¹ for rice.

• NE optimizes agronomic practice that balances yield, profitability and sustainability.

Abstract

CONTEXT

To avoid excessive chemical-fertilizer application and improve agricultural productivity in rice, a fertilizer recommendation system called Nutrient Expert® (NE) was designed. However, the ability of NE to balance yield, profitability and environmental sustainability in rice production needs to be further evaluated, as it is still difficult for farmers to assess the proper nitrogen (N) application rate.

OBJECTIVE

The objective of this study was to demonstrate the advantages of the NE system in balancing yield, profitability and N loss in rice production, and recommend proper N application rates for different cropping seasons of rice.

METHODS

This study describes results from field experiments conducted in five main rice cropping provinces from 2017 to 2020 in China, to investigate any advantages of NE compared with local farmers' practice (FP), and to determine the proper N application rates for different cropping seasons of rice.

RESULTS AND CONCLUSIONS

Compared with FP, NE had 12.1% lower N-fertilizer application, but increased rice grain yield by 4.3% and net profit by 7.4%, and decreased yield-scaled N loss by 20.7%. We showed how yield, profitability and N loss were affected by N balance (i.e., N applied to the field minus N removed from the field by the harvested crop biomass), and quantified relationships between N balance and N application rate, and between N output and input. Based on relationships between N balance and N application rate, we recommend N application rates in a range from 122 to 214 kg ha⁻¹, depending on cropping seasons of rice. We demonstrated that NE can simultaneously improve yield, profitability and environmental sustainability.

SIGNIFICANCE

Our study provided quantitative support for NE-based recommendations on the N application rate for smallholders farming in different rice cropping systems, and these recommendations can serve as a reference for avoiding excessive N application rate in paddy fields in other regions with similar eco-environment.

Introduction

Rice (Oryza sativa L.) is one of the most important staple food crops and plays a dominant role in global food security. China is the largest rice producer in the world as it produces 30% of global rice on 18.5% of the world's cultivated area (FAO, 2020). In recent decades, rice yields have increased significantly in China, which has primarily been attributed to the genetic improvement and increase in input of inorganic fertilizers, especially nitrogen (N) fertilizers (Ju et al., 2009; Li et al., 2019). However, rice production in China needs to be further increased by 20% to feed the growing population by 2030 (Peng et al., 2015; Kamir et al., 2020).

N fertilizer plays a vital role in the pursuit of high rice yield and economic benefits, but it also results in significant effects on the environment and ecosystem when over-applied (Tilman et al., 2011; Yin et al., 2019a). Since the 1980s, the consumption of N fertilizer in China has increased by a threefold, and the rice yield only increased by 50% (National Bureau of Statistics of China, 2022). This was partly because most Chinese smallholder farmers generally believe that applying more inorganic fertilizer will achieve higher yields and economic benefits. Recent studies showed that the average N input in paddy fields in China was 209 kg ha⁻¹ (Chen et al., 2014), while 300 kg N ha⁻¹ was applied in paddy fields in Jiangsu province (Sui et al., 2013). These values are much higher than the world average and the crop needs. Such practices of excessive N fertilizer input combined with improper field management will not only cause a massive waste of resource and energy, and reduce N use efficiency (NUE), but also threatens the surrounding environments and ecosystems (Xia and Yan, 2011; Chai et al., 2019). In recent decades, a sharp increase in reactive N in farmland occurred due to a large amount of chemical N fertilizer applied to the agricultural system. The reactive N will inevitably enter the atmosphere and hydrosphere systems, through ammonia (NH₃) volatilization, nitrous oxide (N₂O) emissions, nitrate (NO₃⁻) leaching and runoff (Vitousek et al., 1997; Zhang et al., 2011; Gu et al., 2015; Pittelkow et al., 2015; Zhang et al., 2021). How to increase grain production for coping with growing populations by proper management of inorganic N fertilizer, while maintaining environmental and agricultural sustainability is extremely challenging (Godfray et al., 2010; Foley et al., 2011; Stephens et al., 2018).

A science-based fertilization advisory has long been advocated (Fotyma and Pietras, 1981), such as those based on soil property and nutrient supply maps (Sarkadi and Várallyay, 1989) or based on the expected yield and nutrient balance (Várallyay et al., 1992). More recently, researchers have proposed several frameworks of nutrient management taking environmental sustainability into account, such as “nutrient management planning” (Beegle et al., 2000), “agricultural sustainability and intensive production practices” (Tilman et al., 2002), “ecological intensification” (Cassman, 1999), and “nutrient budgets” (Oenema et al., 2003). Chinese agronomists also proposed fertilizer recommendation strategies suitable for the agricultural economy of China. The aim of those strategies is to improve the agricultural productivity and profitability while reducing the environmental footprints, for instance, the integrated soil-crop system management (Zhang et al., 2011; Chen et al., 2014; Wu and Ma, 2015; Cui et al., 2018). Although such methods have been tested extensively, it is difficult for smallholder farmers to use these methods, due to the complexity of the assessment principle. Promoting crop yield, profitability and sustainability in a balanced way is still a daunting task in countries, such as China, India, Nepal, etc., where farming is mainly done by smallholder farmers. In view of spatial variability of crop field ecosystems associated with smallholder farming, a site-specific nutrient management decision support tool, Nutrient Expert® (NE), was developed. The NE system was designed based on the 4R nutrient stewardship (using fertilizers from the Right source, at the Right rate and at the Right time, and in the Right place) (Roberts, 2007; Pampolino et al., 2012; Xu et al., 2015; see the Supplementary text for additional information about NE). This NE system uses computer-based decision support technology and a questionnaire to provide a simple advice.

On-farm use of the NE-based fertilizer recommendation has been proven to significantly improve yield (Pampolino et al., 2012; Majumdar et al., 2016; Mandal et al., 2016; Dutta et al., 2020; Rurinda et al., 2020; Amgain et al., 2021), nutrient use efficiency (Pampolino et al., 2012; Rurinda et al., 2020; Amgain et al., 2021), farm profitability and soil health (Mandal et al., 2016; Amgain et al., 2021), while reducing environmental footprint of fertilizer use (Sapkota et al., 2021) in South and South-East Asia, and Sub-Saharan Africa. At present in China, NE has been successfully applied to rice (Xu et al., 2016a; Xu et al., 2017; Xu et al., 2019; Wang et al., 2020; Xu et al., 2022), maize (Xu et al., 2014a; Xu et al., 2014b; Xu et al., 2016b; Zhang et al., 2017a), wheat (Chuan et al., 2013) and tea (Tang et al., 2021). However, previous researches mainly focused on the comparison of rice grain yield and N usage between NE and farmers' practice (FP) by considering different cropping seasons as a whole. Little information is available on how N application rates based on NE balance agricultural productivity, profitability, and environmental sustainability across different cropping seasons of rice. Here, we hypothesize that the NE system maintains a balance between yield, profitability and environmental sustainability. To test this hypothesis, we conducted field experiments in five provinces in China from 2017 to 2020, covering four popular cropping seasons of rice in China. By analyzing the collected experimental data, we first aim to reveal whether, compared with FP, the NE system has advantages in balancing yield, profitability and N loss in different cropping seasons of rice. We also aim to recommend proper N application rates for different cropping seasons of rice in China, by establishing a set of quantitative relationships based on these data.