On-farm impact of the System of Rice Intensification (SRI): Evidence and knowledge gaps
The System of Rice Intensification (SRI) is being promoted worldwide, but relatively little is yet known about its impacts at farm level. This article reviews available evidence on the impact of SRI practices in terms of yield and productivity. Adoption of SRI practices necessarily changes the mix and allocation of inputs, in particular of water, seeds, fertiliser and labour. However, SRI impact studies have generally failed to distinguish between technological change – a more productive use of inputs, evidenced by a change in total factor productivity – increases in input use, or selection effects and their respective effects on yields. The studies reviewed point not only to modest increases in rice yields associated with SRI adoption, but also to concurrent increases in labour and fertiliser use. Often SRI is selectively practised on more fertile plots. As a result, no firm evidence on changes in total factor productivity can be discerned, while partial productivities of land and labour show mixed results. Though yields tend to be higher under SRI management, risk also seems to increase, which initially favours adoption by better-endowed farmers and on better soils. Evidence on SRI impact is further complicated by the large diversity of SRI practices associated with different biophysical, socio-economic and institutional circumstances. We conclude by identifying knowledge gaps surrounding the SRI phenomenon, encompassing agro-technical aspects, socio-economic issues and (dis)adoption behaviour.
Introduction
The System of Rice Intensification (SRI) is a method of rice cultivation which, according to a diverse community of its supporters, promises to increase smallholder rice yields while using substantially less water and seed. SRI comprises a suite of recommendations for crop establishment, irrigation management, weed control and fertilisation, which diverge from conventional methods. SRI techniques are said to be based on close observation of the physiological characteristics of rice plants, thus exploiting the plants’ innate genetic potential without depending heavily on costly external inputs. Promoters of SRI argue that the system is particularly appropriate, accessible and beneficial to poor and marginal farmers because it can produce higher grain yields without the need for costly improved seeds or expensive chemical fertilisers (Stoop et al, 2002, Uphoff, 2007).
These claims have provoked controversy among agronomists and rice scientists, particularly the assertion that SRI methods can produce dramatically higher and even record-breaking grain yields (see Surridge, 2004). In spite of those misgivings and the hostility of some rice scientists, smallholders in dozens of countries are reported to have adopted SRI methods (Kassam et al., 2011). In this article we address two major topics. First, we consider and evaluate the available evidence on the impact of SRI worldwide: what has been reported and what is the evidence base? Second, we identify remaining gaps in knowledge about the SRI phenomenon, encompassing agro-technical aspects, socio-economic issues and (dis)adoption dynamics.
SRI was first described in a technical journal in 1993 (de Laulanié, 1993). SRI is now typically understood to comprise five or six key cultivation practices: (1) raising seedlings in a carefully managed, garden-like nursery; (2) transplanting of very young seedlings (ideally 8–15 days old); (3) widely spaced, single seedlings, often planted in grid patterns (typically 25 × 25 cm and possibly wider); (4) water management to promote moist, aerated soil conditions, sometimes including dry periods of 3–6 days; (5) early and regular weeding, typically four times at regular intervals, ideally using a mechanical rotary weeder which churns and aerates the soil, or by hand; (6) fertilisation, preferably using organic sources (compost, farmyard manure and green manure) (Stoop et al, 2002, Uphoff, 1999). These practices differ considerably from conventional methods, whereby seedlings are typically transplanted in closely spaced clumps of two to four or even more plants at a time, randomly distributed or in narrowly spaced rows, 20 to 60 days after sowing. Also, rice fields are often kept flooded continuously from transplanting to maturity, which suppresses weeds and curbs the need for regular weeding.
The compilation of the portfolio of SRI practices is attributed to a French agronomist and Jesuit missionary, Fr. Henri de Laulanié, who worked with rice farmers in the highlands of Madagascar from 1961 until his death in 1995. De Laulanié portrayed his methods as ‘a system based on the physiology of rice’ (de Laulanié, 2003, 59), and this notion is widely accepted by contemporary promoters of SRI. The idea is that SRI methods create conditions in which rice plants can achieve their full, innate potential to grow and flourish. The suite of SRI practices enumerated above is said to express three underlying principles, as summarised by Uphoff (2003, 39): the use of healthy seedlings, which accounts for the nursery management component as well as early, quick and gentle transplanting; optimal plant density, which explains the wide spacing of seedlings planted singly; and the promotion of aerobic soil conditions, which underpins the irrigation practices and soil disturbance.
SRI came to the attention of development workers and academics working in Madagascar during the second half of the 1990s (e.g. Uphoff, 2001, Stoop et al, 2002, Uphoff, 1999, Uphoff, 2002, Uphoff, Randriamiharisoa, 2002). An international conference in 2002 generated further attention (Uphoff, Randriamiharisoa, 2002, Uphoff et al, 2002) and SRI is now reported to have spread from Madagascar to nearly 50 countries across Asia, Africa and South America (CIIFAD, 2013).
Many of the early reports about SRI were informal, anecdotal or derived from grey literature. The first systematic effort to document experiences with SRI agronomy was an international conference held in Sanya, China in 2002, which generated a body of papers from 14 different countries (Uphoff, Randriamiharisoa, 2002, Uphoff et al, 2002). Only in recent years has a larger volume of peer-reviewed literature become available.
Scientific support for the agronomic principles underlying SRI – namely, that substantial improvements in yield and productivity can be achieved through changes to crop management practices rather than improved rice varieties – has come from an analysis published by Horie et al. (2005). It is quite widely accepted that SRI techniques promote visible changes in the growth patterns and morphology of individual rice plants, specifically a vigorous production of numerous tillers (shoots with the potential to produce grain-bearing panicles). Some Chinese and Indian studies have confirmed that SRI methods produce physiological and morphological changes in rice plants that can lead to improved yields and higher factor productivity (e.g. Chen et al, 2006, Lu et al, 2005, Thakur et al, 2010, Vijayakumar et al, 2006). However, the relationship between tillering and grain production is not linear and vigorous tillering may not necessarily lead to high yields (Latif et al, 2005, Latif et al, 2009). It is also well established that rice yields can be sustained at existing levels while using significantly less water than in many conventionally managed, irrigated production systems (Bouman et al., 2002).
SRI techniques are reported to give rise to three key benefits. First, grain yields are reported to increase, delivering a direct benefit to both subsistence and (semi-) commercial farming households. Second, SRI methods are widely believed to increase the productivity of two key inputs, namely water and seed. Consequently the system is thought to be more accessible and affordable to poor and marginal communities and farmers facing water scarcity. A more controversial claim holds that the productivity of the system as a whole increases through positive synergetic interactions among the SRI practices; in other words the positive impacts of individual components of the system are multiplied when they are applied in concert (Stoop et al, 2002, Uphoff, 1999). Third, SRI is said to represent a more ecologically sustainable method of rice cultivation, primarily through water conservation but also (organic) soil husbandry and lower methane emissions (Uphoff, 2007).
According to some scholars (e.g., Kassam et al., 2011) these beneficial effects are encouraging many rice farmers to adopt SRI methods but rigorous studies assessing diffusion and adoption are scarce. A handful of published studies provide only localised snap-shots (Anthofer, 2004, Moser, Barrett, 2003, Moser, Barrett, 2006, Namara et al, 2008, Noltze et al, 2012, Palanisami, 2010, Palanisami et al, 2013, Sita Devi, Ponnarasi, 2009, Takahashi, 2013). Consequently it is impossible to answer the question exactly how widely SRI or its components have been adopted worldwide, nor to provide a consistent picture of the factors shaping adoption patterns across time and space. These studies do, however, reveal that patterns of adoption of SRI components differ substantially between sites, which suggests that some components fit better with particular types of farmers, households, rice plots or other specific characteristics, and that productivity changes associated with SRI are heterogeneous.
In the light of the lack of robust information there is a clear need to assess the current state of adoption and impact of SRI techniques. In an effort to compile and synthesise the current state of evidence, we undertook an extensive literature review, paying specific attention to the most recent insights. The main aim of this review is to build an understanding of which production factors become more productive after (partial) SRI adoption and to identify the gaps in knowledge surrounding SRI impact.
Since much of the available literature and documentation on SRI was to be found in informal and grey sources, our search strategy was open-ended and included searches in academic databases including Scopus, Web of Knowledge and Google Scholar, as well as searches of the world-wide web through Google. In addition, we reviewed and downloaded materials from SRI-Rice, the web-portal on SRI maintained by staff linked to the Cornell International Institute for Food, Agriculture and Development (CIIFAD, 2013).
In view of their size and importance as rice producers and consumers, and as countries where SRI activities had been reported on a significant scale, we made a special effort to collect evidence from India and China. In India, we commissioned research assistants from Tamil Nadu Agricultural University to carry out a specific search of the Indian scientific literature for papers on SRI and/or its component practices. This search yielded a total of 28 additional papers. An assistant at the China National Rice Research Institute carried out a similar search of the Chinese scientific literature on SRI and, where necessary, translated the abstracts from Chinese into English. This search yielded a total of 60 documents published in 28 Chinese journals between 2001 and 2010. In total, we collected 345 documents including peer reviewed journal articles, draft scientific papers, consultants’ reports, working papers, project documents, unpublished memos, and a few official documents. The full list of documents collected is provided in an online annex.
The resulting database was used to record, where applicable, (1) the definition or specification of SRI that was used in documents; (2) the control treatment or reference practice to which SRI was being compared, if any; (3) whether statistical methods were applied and if so, how this had been done; and (4) whether the statistical methods had been corrected for possible differences in inputs between SRI and non-SRI treatments (e.g. labour use, nutrient application or soil quality), and/or potential selection effects. Through these steps we identified the subset of papers which we used in our review in Section 3.
Our selection criteria placed strong emphasis on the sound use of statistical methods. As we explain later on, deriving firm conclusions from the studies reviewed is seriously hampered by methodological limitations, great diversity in SRI practices and extension and incompletely documented changes in relevant inputs. These limitations made it impossible to carry out a more extensive statistical analysis, such as a meta-analysis.
Given the importance of these methodological issues and the many potential pitfalls, we first discuss some methodological considerations in Section 2. Section 3, reviewing the on-farm impact of SRI, forms the core of this paper and we focus particularly on the productivities of seed, land, labour and water. Section 4 brings the empirical evidence on SRI practices together and identifies knowledge gaps.
Article source: https://www.sciencedirect.com/science/article/abs/pii/S0308521X14001322