UNDERSTANDING THE SYSTEM OF RICE INTENSIFICATION
The system of rice intensification is a set of insights and principles applied through certain management practices that promote more productive phenotypes from existing genotypes of rice, whether improved or local varieties.
This is accomplished by:
- Inducing greater root growth; and
- Nurturing more abundant and diverse populations of soil biota which provide many benefits for plants (Wardle, 2002).
Altering the management of rice plants’ soil, water and nutrients is a low-cost way of enhancing plant root growth and the activity of soil organisms. Non-SRI practices can be detrimental in various ways:
- Flooding of rice plants has been practised for centuries, even millennia. It constrains growth, functioning and survival of the roots. Up to threequarters of the rice roots degenerate by the start of the plant’s reproductive period (Kar et al., 1974).
- Crowding rice plants in dense hills or close spacing of hills results in the growth potential of the canopies and root systems being inhibited. The “edge effect” – i.e. the more vigorous and productive growth of widely-spaced plants – is thus limited to the borders of rice fields.
- Heavy application of fertilizers and agrochemicals can have adverse impacts on the soil biota, which provide numerous services to plants: N fixation, N cycling, P solubilization, protection against diseases and abiotic stresses, and induced systemic resistance, for example (Tan, Hurek and ReinholdHurek, 2002; Doebbelaere, Vanderleyden and Okon, 2003; Randriamiharisoa, Barison and Uphoff, 2006).
SRI methods create above-ground and below-ground environments that are more favourable for the rice plant’s growth (Stoop, Uphoff and Kassam, 2002; Randriamiharisoa, Barison and Uphoff, 2006). SRI involves transplanting young seedlings (<15 days, preferably 8-12 days), singly (not in clumps), very>carefully and gently, with optimal wider spacing (starting at 25×25 cm and increasing whenever better soil fertility permits). Irrigated paddy soils are kept moist but are not continuously saturated, maintaining mostly aerobic soil conditions, either by daily applications of small amounts of water or by alternate wetting and drying.
For best results, weed control is done with a rotary hoe several times during the vegetative growth phase before the canopy closes, aerating the soil as well as removing weeds. Organic fertilization (compost, manure, mulch etc.) is utilized to the greatest extent possible, although synthetic fertilizers can be used if insufficient biomass is available.
Although SRI was developed for irrigated rice production, a new variant is rainfed SRI, where SRI concepts and methods are adapted to upland circumstances. Yields of 6 to 8 tonnes/ha have been reached with such adaptations in northern Myanmar, southern Philippines and eastern India (Kabir, 2006; Gasparillo et al., 2003; Sinha and Talati, 2005).