What is SRI?

The System of Rice Intensification

The System of Rice Intensification (SRI) is a yield-increasing methodology practiced by probably more than 30 million farmers, with benefits having been demonstrated in over 60 countries. SRI methods modify the most common rice-growing practices in a number of ways (Figure 1). The changes include: (1) growing seedlings in nurseries with a minimum of water, a maximum of organic matter, and low plant density; (2) transplanting seedlings into rice fields at a young age, as little as 10-12 days old and no more than 15 days; (3) planting single (rather than multiple) seedlings in hills in a square pattern at a distance of 25-30 cm; this encourages healthy root growth with reduced competition for nutrients and induces profuse tillering and canopy growth; (4) mechanical weeding that eliminates weeds at the same time it aerates the top layer of soil; (5) using organic matter, as much as available, to enhance soil fertility in preference to chemical fertilizers; and (6) intermittent irrigation, alternating wetting, and drying of rice paddies instead of continuous flooding as this favors aerobic over anaerobic microorganisms. Fertilizers can be used where there is not sufficient organic matter to meet soil and plant needs, but results are better to the extent that the soil’s reserves of organic matter are enhanced. Also, organic and inorganic nutrient sources can be combined (optimized) when the first are limited or the soil has particular deficiencies, but the purpose is to be supporting soil microbial communities, not just the plants

Fig 1 SRI management of the rice field: a) Young seedlings 10-12 days old are transplanted. b) For crop establishment, a grid pattern (25 × 25 or 30 × 30 cm) is scored on the field surface, then planting only one seedling in each hill; transplanting is done quickly after removal from the nursery, and seedlings are planted shallow (less than 1 cm deep). c) Soil management: Surface soil is aerated by using a two-row weeder or cono-weeder every 10-12 days before the canopy closes; such weeding gives oxygen to the root system and aerobic soil biota whileeliminating weeds. d) Water management: Soil is kept moist but without continuously standing water

SRI methods not only increase the production of rice but also the biodiversity in the soil, giving plants greater resistance against pest infestation and to some extent reducing the uptake of arsenic. SRI also helps to conserve rice biodiversity by giving farmers financial incentives to plant local/indigenous/heirloom varieties. Thousands of these varieties have already become extinct, and most of the surviving varieties face extinction. SRI methods can make producing traditional varieties more profitable by raising their yields while reducing costs of production; these varieties usually command a higher market price because of consumers’ tastes and preferences. So even if their yields are not as high as from ‘improved’ varieties, they can be more remunerative. Furthermore, when SRI methods are used, soil and water quality are improved. Table 1 summarizes differences between SRI vs. conventional rice crop management.

Table 1 SRI vs. conventional methods

Characteristics	SRI	Conventional
Seedling transplant age	Younger seedlings (<15 days)	Older seedlings (>20 days)
Plant spacing	Single plants with wider spacing, 25 x 25 cm or more, with hills in a square pattern	3 and more seedlings per/hill, with closer spacing of hills in rows or helter-skelter
Water management	Intermittent application to have mostly aerobic and unsaturated soil	Continuous flooding with plants kept inundated
Weed control	Mechanical weeding with active soil aeration	Herbicide use or manual weeding
Nutrient management	Organic matter as fertilizer and soil enhancer	Use of chemical fertilizers

(a)	(b)
(c)	(d)