Status of boro (summer) rice in Assam:
a case study

P.K. Pathak, R.K. Saud, D.K. Bora, K.D. Singha and A.K. Pathak

Regional Agricultural Research Station, Assam Agricultural University, Titabar-785 630, Assam, India

In Assam, geoclimatic variations and agriculture's dependence on rainfall have resulted in three distinct rice growing seasons: sali or winter rice (June/July to November/December); ahu or autumn rice (March/April to June/July); and boro or summer rice (November/December to May/June). Of the state's total area of 2.5 million ha under rice, boro rice covers only about 0.15 million ha (Anon., 1993). However, although this apparently indicates that boro rice is relatively unimportant within Assam, in reality this crop assumes tremendous importance because, unlike the ahu and sali seasons, which are affected by flood, the boro rice season is relatively risk-free, which means that improved rice production techniques could be adopted totally, and there is ample scope for area expansion by bringing the chronically flood-affected and deep-water rice areas under boro rice cultivation by creating irrigation facilities.

Considering the vast potential of boro rice in Assam, it is imperative that rice scientists develop suitable rice varieties and management practices that are ideally suited to diverse boro rice-growing situations. An understanding of the target environments and farmers' needs is the first step in the process of developing varieties and agrotechniques that are specifically suited to the environments concerned. An attempt was made to survey the boro rice-growing situation in the central Brahmaputra valley zone, comprising Nagaon and Marigaon districts, which accounts for about 37 percent of the total boro rice area in Assam.

MATERIALS AND METHODS

Boro rice in Assam is mainly concentrated in three agroclimatic zones - the central Brahmaputra valley zone (CBVZ), the lower Brahmaputra valley zone (LBVZ) and the Barak valley zone (BVZ) - in addition to scattered areas in other zones. Of the total area under boro rice in the state, 37 percent is in CBVZ so, because of resource limitations, the survey was restricted to CBVZ.

The survey was conducted during April 1996 through multistage random sampling. Five blocks were selected randomly from the total of 24. For the second stage of sampling, four villages were randomly selected from each block, while the final sampling unit for questioning was made up of ten farmers, selected randomly from each village. Thus, a total of 200 farmers were interviewed.

RESULTS AND DISCUSSION

Field observations and the farmers' responses to specific queries revealed that the boro rice areas could be broadly delineated into the following three different ecologies, on the basis of land and water conditions:

• rainfed, swampy, flood-prone ecologies;
• irrigated flood-prone ecologies;
• irrigated flood-free ecologies.

Rainfed swampy ecologies occur in depressed land conditions where the soil remains either submerged or saturated for a substantial period of the year. These areas are generally saucer-shaped and have various levels of soil saturation or submergence - the central low-lying zone generally remaining saturated or submerged throughout the year while the periphery shows gradual moisture depletion after the monsoon finishes, making it ready for rice transplanting in late December or early January. Being very low-lying, swampy ecologies are chronically flood-prone during the monsoon, rendering them unusable for crop cultivation from June to November.

The survey also revealed that 90 percent of the farmers in these areas grew boro as a monocrop and only 10 percent grew deep-water rice in sequence with boro (Table 1).

Although boro rice is traditionally cultivated in swampy ecologies, recently, as a result of serious damage to the main sali crop by chronic flooding, a large atypical area has been brought under boro rice cultivation by the creation of irrigation facilities. These ecologies comprise low-lying deep-water rice areas as well as chronically flood-affected sali rice areas. The survey revealed that, among the respondent farmers operating in these ecologies, 19 percent grew only boro rice, 30 percent followed the boro-deep-water rice sequence and 51 percent grew sali rice late in the season (after the floods recede in late September) in sequence with boro rice (Table 1).

Farmers in irrigated flood-free areas have taken up boro rice cultivation recently for its high yield potential. The survey revealed that 100 percent of the farmers in such ecologies grew sali rice in sequence with boro.

Varietal status

In rainfed swampy ecologies, both traditional boro rice varieties and modern rice varieties were cultivated. Among the farmers working in these conditions, 45 percent reported growing traditional varieties, while 55 percent grew modern varieties (Table 2). Among the traditional varieties, Jagli boro was the predominant variety and, among the modern varieties, Mahsuri and Biplab were.

In irrigated flood-prone ecologies, modern varieties were grown predominantly (95 percent), and only 5 percent of the respondent farmers reported growing traditional boro varieties. In these conditions, Jagli boro was again the predominant traditional variety, while Mala, Jaya, Joy Bangla, China, Biplab and Mahsuri were the predominant modern varieties (Table 3).

In the irrigated, flood-free ecology, 100 percent of the farmers grew modern varieties, viz., Mala, Jaya, Biplab and Mahsuri.

The cultivation of traditional varieties in the rainfed swampy situation is mainly owing to the favourable seedling height attained by these varieties. From the time of sowing through the early vegetative phase, the temperature situation is not ideal for the growth of boro rice (see Figure). Low temperatures cause slow seedling growth in susceptible varieties. In irrigated ecologies, where farmers have good control over the water supply, the shorter seedling height of improved varieties does not encourage the use of traditional varieties, resulting in the predominance of improved varieties in irrigated ecologies.

Temperature and rainfall pattern during boro growing season

Farmers reported rice yields that varied between 2.3 and 3.0 tonnes/ha for traditional boro rice varieties while, for modern varieties, yields varied from 4.3 to 7.1 tonnes/ha, on a fresh weight basis. The results also indicated that the varieties performed similarly across all three growing ecologies. In addition to yield and seedling height, the existing varieties differed in other major agronomic traits such as plant height, tillering ability, crop duration and grain characteristics (Table 3).

Farmers' responses indicated that the best varieties for rainfed swampy ecologies should be high-yielding, semi-tall (120 to 130 cm), high-tillering and early-maturing (160 to 165 days), with the crop becoming ready for harvest by the end of April or in mid-May. The grain type should be fine with good milling and cooking qualities (Table 4). As the swampy ecology is chronically flood-prone, the time of harvesting for boro rice is very important. The survey revealed that 55 percent of the respondents were in favour of harvesting the crop by mid-May and 45 percent of harvesting by the end of April. The farmers considered seedling height to be one of the most important characteristics; a large majority of respondents wanting varieties that attain a height of 35 to 40 cm.

Farmers in both flood-prone and flood-free, irrigated ecologies needed the same type of boro rice. In general, they regarded that, for irrigated situations, the ideal boro rice should be high-yielding, semi-dwarf, high-tillering, early-maturing (160 to 165 days) and fine-grained (Table 4). The duration of the boro rice variety is very important in irrigated, flood-prone situations (where crops can suffer flood damage) and in flood-free situations (to permit the timely planting of the succeeding sali crop). The survey revealed that 100 percent of the respondents from flood-free ecologies favoured harvesting their boro crop by mid-May while, in flood-prone situations, 84 percent favoured harvesting by mid-May and only 16 percent, harvesting by the end of April. In these situations, seedling height was also considered to be one of the most important characteristics for the ideal boro rice variety. The modern varieties that are currently being cultivated are not cold-tolerant and do not attain the desired seedling height, which makes transplanting difficult and time- and labour-consuming. The majority of farmers from these ecologies favoured boro varieties that attain seedling heights of 25 to 40 cm in a period of 40 to 45 days (Table 4).

Cultural management

The survey indicated that wet seed beds are always used for raising boro rice seedlings and that the large majority of farmers raise seedlings in large, flat beds rather than narrow strip beds. The survey also revealed that the majority of farmers applied some form of fertilizer, which could be organic, inorganic or a mixture of both, in boro nurseries. This is because they wanted to encourage the growth of seedlings, which is very slow during the boro season compared with the ahu and sali seasons.

The survey revealed that 65 percent of respondent farmers in swampy ecologies grew boro rice without ploughing the land, 20 percent ploughed once and 15 percent ploughed two or three times. Variation in the number of ploughings was the result of differences in farmers' situations and perceptions of good practice. In contrast with this, farmers in irrigated ecologies prepared their land by ploughing it four to six times with country ploughs drawn by bullocks (Table 5).

Seedling age is considered one of the most important management factors for higher rice yields. Compared with other rices, relatively old seedlings are used in boro rice. The survey revealed that the majority of farmers in the swampy ecology used seedlings that were between 45 and 60 days old while, in irrigated ecologies, 30- to 45-day-old seedlings were used for transplanting (Table 5). The use of older seedlings in swampy conditions is owing to the requirement for taller seedlings and to a prolonged planting period, because farmers start planting from the upper periphery, working towards the low-lying centre as the water gradually recedes. In irrigated conditions, farmers have good control over water and, therefore, could transplant their crops within a shorter time and with smaller, younger seedlings.

The number of seedlings per hill and the maintenance of optimum plant populations are also important aspects of good cultural management. The survey revealed that, irrespective of growing ecology, the majority of farmers used four to five seedlings per hill instead of the recommended two (Table 5). Furthermore, the large majority of farmers in all growing ecologies maintained fewer than 20 hills/m², with only 10.3 and 15 percent of farmers from swampy, irrigated flood-prone and irrigated flood-free ecologies, respectively, maintaining 20 or more hills/m².

Regarding fertility management, the survey revealed that, in general, farmers in swampy situations did not apply fertilizer, while all the farmers in irrigated situations did. A large majority of the farmers had no idea of the balanced use of fertilizer, with the majority using a very high dose of nitrogen with no or relatively very low doses of phosphorus and potash (Table 6). The farmers were also observed to differ in the method of fertilizer application: 100 percent of those in swampy ecologies resorted to only top dressing with nitrogen; in irrigated, flood-prone ecologies 37 and 63 percent, respectively, applied fertilizer as basal followed by top dressing, or as top dressing alone; while in irrigated, flood-free ecologies, 100 percent applied fertilizer as basal followed by top dressing. The survey also revealed that the farmers, in general, were not aware of the benefit of incorporating applied fertilizers.

The irrigation source has an important role in agriculture from the points of view of water use efficiency and impact on crop growth. Among the respondents, 84 percent used shallow tubewells and 16 percent had lift irrigation. A majority of the farmers adopted intermittent irrigation to keep the soil saturated, although most of them are also unaware of irrigation measurements. A total of 12 to 15 irrigations were necessary, depending on the intensity and frequency of pre-monsoon rains. It is therefore essential that farmers know about and understand the most effective and economic water management schedule for boro rice.

Slow vegetative growth during the early crop season, combined with intermittent irrigation, result in weed problems in boro rice, particularly in irrigated situations. The survey indicated that 40 percent of farmers in swampy conditions did not adopt any weed control measures, while 60 percent carried out needs-based hand weeding. In irrigated ecologies, on the other hand, some 90 percent of farmers hand weeded (Table 5). A majority of the farmers understood the importance of weed control and used manual weeding measures, which are labour-intensive and expensive. Evolving effective and economic weed control measures would reduce farmers' workloads and help to increase productivity.

Insect pest and disease of boro rice

Stem borers, case worms, leaf folders and rice bugs were reported as pests of boro rice (Table 7). Of these, yellow stem borer (Scirpophaga incredulous [Wlk.]) was reported as the major pest in all the three boro rice ecologies, at both the vegetative and reproductive stages.

The survey revealed that a majority of the farmers were aware of damage from insect pests and adopted appropriate management practices. In swampy situations, 65 percent of the farmers adopted chemical control measures against the prevailing pests, and 35 percent did not adopt any control measures. In the irrigated, flood-prone ecology, pest control was practised by 75 percent, of whom 52 percent used indigenous measures, such as bamboo perches for bird predators and traps baited with Jack fruit and rotten frogs, in addition to insecticides. In the irrigated, flood-free ecology, 92 percent of the respondents adopted control measures; 46 percent of those used being integrated control measures comprising cultural, mechanical and chemical methods. The most commonly used insecticides were Dimecron, Decis, Thiodan and BHC dust.

The survey revealed that the farmers are not particularly concerned about diseases in boro rice. However, their responses and the researchers' own observations revealed that brown spot (Drechslera oryzae Subramanian & Jain), neck blast (Magnaporthe grisea [anamorph Pyricularia grisea Cav.]) and stem rot (Sclerotium oryzae Catt.) were the most important diseases. Brown spot was recorded in almost all the existing varieties and was associated with poorly managed crops. The disease incidence was reported to be higher in nurseries. Stem rot was also reported, although at very low intensity. Neck blast was reported by most of the farmers and was associated with the variety Mahsuri.

It is, therefore, necessary that the biology and distribution of pests be thoroughly studied and an integrated pest management (IPM) strategy for their control developed. Further research should be made into tolerant or resistant boro varieties. Although the survey did not implicate disease as a major concern for boro rice, in the near future diseases such as blast and stem rot may become far more significant. It is therefore recommended that the incorporation of resistance or tolerance against neck blast and stem rot in future boro varieties would be a good strategy for sustaining productivity at higher levels.

CONCLUSIONS

The survey, which was conducted in CBVZ where there is a high concentration of boro rice, revealed that there are no rice varieties ideally suited to boro growing ecologies. Diversity in growing situations and farmers' needs warrant the development of needs-based and ecology-specific boro rice varieties. The following distinct plant characteristics are recommended:

1. high-yielding plant architecture;

2. semi-tall (swampy situations) and semi-dwarf (irrigated situations) plant heights, with stiff straw and moderate tillering ability;

3. cold-tolerance at the vegetative phase, with early seedling vigour in terms of seedling height (35 to 40 cm) at 40 days of seeding;

4. early-maturing (165 days);

5. grain types, both coarse and fine;

6. seed dormancy;

7. resistance or tolerance to stem borer and neck blast;

8. tolerance to iron toxicity (irrigated situations).

Besides developing ideal varieties, cultural management practices specifically suited to various growing situations and based on farmers' socio-economic conditions must be developed. Comprehensive management strategies for controlling stem borer must be formulated with particular emphasis on host resistance, biological control and the needs-based use of chemicals. The efficacy of farmers' indigenous technical knowledge should be tested and effective indigenous techniques incorporated into an IPM strategy.

REFERENCES

Anonymous. 1993. Statistical handbook of Assam. Directorate of Economics and Statistics, Government of Assam, India.

Le riz boro (d'été) à Assam: étude de cas

Le riz boro (riz d'été), bien qu'il n'occupe que 6 pour cent environ de la superficie totale consacrée au riz à Assam, est important à cause de son rendement potentiel élevé par rapport aux riz d'hiver (sali) et d'automne (ahu). Une enquête menée en 1996 dans le centre de la vallée de Brahmaputra où se trouve la plus forte centration de riz boro a révélé que ce riz était cultivé selon trois méthodes distinctes, à savoir en culture pluviale marécageuse, en culture irriguée sujette aux inondations et en culture irriguée exempte d'inondations. L'enquête a aussi révélé que le manque de variétés boro idéales justifierait l'élaboration de variétés correspondant à des besoins et à des situations spécifiques. La population optimale de plants, la fertilisation équilibrée et l'utilisation économique de l'eau sont quelques-uns des aspects de la gestion des cultures à étudier de plus près. Enfin, des stratégies de gestion globale de la pyrale du riz s'imposent.

Situación del arroz boro (de verano) en Assam: estudio monográfico

Aunque el arroz boro (arroz de verano) ocupa sólo un 6 por ciento de la superficie arrocera total en Assam, cobra importancia debido a su elevado potencial de rendimiento si se lo compara con los arroces de invierno (sali) y de otoño (ahu). En un estudio llevado a cabo durante 1996 en la zona central del valle del Brahmaputra, donde se produce la mayor concentración de arroz boro, se comprobó la existencia de tres situaciones distintas en los cultivos de este tipo de arroz, a saber, las zonas pantanosas de secano, las zonas de regadío propensas a las inundaciones y las de regadío exentas de inundación. En el estudio también se reveló que la falta de variedades ideales de boro justificaba el desarrollo de nuevas variedades con arreglo a las necesidades propias de cada situación. La población óptima de plantas, la fertilización equilibrada y la utilización económica del agua eran algunos de los principales problemas de ordenación de los cultivos que requerían más investigación. Es preciso formular también estrategias completas de lucha contra el barrenador del tallo.