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RICE ECOSYSTEMS IN INDIA

        Rice is grown in vastly diverse conditions in India from below the sea level in parts of Kerala state to, on the hills upto an elevation of almost 3000m above mean sea level in Himachal Pradesh and Jammu and Kashmir states. It is grown as upland rice with no standing water whatsoever in the field to, as deep water rice with 3-4 meters of standing water particularly in West Bengal state. In between this wide range, there are shallow lowlands, medium lowlands and irrigated rice with controlled water supply etc. The area under rice in India is highest among all the rice growing countries, around 42-44 million hectares. In India rice is grown in some part of the country or the other, throughout the year. The main seasons being kharif (rainy season), from June - October and the second major season being, rabi (post rainy season) from Nov - April. Of the total rice area, about 90% is covered during kharif season in almost all the states of the country and only 10% of the area, (i.e.) around 4 million hectares is cultivated in rabi season, mainly in southern and eastern states. In Tamil Nadu, there are more than five seasons and rice is cultivated practically throughout the year. In eastern India rabi season rice is called as boro rice with cold tolerance at seedling stage and heat tolerance at harvest being important requirements of the boro varieties.

        In India, the diverse rice growing conditions are mainly classified into five major ecologies, viz., 1. Irrigated ecology 2. Uplands, 3. Rainfed lowlands, 4. Deep water and 5. Coastal wetlands. Area, production and productivity under these ecosystems during 2001¬02, is given in Table-1.

Table - 1: Rice ecologies, area, production and productivity in India (2001-02)

    Source: Singh, B.N.(2006). Rainfed lowland Rice Improvement: Current status in India and Future strategies.Journal of Rice Research, Vol.1 (1), 104-112

        Almost half of the area is under irrigated ecosystem which contributes more than 60% of the rice production, with an average productivity of 2.8 t/ha of milled rice. Rainfed shallow lowlands occupy almost 30% of the area, contributing 25% of the rice production with an average productivity of 1.8 t/ha of milled rice. Upland ecosystem occupies 13% of the area, contributing only 7% of the production with an average productivity of only around 1.0 t/ha milled rice.Deep water rice occupy 7% of the area contributing 3% of production with average productivity of 0.7 t/ha, whereas the coastal wetlands occupy 2% of the area with 2% of the total rice production with an average productivity of 1.0 t/ha.

        All these ecosystems suffer from one or the other major constraints for rice production. Some of the major significant constraints of different ecosystems are briefly mentioned below.

CONSTRAINTS IN DIFFERENT RICE ECOSYSTEMS

1. Irrigated ecosystem :

        The main yield limiting factors in irrigated ecosystem are (i) Poor management of production inputs; (ii) losses from weeds, pests and diseases, (iii) Inadequate water management, particularly drainage leading to salinity/alkalinity etc. Research accomplishment for irrigated ecosystem have been significant. They include development of semi-dwarf high yielding varieties and hybrids, short growth duration, greater yield stability due to incorporation of genetic resistance to pests and diseases and to lesser extent tolerance for some environmental stresses such as problem soils. The benefits of green revolution have been realized mainly in the irrigated ecosystem.

2. Shallow lowland ecosystem :

        Uncertainty the farming in rainfed lowland ecosystem. Rice crop suffers from drought, floods, pests, weeds and soil constraints. Since most of the rainfed lowlands depend on erratic rainfall, conditions are widely diverse and unpredictable. Most of the rainfed lowland farmers are poor and must cope with unstable yields and financial risks. They adopt their cropping practices to complex risks, potentials and problems they face. They typically grow traditional, photoperiod-sensitive varieties and invest their labour. They use very low or no purchased inputs.

3. Upland ecosystems :

        Biological and physical constraints to upland rice yields are numerous. Weeds are the most serious biological constraint, followed by blast and brown spot diseases. Small farmers using traditional production systems cannot afford chemical weed control. Stem borer and rice bugs are predominant insect pests. Nematodes can cause yield losses up to 30%. Rodents and birds are also sometime very serious problem. Amount and distribution of rainfall and poor soil fertility are the most serious physical constraints. Upland rice soils are predominantly acidic and depleted in major nutrients. Phosphorous is most often a limiting high aluminum and manganese content in highly acidic soils.

4. Deep Water Ecosystem :

        Fertilizer use is very limited, due to problems in application. Salinity, acidity, cold tolerance at seedling stage, survival of the seedlings etc. are the major constraints in this ecosystem.

Table 2 : List of rice varieties / hybrids released for different ecologies and states

      Bold - BSP; * Variety release by CVRC

A list of some of the varieties with resistance/tolerance to major pests/deseases is given below in Table-3.

Table 2: Varieties Resistant / tolerant to various Insect Pests/Diseases

Yield gaps:

        Yield gap is difference in the achievable (potential) yield and the actual yield obtained. There are different types of yield gaps (see the figure below):

Fig. : Types of Yield Gap

Yield gap 0:

is difference between the theoretical potential yield calculated and the experimental station yield. This yield gap is difficult to bridge with the existing technologies. Scientists have to breed new hybrids/varieties with novel characteristics, develop new production and protection technologies to bridge even partly this yield gap.

Yield gap I :

This is the difference in yield obtained at the research station's farm and the potential or possible yield obtainable at the farmers' field. This yield gap is due to non-transferable technologies, environmental difference between research station farm and farmers field etc.

Yield gap-II:

This is the difference in potential obtainable yield at farmer's field and the actual yield obtained by the farmer. This yield gap is bridgeable. In fact, through Frontline Demonstrations by implementing the entire package developed in a holistic way, the potential obtainable yield at the farmer's field can be demonstrated to the concerned FLD farmer and his neighbour. The actual causes for this yield gap-II may be many, which can be broadly classified as biological constraints and (b) socio-economic constraints.

(a) Biological constraints

  • Not using the appropriate high yielding vari¬ety/hybrid.
  • Not able to control weed infestation properly.
  • Incidence of diseases/pest and no proper control of them.
  • Problematic soils and no proper measure taken to ameliorate them.
  • Improper water management.
Infertile soils, where no attempts have been made to maintain fertility.

(b) Socio-economic constraints

  • Lack of credit facilities
  • Traditions and attitudes
  • Lack of requisite knowledge
  • Lack of timely availability of inputs
  • Lack of easy access to sources of requisite knowledge.

        By overcoming some of the above mentioned constraints, the potential, achievable yield at the farmer's field can be demonstrated through frontline demonstrations (FLDs). Then by comparing the yields obtained in FLDs with those of the neighbouring farmers in the region/village, the yield gap-II can be calculated for various ecosystems. As this kind of data for various ecosystems and the states were not readily available, the yield gaps for various rice growing states have been calculated by taking the difference in yield at the research station farms (AICRIP data for three years) and the state average yields. In absence of the requisite data sets, this approximates the yield gap-II. Such data on yield gap-II for the various states are given below in Table - 3.

Table: Yield gap in major rice growing states, 1990/91-1997/98

      Mean yield of best entry (irrigated medium) at AICRIP test locations over a seven year period.

Source: Siddiq et. al., (2001). Yield and Factor productivity Trends in Intensive Rice Production Systems in India: A case Study, IRC Newsletter 50. 17-35

        In southern and northern zone of the country, which has predominantly irrigated ecologies, the average yield gap works out to be around 37%. Eastern zone of the country is predominantly rainfed shallow lowlands, whereas the western zone contains predominantly upland ecologies. The average yield gap in these two regions is around 53%. Hence there is a very good scope to atleast bridge this gap partially, by organizing large number of frontline demonstrations in rainfed shallow lowlands and upland ecologies in eastern and western zones of India.

Concept : Dr. Shaik N Meera (Senior Scientist & CPI)      Copyright © 2010-2012 by DRR Hyderabad. All Rights Reserved.