2. Rainfed dryland agriculture in India: An overview, Contd.

Transcript

Hi! Friends, welcome back to the course. And in the last lecture we studied about some of the status and also some of the terminologies and background information with respect to rainfed drylands. In this lecture let us study the limiting factors and the constraints involved in the rainfed agriculture. The rainfed drylands agriculture, in this the limiting factor in rainfed drylands is the soil moisture. The soil moisture is the most limiting factor. Here it can be called by the term ‘water deficit’ or ‘moisture deficit’. So soil moisture is the single most limiting factor in case of rainfed drylands.

So how this moisture stress affects. This moisture stress affects on water relations. So water relations are mainly affected by the transpiration, translocation and absorption of water. Then coming to the effects of moisture stress on photosynthesis. The photosynthesis is decreased due to the decrease in photosynthetic weight and decrease in leaf area and the reduction in the production of leaf area. Then coming to the anatomical changes. Anatomical changes results in reduction in the size of the cells. Then the thickened cell walls, and in the formation of greater tissue; mechanical tissue. Then coming to the metabolic reaction. Almost all the metabolic reactions are affected. Enzymatic activity is decreased. During the moisture stress, sugars and amino-acids will accumulate.

Then coming to the hormonal relationships. The moisture stress greatly affects the hormonal balance. There are two types of hormones. Growth promoting hormones and growth regulating hormones. The activity of the growth promoting hormones decreases, that is in case of IAA and cytokinins. While that of activity of growth regulating hormones increases, that is ethylene and betaine. The leaf senescence induced by moisture stress is due to the because of ethylene production. On the other side what is the effect of moisture stress on nutrition; mainly absorption and uptake of nitrogen is affected. Then on the growth. The growth of the cells, the growth of the stems, growth of the leaf will be affected. Then on the development. The development of the reproductive growth will be affected, and there will be stunted growth. Then the effect of moisture stress on reproduction. In this the pollen viability or the pollen viability will be reduced to a greater extent. Finally the moisture stress affects the yield, wherein there will be significant reduction in the dry matter accumulation.

Then coming to the constraints in rainfed drylands. These constraints in the rainfed drylands have been divided into two disciplines, two wings. Climatic constraints and the soil constraints. Climatic constraints are highly variable rainfall, late onset of the monsoon, inequitable distribution of the rainfall and early withdrawal of the monsoon. The highly variable rainfall. That means in a rainfall region, the rainfall is very uncertain. Sometimes the quantity of the rainfall occurred is very high. Sometimes the quantity is very less. In this way highly variable rainfall and it is uncertain. The second most is the late onset of the monsoon. The late onset of the monsoon will delay the sowing operations, and the plants will not be established properly. The third one; inequitable distribution of the rainfall. This happens in the crop growth period, which is related to the distribution. The distribution of the rainfall is very erratic. In the sense when the crop needs the rainfall most, there will be low rainfall. When the crop needs most, it will be very less; vice versa and when the crops needs it, there will be very less rainfall. When the crop doesn’t need there will be high amount of rainfall. So this is inequitable distribution of the rainfall.

Next coming to the early withdrawal of the monsoon. During the crop growth, when the crops are at a reproductive stage. The cessation of the rainfall will be there. The rainfall will be withdrawn early, which affects the pollination and the reproduction, then the grain formation in the crops. Ultimately it affects the grainage. Coming to the second set of constraints; that is soil constraints. In this, soil erosion, low water retentivity, low soil fertility and soil reaction are the four important soil constraints. Soil erosion, wherein the top fertile soil will be eroded because of the high intensity of the rains. Along with the top soil the nutrients present in the topmost soil will also be eroded. Then the second thing is low water retentivity. This is because of the fact that the rainfed dryland soils or coarse textured soils; the nature of the soils is that the infiltration capacity is very limited, and coupled with that the top soil will be eroded and as such there will be low water retentivity. Then low soil fertility. So the dryland soils or marginal soils, wherein the inherent fertility content will be very less, and soil reaction is also around neutral. Coupled with both these factors the soil fertility is very low.

In a sense, combined with climatic and soil constraints, we can say that drylands are not only thirsty, but also hungry. That means to say that they have a moisture constraints and also soil fertility constraints related to soil fertility. That means they are not only thirsty but they are also hungry.

Coming to the monsoons. What are monsoons? Monsoons are periodic wind, especially in the Indian Ocean that bring rains. So monsoon is a terminology, which is associated with the periodic wind in the northerly hemisphere, which brings rains during the rainy season in India. There are four types of monsoon seasons.

• One is south-west monsoon, which is popularly called as kharif rains.
• Then north-east which is popularly called as rabi rains
• Then the winter rainfall
• And the summer rainfall

In a year in all the four seasons, the India will be receiving the rains. The average annual rainfall of the country is around 1200 millimeters. This 1200 millimeter is spread over four seasons. So if you convert this 1200 millimeter into rain water amount; it will come to around 400 million hectare meter. So about 74% will be received in the south-west monsoon, 10% will be received during the north-east monsoon, then 3% will be received during the winter rainfall. Then summer rainfall accounts for about 13%. So of all the four rainy seasons, the south-west monsoon contributes a lot.

And Indian agriculture is more dependent on the south-west monsoon, rather than the north-east monsoon. Because in south-west monsoon which starts from June to September

• about 296 million hectare meter of rain water will be collected.
• Coming to the north-east monsoon, about 40 million hectare meter will be collected.
• Then coming to the winter rainfall, 12 million hectare meter
• And from summer rainfall, 52 million hectare meter will be collected.

So all in all Indian agriculture mainly depends upon the south-west monsoon. Coming to what are all the vagaries of the monsoon rain. These monsoon rains are not continuous. They are erratic. Their distribution is also not uniform. Then what are these vagaries of monsoon.

• Intensity and distribution
• Late onset of the monsoon
• Early withdrawal of the monsoon
• Then prolonged dry spell

If you take intensity and distribution, the rainfall will be occurring at a high intensity, and distribution will also be erratic. At sometimes it will bring heavy rainfall, and some parts it will bring less rainfall. The intensity will be very high in a sense that the soil particles will be displaced to a much extent, and there will be no penetration, there will be no infiltration of water into the soil. Whatever the rainfall falls on the earth, on the soil will flow as surface runoff. Then coming to the late onset. This is something when the rainfall is such, in a delayed condition; then the sowing will be delayed, then the crop establishing will be a problem. Germination and establishment of the crop will be a problem. Coming to the third one, early withdrawal in a sense that the rainfall will be withdrawn before normal ending of the rainfall season. So the crops which are being sown, by the time will be in the reproductive stage. That’s a very critical stage for the moisture. The crops will be devoid of the essential moisture. And this results in terminal stress. This terminal stress will result in reduction in yield.

Then coming to the prolonged dry spell. This prolonged dry spell during a crop growth are a very regular feature of Indian monsoons. When the crop is in good condition, if the dry spell sets in, the moisture availability will not be there during the critical stages of the crop, and it will also result in yield loss. So rainfall is the only source of soil moisture for dryland crops. In India rainfall is the only source of soil moisture for the crops. This availability of moisture is entirely dependent on onset, intensity and distribution of monsoon rains and also withdrawal of the monsoons. This rainfall, which is a one and only soil moisture source for the dryland crops. So the success or failure of the Indian agriculture depends upon onset, distribution and withdrawal of the monsoon.

Then coming to the droughts. What are droughts? The droughts are also associated with the moisture deficit factors. So that the definition of the droughts goes like this. The conditions under which the crops failed to mature because of the insufficient supply of water through the rain. So it’s a condition. Drought is a condition, where there is an insufficient supply of moisture through the rains. Because the rains are not normal, and there will be a problem with the rainfall occurrence. In those situations the drought set in. So what are the types of droughts. There are three types of droughts.

• Meteorological drought
• Hydrological drought
• And then Agricultural drought

Meteorological drought is a drought, wherein in a certain place or a certain region, wherein the annual rainfall it will become short of the normal rainfall of that region. Then the meteorological drought sets in. In each of the States all the regions are in the receipt of certain amount of normal rainfall. So based on this crop planning activities will be finalized. Then coming to the hydrological drought. In case of hydrological drought there will be surface water depletion. There will be drying of lakes, rivers and also oceans. So in this, the industry, power generation, and other income generating activities will be affected to a larger extent, and here mainly the ground water depletion also takes place. Coming to the soil moisture deficit, that is in case of agricultural drought. In case of agricultural drought, there will be insufficient supply of moisture, due to moisture stress. So it is divided into three droughts.

• Early season drought
• Mid season drought
• And the Late season drought.

This early season drought is associated with delay in the onset of monsoon. And as such when the monsoon doesn’t sets in a proper time, the development and establishment of the crop will be affected. Then coming to the mid-season drought. This mid-season drought is associated with long dry spells in the cropping period. When there are long dry spells, there will be poor transplant, the plant population will be very less, and as such there will be no development of the plant growth. Then coming to the late season drought. The late season drought is associated with early withdrawal of the monsoon. Then when the normal; when the rainfall is withdrawn early, then there will be no moisture supply, the crops will be at the critical stages. The critical stages like grain formation, then the reproductive stage will be affected badly; which in turn leads to the yield loss.

Coming to the conclusion. Understanding of the physiological processes that occur during the moisture stress is very much necessary, so as to ameliorate the stress effects, either by the management practices or by the plant environment. It is very important to understand the physiological processes that affected by the moisture stress. Secondly the dryland soils are not only thirsty, but also hungry too. Here moisture conservation as well as soil management practices should be given equal importance. Because of the fact that the dryland soils are not only thirsty but also hungry. Then vagaries of monsoons, drought factors are to be critically analyzed for adopting management practices. These vagaries of monsoons and drought effects can easily be managed if they can be analyzed properly. So the monsoon drought effects can also be managed by the management practices.

Thank You.