Aberrant weather situations and Contengency Crop Planning

Dryland Agriculture an Introduction:-

At present there is a talk about second green revolution. The International Food Policy Research Institute, Washington, opined”with the rising demand for food in coming decades, India will have to depend on the rainfed areas to help increase supply”. India contains about 47 mha as drylands out of 108 mha of total rainfed are which amounts nearly 43 %. The semi arid tracts are not only large but also agriculturally important. In India, such tracts cover 84 districts, spreading over 47 mha which is more than one-third net sown area. But their contribution to total food grain production is about a fifth in the country.

WEATHER: MOST VARIABLE FACTOR IN DRYLAND AREAS

Unfavourable deviated weather from the normally expected one is called aberrant weather. Aberrant weather is a common feature of rainfed agriculture. Crop production in dry areas is mainly dependent upon rainfall, which is received during the south west monsoon. The rainfall is seasonal, erratic and highly variable with space & time. Vagaries of monsoon rains and breaks of varying duration are most common in India. Three important aberrations in the rainfall behavior have been commonly observed. These are:

• The commencement of rains may be quite early or considerably delayed.
• There may be prolonged breaks during the southwest monsoon season during which most of the dryland crops are grown
• Rains may terminate earlier than normal cessation date or may continue beyond the normal rainy season.

Anomalies in the distribution of south west monsoon rainfall are well known. Based on the analysis of historical rainfall records, have brought out the following main features of rainfall distribution in India.

• There is large variation in the dates of commencement of the southwest monsoon rainfall from year to year in different parts of the country.

• The monsoon rainfall is of sequential nature with dry spells interspersed with wet spells, dry spells extending from few days to several weeks.

• There is a large year to year variation in the dates of cessation of south west monsoon rainfall in different parts of country.

• There is variation in the quantum of rainfall received from year to year and t he coefficient of variation of rainfall increases with decrease in monsoon rainfall.

• High intensity rainfall occurs in association with the movement of cyclones/depressions resulting in sizeable loss of rain water through run-off and deep drainage.

Weather is the most variable factor in rainfed crop production. It is the one which can be least controlled. However, various approaches, often referred as contingent plans, have been evolved over the years, for efficient weather management. The infrastructure requirements have to be developed and established by the government and other agencies as people themselves will not be in a position to adopt contingency measures more effectively because of their poor resource base. Some of the management options that can be adopted to mellow down the adverse effects of aberrant weather are discussed here.

CONTINGENCY CROP PLANNING

Contingency planning refers to mitigate any unexpected, unusual, unfavourable and hence unwanted accidental weather situations occurring at any time without prior knowledge at any time before the crops are sown or even after the crops are sown. The contingency crop planning therefore is proposed to mitigate such situation through the choice of appropriate crop and varieties, cropping systems or other necessary relevant farm practices. To develop a contingency plan for an area, a detailed study of the rainfall data should be done first. Based on this rainfall data, the planning should be done. In any areas generally following rainfall situation may occur:

1. Early onset of monsoon.
2. Normal onset of monsoon followed by immediate prolonged dry spell.
3. Delayed onset of monsoon.
4. Early cessation of rains.
5. Extended monsoon.
LATE ONSET OF MONSOON

During some of the years the onset of south west monsoon gets delayed so that the crops/varieties which are regularly grown in the region cannot be sown in time. Delayed sowing of the crops can lead to reduced and even uneconomical crop yields. Under these circumstances, two management options are available.

1. Transplantation-This is the surer way of compensating the delay in the commencement of sowing rains, through transplantation is labour intensive operation. Extensive studies carried out indicated that both long and medium duration varieties of finger millet should be transplanted for maintaining yield levels whenever sowing is delayed.

2. Alternate Crops/Varieties-certain crops/varieties can perform better even if sown late in the season. Depending on the receipt of rains, such crops and varieties can be selected. Castor (Aruna) is more remunerative in red soils of telengana (AP) then pigeonpea under late sown conditions. Sunflower, because of its shorter duration, performs better than groundnut when sowings are delayed beyond September first fortnight in relatively deeper red soils. In western Rajasthan, short duration green gram and cowpea are more remunerative than pearl millet when sown late.

DRY SPELL IMMEDIATELY AFTER SOWING

Dry spells are common in dryland agriculture. Due to dry spell after sowing of crop it might result in poor germination due to soil crusting, withering of seedlings and poor establishment of crop stand. The adverse effect of moisture stress should be mitigated to avoid total crop failure. It is necessary to maintain proper plant stand to ensure better yield. Therefore it is better to resow the crop than to continue with inadequate plant stand.

MID SEASON CORRECTION OR DRY SPELLS DURING CROP PERIOD

After sowing of crops and early growth any unexpected or unfavourable weather abnormality like long dry spell of 3 to 6 weeks, drought or early cessation of monsoon may occur. Unexpected or accidental occurrence of unfavourable weather after sowing is contingency and crop planning to overcome this contingency is called contingency crop planning. To mitigate the damaging effects of droughts after sowing of crop following mid season corrections are recommended:

1. Ratooning-The rate of soil moisture depletion increases with increasing leaf area. If drought occurs at 40- 50 DAS, reduction in leaf area either by rationing or thinning plant population can mitigate the adverse effects of drought. Sorghum and pearl millet responds to rationing. 2 % urea sprays after drought period is useful for indeterminate crops like castor, pigeon pea and groundnut.

2. Mulching-If the break in monsoon is very brief, soil mulching was found to be tool in extending the period of storage of water in the soil profile due to reduced heat load on the soil and hence the evaporation losses which in turn leads to extended periods of water availability. Repeated intercultivations in black soils results in formation of soil mulch on the surface. It acts as barrier to evaporation loss from soil profile. Deep cracks formed due to drought increases the loss of stored water by evaporation. Soil mulch minimizes deep cracking leading to reduced evaporation losses.

3. Thinning-If drought occurs during pre-flowering stage thinning is useful. Every third plant or alternate row may be removed to reduce the soil moisture loss and preserve it. Moisture stress of 35-50 days can be lessened by such thinning.

4. Weed Control-Weed control is very essential to save the crop from onslaught of drought as weeds rob soil moisture and nutrients as well.

5. Rain water harvesting and recycling-In situ water harvesting and / or runoff recycling are the potent measures for crop life saving during the periods of moisture stress. There is no control over the receipt of rainwater but it can be managed in a way better what is being done at present after it is received. Supplementary irrigation provided to the crop through rainwater harvesting and recycling particularly during the grain formation stage will be very much rewarding. Run-off recycling holds immense prospects in deep black soil where the seepage losses are very less. High intensity rains are quite common during the rainy season contributing 75% of seasonal rainfall. The inevitable runoff (10-40% of the total rainfall) could be stored in dugout ponds of appropriate sizes and recycled to the donor area, in the event of severe moisture stress.

6. Stripping of crop leaves- Generally, photosynthesis occurs in the upper 3-4 leaves. Hence excluding these leaves, lower leaves from the plant may be removed to reduce transpirational losses.

7. Intercropping and risk distribution-Application of meteorological information in terms of the frequency and probability of breaks in monsoon rains can be made to select a combination of crops of different durations in such a way that there is time lag in the occurrence of their grow for appropriate intercropping systems. The choice of intercrop depends upon the pattern of rainfall. There are 3 possibilities as:

1. Rainfall more uncertain in the early part of season.
2. Rainfall more uncertain in the later part of season.
3. Rainfall more or less uniformly distributed (in other words, the risk is uniformly distributed).
Region System
Hisar Pearlmillet + Cowpea
Agra Pearlmillet+ greengram
Banglore Pigeonpea + Cowpea
Hyderabad Sorghum + pigeonpea
Akola Sorghum + greengram

EARLY WITHDRAWAL OF MONSOON

Early withdrawal of monsoon before rabi seeding leads to problem of crop stand establishment and terminal drought. Therefore, rabi seeding should be as far as possible in early September to avoid the above two problems. All the suggested measures to mitigate the adverse effect of prolonged dry spells during crop period are necessary to overcome the soil moisture stress during the early withdrawal of monsoon.

EXTENDED MONSOON
Extended monsoon is seldom a problem in dryland agriculture. It benefits long duration kharif crops taken as a component crops in intercropping system and is also advantageous for rabi crops.


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References:
1-Principles & Practices of Dryland Agriculture- K. Govindan & V. Thirumurugan
2-Dryland Agriculture- S.C. Panda
3-Sustainable Development of Dryland Agriculture in India- Editor R.P. Singh
4-Principles of Agronomy-S.R. Reddy
5-Handbook of Agriculture- ICAR publications