The present article is meant to place some suggestions before planners and guide the fruit tree growers about what to do in case of drought, like the present and not cut down the orchard trees for fear of drought or allow them to be killed by it.
The present article is based on experience gained by the writer in 1979, when under a Martial Law Order, General Iqbal ordered closure of 82 watercourses from Rohri canal and reverting back to old source of their supply.
The strategy was to save more paying crops of mangoes and lychee and scarify one crop of citrus, guava and banana for one year and buying water from other growers of near by watercourse for the mango and lychee crops.
The crops mentioned above were not to be destroyed totally, but were to be pruned and conditioned for mere survival. The method varied with crops, but was executed very fast within days as moisture under the ground had to be preserved.
We had a few days notice of watercourse closure, during which, we carried out the operations of strategy and irrigate the whole land to soil capacity and treat the trees for their survival. This was an experience we gained, which can be used in the present or future drought.
The data provided by Meteorological Department for Sindh are interesting and show that in every eleven years, there are two years of very heavy rainfall and another two years of no rainfall or two consecutive years of scanty rainfall, when famine conditions prevail and couple of million animals die in Thar and Kohistan and then invariably the Government, social workers and NGOs awaken to the plight of people, but soon forget it for a few years, until its another recurrence, with no planning for future.
Strategies for drought have to be developed by a continuous process. Returning strategies against drought, for horticultural crops, the following are few suggestions.
* In recent drought, thousands of mango trees have been killed. The present mango disease is caused directly by virus but virus easily attacks weak or diseased or old trees.
* The aim in drought should not be towards getting the harvest but towards survival of the trees for future.
* Trees have to be conditioned to withstand onslaught of drought, a management strategy, but this is has to be better than allowing trees to be killed. To condition them against drought, trees are pruned and mulched so that evapo transpiration from foliage and surface reduced to make very minimum use of water.
* One of the solution in tree crops is to breed varieties tolerant of drought and the other solution is replacement with other fruit trees needing less water but this will take long time.
* The aim again is to have profitable farming, despite unfavourable irrigation or patterns of rain water conditions. Under this programme will come Thar and Kohistan and now the Indus rive rain area.
* Comparison of long term average and seasonal rainfall, will help in understanding its patterns and can be used for long- term planning.
* In view of drought world over, scientists are likely to develop new technologies and strategies to manage drought risks, but until then we have to use some methods to cope up with the problem.
Mulching as strategy for reducing water use by 40-50 per cent: One, the solution to reduce water consumption by plants is mulching. In case of banana we had found that removing the stems which had already produced fruit from the field, was a very costly operation. Besides cost of labour, this material dumped out side the plantation occupied lot of area and material having high carbohydrates to nitrogen ratio, took years to decay.
We found it was most economical to chop banana stems, leaves and suckers to pieces and spread them in the field. The material was enough to cover the whole ground to a depth of 6-8 inches and took a few moths to be digested, during which another layer was applied from new stems and extra suckers. The mulch retained soil water, lowered soil surface evaporation, reduced soil temperatures in summer and thereby reduced evaporation.
Mulch also suppressed weed growth. Digestion of mulch reduces soil compaction, as its digestion involves insects and earthworms, which make soil porous to a depth of at least a foot. Banana stems and leaves are rich in potash and in each acre they account for 1000 to 2000 kilograms of potash.
They also contain nitrogen, phosphate, micro-nutrients like, copper, zinc, manganese, boron, iron and molybdenum. During drought we left one sucker per plant and cut down all stems and suckers to small size of about 2-3 inch pieces, spread them evenly, covered them with thin plastic sheets, on which was spread some banana shredded trash and earth to seal joints and protect plastic from ultraviolet ray of sun and only one hold for each sucker was cut in plastic.
Moisture in the soil and also from banana stem trash, kept suckers alive and healthy and they attended a large size in next three months. When water became available after three months, fruit production next year was more than fifty percent of other farms.
Under drought conditions, mulching can save forty percent or more water. Incidentally polythene, plastic mulch is costlier, than using banana leaf and trash mulch.
In case trees like lychee, we reduced the wetted area by construction of ten feet diameter circular embankments above ground and applied water in it. Since in our soils, horizontal permeability is more than vertical, we mulched the whole tree canopy to suppress weed growth and reduce evaporation from area wetted by horizontal permeability.
Plastic mulch covered with lychee leaf trash was quite successful and yet due to miner drought lychee fruit split. In case of drought wetting diameter can be reduced but wetting depth is not reduced. Weed control is essential during drought as weeds evapo transpire substantial qualities of water.
DISEASES OF TREES STRESSED BY DROUGHT:
Trees under prolonged drought suffer from diseases in the following manner:
(i) Trees diseases prompted by sufficient irrigation water will disappear temporarily.
(ii) Trees suffering from diseases caused by high humidity may also be unaffected or in some case infections may increase but only slightly.
(iii) Pathogen increase on drought stressed crops.
(iv) Powdery mildew in grapes, papaya and mango occur with some intensity as those unstressed and same happens to viral diseases like Fusarium Phytophthoro.
(v) Branch die back is common in most fruit trees.
