Cotton (GossypiumhirsutumL.) is an important fiber and cash crop of Pakistan. Being an industrial commodity, it has an assured world demand and thus holds a unique position in the international commerce. At present, Pakistan is the fifth largest producer of cotton in the world, the third largest exporter of raw cotton, the fourth largest consumer of cotton and the largest exporter of cotton yarn.Cotton contributes nearly 10 % in the agriculture GDP and a source of 55 % foreign exchange earnings. Cotton accounts for 8.2 % of the value added in agriculture and about 1.6 % to GDP. The crop has been sown on the area of 3.05 million hectares with total production of 11.7 million bales.
Cotton yield is stagnant for the last several years. Factors responsible for the yield of seed, poor intercultural practices, improper handling of the weeds and most importantly unavailability of water at critical stages to ensure healthy crop stand. Among other yield contributing factors phosphorous plays a vital role particularly for cotton. Phosphorus (P) fertilization practices help to insure an adequate supply of P during peak growth demand periods of a crop. Phosphorus affects the availability of nutrients at various important crop growth stages and interestingly it is itself affected by the availability of other nutrients as well.Lint yield increases with P fertilization due to an increased number of bolls and boll size. Increase in boll size with P fertilization is a function of increased micronair (fineness and maturity of fiber).
A one ton crop of cotton removes 63 lb P2O5/acre and 126 lb K2O/acre.Soils with deficient phosphates can improve the seedling vigor and crop maturity by phosphate fertilization. Phosphates applied with adequate nitrogen do not materially alter the morphology of the cotton plant, but through better nutrient balance increase seed cotton yields.
Crop response to applied P can be improved by making adjustments for time, rate, and method of application. It varies with soil physical and chemical properties, crop management practices and crop stress conditions such as drought or nutrient deficiencies.Early diagnosis of P deficiencies and other nutrients can help minimize losses in crop yield, quality and farm profitability. In-field inspection, along with soil and plant analyses, helps to provide needed facts for immediate correction and next-season planning. This study provides the basis for crop adjustment, better agronomic practices, proper and effective doses of phosphorus fertilizers to ensure better production and water management.
There are numerous yield reducing factors in Pakistan most importantly un availability of quality seed, poor seed bed preparation, not up to the mark fertilization, inadequate weed management, poor irrigation, faulty pest control due to adulterated pesticides and finally no marketing system and post-harvest technologies. Nature of cotton is that irregular and imbalance nutrient availability affects vegetative and reproductive growth of cotton by affecting different metabolic pathways. In cotton, chemical fertilizers especially nitrogen, potassium and phosphorous are most important yield increasing inputs. Nitrogen is important in improving the vegetative growth of cotton and many energy rich compounds are produced as well. Phosphorus has a very important and vital role for energy regulation, photosynthesis and other physiological processes for better crop production. Unluckily, Phosphorus is the least available nutrients in particularly less availability of phosphorus fertilizer in tropical areas are a big challenge to profitable crop production.
Intensive crop production requires large amount of nutrients to increase the yield and to fulfill the growing needs of Pakistan. According to different surveys of Punjab all most all the farmers are biased in the application of phosphorus and they prefer nitrogenous fertilizers because of its low price and conventional thinking. Cost of fertilizers is second largest variable factor and accounts for 22 percent of total production costs. Different tests of soils show that there is a deficiency of nitrogen; secondly of phosphorus and potassium is not critically deficient in Pakistan.
There are several deficiency symptoms in cotton facing phosphorous deficiency. Phosphorus deficient plants can be undersized, with darker green leaves than the normal; flowering may be deferred and boll maintenance poor; spontaneous death of leaves may occur in P-deficient plants in the late season. However in early growth periods of cotton the deficiency of phosphorus has not been found yet. Cool temperature and suboptimal availability of phosphorous and nitrogen also affect the hydraulic conductance (K) of cotton. Past experience has shown that phosphatefertilizers when used alone do not increase cotton yields significantly and when used without enough nitrogen give no-apparent growth response.
It is important that phosphorous must be supplemented with nitrogen for its best effects. Studies have shown that phosphorous affects the quality of cotton to a greater extent by improving the lint and fiber length of cotton. The input responsiveness of cotton cultivar decides the extent of advantage of nitrogen and phosphorus. Cotton cultivars of the modern age are more responsive to phosphorus as compared to the old ones because modern genetics and breeding techniques, agronomic practices and boll weevil (Anthonomous grandis Boheman) suppression in most cotton producing regions of the world. Phosphorous application; its doses and methods of application and related research is the need of the hour because of the growing population and growing needs of more and more production. Farmers of Pakistan are reluctant to apply the phosphorous in proper methods and in proper doses because of various reasons such as superstitious nature, poverty and illiteracy. Moreover, effective and sustainable research has not been taken into this serious account so far. Price hike of the phosphorous fertilizer is one of the major problems in the way of farmers to use it and similarly unplanned and non-technical use of the fertilizer is the second yield affecting factor in Pakistan. It is the dire need of the time that government should take serious steps in making of phosphorous an integral part of current production technology of cotton. This will help resolve the problem of continuous discouraging behavior of WTO and other regional economic forums towards Pakistani cotton.
Muhammad Irfan*, Dr. Rashid Ahmad, Zahoor Ahmad,
University of Agriculture Faisalabad Pakistan