CROP plants require 16 nutrients essential for growth and development and are classified as macro and micro or major and minor. Macronutrients include nitrogen, phosphorous, potassium, calcium, magnesium and sulfur. Macronutrients are required in large quantities while micronutrients such as zinc, iron, magnesium, cobalt, nickel, copper, chlorine and molybdenum in smaller quantities in kilograms and grams, respectively.

In mid 60s, high yielding varieties of cereals wheat, rice, cotton, maize and sugarcane were introduced in the backdrop of green revolution. Cultivation of these crops year after year in an intensive cropping pattern of rice-wheat and cotton-wheat caused depletion of soils from essential nutrients. Moreover, in an arid to semi-arid climate, the organic matter in our soils is very low in the range of 0.42 to 0.57 per cent.

To add to this, our farming community is not using other sources of organic matter such as green manures, farmyard manures (FYM), composts and crop residues for maintaining the nutrient status of soils. As a result, the nutrient deficiency has been reported in hundred of thousands of cultivated fields. The deficiency of macronutrients nitrogen, phosphorous and potassium (NPK) is reported from many fields. For example, the deficiency of potassium and zinc has been reported up to 50 and 80 per cent, respectively in different fields of Sindh.

To counter nutrient deficiency, growers are bound to incorporate commercial fertilizers in order to get desirable level of harvest. Fertilizer off-take has increased from 1892.90 thousand nutrient tons in 1990-91 to 3,222 thousand nutrient tons in 2003-04 while cropped area has increased from 21.82 million hectares to 22.94 million hectares during the same period. Simultaneously, fertilizer off-take for nitrogen and phosphorous has increased from 1471.63 and 388.50 thousand nutrient tons to 2526.73 and 673.46 thousand nutrient tons respectively.

Fertilizers are the major farm inputs for achieving higher agricultural production. Per hectare yields of wheat, rice, sugarcane, maize and gram have increased from 1841, 1543, 40720, 1401 and 486 kilograms in 1990-91 to 2375, 1970, 49738, 2003, and 622 kg in 2003-04, respectively.

While production of important fruit viz. citrus, mango, apple, apricot, grapes and guava has increased from 1609, 776, 243, 81, 33 and 355 thousand tons to 1760, 1056, 334, 211, 51 and 550 thousand tons, respectively during the same period.

Pakistan meets its fertilizer requirements partly from local production and partly from imports. Domestic production has increased from 2298 thousand nutrient tons in 2000-01 to 2539 thousand nutrient tons in 2003-04 while imports have also increased from 579.1 thousand nutrient tons to 764.1 thousand nutrient tons.

Source of fertilizer, time of application, quantity applied, crop type, crop growth stage, soil nutrient status and availability of other inputs like irrigation are factors that determine the response of crop plants toward fertilizer applied. Nutrients are lost from the soil solution in different forms. Leaching, denitrification, volatilization, immobilization and fixation of nutrients with soil complex are major losses of nutrients.

To get maximum benefits from applied fertilizer, it is imperative to curtail nutrient losses from the soil solution. Appropriate and adequate crop management practices would greatly help to cut down nutrient losses and would improve fertilizer use efficiency.

Land levelling is important to prevent losses of nutrients through leaching and run-off. It reduces the incidence of soil salinity and water logging through even distribution of fertilizer and irrigation. Land levelling ensures uniform crop stand that is important for uniform removal of applied nutrients from the soil.

Cultural practices such as deep ploughing with chisel plough after two to three years would help the plants to develop extensive root system that in turn would explore large volume of soil for nutrient and moisture uptake. Placement of fertilizer at appropriate depth would help the plant roots to uptake nutrients in an adequate amount.

The application of balanced amount of fertilizer at right time keeping in view the crop type and growth stage is essential to get maximum crop output. The farmers should apply fertilizers according to soil nutrient status.

Use of artificial or natural mulch helps to control evaporation of moisture and also contain volatilization of nitrogenous fertilizers. Over or under doses of fertilizer have negative impact on crop growth and development.

For example, excessive use of nitrogen fertilizer increases cost of production but also augments incidence of insect, pest and disease attack as well as contributes to pollution. Similarly, excessive application of DAP fertilizer destroys the under soil of the farmland, increases compaction of soil and reduces per acre yield. It also enhances level of acidity of cultivated soil from Ph 7 to Ph 8.

Prices of fertilizers also affect the ability of growers to use fertilizers in balanced amounts. The prices of urea (46%N), ammonium nitrate/calcium ammonium nitrate (26 per cent N), ammonium sulphate (21 per cent N), nitro phosphate (23:23NP), single super phosphate (18 per cent), di-ammonium phosphate (18:46), potassium sulphate (50%k) and NPK (10:20:20) has increased from 195, 90, 85, 173, 93, 249, 150 and 176 rupees per bag of 50kgs in 1990-91 to 420, 208, 373, 622, 329, 913 and 809 rupees in 2003-04 respectively. Inadequate fertilizer source and adulteration also affect the desired results.

It is suggested that the prices should not spin out of the purchasing power of farmers.

Again, the government is duty bound to enhance domestic production of fertilizers by installing new production plants and by increasing the capacity of existing plants in order to curtail fertilizer imports that are a drain on national exchequer. The role of private sector vis-à-vis public sector should be encouraged to get better results. It is a matter of concern for the policy makers that the requirements of fertilizers are increasing every year due to intensive cropping pattern and increase in cultivated area under exhaustive crops.

Appropriate crop management techniques also help to improve fertilizer use efficiency. Factors like timely sowing, recommended sowing method, adequate plant density, appropriate planting geometry, eradication of weeds and control of insects, pests ad diseases are responsible for healthy crop and hence contribute to higher fertilizer use efficiency.

Availability of irrigation affects fertilizer use efficiency. For example, non-availability of irrigation after nitrogen fertilizer enhances volatilization losses. So availability of irrigation is essential to prevent nutrient losses. Similarly, irrigation should be optimum because excessive irrigation contributes to leaching of nutrients.

Last but not the least, proper crop rotation comprising of exhaustive and restorative crop is imperative to prevent depletion of cultivated soils from essential nutrients. Exhaustive crops are wheat, rice, cotton, maize, sorghum, sunflower sugarcane and potato etc. while restorative crops include soybean, lucern, berseem, jantar, arhar and beans cultivars. Crop rotation should include restorative crop after one to two years.