Potassium (K) is described as quality element and it is one of important macronutrient essential for physiological development of plant. K plays an important role in plant metabolism and considerably increases the grain production. Its determinant effect on crop quality and yield are also considerable. Each kind of fertilizers as it is organic, bio fertilizer or synthetic fertilizer has its effect on nutrient availability and maintenance of soil fertility status. Crops requirements for K are as high as that of nitrogen. The demand for potash is particularly large in the period of rapid growth and the crop needs to take up about 8 kg ha-1 K2O per day. Quality and yield of a crop depends upon availability of nutrients to plants in an adequate amount and necessary to meet the food requirements of increasing population. Soils of Pakistan are usually deficient in nitrogen and phosphorous but now a day’s deficiency of potassium has also been reported. Currently about one quarter of the arable soils and three quarters of paddy soils in Pakistan are K deficient. Potassium deficiency in plants may lead to reduction in number and size of leaves which ultimately lead to less photosynthetic rate per unit area.
Various potassium fertilizers including K2SO4, KCl, KH2PO4 and KNO3 are used as sources of K. These fertilizers are selected on the basis of their availability in market, price, easiness of use and solubility. Mostly farmers in our country prefer the use of sulfate of potash (SOP) because it has low salt index and ultimately improves plant potential to disease resistance by up taking less H2O and such salinity hazards do not occur as well as sulfur become readily available to maintain fertility status, improve nitrogen utilization and involve in synthesis of amino acids and proteins, enzyme activity, necessary for crops having oil contents and preferably required by salt and chloride sensitive crop.
However, muriate of potash (MOP) is one of cheaper source of K and contains 60-63% K2O while SOP contains only 50% K2O and has high market price. Chlorine is said as undesirable but unavoidable micronutrient. On the other hand the chlorine contents from KCl increase the pH range of soil and cause salinity problem. Saline conditions produce ROS (reactive oxygen species) and ultimately plants have to suffer from oxidative damage. So there is need to exploit the use of KCl with other organic amendments which will make it effective by reducing its hazardous effects.
Chloride (Cl–) is required in photosystem II at the oxidizing state for the splitting of water molecule. The most favorable Cl– concentration range in most cereal crops is ranges between 0.3-1 g Cl-1 kg-1 dry matter content. K+ from KCl is considered as major macronutrient and Cl– is complementary anion which is said as undesirable but unavoidable micronutrient for plant physiology. The sole use of MOP increases the salinity of soil. Salinity inhibits plants growth due to closing of stomata which decreases the carbon dioxide to oxygen ratio and inhibits carbon dioxide fixation as a results leaf elongation and cell division is reduced. So there is need to exploit the use of MOP with other organic amendments which will make it effective by lessening its hazardous effects.
The shortage and high cost of inorganic fertilizers have limited their use for crop production among the peasant farmers. Therefore the use of organic waste such as farmyard manure, poultry manure, press mud and cow dung is increasing day by day.
Chemical changes attained by using organic amendments are slow but sustainable as it takes about 6 years to reclaim the soil according to a survey. Soil acidity can be improved by using the farmyard manure as it neutralize soil acidity and hence make fixed soil P and K in available form. Adverse effect and rising needs of synthetic fertilizers can be overcome by the integrated use of mineral fertilizer with compost including feedstock, vegetable waste, poultry manure and cow dung etc. So it is revealed that use of K-fertilizer with compost supplies 20% more K than use of chemical fertilizer separately.
Compost application increases the nutrient level in soil. Its application causes an increase in organic matter contents and decreases the erosion losses. It reduces plant pathogen and increases water holding capacity of the soil. Compost is a best means for the restoration of fertility status and makes the farmers able to avoid debt which they have to pay for mineral fertilizer. Combine use of chemical and organic fertilizer is preferred as compared to the use of chemical fertilizer alone. This results in increase in soil fertility status and increased N, P, K levels without disturbance of soil properties. Poor farmers cannot afford mineral fertilizers due to high rate so; higher benefit cost ratio was also observed.
Naila Farooq, Shamsa Kanwal, Muhammad Iqbal, Tasawer Abbas
Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad 38040, Pakistan