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Potassium: an essential nutrient
Ateeq Malik
Agriculture worldwide faces a variety of challenges. In some regions, production must be expanded to provide food for growing populations, in other there are surpluses and agricultural production has to be matched to effective demand.
In Asia, in the year 2030 there will be 0.06 ha available arable land per capita, compared with 0.14 ha in 1990. Yields will have to increase correspondingly. If the requirements of the growing population cannot be met by an increase of soil productivity, the poorest people will be obliged to cultivate marginal land, entailing an extension of land degradation and soil erosion.
What has been said for land availability also applies for water. Withdrawal of water in developing countries will increase by 43 per cent between now and the year 2020, in developed countries by 22 per cent. But. In developing countries, the demand for domestic and industrial uses will double, reducing the supply for agriculture.
Although use of organic manures has long been the dominant plant nutrient source in past but now mineral fertilizer is indispensable in increasing crop production. In Pakistan, the use of farmyard manures is inversely related to farm size. Small farms up to 1 ha use on average almost 5 t/ha whereas larger farms of 10 to 20 ha apply less than 100 kg/ha (NFDC, 2000).
Lack of affordable labour, misuse of crop residues as fuel and building material is reasons for this. It has been investigated and concluded that every increment of 5 million tons of food grain needs an additional 400,000 MT of mineral fertilizer (nutrient). Presently about 40 million hectares of the sown area receive fertilizers.
It is a known fact that adverse conditions such as water stress due to low rainfall (drought), or too much of water (floods) are prime culprits of unfavourable soil condition, hereby seriously impairing cop growth and yields. No one can avert natural calamities but there are several ways and means to minimize their severity on crops.
Out of the 16 elements, three are known as the "major plant food elements". They are nitrogen (N), phosphorus (P) and potassium (K). They are called major plant food elements because they are needed by plants in the largest quantities and because soils are, or easily become deficient in them. In Pakistan fertilizer consumption per arable and permanently cropped land is quite low i.e. 112 kg/ha as compared to Sri Lanka, Bangladesh, Malaysia, China, Vietnam and Republic of Korea where the consumption is 123, 141, 185, 259, 269 and 458 kg/ha, respectively.
Although we are using fertilizer in low amounts but the main worrying thing is that we are using them in highly imbalanced manner. Instead of adding nutrients in soil on removal or crop-required basis most of our farmers are conducting this activity by following their forefathers norms. Now-a-days where the development has left far away everything and man is moving from desktop to laptop computers, in agriculture also, development lies in judicious use of each and every input.
The nitrogen potassium ratio that always has important implications for soil fertility has declined in the past 20 years from a roughly balanced value of 1:0.004 to currently 1:0.024. The use of nitrogen alone may increase crop yield but because the yield is increased, the removal from the soil of nutrients other than nitrogen is increased and, as time passes, the soil becomes impoverished of that nutrient to the extent that deficiency levels are reached and crop growth is constrained.
Increasing yields by using nitrogen fertilizer increases the removal of potassium from the soil which means that in the course of time the K supply becomes limiting and it is necessary to replenish soil stocks if yield is to be maintained. The NK ratio contrasts sharply with the ratio in which plants absorb N and K. Cereals for instance take up nitrogen and potassium in almost equal quantities; vegetables and root/tuber crops absorb even more potassium than nitrogen. However, potassium removal by crops exceeds by far use of potash fertilizers, the negative balance in potassium is steadily growing.
In Pakistan, the addition of potash as fertilizer is 0.4 kg/ acre as compared to Egypt, China, and Korea where the consumption stands at 3, 21, and 52 kg/ acre, respectively. Inversely to annual potassic removal from our soils i.e. 0.5 million tones, the usage stands at a mere twenty thousand tones. Thus making the already 35-40% of potash deficient soils unable to produce properly and ultimately handcuffing the country's economy.
It's role and Importance: Many a times potassium is considered as a nutrient to improve yields. It's true but more specifically research shows that N is the most important yield increasing plant nutrient, whereas K is the most significant in stabilizing yields. It's another important role of reducing impact on crops is often not realized.
Potassium minimizes water stress by increase in root exploration; in which root elongation, turgidity, and rate of root regeneration are increased with sufficient K, decreased rate of transpiration because sufficient K make stomata close quickly and prevent the plant from wilting quickly by unnecessary water loss thru transpiration, quick crop growth in which severity of the effect of low moisture can be reduced under delayed planting by advancing date of pollination when most crops are highly sensitive to moisture stress.
Potassium minimizes stress due to water logging by building cellulose thereby giving sturdiness to plant stems and also preventing lodging, maintaining balance between solid, water and gases; for optimum growth plant roots require a proper balance between solid, liquid and gaseous phases (mostly 50:20:30) in the soil. Where there is a risk of lack of oxygen, K fertilization helps improve health.
Like nitrogen and phosphorus, potassium is a nutrient, which is also applied to the field in the shape of different fertilizers. Worldwide Potassium chloride (KCl, 60 per cent K2O), Potassium sulfate (K2SO4, 50 per cent K2O), Potassium nitrate (KNO3, 46 per cent K2O) and mono potassium phosphate (KH2PO4, 34 per cent K2O) are the sources to be used to apply K into the soil. Among them Potassium chloride or muriate of potash is the principal source carrying the highest amount of potash, and hence a relatively low cost per weight making it the least expensive among the major plant food nutrients.
This fertilizer (MOP) is used more than 90 per cent globally for the K source. In Pakistan numerous organizations including Potash Development Institute mostly funded (for educational and promotional programmes) by Canadian International Development Agency through Potash and Phosphate Institute of Canada, have conducted experiments for very long durations to compare efficiency of Potassium chloride (MOP) with Potassium sulfate (SOP).
Balanced fertilization is not an expense. It is an investment in the soil for future. As the investment grows, so does the yield. The best way to meet balanced fertilization is to use NPK compound fertilizers. This is natural, because NPK compounds ensure that each plant receives the correct nutrients in the correct amounts and proportions.
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