ABSTRACT
Most of the nutrients are taken up by the plant in the form of cations which are positively charged. Available cations either in the soil solution or held against leaching by negatively charged clay or humus particles are easily taken up by the plants. Other plant nutrients notably phosphorus, boron and molybdenum are taken up by the plant as anions which are negatively charged. Potassium availability is reduced due excess activity of calcium in saline soils and sodium in alkali soils. Crop growth is controlled by several growth factors. Deficiency or absence of nutrients in the soil hinders the crop growth and productivity. For a single deficient nutrient with increasing addition of a fertilizer the crop yield may be represented by a straight line. Sloping upward from the control yield to a higher yield at which another factor becomes limiting. At this point, the linear increase ceases, and with further additions of the nutrient, the yield remains substantially constant.
