Plants absorb nutrients through the roots and through the foliage. When soil conditions are unfavorable, when micronutrients are needed, or when spraying for insects and disease, it may be desirable to make foliar applications of the plant nutrients. When plant nutrients are applied to the foliage of the plant, smaller quantities of the fertilizer material are required than when applying to the soil. The danger of fixation and/or leaching is also reduced when nutrients are applied to the foliage of the plant.

The most effective means of foliar application is the use of spray equipment. Either low pressure or high pressure equipment may be used. Spray equipment provides better placement, less loss by dripping and more effective coverage of the foliage than most other methods of application.

Irrigated agriculture is dependent on an adequate water supply of usable quality. Water used for irrigation can vary greatly in quality depending upon type and quantity of dissolved salts. The problems that result vary both in kind and degree, and are modified by soil, climate and crop.

SALINITY
Salts in soil or water reduce water availability to the crop to such an extent that yield is affected.

WATER INFILTRATION RATE
Relatively high sodium or low calcium content of soil or water reduces the rate at which irrigation water enters soil to such an extent that sufficient water cannot be infiltrated to supply the crop adequately from one irrigation to the next.

SPECIFIC ION TOXICITY
Certain ions (sodium, chloride, or boron) from soil or water accumulate in a sensitive crop to concentrations high enough to cause crop damage and reduce yields.

MISCELLANEOUS
Excessive nutrients reduce yield or quality; unsightly deposits on fruit or foliage reduce marketability; excessive corrosion of equipment increases maintenance and repairs.

Soils can be naturally acid or alkaline, and this can be measured by testing their pH value. Having the correct pH is important for healthy plant growth. Soil pH affects the amount of nutrients and chemicals that are soluble in soil water, and therefore the amount of nutrients available to plants. Some nutrients are more available under acid conditions while others are more available under alkaline conditions.

However, most mineral nutrients are readily available to plants when soil pH is near neutral. Alkaline soils may have problems with deficiencies of nutrients such as zinc, copper, boron and manganese. Soils with an extremely alkaline pH (greater than 9) are likely to have high levels of sodium.