Boron : an agro-environmental concern

Abstract

Boron is an important micronutrient in plant nutrition. It is essential at low concentration, becoming toxic at higher concentration, producing marked yield decrement. The range between deficient and toxic concentration levels is narrow and an understanding of boron sources and reactions in soils is necessary. Boron is naturally present in most waters; including SASTP treated effluent. Irrigation water containing acceptable levels of boron may not induce toxicity immediately. The soil matrix adsorbs a fraction and the remaining portion is held in the soil solution. If use of boron containing irrigation water continues, the boron concentration in the soil solution may eventually equal that in the irrigation water. The soil matrix will not be able to adsorb increased amounts, with the potential danger that boron in solution eventually increasing in concentration to a level that is toxic to seedlings and boron sensitive agricultural products in general. The study evaluated boron concentration in different matrices; soil, sewage treated effluent, rainwater, drinking water and compost. A significant total boron concentration difference between the area irrigated with sewage treated effluent (Area 1) and area not irrigated with such effluent (Area 2). Though the treated effluent was thought to be the cause of this marked difference, the sources of boron were found to include drinking water together with detergents and other boron containing products that end up in the sewage system. The publication of standardisation orders on detergents and products that have the potential of being discharged into the sewage system, without the appropriate market and scientific research is potentially dangerous. Efforts should be made to obtain the necessary derogation against the full liberalisation of product importation so as to retain and improve the ban on the prevention of importation of boron containing detergents and products that end up in the sewage system. The study also sets future boron evaluation possibilities.