'n Evaluasie van suurmengsels as fosfaatkunsmis vir sproeibemesting

Abstract

The application of nitrogen through irrigation systems also necessitates the application of other soluble nutrients through this medium. Acid fertilizers are suitable for the purpose, but are highly corrosive. Information on the effects of these soluble products on the irrigation system is not accessible. It is thus necessary to investigate the influence of these chemicals on corrosion, to lay down guidelines for these practices and to evaluate the efficiency of the entire system. It is known that in order to prevent accelerated corrosion on galvanized irrigation equipment, pH-values of irrigation water needs to be above six. To verify this, potensiometric titrations were performed with an acid fertilizer in irrigation waters of different qualities. Positive correlations exist between dilution and the carbonate plus bicarbonate content of irrigation water, which can be used as a practical guideline. Electrical conductivity may be used as an alternative. No other side-effects were noted. The evaluation of acid fertilizers as source of phosphorus and the practice of surface application of acid fertilizers after planting, was carried out in pots with the aid of radio-active phosphorus (32p). A high and low level of phosphorus were applied. Four soil types with a phosphorus-status (Bray 1) ranging from 2 to 49mgkg-l were used. Wheat

(Triticum aestivum L.) was planted and irrigation conditions were simulated. Significant differences in yield ( dry material), as well as absortion of total-, soil- and fertilizer applied phosphorus were noted between the different soil types. The reaction of the control regarding the yield, the absortion of total-, soil- and fertilizer applied phosphorus is correlated to the phosphorus-status of the soil. The high phosphorus application led to significant increase in yield and absortion of total- and fertilizer applied phosphorus. No significant differences were noted between the two fertilizer sources ( acid fertilizer and dry fertilizer), with few exceptions. It was concluded that both are equal sources of phosphorus. The surface application of acid fertilizers led to significant increases in absortion of total- and fertilizer applied phosphorus. The yield was however, not significantly increased. The concentration of phosphorus applied on the surface led to increased availability and it seems that plants prefer applied phosphorus. The phosphorus applied through fertigation penetrated the soil to a depth of about five centimetres. The highest concentration of phosphorus still appear in the upper two to three centimetres. No further movement took place during the season.