Nutrient salt balance differences on the growth of potted banana, orange or tomato plants growing in sand or sand/CaCO3 and fertigated with highly saline solutions
2016
Oosthuyse, S. A. | Holwerda, H. T.
The benefit of ameliorating the effects of salinity when using KNO3 as opposed to KCl or K2SO4 as the potassium source in making up fertigation solutions was demonstrated. Three identical experiments were carried out, each on a different crop plant. Nursery 'Valencia' orange trees, and 'Williams' banana and 'Rodade' tomato plants, were transplanted into 2.7-L pots containing river sand or river sand/calcium carbonate (80:20 v/v), and treated with one of four nutrient solutions. One solution contained only Ca(NO3)2 and NaCl, and was applied to all the plants. The remaining three solutions were made up using the same fertilizers except for that supplying K. The K source was KCl, K2SO4 or KNO3. As a consequence the NO3- to NH4+ ratio differed between solutions as well as the Cl- or SO(4)(2-) content. NaCl was added to every solution to impose salinity stress. Elemental content except for that of S and Cl was equal in the K-containing nutrient solutions. Identical experiments were performed on each plant type. In each experiment, growth was most vigorous in the plants treated with the solution made up with KNO3 and least vigorous in the plants treated with the solution made up with KCl. This was reflected by height increases, and fresh weight and number of leaf differences when the plants were lifted. Number of primary roots in banana was commensurate with vigour. Number of leaves showing marginal necrosis in banana or number of wilted leaves in tomato indicated greatest salinity stress following fertigation with the solution made up with K2SO4. In tomato, number of flower trusses, fruit number and yield were greatest where the KNO3 solution was applied and least where KCl solution was applied. Differences in individual fruit weight were not observed. The results clearly indicate a benefit in using KNO3 as opposed to KCl or K2SO4 in fertigating crops growing in desert soils where the irrigation waters are generally saline.
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