Soil Properties, Fruit Nutrient and Biochemical Compositions of Tomato As Affected by Potassium Feldspar Application

Solubility of potassium from soil applied potassium feldspar is one of the constraints to its use as a source of potassium for crop production. Greenhouse experiment was conducted at the University of Newcastle, United Kingdom. Potassium (K) feldspar was applied at 0, 64, 128, 192 and 256 mg kg-1 soil, replicated five times. Soil properties, nutrient and biochemical contents of tomato fruits were determined. The application of 64 to 128 mg K kg^-1 soil significantly (p < 0.05) increased average fruit weight but decreased at 192 to 256 mg K kg^-1 soil compared to controls. Average soil pH was 6.16, total C (2.52%), total N (0.29%), Avail. P (39.52 mgkg-1), EC (112.84ƒÝS), CEC (15.88 cmolkg-1), Exch. Ca (72.78 mgkg-1), K (22.95 mgkg-1), Mg (8.11 mgkg-1) and Na (97.49 mgkg-1). Soil exchangeable K increased while Na decreased with increasing K from 64 to 256 mg K kg-1 soil. The results of the fruit nutrient contents showed a significant (p < 0.05) effect of K-feldspar on macro and micro nutrient elements. Magnesium and boron increased while sulphur and iron decreased significantly with increasing K from 64 to 256 mgkg-1 soil compared with the control. The values of N, K, Na and Ca:P ratio were not different from the control. Sodium and K ratio was significantly increased at 128 to 256 mg K kg-1 soil. The mean Na:K ratio for the fruits at the lower part of the plant was 0.27 and for the fruits at the upper part it was 3.15. Overall the lowest average Na:K ratio value for the fruit was obtained at K-feldspar of 64 mg kg-1 soil. Potassium application correlated positively with fruit N (0.52*), K (0.73**), Mg (0.78**), Cu (0.66**), B (0.72**), Na:K (0.53*) and Ca:P (0.30*). It was also positively correlated with fruit beta-carotene (0.75**), lutein (0.63**), cis-lycopene (0.50*), pH (0.65**) and sugar (0.38*). Negative correlation was obtained between K application and soil EC (-0.39*) and pH (-0.25*), fruit S (-0.51) and lycopene (-0.24). It was concluded that the K from K-feldspar was available for the tomato plant and improved fruit quality. It could serve as an alternative K fertilizer source and hence, reduce the cost and energy required for tomato production. There is the need for further research on the chemistry of K solubility from K-feldspar.