Effect of phosphoros nutrition in peat on tomato plant growth and fruit development

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The effect of P nutrition on the growth of tomato plants in peat was examined. Initially, plants received an adequate supply of P and then received either nil, 0.78 or 2.34 kg superphosphate per m3 in combination with either 50 μg N/ml (N1) or 300 μg N/ml (N2) as ammonium nitrate in a liquid feed. Vegetative growth was restricted in the lower P treatmentsi.e. inhibited shoot growth, reduced duration of leaf expansion phase, thinner stems and reduced vegetative dry wt. Plants receiving N2 showed a greater restriction in growth compared with N1 plants when the P supply was limiting. P deficiency disrupted protein metabolism in the leaves, in that soluble leaf protein was reduced and trichloroacetic acid-soluble N accumulated. Flower development was accelerated by low P applications but the final numbers of flowers and the fruit-setting efficiency were reduced. Lowering the N supply reduced the fruit yield by 36 per cent while an intermediate P level reduced yields by about 15 per cent. Maximum fruit yields and good vegetative growth occurred when plants contained 0.4 per cent P or above in the mature leaves, and this value was achieved by adding the highest level (2.34 kg/m3) of superphosphate to the peat.