PEAT-SAND SUBSTRATES FOR PLANTS GROWN IN CONTAINERS .I. EFFECT OF BASE FERTILIZERS

The N, P, K, and Ca fertilizer requirements of a 75% sphagnum peat 25% sand mixture were studied using 34 quasi-latin square designs with tomato and antirrhinum as test plants. A large interaction with season in the response to N, P, and Ca was obtained. In winter, when plant growth rates were low, high rates of N and Ca with low rates of P gave a significant reduction in growth, delay in development and boron deficiency. The effects have been attributed to the high levels of NH4-N and the accompanying high pH values following mineralisation of the organic nitrogen in the base fertilizer. Under these conditions the beneficial effect of superphosphate is considered to be primarily due to a reduction in the pH and in the rate of nitrogen mineralisation. In summer, when the growth of tomatoes in a 30-day period was found to be of the order of twenty times greater than in winter, the N × P × Ca interaction was not significant and no boron deficiency was observed. Comparison was also made between the nitrogen requirements of peat-sand and loam composts. The standard peat-sand mixture was found to be deficient in available nitrogen by comparison with loam compost. Plants in the peat-sand showed a greater interaction of N levels with season than did plants in loam compost. In winter the highest rate of nitrogen gave a reduction in the growth of tomatoes in peat-sand but not in loam, whereas in summer there was a positive response to each increment of nitrogen in the peat-sand and growth was significantly better than in loam compost. © 1969 Martinus Nijhoff.