Two field trials comparing rates and times of application of borax to lucerne were conducted for 4 years on yellow-brown pumice soils in the Taupo area. Boron deficiency symptoms occurred at one site every year, but only when there was a prolonged dry period. Borax applications prevented boron deficiency symptoms and resulted in dry matter yield increases of 9-43% for individual cuts and an average annual increase of 1530 kglha (14%) over the 4 years. No response occurred at the other site where the soil contained a higher level of available boron. Annual rates of application greater than 11.2 kglha of borax increased the boron concentration of the lucerne at both sites but did not increase yields. Time of application also had no effect on yield. A single application of 22.4 kglha of borax at the start of the trial was as effective throughout the 4 years as repeated annual applications. This rate, applied with the spring topdressing every fourth or fifth year, is recommended to prevent boron deficiency and maintain yields of lucerne hay on the pumice soils in the Taupo area.
INTRODUCTIONBoron is required in only small amounts by plants, but brassicas, lucerne, and some fruits and vegetables have a higher requirement than many other plants.
ABSTRAcrForty yellow-brown pumice soils were examined for sulphur retention, using a laboratory leaching and incubation technique. Leaching losses of sulphate from added superphosphate ranged from 33% to 100 % of that applied.Comparative sulphur losses from four out of five yellow-brown loams examinecl were much smaller (2-6% of the amount applied).On these volcanic ash soils, the concentration of allophane A appears to be an important factor in sulphate retention. N.Z. Jl agric. Res. 9: 93-7
Laboratory studies have shown wide variation in the ability of soils to retain potassium against leaching, the amount of applied K leached varying from 7 to 72%.Four field trials comparing a less soluble potassium salt-potassium metaphmlphate-with superphosphate plus potassium chloride were laid down on soils of low K retention, and dry matter yields were measured over an 18-month period. At three sites the potassium metaphosphate treatment showed significant increases in one year, but not in the other. At the fourth site significant yield increases of 10% were obtained in both years.Potassium metaphosphate has the advantage of lightness, being only about one-third the weight of an equivalent potassic-superphosphate mixture. Its disadvantages are lack of sulphur and a fixed K: P ratio.
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