SUMMARYTwo experiments to investigate the micronutrient requirements of cassava (cv Black Twig) on Malaysian peat soil are described. Cu was found to be the only essential micronutrient and Mn, Zn, Fe, Mo and B were not needed. Fertilizing with 20 kg/ha of copper sulphate approximately tripled tuber dry matter, and starch and Cu uptake, but applying 10 kg/ha of copper sulphate gave the same results. Each crop of cassava absorbed only about 2% of the applied Cu, giving a leaf Cu content of about 14 ppm compared with about 7 ppm in Cu-deficient plants. Cu deficiency symptoms were invariably observed in Cu-deficient plots and these are also described.

SUMMARYIn three field experiments studying the liming needs of cassava on peat, optimum tuber DM was obtained at pH 3.8 and optimum top DM at pH 4.2; liming to higher pH values decreased tuber DM while maintaining top DM. Consequently, the Harvest Index decreased over the whole range of soil pH studied (3.49–5.50). Increases in tuber DM per hectare with liming, and with an increasing growth period, were associated with mean tuber weight (r = 0.86) and with Harvest Index (r = 0.65) rather than with tuber number (r = 0.37).

SUMMARYIn a three-year field experiment on acid peat (pH 3.47) up to 12 t/ha lime increased peat pH (0–30 cm depth) by 0.061/t. Annual guinea grass dry matter increased in quadratic relation with liming up to pH 4.20 (12 t/ha lime) but there was no difference between the cvs Sigor and Colonoa. Liming decreased the N, P and K, but increased the Ca and Mg contents of the harvested grass. Liming also increased the uptake of all five nutrients investigated, either linearly or curvilinearly.

S U M M A R YIn three field experiments, peat pH increased in parabolic relation to liming at the rate of 0.0544 pH unit/t/ha between 0-40 t/ha lime, but only 0.0224/t/ha between 40-72 t/ha. Groundnut and sorghum seed yield and crop residue also showed parabolic responses to peat pH and liming, but groundnut seed yield correlated poorly with soil pH (r J = 0.38, P=0.05), compared with its crop residue as well as with sorghum seed and residue (r J = 0.75, 0.76 and 0.79, respectively, P= 0.01). Groundnut was generally more tolerant of peat acidity (pH 3.35-3.65) than sorghum, giving higher plant survival in unlimed plots, optimum seed and residue at pH 4.60 compared with 5.70 for sorghum, and reduced responsiveness to pH increase. Seed and residue of both crops decreased with continuous cropping, probably because of increasing pest and disease incidence and depletion of available soil nutrients.

SUMMARYOn unlimed Malaysian peat (pH 3.5), flue-cured tobacco produced negligible leaf yields and showed no response to urea. Liming up to pH 5.25 (32 t/ha lime) linearly increased leaf yield. Tobacco responded linearly without reduced leaf quality to 90 k/ha N at pH 4.01 (8 t/ha lime), but to 45 kg/ha N at pH 4.40–5.25 (16–32 t/ha lime), higher N rates at the respective liming levels producing leaves of lower quality. The optimum rates of P and K for flue-cured tobacco appeared to be 26 and 186 kg/ha respectively, with linear responses up to those rates.