Using the sugar cane cultivar Co 421, competition from weeds for the whole growing season was compared at three row spacings with competition for periods ranging from 15–120 days at the start of the season or later, and weed-free conditions all through the season. The critical period for weed competition was the first three months, since weeding during the remaining 11 months did not improve yields, which were similar at row spacings of 1, 1·25 or 1·5 m. There were no interactions between the weeding and spacing treatments.

The effects of plant population on yield and its components were investigated in three experiments in 1969, 1970 and 1971. Increasing populations from 9000 to 36,000 plants/ha. increased yield linearly. The number of tubers produced per plant was not affected by population, but an increase in plant density decreased average tuber weights. Increasing sett weight from 203 to 608 gm increased tuber yields/ha. and the number of tubers per plant but did not affect average tuber weights in two experiments. In 1971 compound fertilizers increased yield up to the highest rates of 90 kg./ha. each of N, P2O5 and K2O respectively.