Growth of Sugarcane and Its Use of Nutrients in Zimbabwe

A sugarcane (Saccharum sp.) crop, planted shortly before mid-summer, produced about 7 000 g of above-ground dry matter rrrby the time it was harvested, 56 weeks later; of this total 32% consisted of sucrose, 41 % of other stem material, 10% of green leaflaminae and sheaths, and 17% ofdead leaves. Number of tillers increased to 23 m? at week 18, then fell to a final number of 14m? by week 32. Leaf area index (L) increased to a maximum of 5,2 at about week 24, then decreased slowly, falling to 4 by week 48. Total number of leavesper tiller increased steadilyto 29 at final harvest; number ofgreen leaves increased to 9 by about week 22, then decreased slowly, to 7 by week 48. Mean area per leaf increased until week 32, then decreased slightly. Specific leaf area increased initially, then decreased slowly until final harvest. Crop growth rate (C) increased with L, reaching 26 g m-2 d:' at week 24, then fell to 21 g m? d' during the winter, and increased again with the onset of the second summer, to reach 28 to 34g m-2 d-I, shortly before the final harvest. Plants contained 14g nitrogen (N) m-2, 2,5g phosphorus (P) rrr? and 46 g potassium (K) m-2 at final harvest; the stem contained more than half the N and about two-thirds of the P and K, green leavescontained a third of the N and about a quarter of the P and K, and dead leaves contained 5 to 10% of the total N, P and K. Approximately 80% of the N, 65% of the P and 75% of the K were taken up during the first half of the growth cycle. The nutrient content percent of dry weight of the green leaves and non-sucrose part of the stem decreased substantially with the ageof the crop; the nutrient content of dead leaves was much less than that of livingparts of the shoot. The N content per unit area of green leaves fell with time, from 19mg drrrat week 8 to less than 12mg drrrby week 40.