The Effect of Row Spacing on an Irrigated Plant Crop of Sugarcane Variety Nco376

The effect of five row spacings (RS) on source/sink processes in a plant crop of NCo376 was investigated at Mount Edgecombe. Tiller population (TPOP), fractional light interception (FI), intercepted radiation (RADI), cane and sucrose yields were recorded over the duration of growth. The crop was fully drip irrigated in order to avoid water stress conditions. Differences in FIPAR between the treatments were most pronounced early in the growing season. It took 140, 188 and 215 days after emergence (DAE) to reach 0.8 FIPAR at 0.73m, 1.69m and 2.66m RS, respectively. The rate of canopy closure had a direct linear relationship with RS and increased by 26%m reduction in RS. The total accumulated incident global radiation from day of planting until final harvest was 5772 MJm, giving a seasonal fraction of radiation intercepted of 0.49, 0.37 and 0.26 for 0.73m, 1.69m and 2.66m RS respectively. The rate of increase in TPOP was directly related to the amount of seed cane planted, and the timing of peak TPOP (or onset of tiller senescence) did not relate to FI for the different RS treatments. These results confirm previous observations that the light environment within the stool zone, rather than in the inter-row zone, dictates tiller phenology prior to peak TPOP. Final TPOP demonstrated a linear increase of 4.29 tillers m with decrease in RS (R=0.86). Radiation use efficiency (RUE) ranged from 1.25, 1.35 and 1.72gMJ for 0.73, 1.69 and 2.66m RS respectively. In addition to achieving higher RUE, wider rows partitioned a higher fraction of aerial dry mass to stalks. At 12 months there was an average response of 13% increase in stalk dry mass per metre decrease in RS. This relates well to previous South African studies.