Stool Populations and Yield of Sugarcane under Irrigated Conditions at Pongola

Yield per unit area increased rapidly to a maximum as the number of stools increased, and either remained relatively constant or declined slightly with higher stool densities, depending upon the particular component of yield. The results imply that under favourable growing conditions, maximum yield per unit area can be achieved with relatively low stool populations. There is considerable potential for reducing seedcane requirements and the number of harvestable stalks in irrigated fields. It may also be economically feasible to transplant nursery-grown seedlings into irrigated commercial fields. Comparisons of the yields of isolated stools of different varieties could be misleading because the relative performance of the same varieties can be different at high stool densities. Introduction The results of row and sett spacing experiments have been described by Thompson and du Toitlo and BoyceR. Whilst the relationship between row or sett spacing and crop yield was studied, no attempt was made to specify the number of stools initially established. The number of buds which germinate and form primary shoots may be as few as 50 per cent of the number planted. I t was decided therefore to determine the number of stools required to achieve the maximum yield per unit area. An experiment was designed to define the relationship between complete stands of stool populations planted "on the square" and crop yield over a very wide range of treatments. Similar studies for vegetative yields of other crops (Holliday5, Bleasdale2, Jarvis7) have indicated that above a relatively low density, the yield response is likely to be negligible. The experiment was located at Pongola on the South African Sugar Association Field Station. The soil is a deep sandy clay of the Makatini series, the characteristics of which were described by Thompson and Boyce! The plant and first ratoon crops were grown over 9and 12-month periods respectively between 26 October, 1967, and 4 August, 1969. Treatments The treatments consisted of seven stool densities established "on the square" and two varieties. These treatments were established with pre-germinated single-bud setts. An extraneous row spacing treatment (S8; N:Co.376) was allotted to two vacant plots on the site. The rows were 144.5 cm apart and were planted with pre-germinated three-bud setts of variety N:Co.376. The purpose of this S8 treatment was to provide some indication of the relationship between the square spacing treatments and current commercial practice. The treatments were as follows: (i) Stool populations per hectare Treatment Square Code per hectare spacing cm S8; N : Co.376 1 75:770 1' 144 cm rows