YIELD RESPONSE SURFACES FOR SPACING OF SUGARCANE PLANTS

YIELD response surfaces for plant cane that describe the effects of varying plant spacing are illustrated. Data from four experiments were used to generate cane yields from the yield components of plant density, final stalk number per plant and stalk weight by compounding equations that separately relate tillering, tiller mortality and stalk weight to the interrow and intrarow distances between established plants. The equations assume that cane stools ‘sense’ distances equally in both the interrow and intrarow directions. Growth effects of irregular spacing within rows, additional to those that can be attributed to mean within row distances, could not be estimated. The surfaces presented show effects of soil fumigation as a soil fertility treatment, and of other unknown environmental factors inherent in differences between years and location on the magnitude of absolute and relative yield responses to changing plant spacing. They allow yield responses to be interpolated within experiments for combinations of interrow spacings from 0.25 to 1.5 m and intrarow spacings from 0.25 to 0.8 m. Tiller and whole plant mortality were high and yield response surfaces unstable below 0.25 m. The inference is that there is no practical value in spacing cane plants closer than 0.25 m. The surfaces do not predict cane yields or the absolute magnitude of yield responses to plant density for other environments. The significance of this to environmental differences across commercial cane blocks and the use of response surfaces for practical system design and guidance are discussed. Establishment of plants per sett decreased at high sett densities. Factors that cause variable establishment confound plant spacing effects with those of other agronomic treatments. They may result in differences up to four-fold above the plant spacings defined by eye spacing of setts, and these must be interpreted in plant responses. It is probable that 75% or more of the maximum response to narrow rows over 1.5 m single rows can be achieved in practice with options that create an average interrow spacing of 0.8–0.9 m and intrarow spacing of 0.25–0.3 m. Band-planting is expected to behave unpredictably, but similar to single rows of the same centre-to-centre row spacing. Given that responses to increased density appear to be reduced at high soil fertility under favourable environmental conditions for growth, it is recommended that research efforts focus on guiding farmers towards more positive control of suboptimal soil fertility in cane blocks.