Increasing water use efficiency of irrigated sugarcane production in South Africa through better agronomic practices

Abstract

In South Africa (SA) approximately 30% of sugarcane is grown under irrigation and there is increasingpressure to demonstrate efficient use of limited water resources. Agronomic practices such as the use ofa crop residue layer, changed row spacing, growing suitable varieties and accurate irrigation schedulingcould potentially increase water use efficiency (WUE) by saving water and/or increasing yield. The aim ofthe study was to investigate to what extent WUE of irrigated sugarcane production in SA can be improvedby better agronomic practices, and to gain a better understanding of the mechanisms involved in cropresponse to these factors.An overhead irrigated field experiment was conducted near Komatipoort, South Africa on a shallow,well-drained, sandy clay loam over a four year period (one plant (P) and three ratoon crops (R1, R2 andR3)). Treatments consisted of factorial combinations of variety (N14 and N26), row spacing (single rowsspaced at 1.5 m and dual rows spaced at 1.8 m) and soil surface cover (bare soil and crop residue layer).Measurements included tiller population, interception of photosynthetically active radiation (FIPAR), soilwater content, and cane yield at harvest. Crop water use (CWU) was estimated using the water balanceapproach.This study showed that significant reductions in water use and irrigation requirements, and increasesin WUE, are possible by using a crop residue layer to cover the soil. Water savings were largest in P (26%in CWU and 32% in irrigation requirement) but substantial savings were also achieved in R crops (about15%). It is essential to practice accurate irrigation scheduling to realise these savings, taking into accountsoil cover and cultivar effects, especially during the period of partial canopy. Although the residue layercaused small reductions in yield in the P, R1 and R2 crops (on average 9%) these were not statisticallysignificant. The combined effect of large CWU reductions and small changes in cane yield resulted inincreased WUE (on average 18%).These responses to a residue layer were achieved through a reduced rate of canopy development dueto delayed emergence of tillers, causing less green canopy cover and reduced CWU, especially during theperiod of partial canopy cover when stalk growth has not yet commenced. CWU and FIPARwere affectedmuch less during the subsequent period of stalk growth, thus affecting cane yield minimally, providedirrigation scheduling was adjusted.Variety N14 consistently developed a canopy more rapidly, intercepted more radiation and achieveda higher yield than N26. Row configuration had a significant impact on canopy development, seasonalFIPAR, final stalk population but did not affect cane yield or WUE.The study produced quantitative data for parameterising crop models which will improve their reli-ability in irrigation management and yield prediction applications.