Mangoes (Mangifera indica L.) are the main horticultural crop in the Northern Territory (NT), grown mainly in the rural areas around Darwin and Katherine. The season’s crop in 2009 was around 17 000 tonnes, valued at $46m (Moore 2009). Water use efficiency (WUE) in horticultural production in the NT has become more important as the National Water Initiative leads to water-allocation planning and licensing. Information is required to improve WUE for economic and environmental outcomes. More than 10 studies have been conducted in the NT by the NT Government and CSIRO on irrigation or water use in mangoes. Most NT Government-led research results are presented in annual reports, while those of CSIRO are published in international scientific journals or presented at conference proceedings.
The authors have attempted to present the key results of those studies in this Technical Bulletin. The aim is to provide a single source of information on past research on the use of irrigation in mango production in the NT, to evaluate past work to support improved WUE practices for mango growers and to identify future areas of research with the potential to improve WUE in mango production. It is intended that this information would be useful to those planning research and extension activities in this area and/or to those in need of information on water requirements for mango production.
Studies on mango water use and irrigation covered a number of important areas, including determining preharvest irrigation cessation and season-long reduced volume applications on fruit quality; effects of irrigation at different phenological periods, including prior to flowering, and the effects of pre-flowering irrigation on trees receiving flowering-promoting treatments; the effect of age, season and variety on water use as determined by sapflow methods; different irrigation schedules on the efficiency of irrigation water use; and irrigation practices by growers.
Key findings included the following points. Early cessation of irrigation prior to harvest often reduced fruit weight; fruit quality could also be negatively affected by the early cessation of irrigation. Paclobutrazoltreated trees tended to have higher yield if irrigated in the pre-flowering period. Pre-flowering water stress improved flowering and fruit production in non-paclobutrazol treated trees in Darwin. Monitoring at an irrigated site with 2030 L/tree/week applied in October indicated that the volume of water applied exceeded requirements. Water use in mango trees as indicated by sapflow was greater during the wet season. A dendrometer irrigation scheduling method gave a high irrigation efficiency of 77% compared with grower practices or 80% of pan evaporation replacement (31% and 38%, respectively).
The results from some studies were used to provide estimates of WUE (fruit weight kg/m3 irrigation water) values. High WUE figures (133 and 174 kg/m3) were achieved with high yields from low irrigation inputs. For example, yields of 62 and 122 kg/tree were achieved with respective inputs of 0.47 and 0.70 m3 /tree. WUE values of less than 10 were related to high irrigation inputs and yields of less than 10 kg/tree. For example, a WUE of 3.1 kg/m3 from a yield of 7 kg and inputs of 2.26 m3/tree. These WUE values from experimental data need to be compared with WUE values from current industry practices, but such data is lacking.
Knowledge gaps were identified that require information to support improved WUE practices for mango growers. A number of gaps related to information on mango ecophysiology and water relations. The central gap in this area was knowledge of the crop’s water requirements in the NT environment in relation to:
Major knowledge gaps on yield and timing of production in the NT included:
Additional research gaps included the potential of selected rootstocks to improve WUE and information on mango rooting depth in relation to water uptake.
Information was lacking on a range of non-tree related areas relevant to improving grower management practices and improving WUE. They included the absence of current industry water use benchmarking information, the absence of an evaluation of on-farm deep-drainage, evaporative losses and delivery efficiencies, the absence of soil water availability information to aid scheduling, particularly the frequency of irrigation and the absence of methods to improve delivery efficiencies or reduce losses, such as the use of mulches.
These knowledge gaps need to be addressed. Research will need to be prioritised in line with industry and government priorities.