VARIATION IN WITHIN-BLOCK ORCHARD CANOPY COVER - IMPLICATIONS FOR CROP WATER REQUIREMENT AND IRRIGATION MANAGEMENT

Abstract

Micro-irrigation systems have improved irrigation efficiency in the viticulture and horticulture industries. Compared to flood and sprinkler irrigation systems, they reduce cover crop and soil evaporation water losses and enable precise scheduling of irrigation events. However, gains in irrigation efficiency can be compromised by variation in crop water requirements and poor distribution uniformity of irrigation supply across an irrigation management unit. These factors can lead to under-irrigation and subsequent yield losses or over-irrigation and wasted water through drainage and runoff. Aerial photographs of orchard blocks in the Goulburn Valley irrigation district of Australia were utilised to determine variation in crop water requirement based on the linear relationship between canopy cover and potential water use. Yield penalties and water losses due to failure to match irrigation supply with individual tree water requirement were calculated. Mean coefficient of variation of canopy cover, and hence crop water requirement, was 20% for peach blocks and 25% for apple blocks. Theoretically, minimising yield penalties by irrigating to meet maximum crop water requirement of a block would result in approximately one-third of applied water being wasted. Innovative methods to address management of variable crop water requirement are needed.