Abstract
Pasture performance of 924 dairy farms in a major irrigation district of Australia was investigated for their water use and water productivity during the 2015-2016 summer which was the peak irrigation period. Using satellite images from Landsat-8 and Sentinel-2, estimates of crop coefficient (Kc) were determined on the basis of a strong linear relationship between crop evapotranspiration (ETc) and vegetation index (NDVI) of pasture in the region. Utilizing estimates of Kc and crop water requirement (CWR), NDVI-dependent estimates of Irrigation Water Requirement (IWR) were derived based on the soil water balance model. In combination with daily weather information and seasonal irrigation water supply records, IWR was the key component in the understanding of current irrigation status at farm level, and deriving two irrigation performance indicators: (1) Relative Irrigation Water Use (RIWU) and (2) Total Irrigation Water Productivity (TIWP). A slightly higher proportion of farm irrigators were found to be either matching the irrigation requirement or under-watering (RIWU ≤ 1.0). According to TIWP, a few dairy farms (3%) were found to be in the category of high yield potential with excess water use, and very few (1%) in the category of limited water supply to pastures of high yield potential. A relatively high number of farms were found to be in the category where excess water was supplied to pastures of low-medium yield potential (27%), and farms where water supply compromised pastures with a sub-maximal vegetation status (15%). The results of this study will assist in objectively identifying where significant improvement in efficient irrigation water use can be achieved.
Highlights
Irrigated agriculture is the major consumer of freshwater worldwide, presently in the order of about 70% [1,2]
We present Irrigation Water Requirement (IWR) for dairy pastures as estimated by using the ETVR approach combined with soil water balance modelling
We demonstrate the use of IWR estimated for the two key indicators for assessing irrigation performance
Summary
Irrigated agriculture is the major consumer of freshwater worldwide, presently in the order of about 70% [1,2]. Actual ET values from this approach can be used to calculate actual Kc estimates for specific fields and crops [21] This approach essentially requires thermal infrared wavebands in addition to visible, NIR and SWIR bands. A number of studies have shown the application of this approach to calculate actual Kc values for estimating crop water use [21,22,23]. There are very few studies that have combined this simple approach with soil water balance modelling in order to adequately determine irrigation water requirement (IWR) of crops [24,25]. We present IWR for dairy pastures as estimated by using the ETVR approach combined with soil water balance modelling. NIRRdedneontoetsens eanre-ainr-frinafrreadrewdavwebaavnedbarenfderrrienfgertroinLgandtosatL-8anBdasnadt-58 (8B4a5n–d88-56 n(m84)5a–n8d86Senmtin)ela-2nAd BSeantdin-8el(-728A0–B9a1n0dn-8m()7.80R–9d1e0nnomtes). rReddewnaovtesbarendd wreafvererbianngdtoreLfearnridnsgatt-o8 LBaanndds-a4t-(863B0a–n6d8-04 n(6m30) –a6n8d0 Snemn)tinaenld-2ASeBnatinnde-l4-2(A64B0–a6n9d0-4nm(6)4. 0T–o6m90ainnmta)i.nTconmsiastinentaciyn, SceonntsinisetleNncDyV, SI evnatliuneeslwNeDreVcIovnavleuretesdwinetroe Lcoanvdesarte-edqiunitvoalLeanntdvsaalut-eesqusivinagleantsevpaaluraetseluysiensgtaablsisehpeadrarteellaytieosntsahbilpish(Feidgurreela3t)io: nYs=hi0p.0(8F6ig2u+re0.39)0:3Y7X=. 0.0862 + 0.9037X
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