Abstract
New technologies have been implemented in the agricultural sector to improve crop production and resource management including irrigation water. A three-year long project was conducted to determine whether vegetation indices (VIs) could be used to estimate the leaf area index (LAI) as well as the soil cover fraction (fc) at different crop growth stages in order to use these parameters in a future study concerning irrigation through drones. A low cost unmanned aerial vehicle (drone) and a multispectral camera were used to calculate different VIs of corn (Zea mays). The irrigation scheduling based on the FAO Penman-Monteith equation and the drip irrigation method were used. Three treatments were organized in three replications and the irrigation doses were equal to 100%, 75%, and 50% of the daily evapotranspiration respectively. The Simple and Multiple Regression analysis were used and different equations were formed where the VIs were the predictor variables and the LAI and fc the predicted ones. According to the two-year period data (2018-2019), during 2018 the average maximum LAI in the full irrigation treatment (100%) was 4.1. In the medium irrigation treatment (75%) the LAI was 4.0. The LAI in the third treatment (50%) was 3.9. In 2019, the LAI was 3.7 (100% treatment). In the second treatment, the LAI was 3.3. The LAI in the third treatment was 3.0. According to the results different VIs and prediction equations could be used to estimate the LAI values with high accuracy with the in situ measurements as well as the soil cover fraction.
Highlights
The agricultural sector is of high economic importance worldwide especially because of the recent economic crisis, as well as the crisis following the Covid-19 pandemic
Vegetation indices based on multispectral photos taken from a drone can be used in leaf area index (LAI) and soil cover fraction estimations
The results showed that the five different vegetation indices, the Normalized Difference Vegetation Index (NDVI), the Wide Dynamic Range Vegetation Index (WDRVI), the Ratio Vegetation Index (RVI), the Green Normalized Difference Vegetation Index (GNDVI), and the CIg, which were used as independent variables, can be used to estimate the LAI values of corn during the whole growing period with high accuracy
Summary
The agricultural sector is of high economic importance worldwide especially because of the recent economic crisis, as well as the crisis following the Covid-19 pandemic. Irrational irrigation planning is applied (USDA, 2004) This problem has even greater dimensions if we take into consideration the need for a sustainable management of these resources so that they remain available in the same quantities for the future generations as well (Chartzoulakis & Bertaki, 2015). In Greece, the needs for water were already on the rise, mainly due to the increased demand during the summer months as a result of the high influx of tourists These needs will further increase as a result of hygiene requirements to deal with emergency situations such as the recent pandemic
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