LWS is an index developed by HEMAV to analyze the water status of the crop, allowing the detection of various degrees of water deficit.
It compares the NDVI index to evaluate the size of the crop and the NDMI index to analyze its moisture content. Traditionally, the NDMI index has been used to evaluate the water status of the crop, but the values given by this index are adequate or deficient depending on the degree of development of the crop (a low NDMI index may be deficient if the crop has a large size, but adequate if it has a small size). By determining the size of the crop using the NDVI value, we can easily determine whether or not the NDMI value is adequate.
It helps to detect deficiencies in the crop caused by failures in the irrigation systems or in the calculation of the water to be supplied, but it also allows us to evaluate the restrictions in the water supply necessary in the final stages of the crop, aimed at drying the plant to prepare it for harvesting. The use of intentional deficit irrigation in the final stages of sugarcane or sugar beet to achieve an adequate sugar level, or grain drying in the case of irrigated cereals, can be adequately evaluated by using this index.
Deficient water conditions produce physiological effects on the crop similar to the attack of pests or diseases when we perform the analysis through satellite indices, therefore, situations detected by LWS may be due to the attack of a pathogen and not to a deficient irrigation level.
In the first weeks of the crop, the influence of the soil on the incipient crop could show deficit states without being real, so it is advisable to evaluate the water status of the crop with LWS when the crop is large enough to be evaluated by satellite image.
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