RELATIONSHIPS BETWEEN CROP WATER STRESS INDEX, EVAPOTRANSPIRATION AND YIELD OF SWEET LIME

Increasing limitations on water supplies have forced growers to use drip irrigation systems. Therefore, irrigation management of higher water use efficiency is of prime interest. Sweet lime (Citrus limetta Swing.) was drip irrigated with water application rates based on 0.6, 0.75, 0.9 and 1.0 times pan evaporation rates in the first year and on 0.4, 0.6, 0.75 and 0.9 times pan evaporation rates in the second year. Crop water stress index (CWSI) values and fruit yields were measured in both years, while evapotranspiration was determined for the first year. Significant differences in seasonal average CWSI and fruit yields were obtained using the different irrigation treatments. Greatest yield was obtained using the 0.75 Epan irrigation treatment which gave a seasonal average CWSI of near 0.1. Higher irrigation application rates resulted in lower CWSI, however, the fruit yield was not the highest due to the possible leaching of nutrients from the light soil of this study. The relative fruit yield decreased linearly with increasing CWSI at irrigation treatments of 0.75 (CWSI of about 0.1) to 0.4 Epan (CWSI of about 0.5). The water use efficiency (fruit yield per unit of water) was highest for the 0.75 Epan treatment. The CWSI was nearly equal to relative evapotranspiration reduction (1-ETa/ETp) and the relative yield reduction (1-Ya/Ym) was equal to 1.6 (1-ETa/ETp). It was found that sensitivity of sweet lime to irrigation water deficit was higher than that for citrus crops in general (medium-sensitive plants to water deficit). Therefore, sweet lime may be classified as a highly sensitive plant to water deficit.