Effects of Inefficient Spatial Allocation of Irrigation Water on Fruit Yield, Leaf Physiology and Spectral Reflectance in a Tomato Crop

An agronomic study was conducted in Central Italy to evaluate the spatial efficiency of drip irrigation in terms of fruit yield and leaf physiology in a tomato crop and the forecasting potential of spectral reflectance. The cv. ‘Perfectpeel’ was transplanted on May 2011 in a twin row spacing, with a final plant density of 30.000 plants ha-1, on a surface of about 1.6 ha. Seasonal water depth was 225 cm, distributed with drip emitters based on locally managed schemes. Georeferred measurements (yield, Vegetation Indices, soil) were performed on a small subplot of about 500 m2, showed excess soil moisture visible from the middle of August, 45 days before harvesting. Soil moisture increased toward the field center (centripetal direction), reaching saturation with time. For all parameters, a gradient was measured starting from the borders toward the center. Increasing leaf yellowing, which led to death of plants in the field center, was observed. Plants at the border grid represented wellwatered control plants. Spectroradiometric canopy reflectance was detected at three dates (29 June, 13 July, 28 August), while physiological readings (leaf photosynthesis parameters, leaf water potentials) were measured on the 28th of August 2011. Transition zone (TZ) showed lower marketable yield due to reduced plant biomass, fruit weight and number, and photosynthetic capacity, whereas the over irrigated zone (OI) showed a complete yield loss. All Vegetation Indices were able to detect significant differences in the spatial allocation of irrigation water.