2017 ASHS Annual Conference

We evaluated soil salinity, yield, and fruit quality in furrow-irrigated (FURROW) and subsurface drip-irrigated (DRIP) processing tomato (Solanum lycopersicum L.) fields from 2013-2015 in the Sacramento-San Joaquin River Delta region of California, which is unique for its organic soils and high groundwater table. Within DRIP, we evaluated two deficit irrigation programs which imposed cut-backs during fruit ripening – the grower’s program, which applied 79% of full canopy evapotranspiration (ET) on average across years, and our own scheme that applied an average of 72% of ET. Soil samples were taken in the spring and fall of each year from DRIP, while samples were taken from different FURROW fields in 2014 and 2015 because of crop rotations. We collected soil samples of 10-cm by 10-cm from sampling grids that began at the soil surface and went to a depth of 100 cm, and ran from the row-middle to the furrow-middle (81 cm of the 152-cm bed). Average root zone salinity (RZS) of the sampling grids, as measured by electrical conductivity of soil saturated pastes (EC_e), ranged from 1.11-3.14 dS/m across years and locations in FURROW. Average RZS in DRIP ranged from 0.78-1.36 dS/m across years and irrigation schemes. While FURROW had a wider range of average RZS than DRIP, most of the salts in FURROW were found below 70 cm. The irrigation water salinity (EC_w) seasonal average was 0.60 dS/m (2014) and 0.87 dS/m (2015) for FURROW. Leaching occurred during the irrigation season but was inconsistent from the top of the irrigation run to the bottom. The EC_w of DRIP averaged 0.40 dS/m (2013), 0.60 dS/m (2014), and 0.75 dS/m (2015) and contributed to slight increases in average RZS over the course of each growing season but leached salts from the soil around the drip tape. Salts moved laterally from the drip tape, accumulating at the furrow, soil surface, and an organic soil layer 90 cm below the surface. Average 2015 yield for FURROW and both irrigation schemes of DRIP was 111.5 Mg/ha. The 2015 DRIP fruit soluble solids were 5.5 ⁰Brix for the grower’s irrigation scheme and 5.65 ⁰Brix for the more severe cut-back, illustrating that soluble solids can improve under deficit irrigation. The adoption of subsurface drip irrigation in processing tomato, although driven by increased yields and improved water use efficiency, was demonstrated to provide localized leaching of salts in the root zone.