Continued from Page 38 tion conditions from year to year. Some saline soils have also poor infiltration rates, which make salt leaching difficult, he added. Pistachio trees are tolerant to salinity levels up to 8.4 dS/m (a measurement of the electrical conductivity of the soil that is highly correlated with salinity). Though trees can adjust to higher salt levels, rootstocks differ in their tolerance to saline soils. The trees are most sensitive to salts during vegetative growth and more tolerant later in the growing season. Some highly salt affected soils are also sodic, which makes them more difficult to manage because of poor infiltration rates. In these soils, normal irrigation application rates based on average ET of non-salt affected orchards are risky, Zaccaria said, because the trees could be exposed to excessive water applications, soil saturation due to less crop ET, and thus roots might be deprived of oxygen. Depending on soil type, salinity, irrigation method, and salt leaching practices, mature pistachios can use 30 to 50 inches of water over the crop season. Real time soil moisture and plant stress monitoring over the growing season is essential to improve irrigation scheduling to maximize yield and water use efficiency, and minimize the risk of diseases. Pistachio trees are most tolerant to water stress from mid May through early July and during post-harvest period. Only 85 percent of full ET will still allow for potential full yields. Full winter recharge of the soil profile, and understanding the soil water holding capacity and salinity are necessary for optimum crop water management. MANAGEMENT CONSIDERATIONS UC researchers have made the following recommendations for sustaining pistachio production in saline growing areas. The first is choosing UCE1 rootstock. Trials showed P. integerrima, P. atlantica, PGII and UCB I tolerate salinity of up to 5,120 parts per million (ppm) or 8dS/m in the root zone. UCB I produced the best yield response among all the rootstocks. Periodic soil sampling at different depths along the root zone and below, and determination of electrical conductivity (EC) of soil samples through laboratory analyses is recommended to track the variation of salinity over time. Zaccaria said that in medium to high salt-affected grounds the soil sampling and lab analyses should be done at least once per crop season, either at mid-season or towards the end as salts can build up. This periodic sampling and lab determinations are crucial for defining the salinity management practices, he added. When possible, it is recommended to keep EC less than 8.4dS/m. Soil saturation by excessive irrigations should be avoided, and the use of good quality water at least during the early vegetative growth is also advised. Zaccaria said flooding salt affected orchards with good quality water once or more times per year is recommended, depending on the level of soil salinity, crop evapotranspiration and quality of available water supply. It is recommended that leaching of salts by flooding be done during periods of low evapotranspiration when the crop is dormant. Another practice that could aid improving water infiltration where soil is salineniversitsodic and thus prone to compaction and asphixia is to establish winter cover crops. Zaccaria said that planting a winter cover crop between rows can be beneficial in creating micro porosity in the soil, allowing more abundant and deeper infiltration of fall and winter rainfall, increasing the effectiveness of salt leaching, and reduce soil sealing and compaction. Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com 40 West Coast Nut December 2017
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