2013 Annual Report
In the third year of the experiment, we conducted two extensive salinity surveys at each of the three sites. Sites are in wine grape production with no leaching during the growing season and variable winter leaching, the third site is in table grape production with relatively high leaching during the season. The imposed leaching treatments consist of two quantities of leaching water applied during the dormant season by sprinkler or drip irrigation within the vine row. During this past year we conducted salinity surveys after winter leaching and after harvest. At each site we performed detailed electrical resistivity surveys and collected a total of approximately 400 soil samples with depth from the treatments and replicates. We also conducted a series of detailed 2-D electrical resistivity surveys. Samples were analyzed for major ions and salinity as per experimental plan. In addition, at one site we prepared split plots to evaluate the impact of cover cropping on increasing infiltration during rain events. One half of one replicate for each of the treatments was stripped of vegetative cover and soil samples collected at the end of the rainy season to evaluate impact on rain infiltration. Below average rainfall this year hampered evaluation of the extent to which cover crop affects soil water recharge from rain. Results to date indicate that winter leaching reduces the upper profile salinity but the extent of leaching is much lower than expected considering the volumes of leaching water applied.
The third site is located in Southern California, with table grape production. Management of table grapes requires more water as the objective is large hydrated fruit for the fresh market. At this site we compared dormant season leaching with drip versus sprinkler irrigation at two application rates. In addition to the pre and post leaching electrical resistivity and soil sampling, we performed an additional series of eight weekly electrical resistivity surveys during the leaching season in order to monitor water movement through the soils during leaching. This series of electrical resistivity surveys established that the surveys can be used to readily monitor the depth of leaching and thus serve as a useful management tool to insure that water applications are sufficient, but not excessive, for salinity control. Although more water is applied at this site than at the Central Coast sites in San Luis Obispo County, California, salinity levels are comparable after the growing season, consistent with application of Colorado River Water and much higher evapotranspiration at the table grape site. Data from this year reinforces the preliminary data suggesting that at the site with table grapes, leaching with sprinklers is more effective then leaching with drip irrigation.
Evaluation of the impact of lower quality waters on infiltration is important for both maximizing infiltration of winter rains for leaching and replenishing water in the soil profile, especially in the inter-row region. We collected approximately 500 kg of surface soil at the Niner Ranch site, dried, sieved and packed the soil into large containers and utilized the soil for infiltration studies in Riverside, as done earlier in soil from another vineyard, all as planned in the project plan. The project also includes evaluation of the grape rootstocks for salt tolerance and interaction of drought and salt tolerance; this part of the project was initiated this spring, delayed by need for the cooperator to graft sufficient vines for the experiment. The rootstocks were grafted with scions of cabernet sauvignon in early winter. In late spring, we planted the three rootstock varieties. The experimental plot at the U.S. Salinity laboratory consists of 198 vines in a 35 meter by 25 meter area. The experiment contains 22 rows (plots) of vines with 9 vines per row. Each row (plot) consists of three repetitions of three different root stocks considered to be salt tolerant. The irrigation consists of a control and three different salinity treatments. We are evaluating three water application rates (control plus two deficit irrigation treatments) and the interaction of water and salt stress on vine biomass. Irrigation applications will be 100%, 75% and 50% of optimal evapotranspiration. The vines are initially being irrigated with Riverside municipal water (EC = 0.45 dS/m). This research is directly related to development of best management practices for the grape industry for salinity control. The research will contribute to development of new recommendations, thus contributing to the NP211 program.