THE SALINITY PROJECT

2022 represented the third season for the Salinity Project at Discovery Farm Langham. This project was established in Spring of 2020, with a goal of evaluating the performance of various treatments of perennial forages (either as monoculture or polyculture) when seeded on salt-affected soils. The treatments consist of Halo2 alfalfa, AC Saltlander green wheatgrass and a mixture of species commercially sold as Salinemaster. Much interest has been placed on perennial forages as a tool to manage salt-affected soils, as many forage species inherently have a higher tolerance to soil salts relative to annual grain crops. Ultimately, soil salinity is as much of a groundwater management issue as it is a soil issue. Salt-affected soils often have poor productivity, and may have no plant cover at all. Under this circumstance, groundwater containing dissolved salts is brought to the soil surface. The water evaporates, leaving the dissolved salts behind on the soil surface, further exacerbating the problem. Once established, an actively growing forage crop is able to prevent the upward movement of salts by taking up water by roots at depth.

Beyond tracking performance (measured as dry biomass yield), soil samples are being collected along a transect through the project area in the fall of each season to evaluate what impact (if any) the forages may have on influencing surface (0-15 cm) soil characteristics. Perhaps over the relatively short duration of the five-year project, forages may have the ability to reduce the salt concentration. The collected soil samples are also evaluated for plant-available nutrient concentrations. Samples collected in the fall of 2021 revealed nutrient deficiencies, and as such, a secondary goal for the 2022 season was a spring fertilizer application to maintain stand productivity. The AC Saltlander and Salinemaster treatments received a fertilizer application of 100 lbs N per acre (ac), with the Halo2 receiving 25 lbs per ac. Additionally, 40 lbs P2O5 per ac was applied to each treatment. A check strip with no fertilizer application was also left on one of the three replicates of each treatment.

Growing season conditions for the 2020 to 2022 seasons are shown in Table 1 on page 16. Drought conditions were evident in the 2022 season, although not as severe as 2021. Notably, dry biomass yields across all treatments in 2022 were significantly higher than those observed in 2021 despite only a relatively minor increase in precipitation (approximately 40 mm) (Figure 1).

The impact of fertilizer application on yield is shown in Figure 2. A positive yield response to fertilizer application was shown for the Halo2 and Salinemaster treatments (104% and 126% of control treatment).

The relatively minor response of Halo2 is expected, given alfalfa’s ability to fix its own nitrogen as a legume. Further, soil test phosphorus values measured in the fall of 2022 (Table 2) showed plant-available phosphorus to not be limiting, supporting only a minor response to application of this nutrient. The positive yield response to nitrogen fertilizer application is clearly seen in the Salinemaster treatment and is supported by the deficient soil nitrogen status measured in the fall of 2022. Given the nitrogen deficiency, a nitrogen fertilizer application is recommended in the spring of 2023 to maintain stand health. The reason for the lack of fertilizer response in the AC Saltlander treatment is unknown, but could be due to micro-scale variability in soil nitrogen status in these treatment plots. Further investigation is warranted.

Examination of the soil results in Table 2 suggests that the forage treatments appear to be influencing the surface soil characteristics. For example, measured electrical conductivity (E.C.) values measured in 2022 are generally lower compared to measurements made in the first trial year (2020). The positive effect of reducing surface salinity appears to be more pronounced under conditions of severe salinity(e.g. transect locations C and D). Continued monitoring of the surface soil will occur in the 2023 and 2024 growing seasons.

Observations made over the three growing seasons of this project provide significant support for the use of perennial forages as a tool to manage salt-affected soils. Beyond the potential harvested or grazed value, the forages appear to be effective in reducing surface salt concentrations, primarily through their ability to lower the groundwater table following establishment. While all three treatments of species have shown to establish well, Halo2 and AC Saltlander have yielded similarly and higher than Salinemaster in the 2021 and 2022 seasons.