- Author: Ben Faber
Why guess how much water to apply to reduce salt damage by going to a simple graphical interface with pull down menus and get a pretty good idea of how to use that water to improve tree performance. Most mature crops are listed, soils, water qualities, and irrigation systems. From UC Riverside - SALEACH Try it, you might like it.
Leaching is essential in irrigated croplands where natural precipitation is insufficient to control salinity buildup. Several useful models exist for salinity management; however, leaching requirement (LR) calculations are based on steady-state approaches that only consider salinity tolerance of crops and irrigation water salinity to estimate the LR. In this study, a web-based soil salinity leaching management model (SALEACH) was developed as an online tool to assist growers for better and easier management of soil salinity to sustain agricultural production in irrigated croplands. SALEACH employs the traditional steady-state approach to estimate LRs but improves outputs by not only considering irrigation water salinity (ECiw) and salinity tolerance of specific crops (ECt), but also root water uptake patterns to account for irrigation system differences, and soil types for differences in hydraulic characteristics, as well as water stress and rainfall input. The SALEACH model can calculate the required irrigation water depth by using the estimated LR or any user-specified leaching fraction (LF) values; it can predict the drainage water salinity and soil salinity in the rootzone based on the applied leaching; and it can estimate relative crop yield for a given LF. SALEACH-estimated LRs were assessed in different soil types and irrigation systems by comparing them with LRs, soil water and drainage water salinity values obtained from an existing steady-state model (WATSUIT) and a transient-state model (HYDRUS-1D). Statistical analyses showed that SALEACH-estimated LRs, soil salinity, and drainage water salinity were all in the acceptable ranges of the corresponding values derived from other models. Thus, we conclude SALEACH is reliable and can be employed by practitioners to produce satisfactory estimations of LRs and soil salinity by considering the soil, crop, water quality, and irrigation system. Adoption of the model can improve water use efficiency and reduce groundwater pollution.
- Author: Ben Faber
With little rain this winter and the erratic weather patterns of wind and heat, avocado is going to be especially prone to salt damage. And the flowering period is one of the most sensitive. Flowers are competing with leaves that have been hanging on for a year and have been salt stressed by a year's worth of irrigation salts. A good understanding of how salt moves and is leached it important to get through til next winter when there will hopefully be sufficient rain again to naturally leach the soil.
Water moves in a wetting front. When irrigation water hits the soil, it moves down with the pull of gravity and to the side according to the pull of soil particles (more lateral with more clay). Soil is a jumble of different sized soil particles, from clay to silt to sand sizes and then often intermixed with stones of different sizes from gravels to boulder. The different textures determine how water moves. It moves fastest through coarse textures and slowest through finer ones – the clays, the ones with the smallest pores. But soils are a jumble of particle sizes and pores.
Water first moves down the larger pores and then it slowly moves through the smaller ones. As water moves through the soil, it carries salts that have accumulated in the soil. At the wetting front is where the salt accumulates. As the water moves through the larger pores, salts migrate/diffuse from the small pores to the larger ones. This diffusion takes a bit of time, so typically the small pores have a larger salt concentration than the larger ones.
So an initial application of water will carry the salts from these large pores and if the irrigator were to stop in mid-application, it allows time for the salts to move out of the small pores into the larger ones. Then when the irrigation recommences, it will carry more of the salts out of the wetted area – the root zone. This technique is called “bumping” where an irrigation is stopped and then restarted in order to improve not only leaching, but also reduce runoff.
This principle also is at play when there are two or more sources of water quality. Soil salinity can be no lower than the irrigation water that is applied. Then as the soil, water is removed through plant absorption or evaporation, the salinity increases. The soil salinity can easily be two to three times higher than the irrigation water.
If there are two sources of water, the initial application can be with the poorer quality water, and once that has reduced the soil salinity, then the better water quality can be applied which will then bring the soil salinity closer to that of the better quality water. By doing this two part leaching, the amount applied of the better quality water can be significantly reduced. This is a type of “bumping” to improve leaching.
Watch this U-Tube video on how water moves through soil, thanks to the work at Walla Walla Community College.
https://www.youtube.com/watch?feature=player_detailpage&v=J729VzBeI_g
Thank you Walla Walla Community College for the video
- Author: Michelle Leinfelder-Miles
- Author: Brenna J. Aegerter
Methods: The trial is a randomized complete block design (approximately 4.5 acres) with three replicates of each treatment. The soil type across the trial is a Valdez silt loam. Baseline soil samples were collected in July 2018 following wheat harvest but prior to tillage. Soil was sampled from 0-6, 6-12, 12-24, and 24-36 inch depths. On July 30, 2018, a cowpea cover crop (Vigna unguiculata cv. ‘Red Ripper', Figure 1) was inoculated with Rhizobium and planted after a pre-irrigation. Pre-irrigation was only applied to the cover crop plots. The cover crop was drill-seeded at 7-in row spacing with a planting density of approximately 50 pounds of seed per acre. A second irrigation was applied approximately one month after planting. End-of-season soil sampling (0-6 and 6-12 inch depths) occurred on October 23, 2018, prior to cover crop termination. Soil properties of interest include bulk density, soil moisture, salinity, pH, total nitrogen (N), and total carbon (C). Soil properties were analyzed by the following methods: pH from the soil saturated paste, salinity by the saturated paste extract, and total N and C by combustion method.
Preliminary Results: Soil properties are presented for the baseline condition (Table 1) and for the end of the first cover cropping season (Table 2). Bulk density averaged 1.0 g/cm3 across sample timings, depths, and treatments. Soil moisture (% by volume) was observed to increase from the baseline condition in the cover crop (“CC”) treatment. At baseline sampling, salinity increased with depth from 0.47 to 2.44 dS/m. After one cover cropping season, salinity increased in both treatments, but increased more in the no cover crop (“No CC”) treatment, averaging 1.22 dS/m from 0 to 12 inches. Soil was acidic, which is typical for the region. The pH averaged 5.5 across sample timings, depths, and treatments, but there may be a trend for cover cropping to increase the pH. Total N and C decreased with depth at the baseline sampling. After one cover cropping season, there was little change from the baseline condition in both treatments.
Summary: The Delta is a unique agricultural region with unique environmental challenges. Some soils in the region are subsided due to oxidation of organic matter, and some soils suffer from salinity, having limited ability to leach salts due to low permeability soils and shallow groundwater. Cover cropping is not a typical practice in the annual crop rotations of the region, and summer cover cropping is particularly rare. After the first year of a three-year study, cover cropping had no observed effect on bulk density, Total N, and Total C. Cover cropping may have slightly raised the pH in the top 12 inches, compared to dry fallow. The cover crop treatment, having received two irrigations, had lower salinity in the upper layers of soil compared to dry fallow. We also observed that the 2018-2019 triticale crop that was planted in the field germinated roughly five days earlier in the cover crop plots compared to the fallowed plots. Thus, it appears that summer cover cropping with a legume has the potential to improve soil tilth at a time of year when the field would otherwise be fallowed and dry with no soil cover, and there could be agronomic benefits to subsequent crops. We will continue to monitor these soil properties in 2019 and 2020, and additionally, we will monitor small grain yields and greenhouse gas (CH4, N2O) emissions.
We would like to thank Dawit Zeleke and Morgan Johnson (Staten Island), Tom Johnson (Kamprath Seed), and Margaret Smither-Kopperl and Valerie Bullard (USDA-NRCS) for their cooperation on this trial. We would like to acknowledge the California Climate Investments program for funding, and our UC colleagues who are cooperating on this grant in other parts of the state (Jeff Mitchell, Will Horwath, Veronica Romero, Sarah Light, Amber Vinchesi-Vahl, and Scott Stoddard).
Survey: We would also like to alert readers of a cover cropping survey that is being conducted by the Contra Costa County Resource Conservation District. The survey is found here. The purpose of the survey is to learn more about cover cropping practices and barriers to adopting cover cropping on-farm. Even if you farm in another county, please consider filling out the survey, which should take about 10 minutes. The survey is open through the end of June. Your responses will help inform CCC RCD and UCCE programming. Thank you for your participation.
- Author: Ben Faber
Water Quality Impacts on California Avocado –
A Collaborative Approach
Sat Darshan S. Khalsa1 and Ben Faber2
1Department of Plant Sciences, UC Davis
2Cooperative Extension Ventura County, UCANR
Avocado consumption continues to grow both in the U.S. and around the globe. Greater demand creates an opportunity for growers to supply an expanding market with quality California fruit. More intensive production increases the need for attention to tree health, crop protection and irrigation practices. Many avocado root rot diseases are related to how growers manage water, and given the salt sensitivity of avocado and limited selection of salt-resistant rootstocks, water quality is an inherent driver of avocado productivity and quality.
In the California avocado-growing regions of the Central and South coast, water quality can be highly variable. Groves can rely on a combination of surface and groundwater yet, water high in total dissolved solids, pH and salts such as sodium and chloride, can be common place. Furthermore, water quality properties are subject to change as California faces more weather extremes and shifting water demand. As a result, avocado growers need to continue to be conscientious of how local and regional water quality conditions impact their groves.
A comprehensive understanding of how water quality impacts avocado tree health and fruit quality is still limited. The consensus is irrigation with poor quality water reduces crop productivity yet, the extent to which crop loss is linked to water quality and specific practices to mitigate the risk is not entirely clear. The clonal rootstocks ‘Dusa', ‘Toro Canyon' and ‘Duke 7' have some salt tolerance, but are still sensitive to salts. Even less information is available on the potential impacts of water quality on fruit quality, including both nutritional value and postharvest storage.
A collaborative approach to problem-solving creates an opportunity for growers to participate in research and to generate regional and site specific solutions. The phases of this project include 1) identify the range of water quality conditions in California avocado-growing regions; 2) build a network of ‘focus sites' identified by grower participants using specific grove characteristics and; 3) monitor field indicators to quantify impacts of water quality on tree health and fruit quality. Results will be shared in aggregate to maintain the privacy of participants and also, allow growers to compare their focus site with a wider population.
If you are interested in learning more about this collaborative water quality project, please contact Dr. Khalsa at sdskhalsa@ucdavis.edu or sign up for a follow-up conversation using this webform (http://madmimi.com/signups/fbeac7dee8264fac90ab8a9b6f0c65ff/join).
Sat Darshan Khalsa is an Assistant Project Scientist in the Department of Plant Sciences at UC Davis (http://www.plantsciences.ucdavis.edu/people/sat-darshan-khalsa) and Ben Faber is the UCANR Soils/Water/Subtropical Crops Advisor for Ventura and Santa Barbara Counties (http://ceventura.ucanr.edu/Staff/?facultyid=638).
Photo: These aren't avocados.
- Author: Steven A. Tjosvold
In the last post, I showed that irrigation should occur when half of the available water in the container is used. That amount of water is what evaporated from the soil surface and the plant extracted (transpiration), collectively called evapotranspiration (ET). You might think that the total ET accumulated from the last irrigation would also be how much water is needed to fill the soil completely back up with water. In some way it is like your car's fuel tank, the volume of available water is analogous to the capacity of the fuel tank. You're supposed to refuel when the fuel tank is half full, and at that point you fill it up with a half of a tank. That's where the analogy ends though. Actually some adjustments are still needed, especially when applying this to the entire irrigated crop. More water than a “half a tank” needs to be applied to compensate for the salinity in the irrigation water and the inefficiency of the irrigation system. First, let's look at the salinity component.
The concentration of salts in the soil solution is a result of the added fertilizer nutrients and the salts in the raw irrigation water. Salinity in solutions are measured by how well they pass an electrical current, the electrical conductivity (E.C.). Many of the ions, from added fertilizer salts, such as ammonium, nitrate, and potassium will be absorbed in large part by the plant. But not all will be absorbed. These ions and others are mostly selectively taken up by the plant and not just drawn into the plant passively with the water pulled in by transpiration. Many of the other salts are taken up at low rates or excluded all together. As a result, the concentration of these salts may accumulate, that is, if there is no leaching. Fig 1.
Salt accumulation in the soil is ameliorated by leaching, which is applying enough water so that some water drains from the pot. The leaching fraction can tell us how much extra water to apply. It is the ratio of the volume of water leached (the water that runs out of the bottom of a pot) to the volume of water applied (the total amount of water applied to a pot). The proper leaching fraction depends on the E.C. of the irrigation water applied (E.C.A) and the E.C.- sensitivity of the crop . Most crops tolerate a leachate EC (E.C. L ) of 6 dS/m to 9dS/m while salt sensitive crops tolerate 3 dS/m. So, recommended leaching fractions are given in the table below. In the middle of the ranges, you can see that the leaching fractions are in the 0.2 to 0.25 range, which means, in this case, that about another 20 or 25% water needs to be added to the water applied to the crop. (The exact amount is explained in the handout). Fig 2.
Surveys of nursery practices indicate that most commercial growers leach excessively. Although this prevents salt accumulation in container media, excessive leaching wastes water and fertilizer and may contaminate groundwater or surface water.
Irrigation systems are imperfect. Some sprinklers or emitters put out more water than average and others apply less than average. To meet the needs of plants that receive less than average amounts of water, growers must supply excessive amounts to other plants. Measuring the uniformity of irrigation systems gives growers two important pieces of information. It provides a measure of how good the system is. In many cases, there are simple steps that can be taken to increase uniformity (for instance, using better nozzles, repairing leaks, and eliminating sources of large pressure drops). Second, the measured irrigation uniformity gives growers a way to decide how much more water needs to be applied to compensate for the inefficient system. Irrigation systems can be evaluated in the field, and an efficiency value can be determined called the distribution uniformity (D.U.). (Measuring D.U. is explained in the handout). Drip irrigation systems are usually very efficient, usually with a D.U. of around 0.9 (A D.U. of 1.0 is perfect). Sprinkler systems are less efficient, with a D.U. between 0.4 and 0.9, and hand watering efficiency is usually unpredictable but usually is not efficient. Fig 3.
In conclusion, the total amount of water that needs to be applied to a crop is equal to the total evapotranspiration since the last irrigation plus the extra water needed to compensate for the salinity in the irrigation water and the lack of uniformity of the irrigation system. Fig 4.
Attached is a really nice article from Richard Evans that gives some examples to increase your understanding of irrigation efficiency, water quality and their impact on the total amount of irrigation water applied.
Next: Container Soil Chemical Properties
Handout