The trick is that fall and winter irrigation are used to manage two separate, but related issues; orchard water status and salinity (general salts and toxic elements). While only a relatively small amount of water may be all that’s needed to limit water stress through the winter, a root zone at field capacity going into the winter helps reduce salinity as any rainfall will dilute rootzone salts and, if there is good rainfall, help leach salts from the root zone (see below). Salt management: Fall is an important time to begin salt management programs, which may be especially important this year with more groundwater used for irrigation. Talk with your CCA about irrigation practices that can reduce root zone salt levels (salinity as well as sodium and chloride). The Almond Doctor (David Doll) has a great new post on postharvest irrigation in a drought year. Read it at: thealmonddoctor.com/post-harvest-leaching-fractions-to- manage-salinity. For information on leaching requirement needed to avoid yield reduction in almonds see the UC ANR publication “Managing Salts by Leaching” available, free, at: anrcatalog.ucanr.edu/pdf/8550.pdf. Almonds are sensitive to rootzone salinity with a threshold of 1.5 dSm for average rootzone salinity beyond which yield is rapidly reduced. For example, average root zone salinity of 2.5 dSm can reduce almond yield by almost 20%. Soil analysis for salinity and toxic elements (sodium, chloride and boron) is an essential step to determining the leaching requirement and planning salt management between harvest and bloom. Samples to 24” depth help assess rootzone health (pH, EC, boron, chloride and sodium) while deeper samples provide a check on leaching programs, especially if irrigation water contains enough salts for concern with salinity and toxic elements. For information on orchard soil sampling, there is a great video series with David Doll and Blake Sanden, both former UCCE Advisors, at: fruitsandnuts. ucdavis.edu/photogallery/Soil_Sampling_Video_Series. As part of a salt management program, consider irrigating in the rain. Having the irrigation water running while the rain is falling allows dilution of existing salts with rainwater and field capacity is reached more quickly allowing more rapid movement of salt out of the root zone than if just one water source (rain or irrigation) is available. If heavy rainfall is forecast, then irrigating is not recommended as the combination of rain and irrigation could saturate soils for extended period of time, harming root health. This is
particularly a problem in poorly drained soils. Irrigating in the rain is especially important for salt management in orchards with buried drip irrigation.
Planting cover crop in organic planting. Photo: Franz Niederholzer.
Infiltration: Growers can take steps to improve rainwater infiltration and get more, relatively clean, “free” water into orchard root zones this fall and winter. Fast growing winter cover crops or resident vegetation help soften rain drop impact on the soil, reducing soil surface sealing and moving rainwater into the soil along root channels. Orchards with micro-sprinkler irrigation are at an advantage when planting a cover crop in low water years compared to drip irrigated orchards as small amounts of irrigation can help establish the cover crop. For more information on cover crops, check out the free publication on cover crops in almonds at: www.almonds.com/sites/default/files/2021-06/ABC_ CoverCropBMP_8.5x11_vmags.pdf. To save water if it’s a dry winter, when should orchard floor vegetation be removed ? While green plants do use some water through the winter, improving infiltration (storing water, leaching salts) and improving orchard access (less ruts) should make orchard floor vegetation a net water plus through the winter. Removal of orchard floor vegetation to save water during the growing season should occur between mid-January and leaf out, but not before then. Spreading gypsum should also improve rainwater infiltration and reduce runoff, and also help release sodium from the
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