{"id":2243,"date":"2024-07-31T21:32:05","date_gmt":"2024-08-01T04:32:05","guid":{"rendered":"https:\/\/blogs.cdfa.ca.gov\/FREP\/?p=2243"},"modified":"2024-07-31T21:32:05","modified_gmt":"2024-08-01T04:32:05","slug":"research-update-using-high-carbon-amendments-to-reduce-winter-nitrate-leaching-in-vegetable-rotations","status":"publish","type":"post","link":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/research-update-using-high-carbon-amendments-to-reduce-winter-nitrate-leaching-in-vegetable-rotations\/","title":{"rendered":"Research Update: Using High Carbon Amendments to Reduce Winter Nitrate Leaching in Vegetable Rotations \u00a0"},"content":{"rendered":"\n<p><em>Note: This is part of a Research Update series that highlights projects funded by the California Department of Food and Agriculture\u2019s (CDFA)&nbsp;<\/em><a href=\"https:\/\/www.cdfa.ca.gov\/is\/ffldrs\/frep\/CompetitiveGrantProgram.html\">Fertilizer Research and Education Program (FREP) annual grant program<\/a><em>.<\/em><strong><\/strong><\/p>\n\n\n\n<p><strong>Project Title:<\/strong><strong> <\/strong>Immobilization of Nitrate in Winter-Fallow Vegetable Production Beds to Reduce Nitrate Leaching<\/p>\n\n\n\n<p><strong>Project Leaders:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Richard Smith, UCCE Vegetable Crops Farm Advisor, Monterey, San Benito and Santa Cruz counties<\/li>\n\n\n\n<li>Michael Cahn, UCCE Irrigation Farm Advisor, Monterey, San Benito and Santa Cruz counties<\/li>\n\n\n\n<li>Joji Muramoto, UCCE Organic Specialist, Dept. of Environmental Studies, UC Santa Cruz<\/li>\n\n\n\n<li>Daniel Geisseler, Associate CE Specialist, Dept. of Land, Air and Water Resources, UC Davis<\/li>\n<\/ul>\n\n\n\n<p><strong>Project Status:<\/strong><strong> <\/strong>Completed in 2023<\/p>\n\n\n\n<p><strong>Project Location: <\/strong>Commercial farms located on the Central Coast<\/p>\n\n\n\n<p><strong>Overview:<\/strong><strong><\/strong><\/p>\n\n\n\n<p>This project evaluated the use of high carbon (C) amendments to reduce nitrate leaching in winter fallow vegetable crop beds. The researchers identified two primary high C materials, a local, inexpensive and abundant green waste material called Forest Mulch and almond shells from the Central Valley. Laboratory incubations and large-scale field trials in commercial vegetable fields were conducted to look at how effectively different particle sizes and application rates of these materials immobilized nitrate and prevented leaching. In-field starter fertilizer trials were also completed to examine the impact of high C amendments on the yield of the subsequent crop. Finally, an economic analysis of the costs associated with using Forest Mulch and almond shells was carried out to examine the feasibility of their use.<\/p>\n\n\n\n<figure class=\"wp-block-gallery has-nested-images columns-default is-cropped wp-block-gallery-1 is-layout-flex wp-block-gallery-is-layout-flex\">\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"513\" height=\"422\" data-attachment-id=\"2245\" data-permalink=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/research-update-using-high-carbon-amendments-to-reduce-winter-nitrate-leaching-in-vegetable-rotations\/forest-mulch\/\" data-orig-file=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Forest-Mulch.jpg\" data-orig-size=\"513,422\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}\" data-image-title=\"Forest Mulch\" data-image-description=\"\" data-image-caption=\"\" data-large-file=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Forest-Mulch.jpg\" data-id=\"2245\" src=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Forest-Mulch.jpg\" alt=\"\" class=\"wp-image-2245\" srcset=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Forest-Mulch.jpg 513w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Forest-Mulch-300x247.jpg 300w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Forest-Mulch-150x123.jpg 150w\" sizes=\"auto, (max-width: 513px) 100vw, 513px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"486\" height=\"423\" data-attachment-id=\"2244\" data-permalink=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/research-update-using-high-carbon-amendments-to-reduce-winter-nitrate-leaching-in-vegetable-rotations\/ground-almond-shells\/\" data-orig-file=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Ground-almond-shells.jpg\" data-orig-size=\"486,423\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}\" data-image-title=\"Ground almond shells\" data-image-description=\"\" data-image-caption=\"\" data-large-file=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Ground-almond-shells.jpg\" data-id=\"2244\" src=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Ground-almond-shells.jpg\" alt=\"\" class=\"wp-image-2244\" srcset=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Ground-almond-shells.jpg 486w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Ground-almond-shells-300x261.jpg 300w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Ground-almond-shells-150x131.jpg 150w\" sizes=\"auto, (max-width: 486px) 100vw, 486px\" \/><\/figure>\n<\/figure>\n\n\n\n<p><em>Locally procured Forest Mulch made from tree branches and trunks (above left) and almond shells ground to less than 0.5 mm particle size (right) were both tested as high C amendments in this project.<\/em><\/p>\n\n\n\n<p><strong>Key Takeaways:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Ground almond shells are a viable high C amendment, while the Forest Mulch green waste is not effective at immobilizing soil nitrate.<\/li>\n\n\n\n<li>The optimal particle size for using ground almond shells as a high C amendment are \u00bc to \u00bd inch. Applications need to be 5 to 10 tons\/acre (T\/A) to be effective.<\/li>\n\n\n\n<li>Applying starter fertilizer can adequately overcome immobilization occurring after high C material application rates with no adverse effect on yield.<\/li>\n\n\n\n<li>Trucking and grinding costs are likely to make the practice of applying almond shells too expensive at the rates required to effectively immobilize soil nitrate-N for most growers at this time.<\/li>\n<\/ul>\n\n\n\n<p><strong>Background<\/strong><strong>:<\/strong><\/p>\n\n\n\n<p>On the Central Coast, growers incorporate vegetable crop residues, which have a high nitrogen (N) content, into the soil after harvest. Due to mild temperatures that support microbial activity in the soil, the incorporated residues contribute to high residual soil nitrate-N in the winter fallow period that is vulnerable to leaching by winter rains. This project evaluated whether high C amendments, which have a C:N ratio &gt; 40, can be used to immobilize the excess nitrate in the soil from incorporated residues. The ideal amendment would immobilize nitrate during the six- to eight-week winter fallow period, and then begin to mineralize during the cropping season, when the risk of leaching has diminished. If immobilization of nitrate continues into the growing season, it may reduce early plant growth unless another source of N is provided. Central Coast growers commonly apply compost in the fall to improve soil tilth and health. Therefore, a high C amendment could be easily substituted if economically viable materials are available that meet the desired immobilization timing.<\/p>\n\n\n\n<p><strong>Methods:<\/strong><\/p>\n\n\n\n<p>Several incubation studies and field trials were conducted during the project. Table 1 briefly describes the treatments, research duration and types of measurements that were collected.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td><strong>&nbsp;<\/strong><\/td><td>&nbsp;<\/td><td>2020-2021<\/td><td>2021-2022<\/td><td>2022-2023<\/td><\/tr><tr><td rowspan=\"3\"><strong>Incubation studies:<\/strong> Examined rates of N immobilization of high C materials and compared rates of almond shells at different rates and particle sizes<\/td><td>Treatments<\/td><td>Almond shells, green waste and other possible high C materials<\/td><td>Almond shells (C:N = 78): unground, 2 mm, 1\/4\u201d and 1\/2\u201d applied at 2.5, 5 and 10 T\/A<\/td><td>Almond shells (C:N = 107): unground, 2 mm, 1\/4\u201d, and 1\/2&#8243; applied at 5 T\/A. Unground, 2 mm and 1\/2&#8243; applied at 10 T\/A<\/td><\/tr><tr><td>Duration<\/td><td>12 weeks<\/td><td>24 weeks<\/td><td>24 weeks<\/td><\/tr><tr><td>Additional data collected<\/td><td>C\/N ratios of materials, application rates <em>See Figure 1<\/em><\/td><td>Treatment with walnut shells (C:N = 248) ground to 2 mm applied at 5 T\/A; percent immobilized N<\/td><td>Percent immobilized N <em>See Figure 2<\/em><\/td><\/tr><tr><td rowspan=\"3\"><strong>Commercial field trials:<\/strong> Evaluated different rates of Forest Mulch and almond shells and incorporation methods to immobilize N following a crop of broccoli<strong><\/strong><\/td><td>Treatments<\/td><td>Forest Mulch (C:N = 37) at 0, 5, 10, 15 and 20 T\/A<\/td><td>Forest Mulch (C:N = 97) and unground almonds (C:N = 88) at 0, 5 and 10 T\/A<\/td><td>Almond shells (C:N = 107) ground to \u00bc inch at 0, 5, and 10 T\/A incorporated with one or two passes of a chisel<\/td><\/tr><tr><td>Duration<\/td><td>October \u2013 May, includes spring lettuce crop<\/td><td>October \u2013 May, includes spring lettuce crop<\/td><td>November \u2013 March, ended due to Salinas River flooding plot<\/td><\/tr><tr><td>Additional data collected<\/td><td>Soil nitrate down to 3 feet, crop biomass, N uptake and yield<\/td><td>Soil nitrate down to 3 feet, crop biomass and yield<\/td><td>Soil nitrate down to 3 feet, crop biomass and yield <em>See Figure 3<\/em><em><\/em><\/td><\/tr><tr><td rowspan=\"3\"><strong>In-field starter fertilizer trials:<\/strong> Evaluated the effect of high C amendments on yield and N fertilizer requirements of the subsequent crop<strong><\/strong><\/td><td>Treatments<\/td><td>Starter fertilizer (6-16-0) at 0, 7.8, 15.5, and 31.2 lbs\/A applied onto beds treated with Forest Mulch (C:N = 186) at 0, 5, 10 and 15 T\/A. Forest Mulch was applied by mulching into top 3 inches of soil with bed shaper. Starter fertilizer was sprayed prior to seeding<\/td><td>Starter fertilizer (6-16-0) at 0, 31 and 62 lbs\/A sprayed onto beds treated with unground almond shells (C:N ratio = 88) applied at 20 T\/A. Shells were incorporated into beds with a harrow and power mulcher to 3\u201d depth prior to seeding<\/td><td>&nbsp;<\/td><\/tr><tr><td>Duration<\/td><td>Jan. \u2013 May, during spring lettuce<\/td><td>Jan. \u2013 May, during spring lettuce<\/td><td>&nbsp;<\/td><\/tr><tr><td>Additional data collected<\/td><td>Soil nitrate, tissue N, phytotoxicity, plant stand and mean head weight at harvest<\/td><td>Soil nitrate, tissue N, crop biomass and mean head weight at harvest<\/td><td>&nbsp;<\/td><\/tr><\/tbody><\/table><figcaption class=\"wp-element-caption\"><em><strong>Table 1.<\/strong> Summary of incubation experiments, field trials, and in-season starter fertilizer trials carried out during the project.<\/em><\/figcaption><\/figure>\n\n\n\n<p><strong>Project Results and Discussion:<\/strong><\/p>\n\n\n\n<p><strong>Quality and particle size affects high C amendment efficacy<\/strong><\/p>\n\n\n\n<p>Results from the first winter field trial showed little reduction in soil nitrate levels in the first, second and third feet of soil at all treatments. An incubation study carried out in the lab comparing different high C amendments also showed that Forest Mulch green waste had a low immobilization rate compared to other materials like ground and unground almond shells and was therefore not a suitable high C material (Figure 1). Researchers attributed this finding to the quality and size of the mulch, which was composed of a triple-screened material of various-sized woody pieces that likely contained a significant amount of lignin. They hypothesized that for this reason, it didn\u2019t have sufficient labile C to effectively immobilize soil N.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"797\" height=\"467\" data-attachment-id=\"2246\" data-permalink=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/research-update-using-high-carbon-amendments-to-reduce-winter-nitrate-leaching-in-vegetable-rotations\/figure-1-3\/\" data-orig-file=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-1.jpg\" data-orig-size=\"797,467\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}\" data-image-title=\"Figure 1\" data-image-description=\"\" data-image-caption=\"\" data-large-file=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-1.jpg\" src=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-1.jpg\" alt=\"\" class=\"wp-image-2246\" srcset=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-1.jpg 797w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-1-300x176.jpg 300w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-1-150x88.jpg 150w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-1-768x450.jpg 768w\" sizes=\"auto, (max-width: 797px) 100vw, 797px\" \/><\/figure>\n\n\n\n<p><em><strong>Figure 1.<\/strong> Overall immobilization rate of N in a range of high C amendments after 12-week incubation.<\/em><\/p>\n\n\n\n<p>In the second- and third-year trials, the researchers evaluated ground and unground almond shells at various sizes to determine their effectiveness as a high C amendment. Incubations of 5 T\/A of almond shells of various sizes showed that peak immobilization occurred two weeks into the incubation period. Greater immobilization occurred with smaller particle sizes and residual immobilization persisted longest with the unground almond shells (Figure 2).<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"835\" height=\"373\" data-attachment-id=\"2247\" data-permalink=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/research-update-using-high-carbon-amendments-to-reduce-winter-nitrate-leaching-in-vegetable-rotations\/figure-2-2\/\" data-orig-file=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-2.jpg\" data-orig-size=\"835,373\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}\" data-image-title=\"Figure 2\" data-image-description=\"\" data-image-caption=\"\" data-large-file=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-2.jpg\" src=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-2.jpg\" alt=\"\" class=\"wp-image-2247\" srcset=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-2.jpg 835w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-2-300x134.jpg 300w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-2-150x67.jpg 150w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-2-768x343.jpg 768w\" sizes=\"auto, (max-width: 835px) 100vw, 835px\" \/><\/figure>\n\n\n\n<p><em><strong>Figure 2.<\/strong> Incubation study showing N immobilization by almond shells that are unground (NP) or ground to \u00bd\u201d, \u00bc\u201d and 2 mm particle size that are applied at the equivalent of 5 T\/A.<\/em><\/p>\n\n\n\n<p>In the third winter field trial, sampling showed reduced residual nitrate in the 10 T\/A almond shell treatment that was incorporated with two passes of a soil chisel. A similar trend indicating less soil nitrate in the second foot of soil was observed, but no differences among the treatments was observed at the third foot of soil (Figure 3).<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"846\" height=\"613\" data-attachment-id=\"2248\" data-permalink=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/research-update-using-high-carbon-amendments-to-reduce-winter-nitrate-leaching-in-vegetable-rotations\/figure-3-2\/\" data-orig-file=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-3.jpg\" data-orig-size=\"846,613\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}\" data-image-title=\"Figure 3\" data-image-description=\"\" data-image-caption=\"\" data-large-file=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-3.jpg\" src=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-3.jpg\" alt=\"\" class=\"wp-image-2248\" srcset=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-3.jpg 846w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-3-300x217.jpg 300w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-3-150x109.jpg 150w, https:\/\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2024\/07\/Figure-3-768x556.jpg 768w\" sizes=\"auto, (max-width: 846px) 100vw, 846px\" \/><\/figure>\n\n\n\n<p><em><strong>Figure 3.<\/strong> Soil nitrate levels in the first foot of soil in the \u00bc\u201d almond shell treatments applied at 0, 5 and 10 T\/A until flooding terminated the field trial. Dotted lines show one pass of the chisel to incorporate the shells, and solid lines indicate two passes.<\/em><\/p>\n\n\n\n<p>Overall, the results from the project showed that unground almond shells immobilize nitrate at a lower rate and remineralize nitrate more slowly than smaller particle sizes. Almond shells ground to \u00bc and \u00bd inch immobilized soil nitrate effectively and remobilized it at a rate that is useful for reducing nitrate leaching during the winter fallow period.<\/p>\n\n\n\n<p><strong>Starter fertilizer can adequately overcome immobilization<\/strong><\/p>\n\n\n\n<p>During the first year of the starter fertilizer trial there was no immobilization from the application of the Forest Mulch at the tested rates. Thus, there was no need for starter fertilizer to counteract the immobilization and no reduction in the yield of the spring lettuce crop was observed. During the second starter fertilizer trial, when an elevated rate of 20 T\/A of unground almond shells was applied, treatments with the use of starter fertilizer showed increased yields. This result indicates that increasing rates of starter fertilizer can offset residual immobilization caused by applying high C amendments (data not shown).<\/p>\n\n\n\n<p><strong>Cost of transporting and grinding almond shells reduces feasibility of adoption<\/strong><\/p>\n\n\n\n<p>The expense of purchasing almond shells and transporting them from the Central Valley to the Salinas Valley is about $60.50\/ton (Table 2). Grinding the almond shells adds an additional $20.00\/ton to the cost. In the incubation and field trials, 5-10 T\/A were shown to be an effective rate for applying ground almond shells. At this rate, the cost to growers would be $402.50-805.00 per acre. This cost is likely to reduce the feasibility of adoption for growers.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td>Expense<\/td><td>Ground almond shells<\/td><td>Unground almond shells<\/td><\/tr><tr><td>Material<\/td><td>$15.00<\/td><td>$15.00<\/td><\/tr><tr><td>Trucking<\/td><td>$37.50<sup>1<\/sup><\/td><td>$37.50<sup>1<\/sup><\/td><\/tr><tr><td>Grinding<\/td><td>$20.00<sup>2<\/sup><\/td><td>$0.00<\/td><\/tr><tr><td>Spreading<\/td><td>$8.00<\/td><td>$8.00<\/td><\/tr><tr><td>Total Costs<\/td><td>$80.50<\/td><td>$60.50<\/td><\/tr><\/tbody><\/table><figcaption class=\"wp-element-caption\"><em>Table 2. Comparison of dollars\/ton of high C amendments.<sup>1 <\/sup>Trucking from Central Valley (2022 cost); <sup>2<\/sup> Ground to 1\/2\u201d screen<\/em><\/figcaption><\/figure>\n\n\n\n<p><strong>Project Impact:<\/strong><\/p>\n\n\n\n<p>These findings support the goal of educating Central Coast Water Board staff, growers, and crop consultants about the benefits and feasibility of applying high C amendments as a best management practice for reducing nitrate leaching in winter fallow vegetable beds. As a result of these efforts, this practice was included in Ag Order 4.0 as an N removal credit. An Agricultural Expert Panel that is being convened in late 2024 by the State Water Board will consider the efficacy and applicability of this and other N credits and discount factors and is currently collecting data from related research for the panel to consider. In addition, these findings provide important information about the efficacy and cost of applying high C amendments that growers can use in the future as they navigate the changing regulatory and economic conditions of their agricultural operations.<\/p>\n\n\n\n<p><em>To learn more about this project and other current and completed FREP projects please visit: <\/em><a href=\"https:\/\/www.cdfa.ca.gov\/is\/ffldrs\/frep\/Research.html\"><em>https:\/\/www.cdfa.ca.gov\/is\/ffldrs\/frep\/Research.html<\/em><\/a><em>.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Note: This is part of a Research Update series that highlights projects funded by the California Department of Food and Agriculture\u2019s (CDFA)&nbsp;Fertilizer Research and Education Program (FREP) annual grant program. Project Title: Immobilization of Nitrate in Winter-Fallow Vegetable Production Beds to Reduce Nitrate Leaching Project Leaders: Project Status: Completed in 2023 Project Location: Commercial farms located on the Central Coast &hellip;<\/p>\n<div class=\"m-y-md text-right\"><a href=\"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/research-update-using-high-carbon-amendments-to-reduce-winter-nitrate-leaching-in-vegetable-rotations\/\" class=\"btn btn-primary\" aria-label=\"Continue reading the blog post...\">Read More<\/a><\/div>\n","protected":false},"author":5105,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_EventAllDay":false,"_EventTimezone":"","_EventStartDate":"","_EventEndDate":"","_EventStartDateUTC":"","_EventEndDateUTC":"","_EventShowMap":false,"_EventShowMapLink":false,"_EventURL":"","_EventCost":"","_EventCostDescription":"","_EventCurrencySymbol":"","_EventCurrencyCode":"","_EventCurrencyPosition":"","_EventDateTimeSeparator":"","_EventTimeRangeSeparator":"","_EventOrganizerID":[],"_EventVenueID":[],"_OrganizerEmail":"","_OrganizerPhone":"","_OrganizerWebsite":"","_VenueAddress":"","_VenueCity":"","_VenueCountry":"","_VenueProvince":"","_VenueState":"","_VenueZip":"","_VenuePhone":"","_VenueURL":"","_VenueStateProvince":"","_VenueLat":"","_VenueLng":"","_VenueShowMap":false,"_VenueShowMapLink":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[39,456],"tags":[527,194,525,58,528],"class_list":["post-2243","post","type-post","status-publish","format-standard","hentry","category-frep-grant-program","category-research-updates","tag-almond-shells","tag-central-coast-agriculture","tag-high-carbon-amendments","tag-nitrogen-management","tag-winter-leaching"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p9r16A-Ab","jetpack-related-posts":[{"id":235,"url":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/research-update-improving-n-use-efficiency-of-cool-season-vegetables-with-broccoli-rotations\/","url_meta":{"origin":2243,"position":0},"title":"Research Update: Improving N Use Efficiency of Cool Season Vegetables with Broccoli Rotations","author":"Brooke Elliot","date":"July 1, 2017","format":false,"excerpt":"Research Project: Improving N Use Efficiency of Cool Season Vegetable Production Systems with Broccoli Rotations. Smith R. et al. Status: Completed Issue: The cool season vegetable production areas of the California\u2019s Central Coast frequently grow two or three crops during the growing season. The dominant crops\u2014like lettuce and spinach\u2014require high\u2026","rel":"","context":"In &quot;All&quot;","block_context":{"text":"All","link":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/category\/all\/"},"img":{"alt_text":"photograph of a field of vegetables","src":"https:\/\/i0.wp.com\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2017\/05\/IMG_5337-300x199.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":184,"url":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/research-update-data-driven-nitrate-leaching-hazard-index-and-bmp-assessment-tool\/","url_meta":{"origin":2243,"position":1},"title":"Research Update: Data Driven Nitrate Leaching Hazard Index and BMP Assessment Tool","author":"Brooke Elliot","date":"March 14, 2017","format":false,"excerpt":"Research Project: A Data Driven Nitrate Leaching Hazard Index and BMP Assessment Tool - O\u2019Geen, A. et al. Status: Second year of a three year study Issue: California growers are faced with the challenge of producing high-quality crops while minimizing the movement of fertilizer nitrogen to groundwater. One major difficulty\u2026","rel":"","context":"In &quot;All&quot;","block_context":{"text":"All","link":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/category\/all\/"},"img":{"alt_text":"Figure 1. Spatial distribution of simulated travel times for a HYDRUS model map of nitrate leaching (50% complete).","src":"https:\/\/i0.wp.com\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2016\/12\/OGeen-blog-810x1024.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":189,"url":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/research-update-fertilizer-value-of-nitrogen-in-irrigation-water\/","url_meta":{"origin":2243,"position":2},"title":"Research Update: Fertilizer Value of Nitrogen in Irrigation Water","author":"Brooke Elliot","date":"February 15, 2017","format":false,"excerpt":"Research Project: Determining the Fertilizer Value of Ambient Nitrogen in Irrigation Water - Cahn, M. et al. Status: Final year of study Issue: Irrigation water from many wells on the Central Coast contains a significant amount of nitrate-nitrogen (NO3-N). The N content in irrigation water has not been accounted for\u2026","rel":"","context":"In &quot;All&quot;","block_context":{"text":"All","link":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/category\/all\/"},"img":{"alt_text":"Manifold and injection system used for simulating irrigation water with different concentrations of nitrate-N.","src":"https:\/\/i0.wp.com\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2016\/12\/Cahn-blog-300x200.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":920,"url":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/frep-awards-projects\/","url_meta":{"origin":2243,"position":3},"title":"FREP Awards Projects to Improve Agricultural Fertilizer Management and Water Quality","author":"Brooke Elliot","date":"November 6, 2018","format":false,"excerpt":"The California Department of Food and Agriculture's (CDFA) Fertilizer Research and Education Program (FREP) is pleased to announce the award of over $1.1 million in grant funds to agricultural organizations and universities. These grants will fund six projects that will improve the efficiency and reduce the environmental impact of fertilizer\u2026","rel":"","context":"In &quot;FREP Grant Program&quot;","block_context":{"text":"FREP Grant Program","link":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/category\/frep-grant-program\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":2775,"url":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/observations-from-the-field-central-coast-growers-adopt-winter-cover-crops-to-improve-nitrogen-use-efficiency-and-facilitate-regulatory-compliance\/","url_meta":{"origin":2243,"position":4},"title":"Observations from the Field: Central Coast Growers Adopt Winter Cover Crops to Improve Nitrogen Use Efficiency and Facilitate Regulatory Compliance","author":"Karen Adler","date":"April 27, 2026","format":false,"excerpt":"Note: This is part of a Research and Outreach Update series that highlights projects funded by the California Department of Food and Agriculture\u2019s (CDFA)\u00a0Fertilizer Research and Education Program (FREP) annual grant program. Project Title: Facilitating Grower Adoption of Cover Crop Nitrogen Scavenging to Minimize Residual Nitrogen Loss and Comply with\u2026","rel":"","context":"In &quot;FREP Grant Program&quot;","block_context":{"text":"FREP Grant Program","link":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/category\/frep-grant-program\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2026\/04\/PIs-and-Karen-150x118.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2026\/04\/PIs-and-Karen-150x118.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2026\/04\/PIs-and-Karen-150x118.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/blogs.cdfa.ca.gov\/FREP\/wp-content\/uploads\/2026\/04\/PIs-and-Karen-150x118.jpg?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":334,"url":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/grants-to-begin-funding-january-2018\/","url_meta":{"origin":2243,"position":5},"title":"Grants to Begin Funding January 2018","author":"Brooke Elliot","date":"January 2, 2018","format":false,"excerpt":"The Fertilizer Research and Education Program (FREP) of the California Department of Food and Agriculture (CDFA) is pleased to announce the award of almost $800,000 in grant funds to agricultural organizations and universities this year. These grants will fund four projects that will improve the efficiency and reduce the environmental\u2026","rel":"","context":"In &quot;FREP Grant Program&quot;","block_context":{"text":"FREP Grant Program","link":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/category\/frep-grant-program\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/wp-json\/wp\/v2\/posts\/2243","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/wp-json\/wp\/v2\/users\/5105"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/wp-json\/wp\/v2\/comments?post=2243"}],"version-history":[{"count":1,"href":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/wp-json\/wp\/v2\/posts\/2243\/revisions"}],"predecessor-version":[{"id":2249,"href":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/wp-json\/wp\/v2\/posts\/2243\/revisions\/2249"}],"wp:attachment":[{"href":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/wp-json\/wp\/v2\/media?parent=2243"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/wp-json\/wp\/v2\/categories?post=2243"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.cdfa.ca.gov\/FREP\/index.php\/wp-json\/wp\/v2\/tags?post=2243"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}