Franz Niederholzer8 CommentsNovember 20, 2012Nutrient, Salinity, Soil

Broadcasting compost within Orchards

Compost spreaders are working in almond orchards in this area.  The addition of composted organic matter – often composted yard waste — to soil should generally benefit soil physical and chemical properties.  However, it isn’t a source of short-term plant available nitrogen.  Research by UC Davis specialists Tim Hartz and Jeff Mitchell has shown that composted yard waste, when mixed with sand and held under constant, optimum moisture and temperature (the optimum conditions for mineralization of organic nitrogen) produces a very little plant available nitrogen (2% of total nitrogen in the compost) in the short run (12-24 weeks).  When compost is broadcast on the soil surface and not incorporated, plant available nitrogen should be even less.  Dr. Hartz did conclude that manures and composts had value in long-term soil building in vegetable crop production, where those materials are incorporated into the soil.  [Untreated/uncomposted manure use in almonds is a food quality risk and not supported by the almond industry.] Why bring up compost use? Growers are willing to pay for it and seem happy with the results.  Here’s why.  If California agriculture ends up in a regulatory situation where nutrient budgets are required of growers, it should be recognized that the short term nitrogen benefits from composted yard waste are almost non-existent and the long term benefits are unknown. Previous entries on compost applications can be found here and here.

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David Doll1 CommentNovember 6, 2011Nutrient

Compost Applications for the Almond Orchard

Compost is applied by many growers as a supplement to their nutrient management program. Composts may contain nitrogen, phosphorous, potassium, and other micro-nutrients. Applications of compost also add organic matter, and the associated organic acids, which has been shown to increase soil tilth in cropping systems.  Since all composts vary in nutrient content due to the variability in source material, nutrient benefits can only be determined through analysis. Nitrogen from Compost. To understand the effect of nitrogen from compost, we must first understand the nitrogen cycle. Organic matter contains nitrogen that is bound to various chemical compounds within the plant material. Termed organic nitrogen, it is unavailable to the plant. It can only be made available to the plant upon mineralization and conversion to nitrate through the process of nitrification. These processes are mediated by the soil microbial community. Once converted to nitrate, the nitrogen is available for plant use. Synthetic fertilizers go through similar processes depending upon their starting point (i.e. ammonium, nitrate, etc.). Figure source: www.physicalgeography.net/fundamentals/9s.html Most finished composts vary from 0.5-2.5% total nitrogen. Since most of the nitrogen is held within plant compounds (organic form), not all of the nitrogen will be mineralized and available upon application. Research by Dr. Tim Hartz, UC Davis, has shown that most composts only release about 5-10% of the nitrogen in the nitrate form. Composts that have a lower carbon to nitrogen ratio release nitrate on the higher end of this range. Higher nitrogen containing composts (> 3% nitrogen) may release more than 10% of the nitrogen. Nitrogen benefits from compost also appear to be reduced in the following growing seasons, with very little mineralization occurring. At this point, it appears that the compost is simply organic matter. Phosphorus from Compost. Phosphorous (P) content within compost can be significant. Since exportation of

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David Doll0 commentsNovember 5, 2011Nutrient

Compost Quality: What the Analysis Reveals

Compost is applied by many growers as a supplement to their nutrient management program. Adding organic matter and the associated organic acids, has been shown to increase soil tilth in cropping systems. All composts vary in nutrient content, which is heavily dependent upon the source material of the compost. Since sources vary, it is important to have an analysis in order to determine nutrient content. To understand how compost works, we must first understand the nitrogen cycle. Organic matter contains nitrogen that is bound to various chemical compounds within the plant material. Termed organic nitrogen, it is unavailable to the plant. It can only be made available to the plant upon mineralization and conversion to nitrate through the process of nitrification. These processes are mediated by the soil microbial community. Once converted to nitrate, the nitrogen is available for plant use. Synthetic fertilizers go through similar processes depending upon their starting point (i.e. ammonium, nitrate, etc.). Nitrogen from Compost.Most finish composts vary from 0.5-2.5% total nitrogen. Since most of the nitrogen is held within plant compounds (organic form), not all of the nitrogen will be available upon application. Research by Dr. Tim Hartz, UC Davis, has shown that most composts only release about 5-10% of the nitrogen. Composts that have a lower carbon to nitrogen ration release on the higher end of this range.Higher nitrogen containing composts (>3% nitrogen) may release more than 10% of the nitrogen.. Nitrogen benefits from compost also appear to be reduced in the following growing seasons, with very little mineralization occurring. At this point, it appears that the compost is simply organic matter. Phosphorous from Compost.Phosphorous (P) content within compost can be significant. Since exportation of P from the almond orchard is low (7 lbs/1000 kernel lbs), attention should paid to prevent over application of P. P is

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