Washington State University Cooperative Extension The Compost Connection for Washington Agriculture WSU CSANR January 1997 Funded by a grant from the W.K. Kellogg Foundation No. 3 Nutrient aspects of compost by Dave Bezdicek and Mary Fauci, WSU Pullman Grass Straw Composting Shows Promise In the last issue of Compost Connection, we touched on some of the important properties to consider when buying compost. In this issue, we will look at how compost supplies the major nutrients nitrogen (N), phosphorus (P), and potassium (K). The end use of the compost will influence what major nutrient content you seek in a compost product. Nitrogen (N) Some growers are particularly interested in compost with a high nitrogen content. This is especially true for organic farmers, who often find that compost is the least expensive N source on a dry weight basis. Composts vary widely in N content, largely due to differences in N of the original materials. Composts vary even more in the amount of N they release over time. It is relatively easy to determine the N content of compost (total N, available N) with laboratory tests as presented in Table 1. However, it is much harder to predict how the N will be released during the growing season and beyond. This is one reason many growers prefer an inorganic fertilizer over an organic source - the former is more predictable. A nitrogen mineralization test can be run on compost to estimate when and how much N will be released. We have conducted a number of these at WSU and will discuss them below. Post-application monitoring of soil N, plant tissue N, and yield can also help track N release indirectly. First, let s start with some terminology. Nitrogen is found in the organic form (bound with carbon, as in plant material or manure) or inorganic form (nitrate, ammonium, nitrite, nitrogen gas, etc.). Organic N is generally the dominant form in soil and plants and is (cont d p. 2 NUTRIENTS) Researchers at Oregon State University and the USDA-ARS in Corvallis, Oregon, have successfully composted grass straw residues in the Willamette Valley. Grass seed production is a large industry there, and previous disposal of the straw after harvest by burning is severely restricted. Farmers and researchers have been looking for alternative uses or low-cost disposal options. Composting of the straw alone has been considered unfeasible due to the high C:N ratio of the material (50 or more). The researchers formed field-sized windrows in mid- August. These were turned either 0, 2, 4, or 6 times throughout the rainy season, generally at 5-8 week intervals. The windrows were monitored for C:N ratio, volume reduction, and temperature.the unturned windrows were at 45% of original volume after 33 weeks, while the other windrows were at about 15% of original volume. Most of the volume reduction had occurred by 20 weeks. In the 6 turn windrow, the C:N ratio declined from an initial 57 to a final 16. The unturned windrows had the lowest temperatures, while the 4 and 6 turn windrows reached maximum temperatures of about 100 o F. These temperatures are probably inadequate to kill most weed seeds or disease propagules. Overall, the project illustrates the feasibility of composting as a low-cost method to convert waste straw into a usable soil amendment. -- from Amer. Journal Alternative Agric., 1996. Vol. 11(1), p. 7-9. (NUTRIENTS cont d)
2 The Compost Connection slowly available for uptake by growing plant roots. In agriculture, available N generally refers to the inorganic forms nitrate and ammonium which plants readily use. The process of conversion of organic N to inorganic N (as ammonium) is called mineralization. Microbes are responsible for this. Another set of microbes then converts the ammonium to nitrate in a two-step process called nitrification. Under normal conditions, there will be little ammonium in soil or in mature compost because it quickly converts to nitrate. Ammonium is not subject to leaching in the soil, but can be lost through volatilization (gaseous loss), and can be toxic to roots. Nitrate is subject to leaching. In Table 1, you will note a wide variation in total N, ammonium N (NH + 4), and nitrate N (NO - 3) among the composts. Total N usually represents the sum of organic N and inorganic N (ammonium plus nitrate). A fraction of the organic N (total N minus ammonium and nitrate) is released slowly over the growing season. From the composts in our study, total N varies from a low of 0.8% for Iddings yard waste to a high 4.2% for Stutzman chicken compost. Essentially all the N in the Iddings compost is in the organic form, while in the Nielson and Sunland chicken composts, a third to half of the total N is in the inorganic form. So those products with more available N can be used more reliably as an immediate N source. [To convert from ppm to percent, divide by 10,000] Available N. This includes the inorganic N fraction as ammonium and nitrate N and is considered available to plants. On a wet yard or ton basis, one can calculate the amount of available N from a compost. For example using the Nielson compost, the table shows that 4.5 lb of N is available per wet yard. This is calculated as follows: dry matter fraction = (100-% moisture)/100 = (100-26)/100 = 0.74 dry bulk density = wet bulk density x dry matter fr. = 611 lb/yd x 0.74 = 452 lb/yd dry % available N = (ppm ammonium-n + ppm nitrate-n)/10,000 = 9928 ppm / 10,000 = 0.993 % lb available N / yd compost = (dry bulk density x % available N)/100 = (452 x 0.993) / 100 = 4.5 lb available N per wet yard Numbers in the table may be slightly different due to rounding off. The amount of available N on a wet ton basis can be calculated for the Nielson compost as follows: lb avail. N / wet ton = (2000 lb/ton x dry matter fraction) x (% avail. N/100) = (2000 x 0.74) x (0.993/100) = 14.7 lb avail. N per wet ton One can see that the chicken composts are high in available N due to their high levels of inorganic N. For composts low in inorganic N, there may be less than a pound of available N per ton and consequently more compost would be needed, depending on the end use for the compost. Release of organic N. A fraction of the organic N will be released over a growing season, depending on factors such as temperature, moisture, soil ph, and C:N ratios. Generally from 10 to 50% of the organic N is released for plant growth over the first growing season. There is a rough relationship between the C:N ratio of the compost and the release rate of organic N to available N. In Table 1 using the Soil and Plant Lab data, the C:N ratio can be calculated by dividing the percent organic matter by 1.8, and then dividing by the total N. Generally, composts with a C:N ratio of 25:1 or higher release little available N immediately. For example, the WSU compost (C:N ratio of 32:1) did not release N for several months in field trials because the high amount of carbon tied up available N in the compost and even in the soil (see Figure 1). Composts in the range of 15 to 25:1 will release N at an intermediate rate. Composts with a C:N ratio of less than 15:1 would release N more quickly and would fall into the higher range of 10 to 50% release rate for most composts. Two of the chicken
3 The Compost Connection TABLE 1. Compost Analysis - July 1996 - Soil & Plant Lab, Santa Clara, CA Nielsen Stutzman Sunland BION Lincoln Lincoln WSU LRI Cedar Gr Iddings chicken chicken chicken dairy dairy feedlot cattle yardwaste yardwaste yardwaste Parameter Bulk dens. lb/yd W 611 878 875 1063 1158 1118 980 942 1176 916 Moisture % 26 24 63 66 43 18 56 21 51 51 Dry matter lb/yd 454 664 327 360 657 922 435 742 581 446 Est. C:N 14.3 10.2 38.5 14.0 10.3 10.9 31.9 13.1 23.2 20.4 Total N % D 3 4.2 1.1 2.1 1.8 1.9 0.9 2 0.9 0.8 NO3-N ppm D 162 847 2460 572 2081 1673 36 1421 324 8 NH4-N ppm D 9766 7836 3607 1528 16 306 25 50 17 21 Total N lb/ton W 45.2 63.2 8.2 14.1 20.6 31.7 8.2 32 9.3 7.3 Avail. N lb/ton W 14.8 13.1 4.5 1.4 2.4 3.3 0.1 2.3 0.3 0.1 Total N lb/yd W 13.8 27.8 3.6 7.5 12 17.7 4 15.1 5.5 3.4 Avail. N lb/yd W 4.5 5.8 2 0.8 1.4 1.8 <0.1 1.1 0.2 <0.1 Total P % 1.6 1.8 0.9 0.3 0.8 0.8 0.3 0.3 0.2 0.2 Avail. P lb/ton W 2.5 3.7 1.3 0.4 0.9 1.7 0.2 0.6 0.3 0.1 Total K % 2.5 2.5 0.6 0.3 1.1 1.4 0.7 1.1 0.4 0.4 Avail. K lb/ton W 28 29.2 4.7 1.1 9.6 18.6 6.4 14.6 4.1 3.8 * W=wet basis; D=dry basis composts, and the Bion, Lincoln, and LRI composts would fall into this category. Keep in mind, these are rough estimates of the N release rate based on C:N ratio. Laboratory tests and field trials provide better estimates of organic N mineralization by measuring inorganic N over time. N mineralization studies. This past year, we ran a number of mineralization studies on compost, soil, and compost-amended soil. We tested three different methods: aerobic mineralization (84 days), anaerobic mineralization (10 days), and hot KCl extraction (no incubation). In general, we found that none of the methods worked well on straight compost. In soil, the aerobic and anaerobic methods were highly correlated. We used the aerobic method on several compost-amended soils. This worked well, although we did experience denitrification in some samples, which lowers the estimate of mineralization. We used the aerobic method to test soil ((Palouse silt loam) that had been amended with 50 ton/ac of WSU compost (C:N ratio 32:1). The compost was applied in the fall, incorporated, and soil samples were taken in spring. In Figure 1, you can see how the compost actually tied up soil N relative to the unamended control, which mineralized about 50 lb N during the incubation.. If one were to use this compost as a N nutrient source, additional N would need to be added. In a laboratory N mineralization study of the Nielson compost added to a Quincy fine sand soil at various rates, mineralization occurred as expected at the 10 ton/ac rate (Table 2). The ammonium released was converted quickly to nitrate. From this test, we estimate that about 280 lb of N would be available during the first season with the 10 ton/ac rate. About 30% of this came from the organic N in the compost, while the rest was available at application in the ammonium and nitrate. During the incubation about 25% of the organic N was mineralized.
4 The Compost Connection Figure 1. Nitrate mineralized during aerobic incubation - soil only vs. compost-amended soil. Pullman, WA. Nitrate-N (mg/kg) 25 soil control 20 compost 15 10 5 0 0 20 40 60 80 100-5 Days Table 2. Nielson compost in Quincy soil aerobic mineralization assay, inorganic N between day 0-84 Compost rate Nitrate N (ppm) Ammonium N (ppm) (ton/acre) 0 14 28 42 63 84 0 14 28 42 63 84 0 14 16 19 19 26 22 3 3 1 1 1 1 10 14 26 127 123 160 162 79 92 2 2 2 1 80 14 3 3 137 861 654 920 1274 1150 959 869 645 With the high rate ( 80 ton/ac), ammonium was released from the compost immediately, but the formation of nitrate though nitrification was delayed until 42 days. This delay in nitrification was likely due to high salts and possibly high ammonium. Obviously, a product such as this should not be used in the field at high rates due to the excessive N it would supply. Compost maturity. A mature compost is one where most of the biological activity has ceased and it is relatively stable. Tests based on biological activity and temperature rise are available commercially from Woods End Research Laboratory, Inc., Mount Vernon, Maine. Mature compost will generally have a dark color, an earthy smell, and will not have a detectable ammonia smell. Mature compost is generally at or near air temperature, and not hot or steaming. As a rule, these composts will generally contain more nitrate than ammonium. Nitrate is formed through the process of converting ammonium to nitrate and occurs later in the composting process. Composts made from chicken manure may have a detectable ammonia smell because of the high N content from uric acid in poultry manure or because the compost is not mature. This compost still may be used, but more caution is needed where the material may contact plant roots. Phosphorus. Composts are generally a good source of P depending on the feed stocks. Animal sources contain higher levels of P than yard waste. Total P ranges from 0.2 to nearly 2%. About 5 to 15% of the total P is available to plants, which can be expressed on a ton basis as shown in Table 1. Phosphorus is seldom toxic to plants, although the soil P can build up to high levels with repeated applications of compost which can affect the availability of some micronutrients. Excess P can also contribute to surface water contamination when soil erosion moves sediment with high P levels to streams and lakes. Potassium. Composts from animal sources contain relatively large amounts of K for plant growth. Most of the K in compost is soluble and therefore most of
5 The Compost Connection the total K is available for plant growth. Potassium is seldom toxic as a nutrient, although K salts in compost made from animal sources contribute significantly to the overall salinity. End use for compost The type of compost you purchase should reflect what it will be used for. The feed stocks in compost determine to a large extent what the quality of compost will be. Composts can generally be used for one of the following purposes: an organic matter source, a nutrient source, a mulch, or some combination. In all cases, quality composts serve to enhance the nutrient, biological, and physical attributes of soil. If organic matter additions are the primary purpose, such as land reclamation, then composts with low nutrient levels may be desirable in order to protect water quality. The WSU compost is a good example. It was used at rates of 100 and 200 tons/ac on eroded hills, and soil nitrate levels were consistently lower than the control. Thus, high rates can be used for soil improvement without jeopardizing water quality. more likely to be observed in orchards that rely on compost for N (e.g. organic growers) and when compost is mixed into the planting hole versus spread and incorporated. Our results support this. A few of the findings will be presented in this and upcoming newsletters. Individual trial results will eventually be posted on a Web site. Ted Goehry, an orchardist in Brewster, WA, tested various composts and application methods during 1996. His orchard sits on very sandy soil. He planted a block of apples (Cameo var.) on previously unfarmed land and tested the benefit of compost in this setting. The primary test was the use of 3 rates of Cedar Grove yard waste compost (0, 10, and 20 wet tons per applied acre) banded on the planting row and incorporated before tree planting. All trees grew very well this first year and there were no differences due to compost rate. Table 3. Trunk growth and soil E.C. after banding yardwaste compost prior to apple planting. If nutrient additions are the primary purpose, then the balance of major nutrients must be considered and agronomic rates determined. A compost for mulch might be best with relatively low nutrients, a high C:N ratio, and larger particle size. Guidelines for compost end use are being developed in several states, including Washington, that give specifications for landscaping, public parks, construction areas, and other specific situations. These can help identify compost qualities that should be sought or avoided. On-farm Compost Trials - 1996 Season David Granatstein and Patty Dauer, Washington State University in Wenatchee, WA, worked with central Washington orchardists to conduct 12 different tests of compost in apple orchards. The tests included a top-dress application to bearing trees which were growing poorly, and various applications on newly planted trees. Overall, there were no striking results that were consistent across orchards. This is not surprising, as it will likely take several years for benefits to appear. Immediate benefits are % Trunk Soil E.C. Rate Growth (mmho/cm) 0 99 0.24 10 99 0.66 20 106 0.28 An observational trial was set up in one row on the edge of the block. The following treatments were mixed into the planting hole during planting: A - check B - leonardite (L), 1 cup C - Stutzman chicken compost, 2.5 gal D - Stutzman chicken compost, 2.5 gal + 1 cup L E - Stutzman chicken compost, 4 gal F - Cedar Grove yardwaste compost, 2.5 gal G - Cedar Grove yardwaste compost 5 gal H - Cedar Grove yardwaste compost, 5 gal + 1cup L I - Cedar Grove yardwaste compost, 5 gal + 2 cup L Treatments were applied to 3-tree plots, and for the most part not replicated. As evident in Figure 2 below, the chicken compost stunted growth and killed several trees, due to the high electrical conductivity (Table 4). This confirmed the recommendation to avoid using these products in proximity to the roots.
6 The Compost Connection The Cedar Grove product appeared to give some growth increase over the check, as did the leonardite. Leonardite is a mined humic acid material that acts as a concentrated compost. It is reported to improve growth on sandy soils, and may be a useful product in conjunction with compost for soil improvement. These trials will be monitored again in 1997, and additional studies are planned, including a better comparison of leonardite versus compost on sandy soils. Table 4. Effect of soil amendment on E.C. in tree planting hole. Soil E.C. Treatment (mmho/cm) C > 2.3 D > 2.4 E 1.5 F 0.8 G 0.6 Figure 2. Trunk growth of apple trees with various unreplicated amendments. % Trunk Growth 140 120 100 80 60 40 20 0 A B C D Disclaimer: The mention of specific products or companies in this report does not constitute a recommendation for or against their use. Information is provided to help end users make decision appropriate to their specific needs and conditions E F G H Contributors to this project and to this newsletter edition include David Bezdicek and Mary Fauci, WSU Crops & Soils, and Patty Dauer and David Granatstein, WSU Tree Fruit Center. Newsletter Editor: David Granatstein I Cooperative Extension programs and employment are available to all without discrimination.