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Jared D. Williams, Galen E. Woodward, and Matt A. YostDepartment of Agribusiness, Plant & Animal ScienceBrigham Young University-IdahoIn-season nitrogen and phosphorus availability from fall compost application in spring wheatDepartment of Agribusiness, Plant and Animal ScienceIntroductionIncreased interest in applying compost to crops as an alternative to conventional fertilizer (and to improve soil productivity).

Compost has been successfully used in some areas of the world for supplying sufficient amounts of nutrients

BUT, these areas are generally in warmer environments with longer growing season than southeast Idaho resulting in longer more rapid mineralization of the compost.

Department of Agribusiness, Plant and Animal ScienceIntroductionEstimates of nutrient mineralization rates are based on these warmer and longer growing season and may not be applicable to SE Idaho. For farmers in southeast Idaho to successfully use compost as a substitute for fertilizer or to reduce the amount of fertilizer applied, the rate at which nutrients such as nitrogen (N) and phosphorus (P) are made available must be determined specific to SE Idahos environment.

Department of Agribusiness, Plant and Animal ScienceIntroductionThe potential benefits of applying compost are:Reduced use of commercial fertilizersIncrease soil productivity because of :Improved water holding capacityIncearsed water infiltrationIncreased cation and anion exchange capacity

Department of Agribusiness, Plant and Animal ScienceIntroductionThe objectives of this study were to: Examine the effect of different compost rates on nitrogen (N) and phosphorus (P) availability at two different plot scales.Determine the effect of compost and compost plus fertilizer on yield for a spring wheat crop on small plots.

Department of Agribusiness, Plant and Animal ScienceMaterials and MethodsSmall plots 40 x 25 ftRandomized complete block design9 treatments and 3 replications . Treatments consisted of:Compost only (0, 10, 15, 20, 30, and 40 T ac-1)Compost (10 T ac-1) + fertilizer (115 lbs ac-1)Fertilizer only (115 lbs ac-1). Composted feedlot manure was applied in the spring before planting wheat (2009).Department of Agribusiness, Plant and Animal ScienceMaterials and MethodsLarge plots 200 x 60 ftRCBD4 treatments, 3 replications, and 2 sites Treatments were 0, 5, 10, and 20 T ac-1Composted dairy manure was applied in the fall of the previous year (2008)Wheat was planted in the of 2009

Department of Agribusiness, Plant and Animal ScienceMaterials and MethodsSoil type was a Pocatello Variant silt loam and Ririe silt loamSoil samples were taken to a depth of 12 inSpring (April 23 for small plots and May 5 for large plots)Summer (July 7)Fall (October 20). Samples were analyzed for Nitrate-N and Olsens PGrain yields for small plots were collected by harvesting a 1 m2 area of each plot.Department of Agribusiness, Plant and Animal ScienceFigure 1. Nitrate-N as a function of compost rate on small plots when compost was spring applied.

Department of Agribusiness, Plant and Animal ScienceFigure 2. Phosphorus (Olsens P) as a function of compost rate on small plots when compost was spring applied.

Department of Agribusiness, Plant and Animal ScienceResults and DiscussionSmall Plot StudyNitrate and Olsens P were not different among compost only treatmentsFall and spring NO3-N levels for the plots were not differentThe average fall P level across compost treatments was 98 lbs ac-1 which was higher than spring P levels (52 lbs ac-1)Spring and fall control P levels (56 and 60 lb ac-1, respectively) were not differentCompost application may have increased P fertility.Department of Agribusiness, Plant and Animal Science

Figure 3. Yield as a function of compost rate by treatments. Regression line fitted to compost only treatment (=0.05). Letters denote statistical difference among treatments at =0.05.aabcbcbbbDepartment of Agribusiness, Plant and Animal ScienceResults and DiscussionSmall Plot Study ResultsThe control treatment yield was 60 bu ac-1 which was higher than 10 T ac-1 treatment (45 bu ac-1) suggesting the compost may have caused denitrification.Department of Agribusiness, Plant and Animal ScienceFigure 4. Soil temperature (4 in. depth) over time. The 2008 line begins with fall compost application and 2009 ends with final sampling.

Department of Agribusiness, Plant and Animal ScienceResults and DiscussionSmall Plot Study ResultsSoil temperature during the summer of 2009 were between 5 and 12 F lower than the 14 year average. The cooler temperatures may have slowed N and P mineralization.Department of Agribusiness, Plant and Animal Science

Figure 5. Nitrate as a function of compost rate on large plots. Regression line fitted to spring treatments at =0.05. Letters denote statistical difference among spring treatments at =0.10.abbabDepartment of Agribusiness, Plant and Animal ScienceResults and DiscussionLarge Plot Study ResultsSpring NO3-N levels were higher for the 20 T ac-1 compost treatment (33 lbs ac-1) than the other compost treatments, but not higher than the control (27 lbs ac-1). Summer and fall NO3-N levels were not different among treatments. These results suggest that compost did not provide adequate N fertility for the spring wheat crop which resulted in a lower crop yield (data not shown).Department of Agribusiness, Plant and Animal ScienceFigure 6. Phosphorus (Olsens P) as a function of compost rate on large plots when compost was fall applied.

Department of Agribusiness, Plant and Animal ScienceResults and DiscussionLarge Plot Study ResultsFall P levels were 46 lbs ac-1 which were higher than spring P levels (55 lbs ac-1)But a comparison of spring and fall P levels of individual treatments showed no differences except for the fall 20 T ac-1 treatment which had highest P levels (63 lbs ac-1)These results were similar to the small plot study results for PDepartment of Agribusiness, Plant and Animal ScienceResults and DiscussionLarge Plot Study ResultsNitrate and P levels varied greatly within treatments Nitrate-N and P levels showed similar level of variation within treatments in the small plot study These results suggest that the variation may be influenced by the nutrient heterogeneity of the compost and less by the effects of spatial variation of soil properties and landscape attributes.Department of Agribusiness, Plant and Animal ScienceConclusionsCompost had little affect on N fertility in spring soft white wheat in southeast Idaho which could be the result of cooler soil temperatures and volatilization of N during the composting process (increased C:N ratio potentially caused denitrification).Phosphorus levels increased when large amounts of compost (20 T ac-1) were applied, and these levels may be adequate for optimal yield (but not economically feasible).

Department of Agribusiness, Plant and Animal Science