In-season nitrogen and phosphorus availability from fall compost application in spring wheat

1. In-season nitrogen and phosphorus availability from fall compost application in spring wheat Jared D. Williams, Galen E. Woodward, and Matt A. Yost Department of Agribusiness, Plant & Animal Science Brigham Young University-Idaho

2. Introduction • Increased 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.

3. Introduction • Estimates 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 SEIdaho’s environment.

4. Introduction • The potential benefits of applying compost are: • Reduced use of commercial fertilizers • Increase soil productivity because of : • Improved water holding capacity • Incearsed water infiltration • Increased cation and anion exchange capacity

5. Introduction • The 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.

6. Materials and Methods • Small plots • 40 x 25 ft • Randomized complete block design • 9 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).

7. Materials and Methods • Large plots • 200 x 60 ft • RCBD • 4 treatments, 3 replications, and 2 sites • Treatments were 0, 5, 10, and 20 T ac-1 • Composted dairy manure was applied in the fall of the previous year (2008) • Wheat was planted in the of 2009

8. Materials and Methods • Soil type was a Pocatello Variant silt loam and Ririe silt loam • Soil samples were taken to a depth of 12 in • Spring (April 23 for small plots and May 5 for large plots) • Summer (July 7) • Fall (October 20). • Samples were analyzed for Nitrate-N and Olsen’s P • Grain yields for small plots were collected by harvesting a 1 m2 area of each plot.

9. Figure 1. Nitrate-N as a function of compost rate on small plots when compost was spring applied.

10. Figure 2. Phosphorus (Olsen’s P) as a function of compost rate on small plots when compost was spring applied.

11. Results and Discussion • Small Plot Study • Nitrate and Olsen’s P were not different among compost only treatments • Fall and spring NO3-N levels for the plots were not different • The average fall P level across compost treatments was 98 lbs ac-1which 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 different • Compost application may have increased P fertility.

12. a a b b b b bc c Figure 3. Yield as a function of compost rate by treatments. Regression line fitted to compost only treatment (α=0.05). Letters denote statistical difference among treatments at α=0.05.

13. Results and Discussion • Small Plot Study Results • The 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.

14. Figure 4. Soil temperature (4 in. depth) over time. The 2008 line begins with fall compost application and 2009 ends with final sampling.

15. Results and Discussion • Small Plot Study Results • Soil 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.

16. ab a b b Figure 5. Nitrate as a function of compost rate on large plots. Regression line fitted to spring treatments at α=0.05. Letters denote statistical difference among spring treatments at α=0.10.

17. Results and Discussion • Large Plot Study Results • Spring 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).

18. Figure 6. Phosphorus (Olsen’s P) as a function of compost rate on large plots when compost was fall applied.

19. Results and Discussion • Large Plot Study Results • Fall P levels were 46 lbs ac-1which were higher than spring P levels (55lbs ac-1) • Buta 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 (63lbs ac-1) • These results were similar to the small plot study results for P

20. Results and Discussion • Large Plot Study Results • Nitrate 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.

21. Conclusions • Compost 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).