2008 Annual Report. Fertilizer Requirements for Native Perennial Plants Harvested for Biomass

Transcription

1 2008 Annual Report Fertilizer Requirements for Native Perennial Plants Harvested for Biomass Craig Sheaffer* and John Lamb *Department of Agronomy and Plant Genetics University of Minnesota Department of Soil, Water, and Climate University of Minnesota Native perennial, warm season prairie plants have been designated by the Department of Energy as a source of biomass for energy production. They have potential for conversion to ethanol, gasification, or direct combustion. Perennial prairie species can generate significant biomass and provide many ecological services like nutrient recycling, soil erosion control, and wildlife habitat. Switchgrass, a native perennial grass, is a primary candidate for production of cellulosic fuels. In addition to pure stands of switchgrass, mixtures of native grasses (e.g., switchgrass, big bluestem) with forbs (e.g., sunflowers) and legumes (e.g., Canada milkvetch) have been recommended to provide greater long-term stress tolerance and yield stability compared to grass monocultures. Economically and environmentally sound fertilizer nutrient recommendations are lacking for native grasses and native plant mixtures proposed for biomass crop removal systems. Our objectives were to determine the N, P, and K fertilizer requirements for native perennial prairie plants used for biofuel production. This report provides some basic results from the 2008 cropping season. The experiment will be repeated again in 2009 at four sites. At the conclusion of the experiment, specific recommendations will be made based on these results and previous data. As in all soil fertility research, it is risky and often inappropriate to base conclusions on only one year of information. Methods Research was conducted in established stands of native perennial plants at Austin, Lamberton, New Ulm, and Rosemount in southern Minnesota in Soil characteristics are described in Table 1. The experimental design was a randomized complete block with 4 replications per location. Plots were 10 by 10 ft. All plots received variable rates of nitrogen (N) fertilizer: 0, 50, 100, 150, and 200 lb/acre that were combined in a factorial arrangement with variable levels of P 2 O 5 or K 2 O fertilizer depending on the soil fertility at each location. Soil fertility at each site was determined by soil sampling and testing at the University of Minnesota. For low P soils, we applied P 2 O 5 rates of 0, 30, 60, 90 and 120 lb/acre and for low K soils, K 2 O was applied at 0, 40, 80, 120, and 160 lb/acre. Based on soil test results (Table 1), variable P 2 O 5

2 rates were applied at Austin, Lamberton, and New Ulm. At Rosemount variable K 2 O rates were applied. Fertilizers were broadcast in mid-may Biomass yield was determined by harvesting a 4 by 4 ft area to a 3 inch height within each plot in early November 2008 following freezing and drying of the biomass. A 2 lb subsample was collected to a 3 inch height and oven dried. Biomass yield was expressed on a dry matter basis. Botanical composition (weeds, native grasses, and forbs) based on relative contributions by dry weight were measured. The subsample was ground and is being analyzed for energy and mineral content. Results The botanical composition of the harvested vegetation was not affected by fertilizer treatments at each location. The average botanical composition was as follows: Austin: 65% big bluestem, 10 % indiangrass, and 25% forbs (goldenrod, sunflower, brown eyed Susan, prairie clover); Rosemount: pure switchgrass; Lamberton: 90% big bluestem and 10% forbs (goldenrod, butterfly weed; and New Ulm: 60% big bluestem, 30% forbs (Canada milkvetch, goldenrod, butterfly weed), and 10% annual grass weeds. Shifts in vegetative composition in response to fertilizer application typically occur over time and we will continue to measure fertilizer treatment effects. Biomass yield response to nutrient additions is shown in Figures 1, 2, 3, and 4. Biomass yields were increased by nitrogen applications at all locations except New Ulm. At Austin and Lamberton, a linear response to nitrogen fertilizer occurred indicating that we had not reached a nitrogen fertilizer rate that maximized yield. At Rosemount, the response was curvilinear and plateaued at an agronomically optimum N rate (AONR) of 98 lb N per acre. Maximum yields were 2, 4, 4.5, and 6 ton/acre at Lamberton, Austin, Rosemount, and New Ulm, respectively. The low yields at Lamberton may have been associated with lower rainfall compared to the other sites. The June through September rainfall at Austin, New Ulm, Lamberton, and Rosemount was 14, 13, 9 and 12 inches, respectively. The response to P 2 O 5 or K 2 O fertilization was less consistent. At Austin, there was a linear response in biomass yield to P 2 O 5 fertilization, but no N fertilization by P 2 O 5 fertilization interaction occurred. However, there was no response in biomass yield to P 2 O 5 at Lamberton or to K 2 O at Rosemount. A N fertilization by P 2 O 5 fertilization interaction did occur at New Ulm but there was no discernable trend in the biomass yield response. This trend at New Ulm was likely due to variability in the soil beneath the prairie. This occurred due to soil disturbance at the site during construction and before planting of the native prairie. Conclusions Based on this first year of data, we conclude that nitrogen fertilization is necessary to increase the biomass yield of native perennial herbaceous plantings; however, the response varied by location. The AONR rate was not determined at three of the four locations. It appears that warm season prairie systems use more nitrogen to maximize yields than was originally anticipated. Additional field research in 2009 should help clarify optimum rates. Response to K 2 0 and P application was less consistent than for nitogen. The experiment will be repeated again in 2009 on native plantings at Austin, Lamberton, and Rosemount. A new site in southern R Fertilizer Requirements for Native Perennial Plants Harvested for Biomass -2-

3 Minnesota will be identified to replace the New Ulm site. Mineral and energy analysis of the native plant material collected in 2008 is being completed. Table 1. Trial locations and soil characteristics for native plant fertility trials in 2008 Soil texture ph Organic Phosphorus Potassium Location matter % ppm ppm Austin Silty clay loam Lamberton Silty clay loam Rosemount Silt loam New Ulm Silty clay loam R Fertilizer Requirements for Native Perennial Plants Harvested for Biomass -3-

4 Figure 1. Biomass yield response to N and P 2 O 5 fertilization of a mixed native prairie poloyculture near Austin, MN. The response to fertilizer was significant (P<0.05) for both N and P 2 O 5. Austin y = x R 2 = N rate (lb/a) Austin y = x R 2 = Phosphate rate (lb/a) R Fertilizer Requirements for Native Perennial Plants Harvested for Biomass -4-

5 Figure 2. Biomass yield response to N and P 2 O 5 fertilization of a mixed native prairie poloyculture at Lamberton, MN. The response to P 2 O 5 fertilization was not significant (P >0.05). Lamberton Phosphate rate (lb/a) R Fertilizer Requirements for Native Perennial Plants Harvested for Biomass -5-

6 Figure 3. Biomass yield response to N and P 2 O 5 fertilization of a mixed native prairie poloyculture near New Ulm, MN. The responses was significant (P<0.05) but the fertilizer response trend was inconsistent. New Ulm N rate (lb/a) 0 phosphate 30 phosphate 60 phosphate 90 phosphate 120 phosphate R Fertilizer Requirements for Native Perennial Plants Harvested for Biomass -6-

7 Figure 4. Biomass yield response to N and K 2 O fertilization of a switchgrass prairie near Rosemount, MN. The response to K 2 O fertilization was not significant (P >0.05). R Fertilizer Requirements for Native Perennial Plants Harvested for Biomass -7-