Effect of Nitrogen Fertilization and Residual Nitrogen on Biomass Yield of Switchgrass
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Effect of Nitrogen Fertilization and Residual Nitrogen on Biomass Yield of Switchgrass Tim L. Springer 1
# Springer Science+Business Media New York (outside the USA) 2017
Abstract Switchgrass, Panicum virgatum L., grown for biomass has been extensively researched where the annual precipitation >760 mm and the climate varies from humid to moist-subhumid. Research is needed for areas that receive 0.56), and the effect of production year was insignificant (P > 0.53). In 2011, switchgrass biomass yield was again curvilinear (P < 0.01; Fig. 1). The regression equation for 2011 data was Y = −0.00056x2 + 0.15x + 2.67, r2 = 0.89, and RMSE = 1.46, where Y is the biomass yield in megagrams per hectare and x is the rate of applied N in kilograms per hectare. The regression equation predicts that biomass yield would peak at 12.6 Mg ha−1 at a N rate of 133 kg ha−1. This was outside the range of the values for N rate in this experiment; thus, the biomass yield effectively peaked at 12.5 Mg ha−1 at an N rate of 120 kg ha−1. The biomass yield of unfertilized plots continued to decline in 2011 to 2.7 ± 0.6 Mg ha−1, a decline of 4.4 Mg in 4 years. The growing season precipitation in 2011 was 194 mm, 240 mm below the long-term average growing season precipitation. The variation observed from 2008 to 2009 is not uncommon during the growth phase of perennial forage grasses. The growth phase is characterized by root, shoot, and crown development, and the expansion of roots, shoots, and crowns into available space both above and belowground level [54]. Once the growth phase is complete, the plants transition into an equilibrium phase where growth is limited by competition for light and available nutrients. A similar result was found for biomass yield of switchgrass at Stephenville, TX, for the first harvest year after establishment [24], and it has been found that full biomass production may not be achieved until the third growing season [40]. Once plants reached an equilibrium phase, the response of N fertilization was similar in 2009 and 2010. The 2008 biomass harvest of unfertilized plots removed approximately 15 kg ha−1 of N from the soil reducing the biomass yields of unfertilized plots in 2009 and 2010. The average N removed in the biomass in 2009 and 2010 was 4.7 ± 2.0 and 6.2 ± 1.9 kg ha−1, respectively. These values are similar to the average annual N received in precipitation at Woodward, OK, of 6.1 ± 0.5 kg ha−1 [55]. Except for the 80 kg ha−1 N rate in 2011, the biomass yield of N fertilization treatments was reduced due to drought. In 2011, there was a 55% reduction in growing season precipitation and a 24% reduction in dormant season precipitation. This resulted in a 15% reduction in annual biomass yield (averaged across N fertilization treatments) in 2011 (a drought
year) compared with the average of the previous 3 years. Similarly, Harlan and Ahring [6] showed a 33% reduction in switchgrass biomass yield for dryland production (5.9 Mg ha − 1 ) compared with irrigated production (8.8 Mg ha−1) in OK. Heaton et al. [45] r
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