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United States Department of Agriculture

Agricultural Research Service

Research Project: ECOLOGICALLY-BASED SOIL AND CROP MANAGEMENT SYSTEMS FOR SUSTAINABLE AGRICULTURE

Location: North Central Agricultural Research Laboratory

Title: Grassland Management Effects on Long-term C and N Changes in Soil and Mixed Native Grass Canopies

Authors
item Riedell, Walter
item Osborne, Shannon
item Pikul Jr, Joseph

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 20, 2009
Publication Date: July 1, 2009
Citation: Riedell, W.E., Osborne, S.L., Pikul Jr, J.L. 2009. Grassland Management Effects on Long-term C and N Changes in Soil and Mixed Native Grass Canopies. p. 165. In: K. Paustian (ed.) Proceedings International Symposium on Soil Organic Matter Dynamics: Land Use, Management, and Global Change. July 6-9, 2009. Colorado Springs, CO.

Interpretive Summary: Soil organic matter, roughly half of which is composed of carbon, is an important part of the soil that consists of plant and animal residues in various stages of decay. Soil organic matter helps to maintain (or even improve) soil physical properties, increases water holding capacity, and increases water infiltration which in turn prevents water from running off farm fields. Therefore, soil organic matter is an essential component of healthy soil. Managing soil organic matter is an important priority on all farms. One way to increase soil organic matter is to plant grasses in areas where soil erosion is an important problem. There are 2.9 million conservation reserve program (CRP) acres in South Dakota and Minnesota. This region is also slated to provide cellulosic feedstocks for biofuels. Thus, scientific inquiry on CRP/grass management and its effect on soil organic matter (i.e. soil carbon) as well as the transfer of this knowledge to producers in this region are important priorities. This study was conducted to determine whether levels of soil carbon and nitrogen as well as grass plant carbon and nitrogen could be manipulated through canopy management and different native grass mixtures. Our results show that spring burning as a grassland management treatment was detrimental to soil C concentration and C/N ratio as well as to the growth of cool season grasses. Mow and remove management, which would be compatible with cellulosic biomass production, showed values of soil C concentration and C/N ratios comparable with those seen under the no management treatments. However, mow and removed also reduced grass biomass as well as grass tissue C/N ratio. Collection of additional time-course data is needed to determine if mow and remove would be sustainable in terms of long-term soil resource quality.

Technical Abstract: There are 2.9 million conservation reserve program (CRP) acres in South Dakota and Minnesota. This region is also slated to provide cellulosic feedstocks for biofuels. Thus, scientific inquiry on CRP/grass management and its effect on soil condition as well as the transfer of this knowledge to producers in this region are important priorities. This study was conducted to determine whether soil and grass C and N could be manipulated through canopy management and different grass mixtures. Effects of forced management (burning in early spring, mowing and residue removal at grass anthesis, or no management) on grass (native grass plantings of mixtures of cool season species, warm season species, or combined cool and warm season species) growth as well as C and N levels in soil and grass tissues were investigated at Brookings, SD, on a Barnes clay loam (fine-loamy, superactive, frigid Calcic Hapludoll). Soil C (0-15 cm depth) increased linearly over the 8 years of the experiment. Soil C accumulation rate was significantly greater under no management (714 kg C /ha/year) than burn treatment (333 kg C /ha/year) while that under mow was intermediate (504 kg C /ha/year). In years 7 and 8, soil C (burn 22.0 g/kg; no management 23.4; mow 23.2; P=0.009) and soil C/N ratio (burn 11.4; no management 11.9; mow 11.8; P=0.02) were all reduced by burn treatments. The burn treatment significantly reduced grass biomass (burn 2730 kg/ha; no management 4656; mow 3421; P=0.0001). Cool season grasses also produced less biomass than the other grass mixtures (cool season 2814 kg/ha; warm season 3989; and mix 4004; P=0.0001). Significant management by grass mixture (2-way) interactions for biomass (P=0.02) resulted from increases in biomass for the warm and warm/cool grass mixtures under the no management treatment. Grass C/N ratio was less under the mow treatment (burn 48.9; no management 51.4; mow 43.8; P=0.0001). In conclusion, the burn treatment was detrimental to soil C concentration and C/N ratio as well as to the growth of cool season grasses. Mow and remove management, which would be compatible with cellulosic biomass production, showed values of soil C concentration and C/N ratios comparable with those seen under the no management treatments. However, mow and removed also reduced grass biomass as well as grass tissue C/N ratio. Additional time-course data is being collect to determine if mow and remove would be sustainable in terms of long-term soil resource quality.

Last Modified: 9/2/2014