Root, Residue and Removal-C and -N Pools Compared to Above Ground Production for Forage-Based Management Practices.

Sustainable forage-based management practices should have high above ground production (AGP) and leave high quantities of root and residue C and N in the ecosystem. The objective was to compare hay and pasture systems with an old grass (OG) baseline on the basis of C and N pools of above ground residue, roots, harvested removals and AGP (removal plus residue). The OG baseline was treated as hay with no inputs; other treatments were: fertilized-N barley silage (FB); 3 yr-old meadow bromegrass (MB) hay and pasture, each with control, alfalfa mixture and fertilized-N sub-treatments. All parameters were subjected to ANOVA. A bi-plot analyses was conducted between AGP-C and root plus residue (RR)–C and AGP-N and RR-N to determine the best system combinations of high AGP and RR retained in the ecosystem for C and N pools. Pasture systems had half the C-removals and twice the residue-C levels as hay systems. Pastures returned greater than 90% of AGP-N to the residue pool. The pasture MB-alfalfa mixture was identified as having high AGP and high RR for both C and N pools. The OG and pasture controls had low AGP, but high RR-N and RR-C. The OG had high root-C and N, but low AGP.  The FB had high AGP, but low RR-C and -N values due to high removals and very low root- C and -N pools. For MB hay and pasture systems fertilizer-N and alfalfa mixture tended to increase AGP and residues over controls. At completion the study will determine greenhouse gas emissions for systems expressed on an AGP basis.