Effects of Both Above and below Ground Biomass On Soil Chemical, Physical and Biological Properties On A Coastal Plain Soil in North Carolina.

The literature has shown the possibility to enhance many of the soil properties that improve production with additions of plant biomass to the soil in conjunction with long-term conservation tillage. Since it has been proven that reduced tillage is extremely beneficial to a soil’s health, the key question is if the incorporation of deep rooted cover crops and/or large quantities of above ground biomass over a two-year period would result in extensive improvements on a soil’s natural properties throughout the effective rooting depth, or is this too short of a time period for any beneficial effects to occur to the chemical, physical and biological properties of the soil? While SOC additions to the soil surface through decaying biomass can make measurable improvements to a soil in the humid, tropical southeastern U. S., the dynamics of total carbon (total SOC), total nitrogen (TKN), particulate organic matter (POM), potentially mineralizable nitrogen (PMN), CEC and bulk density (Db) in the 0-5, 5-10, and 10-18 cm depths in a production system that incorporates deep rooted cover crops and/or additions of organic matter from cover crops at rates >6 Mg/ha/yr (3 T/ac) are unknown. The objectives of this research were to determine what effect rye (Scale cereale), barley (Hordeum vulgare), alfalfa (Medicago sativa), wheat (Triticum aestivum), triticale (Triticale hexaploide Lart.), annual white sweetclover (Melilotus officinalis), blue lupine (Lupinus angustifolius), rye/hairy vetch (Scale cereale/Vicia villiosa) and alfalfa/rye (Medicago sativa/Scale cereale) would have on the following parameters: total SOC, POM, TKN, PMN, CEC, and Db after two (2) years of seeding. Significant spatial/temporal interactions and main effects were found in Db, PMN, POM and CEC while significant main effects were found in total C and total N. Significant treatment interactions were found in Db, total C, PMN, POM and CEC. Relative to treatment biomass, significant effects were seen between treatments and treatment*year interaction. Results on Db found spatial variability with depth but not with season and a minimal treatment effect depending on surface texture.  Total C and total N decreased with depth but were independent spatially and temporally; however, treatment effect on total C was <5 months. Between Db and total C, the two parameters were inversely correlated. PMN either fluctuated between sampling times or declined with time. Notably, rye and rye/hairy vetch effected PMN in the 0-5 cm depth where other treatments showed no effect. POM declined with time regardless of depth implying a priming effect was occurring; however, rye/hairy vetch appeared to show an early reversal trend. As for CEC, there was no consistent trend. Additionally, CEC exhibited a moderate correlation to POM but not total C. Biomass measurements indicated no treatment consistently exceeded >6 Mg/ha/yr. Rye and rye/hairy vetch more often produced the most biomass and lupine achieved the overall maximum yield. Relationships between biomass and N parameters found a moderate, positive effect from the biomass inputs that appeared to compound with time. Overall, rye and rye/hairy vetch were the best cover crop treatments but two years of biomass inputs were not enough to prevent declines in POM. Conversely, PMN fluxed from applied N, and biomass with low C:N ratios oxidized quickly resulting in less carbon. Total C, total N and Db were not responsive to short term management indicating more effort is needed to define and/or develop a cover crop that will consistently reach the >6 Mg/ha/yr.