Conversion from a sycamore biomass crop to a no-till corn system : soil effects and management implications

It is not known if a short-rotation woody crop (SRWC), grown on an agricultural site, will affect subsequent row crops if the site is returned to agricultural production after harvest of the SRWC. In this study, a woody biomass crop was integrated with an annual row crop system in a row crop-woody crop-row crop rotation. The objectives were to: i) document the post-harvest effects of a woody crop rotation on soil C, N, and aggregate stability, ii) determine the woody crop's impact on future row crop production and N fertilization efficacy, and iii) measure changes in C and N fluxes due to the woody crop rotation. The study was in southwestem TN on a Memphis-Loring silt loam intergrade (Typic Hapludalfs - Oxyaquic Fragiudalfs). Soybean [Glycine max (L.) Merr.] was followed by four-year (SY4C) and five-year (SY5C) rotations of American sycamore (Platanus occidentalis L.), followed by no-till corn (Zea mays L.). Continuous row crops (soybean converted to corn) served as a control (SBC). Four rates of broadcast NH₂NO₃ were applied to corn (0, 73, 146, and 219 kg N ha^-1).

Four- and five-year sycamore rotations significantly affected soil properties and post-sycamore corn grain production. During three years of com production immediately following sycamore harvest, increases in total soil C and N concentrations below a 2.5 cm depth were attributed to the sycamore rotation, specifically to sycamore roots. Soil inorganic N concentrations were higher in the SBC than the SY4C system at a depth of 0 to 2.5 cm. Soil aggregate stability, at depths from 2.5 to 15 cm, was greater in the SY4C than the SBC system. No mechanical problems were encountered when planting no-till corn over sycamore stumps. Significant increases in N were observed in decomposing sycamore roots and stumps. Microbial immobilization of soil inorganic N during decomposition of woody sycamore residues was suspected to have reduced the amount of N available to corn plants during the first two years following sycamore harvest. First and second-year com after sycamore harvest required a 50% higher rate of N fertilization to maximize yield than com in the SBC system.