AbstractsBiology & Animal Science

Managing soil fertility is important to sustain both a productive agricultural economy and to preserve our natural environment. However, soil management practices will vary depending on the agro-ecosystem; agricultural soils in the temperate world often experience excess applied nutrients, while soils in the humid tropics often have a net negative nitrogen economy. Co-applications of organic amendments with synthetic fertilizers have been proposed to increase the efficiency of nutrient cycling and reduce nutrient losses in diverse agroecosystems. Soil applications of biochar may be an effective nutrient management technique with applications in both temperate and tropical cropping systems. Biochar derived from maize stover was applied to a maize cropping system in central New York at rates of 0, 1, 3, 12, and 30 t ha-1 in 2007. Secondary nitrogen fertilizer applications were added in treatments consisting of 100, 90, 70, and 50% of the recommended rate. Nitrogen fertilizer enriched with 15N was applied in 2009 to the treatment combinations of 0 and 12 t ha-1 of biochar and 100 and 50% secondary N application. Maize yield and plant N uptake did not change with any biochar treatment (P>0.05; n=3). However, significantly less N (by 75%) was lost through leaching at 100% N fertilization, albeit at low total losses of applied 15N (0.42% of applied N). The reason for an observed 140% greater N retention in the topsoil may have been the incorporation of N into microbial biomass which increased 3-fold. The resulting total N recovery in the soil-plant system of 83% with the addition of biochar in comparison to 61% without biochar after one cropping season may also indicate lower gaseous losses with biochar. The residual effects of organic inputs of contrasting quality on maize productivity were investigated as a function of soil degradation in the highlands of western Kenya. Tithonia (Tithonia diversifolia (Hemsl.) A. Gray) green manure, cypress sawdust, and biochar made from eucalyptus wood were applied at a rate of 6 t C ha-1 for three cropping seasons, both with and without mineral fertilizer additions (120 kg N ha-1, 100 kg K ha-1, 100 kg P ha-1). Maize grain yield was monitored for four years beyond the initial organic matter additions. The greatest yield responses for all amendments were found on the most degraded soil. During those years when amendments were added, tithonia applications resulted in the greatest yield increases, between 153 and 183% more than the unamended control in comparison to 136% with biochar and 107% with sawdust additions. However, four years after tithonia applications to highly degraded soils stopped, yields rapidly declined to only 110% of the unamended control, whereas yields after biochar additions remained constant at 0.3-1.8 t yr-1 or 9-265% greater than yields without organic amendments. Four years after organic matter additions ended, maize yields were not significantly different irrespective of additions of the quality of organic amendments. Even four years after organic matter…