Capacity of biochar application to maintain energy crop productivity: soil chemistry, sorghum growth, and runoff water quality effects.

Pyrolysis of crop biomass generates a by-product, biochar, which can be recycled to sustain nutrient and organic C concentrations in biomass production fields. We evaluated effects of biochar rate and application method on soil properties, nutrient balance, biomass production, and water quality. Three replications of eight sorghum [ (L.) Moench] treatments were installed in box lysimeters under greenhouse conditions. Treatments comprised increasing rates (0, 1.5, and 3.0 Mg ha) of topdressed or incorporated biochar supplemented with N fertilizer or N, P, and K fertilizer. Simulated rain was applied at 21 and 34 d after planting, and mass runoff loss of N, P, and K was measured. A mass balance of total N, P, and K was performed after 45 d. Returning 3.0 Mg ha of biochar did not affect sorghum biomass, soil total, or Mehlich-3-extractable nutrients compared to control soil. Yet, biochar contributed to increased concentration of dissolved reactive phosphorus (DRP) and mass loss of total phosphorus (TP) in simulated runoff, especially if topdressed. It was estimated that up to 20% of TP in topdressed biochar was lost in surface runoff after two rain events. Poor recovery of nutrients during pyrolysis and excessive runoff loss of nutrients for topdressed biochar, especially K, resulted in negative nutrient balances. Efforts to conserve nutrients during pyrolysis and incorporation of biochar at rates derived from annual biomass yields will be necessary for biochar use in sustainable energy crop production.

Effect of turfgrass establishment practices and composted biosolids on water quality.

Land application of composted municipal biosolids (CMB) enhances soil physical properties and turf establishment. Yet large, volume-based rates of CMB can increase nonpoint source losses of sediment and nutrients from urban soils to surface waters. The objectives were (i) to compare runoff losses of sediment, N, P, and organic C among contrasting establishment treatments for bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy, var. Tifway] and (ii) to evaluate relationships between runoff and soil measurements of N, P, and organic C. Three replications of seven establishment treatments were installed on an excavated slope (8.5%) under field conditions. Five treatments comprised sod transplanted from Tifway bermudagrass grown with and without CMB on soil with and without incorporation of CMB. Two other treatments were composed of Tifway sprigged in soil with and without CMB. Runoff from seven natural rain events was channeled into collection tanks for sampling and analysis. Runoff concentrations and mass loss of dissolved P and organic C forms were greater for CMB-amended sod than for sprigs planted in soil with or without CMB or treatments comprising sod established without CMB. In addition, a linear relationship (R(2) = 0.87) was observed between water extractable soil P of sodded and sprigged treatments and concentrations and mass losses of dissolved P in runoff. Transplanted sod reduced sediment loss compared with sprigged treatments and incorporation of CMB reduced sediment loss from sprigged treatments. Incorporation of CMB within soil on which sod grown without CMB was transplanted proved the best option for achieving benefits of CMB while reducing nutrient runoff loss compared to sod transplanted from Tifway grown with CMB.

Compartmentation of sucrose during radial transfer in mature sorghum culm.

BACKGROUND: The sucrose that accumulates in the culm of sorghum (Sorghum bicolor (L.) Moench) and other large tropical andropogonoid grasses can be of commercial value, and can buffer assimilate supply during development. Previous study conducted with intact plants showed that sucrose can be radially transferred to the intracellular compartment of mature ripening sorghum internode without being hydrolysed. In this study, culm-infused radiolabelled sucrose was traced between cellular compartments and among related metabolites to determine if the compartmental path of sucrose during radial transfer in culm tissue was symplasmic or included an apoplasmic step. This transfer path was evaluated for elongating and ripening culm tissue of intact plants of two semidwarf grain sorghums. The metabolic path in elongating internode tissue was also evaluated. RESULTS: On the day after culm infusion of the tracer sucrose, the specific radioactivity of sucrose recovered from the intracellular compartment of growing axillary-branch tissue was greater (nearly twice) than that in the free space, indicating that sucrose was preferentially transferred through symplasmic routes. In contrast, the sucrose specific radioactivity in the intracellular compartment of the mature (ripening) culm tissue was probably less (about 3/4's) than that in free space indicating that sucrose was preferentially transferred through routes that included an apoplasmic step. In growing internodes of the axillary branch of sorghum, the tritium label initially provided in the fructose moiety of sucrose molecules was largely (81%) recovered in the fructose moiety, indicating that a large portion of sucrose molecules is not hydrolysed and resynthesized during radial transfer. CONCLUSION: During radial transfer of sucrose in ripening internodes of intact sorghum plants, much of the sucrose is transferred intact (without hydrolysis and resynthesis) and primarily through a path that includes an apoplasmic step. In contrast, much of the sucrose is transferred through a symplasmic path in growing internode (axillary branch) tissue. These results contrast with the probable symplasmic path in mature culm of the closely related species, sugarcane. Phylogenetic variability exists in the compartmental path of radial transfer of sucrose in culms of the andropogonoid grasses.