To mitigate negative impacts on crop yield from water-saving limited irrigation, we tested the effect of two organic amendments on soil water holding capacity and nutrients. In an experimental maize field in northern Colorado, we tilled in conventional steer manure (30 Mg ha-1) and a fast-pyrolysis pine-wood biochar (30 Mg ha-1). We quantified impacts on soil moisture, total carbon and nitrogen, mineral nitrogen, available phosphorus, microbial biomass, and seven extracellular enzymatic activities (EEAs). Compared to the control, manure amendments increased gravimetric soil moisture by approximately 15%, total nitrogen by 10%, available phosphorus by 45%, and microbial biomass carbon by 15% (p<0.05). Relative to the control, biochar increased total soil carbon by 80% and altered EEAs (p<0.05). Biochar significantly increased α-1,4-glucosidase, β-D-cellobiohydrolase and β-1,4-Nacetylglucosaminidase and significantly decreased β-1,4-glucosidase and phosphatase activities (p<0.05). Despite the effects on soil moisture, nutrient availability, and microbial dynamics, neither amendment significantly impacted maize yield under limited irrigation. Ongoing measurements will allow us to fully assess longer-term impacts on yield.

No abstract

Extracellular enzymes catalyze biogeochemical reactions in soil, cycling carbon and nutrients in agricultural systems. Enzymes respond quickly to soil management, including organic amendment inputs, such as biochar, a charcoal-like solid byproduct of bioenergy production. In a previous agricultural field trial, a pine biochar amendment caused an approximately 40% decrease in the enzyme activities of β-glucosidase (BG) and phosphatase (PHOS). The large surface area of the pine biochar has the potential to sorb nutrients and other organic molecules. To test if sorption caused decreased enzyme activity, we used a laboratory assay to quantify the activity of two sorbed enzymes: BG and acid PHOS, involved in the cycling of carbon and phosphorous. The enzymes were incubated with three solid phases: (1) the high surface area pine biochar, (2) the agricultural soil, and (3) a low surface area grass biochar, for an additional comparison. We quantified the sorbed enzymes at pH 6, 7, and 8, using a Bradford protein assay, and measured the immobilized enzyme activities via high-throughput fluorometric analysis. After sorption onto pine biochar, detectable BG and PHOS activity levels dropped by over 95% relative to the soil, supporting direct sorption as one mechanism that reduces enzyme activity in biochar amended soil. This laboratory assay demonstrated that sorption could account for the lack of priming of native soil organic matter and changes in soil phosphorous cycling after pine biochar addition.

No abstract

Climate change is predicted to increase climate variability and frequency of extreme events such as drought, straining water resources in agricultural systems. Thus, limited irrigation strategies and soil amendments are being explored to conserve water in crop production. Biochar is the recalcitrant, carbon-based coproduct of biomass pyrolysis during bioenergy production. When used as a soil amendment, biochar can increase soil water retention while enhancing soil properties and stimulating food webs. We investigated the effects of coupled biochar amendment and limited irrigation on belowground food web structure and function in an irrigated maize agroecosystem. We hypothesized that soil biota biomass and activity would decrease with limited irrigation and increase with biochar amendment and that biochar amendment would mitigate the impact of limited irrigation on the soil food web. One year after biochar addition, we extracted, identified, and estimated the biomass of taxonomic groups of soil biota (e.g., bacteria, fungi, protozoa, nematodes, and arthropods) from wood-derived biochar-amended (30 Mg ha À1) and nonamended soils under maize with limited (two-thirds of full) and full irrigation. We modeled structural and functional properties of the soil food web. Neither biochar amendment nor limited irrigation had a significant effect on biomass of the soil biota groups. Modeled soil respiration and nitrogen mineralization fluxes were not different between treatments. A comparison of the structure and function of the agroecosystem soil food web and a nearby native grassland revealed that in this temperate system, the negative impact of long-term conventional agricultural management outweighed the impact of limited irrigation. One year of biochar amendment did not mitigate nor further contribute to the negative effects of historical agricultural management.