Michael A. Blazier

Straw harvesting, fertilization, and fertilizer type alter soil microbiological and physical properties in a loblolly pine plantation in the mid-south USA

Harvesting fallen needles (straw) in loblolly pine (Pinus taeda L.) plantations provides forest owners with a substantial source of income, but this practice and the type of fertilizer used to replenish nutrients removed with straw harvests may alter soil microbiological and physical properties. This study was conducted to explore the influence of annual straw harvesting, fertilization, and fertilizer source (inorganic vs. broiler poultry litter) in a loblolly pine plantation in the mid-south USA on: (1) soil microbial biomass C, (2) soil dehydrogenase activity, and (3) key soil physical properties (soil strength, bulk density, porosity, aeration, soil moisture content, organic matter, and available water holding capacity). All treatments that included straw harvesting increased bulk density and reduced soil porosity. Annual straw harvesting conducted with annual fertilization of inorganic nitrogen and phosphorus fertilization was associated with the most pronounced increases in soil strength and reductions in organic matter, available water holding capacity, microbial biomass C, and dehydrogenase activity.

Mobility of Poultry Litter Phosphorus in a Coastal Plain Forest Soil

Abstract Loss of phosphorus (P) to surface waters from forest soils fertilized with P-rich poultry litter (PL) is likely less than P loss from pasture because forest soils are typically lower in P. This study examined P mobility where PL was applied to forest soil in amounts constituting disposal. Triplicate plots (13.4 × 3.1 m) of 4-year-old loblolly pine (Pinus taeda) were amended once per year at 0, 5, 10, and 20 Mg PL/ha in 1996 and 1997–2001. Surface soil (0–15 cm) P was monitored annually during the application period and at varying frequencies until 2013. Cores to 1 m were taken in 2002 and 2013. Phosphate sorption in surface and subsoil was measured, and transport in surface soil was investigated. Sorption after 24 h followed the Langmuir model, which described retention during transport better than a linear model but not as well as a two-site kinetic Langmuir model with sorption capacity based on oxalate-extractable aluminum (Al) + iron (Fe). Phosphate sorption was least in 15- to 30-cm depth soil; sorption increased deeper into the Bt horizon. Neither the increase nor the decrease in surface soil P showed a clear effect of sorption nonlinearity. Treatment effects were significant to a depth of 45 cm in 2002 except for organic P (surface only). The profile distribution of P was generally consistent with sorption, with some evidence of preferential flow. Leaching from 2002 to 2013 was slow, moving P in 20-Mg ha−1 plots to 60 cm. However, leaching was likely increased by initial concentrations and fast relative to tree uptake.

Soil Gas Efflux in Perennial Bioenergy and Conventional Agricultural Crops in the Lower Mississippi Alluvial Valley

ABSTRACT The Lower Mississippi Alluvial Valley (LMAV) has favorable attributes for producing biofuels. Two study sites were established on retired agricultural fields in the LMAV to explore switchgrass (SWITCH) and eastern cottonwood (CTWD) as biofuel feedstocks. A soybean-sorghum rotation (CROP) was also established as a conventional cropping system. Soil efflux gas (carbon dioxide [CO2], methane [CH4], and nitrous oxide [N2O]), microbial biomass carbon (Cmic) and dehydrogenase activity were measured for two years. Cumulative growing-season soil CO2 efflux of SWITCH exceeded that of CROP; SWITCH had higher daily CO2 efflux than CTWD and CROP in some months. SWITCH and CTWD had greater Cmic than CROP at both sites. Soil CH4 and N2O efflux rates were low for much of the study, with only short-term differences in soil CH4 observed. Converting these retired agricultural sites to SWITCH increased soil CO2 efflux relative to CROP, with increases attributable to greater plant and microbial respiration.

Assessment of Labile Organic Carbon in Soil Using Sequential Fumigation Incubation Procedures

Management practices and environmental changes can alter soil nutrient and carbon cycling. Soil labile organic carbon, a readily decomposable C pool, is highly sensitive to disturbance. It is also the primary substrate for soil microorganisms, which is fundamental to nutrient cycling. Due to these attributes, labile organic carbon (LOC) has been identified as an indicator parameter for soil health. Quantifying the turnover rate of LOC also aids in understanding changes in soil nutrient cycling processes. A sequential fumigation incubation method has been developed to estimate soil LOC and potential C turnover rate. The method requires fumigating soil samples and quantifying CO2-C respired during a 10 day incubation period over a series of fumigation-incubation cycles. Labile organic C and potential C turnover rate are then extrapolated from accumulated CO2 with a negative exponential model. Procedures for conducting this method are described.

Phosphorus Runoff from Coastal Plain Forest Soil in Louisiana

ABSTRACT Although not a common practice, poultry litter (PL) may be used for forest fertilization. Despite usually low soil phosphorus (P) and runoff under forest, repeated or high rates of PL application may cause appreciable P loss. Phosphorus in natural runoff under loblolly pine (Pinus taeda L.) fertilized with PL, downslope P enrichment of surface soil, and P runoff during simulated rainfall (a) 5 years post-application and (b) where straw was harvested were measured. Relationships of runoff P (dissolved reactive, dissolved, and total) concentration and load to soil P (Bray 2 and water-extractable in two depths) and hydraulic conductivity were examined. Post-application loss of P was lower than reported for pasture. There was little downslope P movement. Runoff P was related to the corresponding form of soil P (R2 = 0.28–0.48) but likely affected by P leached from the O horizon. Loads could be estimated from regressions.

Poultry Litter Fertilization Impacts on Soil, Plant, and Water Characteristics in Loblolly Pine (Pinus taeda L.) Plantations and Silvopastures in the Mid-South USA

Increasing global human populations and wealth have resulted in increased demands for animal protein and widespread use of confined animal feeding operations to meet added animal protein consumptive demands. Disposal of animal wastes from these operations can be ecologically and environmentally problematic (Kellogg et al., 2000; Roberts et al., 2004; Shober & Sims, 2003). Poultry production is an important source of this protein and is a major agricultural industry in the United States. The United States is the world’s largest producer and second largest exporter of poultry meat (UDSA Economic Research Service, 2009). Four-fifths of the United States poultry industry is comprised of broiler meat production. Broiler meat production is largely concentrated in Southeastern states (Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas and Virginia), with 82% of U.S. broiler production occurring in these states (National Agricultural Statistic Service, 2008). Broiler production results in the generation of massive amounts of litter, a mixture of feces, feed, feathers and bedding materials such as straw, peanut or rice hulls, and wood shavings (Gupta et al., 1997; Weaver, 1998). The U.S.A. poultry industry produces more than 11 million Mg of litter per year (Cabrera & Sims, 2000). Broiler poultry litter contains several plant macroand micronutrients (Table 1), which makes it desirable as an agricultural fertilizer (Sistani et al., 2008). Following removal from poultry production facilities, litter is commonly applied to nearby pastures, hay meadows, and agricultural crops such as corn and cotton to increase crop production and quality (Harmel et al., 2004; Sims & Wolf, 1994). Applications of poultry litter ranging from 4.5 to 11.2 Mg ha-1 yr-1 are common to supplement or replace inorganic annual fertilizer additions to pastures (Adams et al., 1994). Thus, poultry litter application is an efficient and potentially cost-effective method for improving forage production within the vicinity of production facilities, which helps to sustain non-poultry related agriculture economies in poultry producing regions. Substitution of broiler litter for inorganic fertilizers continues to increase in the southeastern U.S.A. as prices of inorganic fertilizers escalate (Funderberg, 2009).