Long‐term tillage and manure application can alter a soil's ability to sequester nutrients and mineralize C and N. A laboratory incubation study (C and N mineralization) evaluated the long‐term impact of poultry litter (PL) application (>10 yr) and tillage practice (>25 yr). Soil chemical properties (pH, total C, total N, and Mehlich‐1 extractable P, K, Ca, and Mg) were also assessed. Soil was collected (0–5‐, 5–10‐, and 10–20‐cm depths) from continuous soybean [ Glycine max (L.) Merr.] and corn ( Zea mays L.) systems managed under conventional tillage (CT) or no‐till (NT) with either PL or inorganic fertilizer (IF) applications. The study was located in northeast Alabama on a Hartsells fine sandy loam (a fine‐loamy, siliceous, subactive, thermic Typic Hapludult). Poultry litter and NT increased soil nutrients (N, P, K, Ca, and Mg), primarily at the 0‐ to 5‐cm depth. No‐till concentrated nutrients near the soil surface as opposed to the more even distribution seen under CT. The NT‐PL treatment had higher soil C for corn and soybean (2.25 and 1.83 g kg ⁻¹ C, respectively), followed by NT‐IF (1.73 and 1.11 g kg ⁻¹ C, respectively). Carbon and N mineralization was higher at the 0‐ to 5‐cm depth for NT and CT compared with lower depths. Long‐term PL application increased C and N mineralization more than IF. As depth increased, more C and N mineralization occurred under CT due to plow layer mixing. Results indicated that long‐term tillage with PL application can increase soil C and N mineralization, nutrient retention, and organic matter.

Manure applications can benefit crop productivity by adding required nutrients and organic matter to soil. There is a paucity of information on how soil microbial community dynamics will be altered by the application of manure to different landscape positions. Thus, an in situ field study was conducted during the summer and winter months to evaluate microbiological properties of three soil types that have evolved because of different landscape positions in an agricultural field. The three Coastal Plain soils investigated were Bama (sandy loam), Lynchburg (loam), and Goldsboro (loam) representing the landscape position of a summit, drainageway, and sideslope, respectively. Composted dairy manure was incorporated into in situ soil cores at a rate of 350 kg N ha⁻¹ and compared with unamended controls. Soil microbial biomass N and dehydrogenase enzyme activity were determined to evaluate changes in the microbial biomass size and activity, whereas phospholipid fatty acid analysis was used as an indicator of the microbial community structure. Addition of composted dairy manure increased microbial activity and N immobilization, representing a shift in microbial response resulting from changes in substrate availability. This was most evident during summer months, with the composted dairy manure increasing dehydrogenase enzyme activity 21% and microbial activity 20% compared with without manure, suggesting that seasonal timing of application will influence microbial activity. Microbial properties were also impacted by landscape position. The drainageway landscape position soil, a loam, had the highest microbial biomass and microbial activity. Changes in microbial community structure using phospholipid fatty acid profiles were evaluated with canonical discriminate analysis. This analysis indicated that a shift in microbial community structure occurred between season, manure application, and landscape position. Findings from this study suggest that changes in soil variability from landscape positions and season can impact the growth and dynamics of the microbial community when manure is applied to agricultural fields.

Water availability is a major constraint affecting the growth and yield of crops/plants worldwide. Some studies have shown that specific strains of free-living bacteria found in the plant rhizosphere can improve the tolerance of plants during water stress. A greenhouse study was conducted to evaluate the effects of two mixtures of plant growth-promoting rhizobacteria (PGPR) and two fertilizer sources on root establishment and biomass production of corn (Zea mays L.) during the early growth stages under drought conditions. This study was conducted as a randomized complete block design with five replications. Treatments included three irrigation levels (watering every 3, 6, and 12 days), two fertilizer materials (poultry litter and urea), and two PGPR strain mixtures and a non-inoculated control. Irrigation significantly affected plant growth and biomass accumulation of corn at the V6 to VT stages. Compared to poultry litter, urea application significantly increased plant height, leaf chlorophyll (SPAD readings), leaf area, and plant biomass. PGPR significantly improved plant height, stem diameter, leaf chlorophyll, and root morphology under drought stress conditions. The results demonstrate that PGPR inoculation can stimulate enhanced plant root development (through the production of plant growth regulators), thereby resulting in better absorption of water and nutrients from the soil.

A greenhouse study was conducted to evaluate the effects of plant growth-promoting rhizobacteria (PGPR) on root establishment and biomass production of corn (Zea mays L.) using three fertility sources (poultry litter (PL), biosolids, and urea). Applying PL significantly improved root morphological parameters and increased plant biomass at the V4, V6, and VT growth stages when compared to the other fertility sources. At the V4 stage, PGPR stimulated root growth and enhanced aboveground biomass with urea and PL, while no differences were observed with biosolids. At the V6 stage, PL, biosolids, and urea with PGPR significantly increased some growth parameters (e.g., plant height, leaf area, and root morphology). However, at the VT stage, PGPR’s influence on plant growth was minimal regardless of fertility source. Applying the fertility sources at 135 kg N ha⁻¹ may have masked PGPR’s influence on corn growth as the plants reached their later vegetative growth stages.