Brett L. Allen

Runoff phosphorus loss immediately after poultry manure application as influenced by the application rate and tillage.

Excessive or N-based application of poultry manure for crops may result in significant risk of P loss with surface runoff. This study assessed P loss immediately after poultry manure application to soybean [Glycine max (L.) Merr.] residue with and without tillage at eight Iowa fields. Manure from chickens (Gallus gallus domesticus) or turkeys (Melleagris gollopavo) was applied at intended rates of 0, 84, or 168 kg total N ha(-1) (total P was 0, 21-63, 50-123 kg P ha(-1), respectively) with three replications. Simulated rainfall (76 mm h(-1)) was applied to 3-m2 sections of larger field plots with 2 to 7% slope, usually within 2 d of application, to collect runoff during 30 min. Runoff was analyzed for concentrations of sediment, dissolved reactive P (DRPC), bioavailable P (BAPC), and total P (TPRC). Non-incorporated manure consistently increased (P < or = 0.10) concentrations of all runoff P fractions in five sites, but there were increasing trends at all sites, and on average manure increased DRPC, BAPC, and TPRC 32, 23, and 12 times, respectively, over the control. Tillage to incorporate manure reduced DRPC, BAPC, and TPRC by 88, 89, and 77% on average, respectively, although in non-manured plots tillage seldom affected DRPC or BAPC and often increased TPRC. Tillage increased sediment concentration in runoff but not enough to offset the benefits of manure P incorporation. Runoff P loads generally followed trends of runoff P concentrations but were more variable, and significant treatment effects were less frequent. Overall, incorporation of manure by tillage was very effective at reducing P loss during runoff events shortly after poultry manure application under the conditions of this study.

Soil total carbon and nitrogen and crop yields after eight years of tillage, crop rotation, and cultural practice

Information on the long-term effect of management practices on soil C and N stocks is lacking. An experiment was conducted from 2004 to 2011 in the northern Great Plains, USA to examine the effects of tillage, crop rotation, and cultural practice on annualized crop residue (stems + leaves) returned to the soil and grain yield, and soil total C (STC) and total N (STN) stocks at the 0–120 cm depth. Tillage practices were no-tillage (NT) and conventional tillage (CT) and crop rotations were continuous spring wheat (Triticum aestivum L.) (CW), spring wheat-pea (Pisum sativum L.) (W-P), spring wheat-barley (Hordeum vulgaris L.) hay-pea (W-B-P), and spring wheat-barley hay-corn (Zea mays L.)-pea (W-B-C-P). Cultural practices were traditional (conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height) and improved (variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height). Crop residue and grain yield were greater with CW and W-P than W-B-P and grain yield was greater with the traditional than the improved practice. The STC at 10–20 and 90–120 cm was greater with CW or W-P than other crop rotations in CT and greater with CW than W-B-P in NT. The STN at 20–40 cm was greater with W-P than CW and W-B-P in CT. With NT and the improved cultural practice, STN at 0–5, 5–10, 20–40, and 60–90 cm was greater with W-P and W-B-C-P than other crop rotations. The STN at 0–10 cm correlated with annualized crop residue and grain yield (r = 0.94–0.97, P ≤ 0.05). Increased crop residue returned to the soil increased soil C stock with CW and W-P and N stock with W-P, but removal of aboveground crop biomass for hay decreased stocks with W-B-P. Increased soil N stock had a beneficial effect on crop grain yield.

Simulating Dryland Water Availability and Spring Wheat Production under Various Management Practices in the Northern Great Plains

Agricultural system models are useful tools to synthesize field experimental data and to extrapolate the results to longer periods of weather and other cropping systems. The objectives of this study were: 1) to quantify the effects of crop management practices and tillage on soil water and spring wheat production in a continuous spring wheat system using RZWQM2 model under a dryland condition, and 2) to extend the results to longer term weather conditions and alternate cropping systems and management practices. Measured soil water content, crop yield, and total above ground biomass under different tillage and plant management practices were used to calibrate and validate the RZWQM2 model. The model showed inevident impacts of tillage and significant reduction in grain yield and biomass under late planting, in agreement with observed differences among treatments. The hydrologic analysis under long-term climate variability showed a large water deficit (32.3 cm) for the spring wheat crop; Fallowing the dryland every other year conserved 4.2 cm water for the following wheat year, of which only 1.7 cm water was taken up by wheat, resulting in a yield increase of 249 kg ha-1 (13.7%). However, the annualized average total yield decreased 782 kg ha-1 (43.1%) due to one year fallow; thus the spring wheat-fallow rotation was not economical. Other long-term simulations showed that optimal planting dates ranged from March 1 to April 10, and the seeding rate with optimum economic return was 3.71 and 3.95 × 106 seeds ha-1 for conventional and ecological management treatments, respectively.