Assessing the Effects of Agronomic Management Practices on Soybean (Glycine max L.) Post-Grain Harvest Residue Quality in the Lower Mississippi Delta

Livestock producers often resort to either baling or grazing of crop residues due to high hay prices and reduced supply of other forages and silage in the markets. Soil-water-crop management practices can affect residue nutrient qualities for its use as cattle feedstock. A two-year study (2018–2019) was conducted to investigate the effects of irrigation (AI, all row-irrigation; ARI, alternate row irrigation; and RF, rainfed) and planting pattern, PP (SR, single row; and TR, twin-row) on soybean (maturity group IV cv. 31RY45 Dyna-Gro) post-grain harvest residue quality such as crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), acid detergent lignin (ADL), net energy for maintenance (NEM), net energy for gain (NEG), net energy for lactation (NEL), total digestible nutrients (TDN), and relative feed value (RFV). Irrigation has a significant effect on CP, ADF, NDF, and TDN while PP affected only NDF. All the above parameters were significantly affected except NEM by the contrasting climate conditions, particularly during July through August coinciding with early crop reproductive stages and maturity. The RFV values ranged from 70.4 to 81.6 and this lower range was attributable to nutrient translocation to seeds and higher lignification during plant senescence towards the grain filling stage of the crop as good quality hay records over 120 RFV. These results indicate that both irrigation and weather during soybean seed development can alter post-grain harvest residue quality parameters, thereby playing critical roles in its RFV.

Influence of Application of Organic Residues of Different Biochemical Quality on Phosphorus Fractions in a Tropical Sandy Soil

Understanding phosphorus (P) dynamics in tropical sandy soil treated with organic residues of contrasting quality is crucial for P management using organic amendments. This research determined P fractions in a tropical sandy soil under the application of organic residues of different quality, including groundnut stover (GN), tamarind leaf litter (TM), dipterocarp leaf litter (DP), and rice straw (RS). The organic residues were applied at the rate of 10 t DM ha−1 year−1. The P fractions were examined by a sequential extraction procedure. Organic residue application, regardless of residue quality, resulted in P accumulation in soils. For unamended soil, 55% of total P was mainly associated with Al (hydr)oxides. Organic residue application, regardless of residue quality, diminished the NH4F-extractable P (Al-P) fraction, but it had a nonsignificant effect on NaOH-extractable P (Fe-P). The majority of Al-P and Fe-P fractions were associated with crystalline Al and Fe (hydr)oxides. NH4Cl-extractable P (labile P), NaHCO3-extractable P (exchangeable P and mineralizable organic P), HCl-extractable P (Ca-P), and residual P fractions in soil were significantly increased as a result of the incorporation of organic residues. The application of organic residues, particularly those high in ash alkalinity, increase soil pH, labile P, and Ca-P fractions. In contrast, applications of residues high in lignin and polyphenols increase residual P fraction, which is associated with organo-mineral complexes and clay mineral kaolinite.

Effect of crop residue incorporation and crop residue quality on soil N2O emissions and respiration - A laboratory measurement approach

<p>Crop residues are a significant source for soil N<sub>2</sub>O emissions and major component affecting the C storage in arable soils. The balance between C sequestration and N<sub>2</sub>O emissions is delicate and depends on the type of residues and its management. Thus, residue management might be a feasible option to reduce the GHG footprint of crop production. However, the mitigation potential of residue management is highly variable and strongly affected by the crop residue quality (C and N content, C:N ratio, concentrations of lignin, cellulose and solutes), field management (incorporation depth, amount applied) as well as soil physical and soil biogeochemical properties. In the frame of the EU-ERAGAS project RESIDUEGAS, we investigated the impact of different crop residue qualities on soil respiration and reactive N fluxes as well as soil ammonium (NH<sub>4</sub><sup>+</sup>) and nitrate (NO<sub>3</sub><sup>-</sup>) concentrations in order to test and possibly improve existing IPCC emission factors for GHG emissions from crop residue management.</p><p>In this study, we used sieved and homogenized soil columns of 8 cm height and 12 cm diameter filled with arable soil taken from a site near Gießen, Germany. Soil columns were incubated in the laboratory for 60 days at constant soil temperature (15°C) and water-filled pore space (60 %). Residues from nine different crops (oilseed rape, winter wheat, field pea, maize, potato, mustard, red clover, sugar beet, ryegrass) were re-wetted according to field moisture level and incorporated over approx. 0-4 cm topsoil layer one week after soil re-wetting and start of the measurements. The CO<sub>2</sub>, N<sub>2</sub>O (as well as NO and NH<sub>3</sub>) fluxes were measured automatically using a dynamic chamber approach. Soil samples were additionally analyzed for soil NH<sub>4</sub><sup>+</sup> and NO<sub>3</sub><sup>-</sup> concentrations at specific time steps during the experiment.</p><p>Re-wetting of the dry soil immediately resulted in a sharp increase of soil N<sub>2</sub>O and CO<sub>2</sub> emissions, which, however, was less pronounced than peak emissions following residue incorporation. Those were 4-5 times higher as compared to soil cores without residue amendment. Elevated emissions were short-lived and declined to background levels within 10 days for N<sub>2</sub>O and within 30 days for CO<sub>2</sub>. However, a small but significant period of higher than background N<sub>2</sub>O emissions was observed in the second half of the incubation period, which might be directly related to the decomposition of slower decomposable organic matter such as lignin and cellulose from crop residues. Generally, the emission magnitude was strongly affected by the crop residue quality, with highest N<sub>2</sub>O as well as CO<sub>2</sub> emissions being calculated for residues with a narrow C:N ratio. However, C:N ratio was not the single explaining factor. The range of calculated emission factors (fraction of cumulatively emitted N<sub>2</sub>O-N to crop residue N input) over a 60 day period was larger than the range given by IPCC in 2006.</p>

The interactive effects of soil disturbance and residue quality on soil nitrogen mineralisation in a tropical sandy soil

Soil conservation practices, such as reduced and no tillage, have been found to enhance soil nitrogen (N) sequestration through decreasing the rate of N mineralisation of added organic materials. Nitrogen mineralisation is not only affected by tillage, but also by the quality (chemical composition) of the organic residues. This study evaluated the interaction of residue quality and soil disturbance on N mineralisation in a sandy soil. A 112-day incubation experiment was conducted with two levels of soil disturbance (undisturbed and disturbed conditions) and five plant residue amendments of contrasting quality. The contrasting quality (N, lignin (L), and polyphenols (Pp)) (in g kg–1) amendments follow: (i) unamended; (ii) Sesbania grandiflora (N 44, L 173, Pp 9.2); (iii) Indigofera hirsuta (N 41, L 177, Pp 30); (iv) Dipterocarpus tuberculatus (N 8.2, L 203, Pp 71); and (v) Eucalyptus camaldulensis (N 9.7, L 126, Pp 110). Residues (ii) and (iii) were fresh legume leaves, while (iv) and (v) were non-legume leaf litter. Disturbance only significantly increased N mineralisation rates in the legume-residue treated soils (increases of 18.8% for S. grandiflora and 27.1% for I. hirsuta) during the early stage of decomposition (first 14 days). In the legume treatment, disturbance significantly increased the ammonification, but decreased nitrification in soil relative to undisturbed soils. The difference in patterns of ammonification and nitrification was more pronounced in the early than in the later period of decomposition. This indicated an inhibitory effect of soil disturbance on nitrification, which was particularly pronounced in the legume-treated soils. The Pp content of residues was the major quality parameter regulating the soil ammonium-N and nitrate-N concentrations. Minimum soil disturbance should be adopted under legume soil organic amendment so that both ammonification and nitrification components of N mineralisation process can occur normally, and nitrate-loving crops can take up N in the form of nitrate-N which will enhance their yields. Moreover, undisturbed conditions under legume organic amendments reduced N mineralisation, resulting in enhancing soil N sequestration.