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Corn (Zea mays) biomass accumulation and nutrient uptake by the six-leaf collar (V6) growth stage are low, and therefore, synchronizing nutrient supply with crop demand could potentially minimize nutrient loss and improve nutrient use efficiency. Knowledge of corn's response to nutrient stress in the early growth stages could inform such nutrient management. Field studies were conducted to assess corn recovery from when no fertilizer application is made until the V6 growth stage, and thereafter, applying fertilizer rates as those in non-stressed conditions. The early season nutrient stress and nonstress conditions received the same amount of nutrients. As the availability of nutrients for plant uptake is largely dependent on soil moisture, corn recovery from the early season nutrient stress was assessed under different soil moisture regimes induced via irrigation scheduling at 50% and 80% field capacity under overhead and subsurface drip irrigation (SSDI) systems. Peanut (Arachis hypogaea) was the previous crop under all conditions, and the fields were under cereal rye (Secale cereale) cover crop prior to planting corn. At the V6 growth stage, the nutrient concentrations of the early season-stressed crops, except for copper, were above the minimum threshold of sufficiency ranges reported for corn. However, the crops showed poor growth, with biomass accumulation being reduced by over 50% compared to non-stressed crops. Also, the uptake of all nutrients was significantly lower under the early season nutrient stress conditions. The recovery of corn from the early season nutrient stress was low. Compared to non-stress conditions, the early season nutrient stress caused 1.58 Mg ha-1 to 3.4 Mg ha-1 yield reduction. The percent yield reduction under the SSDI system was 37.6-38.2% and that under the overhead irrigation system was 11.7-13%. The high yield reduction from the early season nutrient stress under the SSDI system was because of water stress conditions in the topsoil soil layer. The findings of the study suggest ample nutrient supply in the early season growth stage is critical for corn production, and thus, further studies are recommended to determine the optimum nutrient supply for corn at the initial growth stages. [ABSTRACT FROM AUTHOR]

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As plant litter decomposes, its mass exponentially decreases until it reaches a non-zero asymptote. However, decomposition rates vary considerably among litter types as a function of their overall quality (i.e., carbon:nitrogen (C:N) ratio and litter chemistry). We investigated the effects of hairy vetch (HV: Vicia villosa Roth):cereal rye (RYE: Secale cereale L.) biomass proportions with or without broadcasted poultry manure on overall litter quality before and during decomposition. As HV biomass proportions increased from 0 to 100%, the relative susceptibility of HV:RYE mixtures to microbial decomposition increased due to: (i) decrease in the initial C:N ratio (87:1 to 10:1 in 2012 and 67:1 to 9:1 in 2013), (ii) increase in the non-structural labile carbohydrates (33 to 61% across years), and (iii) decrease in the structural holo-cellulose (59 to 33% across years) and lignin (8 to 6% across years) fractions. Broadcasted poultry manure decreased the overall initial quality of HV-dominated litters and increased the overall initial quality of RYE-dominated litters. Across all HV:RYE biomass proportions with or without poultry manure, chemical changes during litter decay were related to proportional mass loss. Therefore, the relative decrease in carbohydrates and the concomitant increase in holo-cellulose and lignin fractions were more pronounced for fast decomposing litter types, i.e., litters dominated by HV rather than RYE. While our results suggest possible convergence of litter C:N ratios, initial differences in litter chemistry neither converged nor diverged. Therefore, we conclude that the initial chemistry of litter before decomposition exerts a strong control on its chemical composition throughout the decay continuum. [ABSTRACT FROM AUTHOR]

• Cover crop residue water retention properties changes during decomposition. • Cover crop residue lignin concentrations can be used as a proxy for water retention properties. • Cover crop surface residues experience extreme diurnal fluctuations in moisture and temperature compared to underlying soils. • Diurnal variations in decomposition tracked variations in cover crop residue moisture content. • Cover crop decomposition in no-till systems is strongly moisture-limited. The effect of cover crop (CC) surface residues on water, carbon, and nitrogen cycling in no-till systems depends in part on the water retention properties of decomposing residues and the extent of decomposition. This study (1) examined the effect of decomposition on residue water retention properties; (2) characterized diurnal variations in residue decomposition rates in response to changes in soil-residue-air environmental conditions; and (3) examined the diurnal relationships between cover crop surface residue decomposition and residue environment (moisture and temperature). Maximum gravimetric water content (θ g) and characteristic water release curves were determined for red clover (Trifolium pratense L.) and cereal rye (Secale cereale L.) residues collected at 0, 4, 10, and 16 weeks after termination for red clover, and at 2, 5, and 18 weeks for cereal rye. In addition, residue carbon dioxide (CO 2 -C) flux, along with soil-residue-air environmental conditions, were measured diurnally for red clover at 4, 10, and 16 weeks after termination, and for cereal rye at 5 weeks after termination. Maximum residue θ g decreased as decomposition progressed. Cover crop residue decomposition also influenced water release curves such that the water retained at any given water potential (ψ r e s i d u e) declined with increasing decomposition. These decomposition-associated changes in residue water retention properties were strongly related to residue lignin concentrations. Cover crop surface residue CO 2 -C flux showed distinct diurnal patterns that were strongly related to ψ r e s i d u e or residue θ g. At a diurnal scale, residue CO 2 -C flux increased during the nighttime from 18:00 to 06:00 h when residues gain moisture from the atmosphere and soil, and decreased during the daytime from 06:00 to 18:00 h when residues lost moisture via evaporation. Increase in temperature decreased residue CO 2 -C flux due to moisture limitations. Therefore, CC surface residue decomposition models must address both diurnal changes in ψ r e s i d u e and the changes in water retention properties as residues decompose. [ABSTRACT FROM AUTHOR]

Soil microorganisms play a critical role in cover crop (CC) residue decomposition and nutrient cycling in agroecosystems. However, the impact of CC residue management and dry-wet cycles on soil and residue microbiota and their potential ecosystem functions is largely unknown. To fill these knowledge gaps, an incubation experiment was conducted with two CC residues, crimson clover (Trifolium incarnatum L.) and cereal rye (Secale cereale L.), and two residue placements (incorporated vs surface-applied). Each CCs by placement treatment was subjected to four dry-wet cycles (20-d each) for a total of 80-d. Crimson clover residues had higher water storage capacities than cereal rye, and the rate at which water was lost from surface-applied CC residues increased after each successive wetting event. Rapid drying of surface-applied CC residues quickly suppressed CO 2 fluxes, which increased immediately upon rewetting. Incorporated CC residues maintained water content for longer duration than surface-applied residues and showed greater colonization by soil prokaryotes and saprophytic fungi. Thus, significantly more C and N were mobilized from incorporated residues by 80-d than from surface-applied residues (p < 0.05). Due to differences in residue chemistry, CC residue types have a stronger impact on soil N levels than residue placement. Thus, residue chemistry strongly influenced soil prokaryotic and fungal diversity, community structure, and functionality. While crimson clover-amended soils (N-rich environments) were dominated by copiotrophs, oligotrophs dominated cereal rye-amended soils (N-poor soil environments). On the other hand, residue placement may have a greater effect than residue type in determining residue microbiota, particularly prokaryotes. Based on these findings, we can conclude that the effect of residue placement on C and N mineralization during repeated dry-wet cycles is primarily explained by differences in water dynamics between incorporated and surface-applied CC residues. • Cover crop residue type, residue placement, and dry-wet cycles strongly influenced microbial processes and functions. • Incorporated residues mineralized more C and N than surface-applied residues. • C mineralization from surface-applied residues quickly dropped following rewetting due to rapid loss of water. • Residue type influenced soil prokaryotic and fungal diversity, community structure, and functionality. • When incorporated, residues are more colonized by soil prokaryotes and saprophytic fungi. [ABSTRACT FROM AUTHOR]