<p> Cover crops and crop residue play a multifunctional role in improving soil hydrological properties, soil water storage and water use efficiency (WUE). This study was conducted to better understand the role of crop residue and cover crop on soil properties and soil water dynamics. The study was conducted at the USDA-ARS North Central Agricultural Research Laboratory, located in Brookings, South Dakota. Two residue removal treatments that include low residue removal (LRR) and high residue removal (HRR) were established in 2000 with randomized complete block design under no-till corn (Zea mays L.) and soybean (Glycine max L.) rotation. In 2005, cover crop treatments which include cover crops (CC) and no cover crops (NCC) were integrated into the overall design. Soil samples were collected in 2014, 2015 and 2016. Data from this study showed that LRR treatment resulted in lower bulk density (BD) by 7 and 9% compared to HRR in 2015 and 2016, respectively, for 0-5 cm depth. Similarly, LRR treatment significantly reduced soil penetration resistance (SPR) by 25% in 0-5 cm depth compared with HRR treatment. In addition to this, LRR treatment significantly increased soil organic carbon (SOC) concentrations and total nitrogen (TN) by 22 and 17%, respectively, in 0-5 cm. Similarly, CC treatment resulted in lower BD and SPR by 7% and 23%, respectively, in 0-5 cm depth in 2015 compared with NCC treatment. The LRR significantly increased soil water infiltration by 66 and 22% compared to HRR in 2014 and 2015, respectively. Similarly, the CC treatment significantly increased infiltration by 82 and 22% compared to the NCC in 2014 and 2015, respectively. The significant impact of a crop residue was observed on soil water retention (SWR) in 2014 and 2015 for the 0-5 cm depth. The LRR and CC treatments increased the soil volumetric moisture content (VMC) and soil water storage (SWS) on the surface 0-5 cm depth. However, the trend was not always significant during the growing season. The CC treatment significantly impacted the soybean yield by 14% and WUE by 13% compared with NCC treatment. Some interaction of residue by cover crops was observed on BD, SPR, VMC, and SWS, which showed that the use of cover crops with LRR can be beneficial in improving the soil properties.</p>

<p> A field experiment was established during 2014 in Northeast Arkansas to evaluate the benefits of cover crop and tillage management for enhanced yield and soil quality. Cover crop management included cereal rye, wheat and crimson clover, and a winter fallow. Tillage management included tillage and no-tillage.</p><p> In the 2015 and 2016 seasons yield was not significantly changed by different tillage treatments. Cover crop out yielded no cover crop at the A-State site in the 2016 season. Organic matter and active carbon were significantly influenced by tillage treatments. Physical and biological properties were significantly increased with cover crops compared with no cover crops in the 2015 and 2016 seasons. Physical properties were also significantly improved with no-tillage as compared with tillage in the 2015 and 2016 season. Biological properties were significantly influenced by different tillage treatments in the 2015 season.</p>

<p> The benchmark Barnes soil series is an extensive northern Great Plains upland Hapludoll that is vital to the region. Accelerated erosion has degraded Barnes agricultural soil quality, but with unknown extent or severity. Samples from three extensive Barnes soil map units, stratified by evapotranspiration values, were collected to 50 cm and analyzed for chemical, morphologic, and physical properties germane to edaphic function. Multi-scale terrain attributes and remote-sensed soil proxies, and geologic covariates were implemented with Cubist to model soil properties. Best models included SOC, EC, pH, SOC-IC, and sand content. Pedons were classified with a clustering algorithm into six classes. Linear discriminant analysis of covariates and subsequent prediction of landscape grouped classes had moderate to nearly substantial agreement with field observations; only fair agreement was attained for all classes. Detailed morphologic observations confirmed extensive topsoil erosion for some landscape positions that merit investigation of soil function and potential state change.</p><p>

Soil organic matter (SOM) plays an essential role in agriculture and environments. Humic substance (HS) is a major component of SOM. This research was to investigate HS using solid state nuclear magnetic resonance (NMR). Several experiments were concluded, and their results and conclusions are reported below. 13C direct-polarization magic-angle-spinning (DP/MAS) corrected by cross-polarization spin-lattice relaxation time (CP/T1) experiments with total sideband suppression (TOSS) were found to be quantitative. None of eight models proposed in the literature totally match compositions determined with this technique. Qualitative and quantitative analyses of HAs with five different 13C solid-state NMR techniques were assessed using different HAs. The techniques compared are: (1) DP/MAS at 13 kHz, (2) conventional CP/MAS at 5 kHz, (3) ramp-CP/MAS at 8 kHz, (4) CP/TOSS at 4.5 kHz, and (5) DP/MAS corrected by CP/T1-TOSS. DP/MAS or DP/MAS corrected by CP/T1-TOSS was used as a quantitative reference. Ramp-CP/MAS and CP/TOSS gave acceptable qualitative results. Conventional CP/MAS spectra at 13C frequency of 75 MHz was neither qualitatively nor quantitatively. Crystalline poly(methylene) exists in an untreated peat, soil humin and HAs but little or none is present in fulvic acids (FAs). The similar characteristics of crystallites in tree leaves and SOM indicate that crystallites in SOM might be from the biopolymers of the protective parts of higher terrestrial plants. New information on the chemical and physical structures of a peat HA was obtained using a series of two-dimensional 1H-13 C heteronuclear correlation solid-state NMR (HETCOR) experiments. COO carbons appeared to be prominently in OCHn-COO environments, but some were also bonded to aromatic rings and aliphatic chains. Compositional heterogeneity was also studied by introducing 1H spin diffusion into the HETCOR experiment. The chain mobility of different HAs was investigated with 1D proton and 2D WISE (wideline separation) solid-state NMR techniques. 1D proton spectra only gave an overall estimate of the mobility of HAs. 2D WISE showed that HS mobility difference may arise from bound water.

Early decomposition-induced changes in fractionated tomato ( Lycopersicon esculentum Mill.), pepper (Capsicum anuum L.), and apple (Malus pumila Mill.) fruit skin cuticular materials were studied to evaluate the contribution of aliphatic cuticular materials to soil organic material (SOM). Aliphatic components of fresh cuticles, decomposed cuticles, and humic substances, were characterized using elemental analysis, 13C NMR, and FTIR, and underwent batch sorption experiments with phenanthrene. Bulk, dewaxed, non-saponifiable, and non-hydrolyzable fractions were isolated for analyses. Results from NMR and FTIR spectra for the fresh cuticles indicated that the cuticles of all the fruits studied were comprised of extractable lipids, polysaccharides and cutin and that pepper and apple fruit also contained non-saponifiable, non-hydrolyzable residues, likely to be cutan. Through decomposition, cutan increased in relative abundance, and cutin content decreased in relative abundance. Based on elemental analysis and NMR data, the polarity generally increased with decomposition, whereas the aliphaticity decreased with decomposition. The results of the decomposition experiment indicated that cutan from plant cuticles persisted through early decomposition and, as such, may contribute to the aliphatic nature of humic substances in SOM. The application of the cuticular fractionation method to humic substances (humic acids and humin) extracted from SOM confirmed the potential contribution of plant cuticular materials to humic materials in soil. NMR and elemental analysis revealed that the isolated fractions of the humic acid (HA) and humin (HU) were highly aliphatic, and spectroscopic data indicated that humic materials exhibited peaks and intensities similar to those observed in cuticle materials. Phenanthrene behavior in the cuticular materials demonstrated that Koc values decreased in the bulk and dewaxed fractions and increased in the saponified and acid-hydrolyzed fraction through decomposition. These decomposition-induced sorption changes made the sorption affinity of the cuticular fractions more comparable to those of the isolated fractions in the HAs and HU. Overall, all analyses performed on fractionated HA and HU exhibited similar trends to that fractionated cuticles, indicating the plant cuticular material is likely a primary contributor to the aliphatic structure in soil humic materials.

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