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Producers make the decision to adopt a particular agricultural practice within a range of social, economic, environmental, and agronomic constraints. The semiarid regions of the US northern Great Plains are dominated by dryland farming practices and the traditional practice has been to rotate small-grain cereals with summer fallow; however, producers are moving away from this practice. The area of fallow in northeastern Montana decreased by one-third and the area of pulse crops increased nearly six-fold during 2001–2012. We previously identified two key practices that are indicative of regionally changing agricultural practices: (1) the broad-scale adoption of cereal–pulse sequences, and (2) the conversion from continuous strip-cropping to block managed cereal-based sequences. Here, we examined the adoption of these two practices from a spatio-temporal perspective to determine if the observed patterns were consistent with those expected from a priori processes: random occurrence, spread and adoption of the practices due to social interaction as described in innovation diffusion theory, or adoption based on environmental factors. Our results suggest that the adoption and spread of both practices were likely constrained by the suitability of the physical environment. Available water, in particular, exerts a fundamental control on the decision whether or not to adopt either practice. We also found evidence for the expansion of these practices due, in part, to social factors, particularly during the early period of adoption. We conclude that producers made the decision whether or not to adopt these practices primarily as a function of environmental suitability and, to a lesser extent, within the context of social interactions. [ABSTRACT FROM AUTHOR]

Highlights: [•] We examined 2- and 3-year cropping sequences in northeast Montana during 2001–2012. [•] Cropping sequences were identified by using string searching algorithms. [•] Farmers grew more cereal and fallowed less, but did not adhere to specific sequences. [•] Cereal–pulse sequences increased dramatically. [•] Strip cropped cereal–fallow sequences were frequently converted to block management. [ABSTRACT FROM AUTHOR]

We conducted this study to quantify long-term cropping related changes in soil organic carbon (SOC) stocks and characterize the optical properties of dissolved organic matter (DOM) after a decadal on-farm experiment in Montana, USA. Soil samples (0–50 cm) were collected from minimum till (MT) and no-till (NT) fields under fallow-winter wheat (Triticum aestivum L.; F-W) and pea-winter wheat (Pisum sativum L.; P-W) rotations. Stocks of SOC (0–50 cm) averaged 65.6 Mg C ha−1 and 60.6 Mg C ha−1 for P-W and F-W, respectively. The net SOC accretion rate for P-W equated to 0.61 Mg ha−1 yr−1 relative to F-W. We used absorbance spectroscopy and excitation-emission matrices to characterize DOM composition of samples collected from MT F-W and NT P-W. The two cropping systems exhibited similar estimates of aromaticity (absorbance at 254 nm; 0.33–0.39 a.u.) and humification index (1.83–1.86). Parallel factor (PARAFAC) analysis revealed humic-like (C1, C2), monolignol/amino acid-like (C3), and amino acid-/tannin-like (C4) components with equivalent fluorescent intensities among MT F-W and NT P-W. Fluorescence efficiencies increased with depth, suggesting a shift from larger, plant-like material to smaller, microbial-derived precursors. Overall, we found DOM composition to be minimally affected by cropping systems in this semiarid climate of the northern Great Plains. • Annual cropping sequestered more SOC than fallow-based systems over a 10 year period. • The accretion of SOC within annual cropping occurred at a rate of 0.61 Mg ha−1 yr−1. • Soil DOM bulk optical properties did not respond to changes in decadal SOC stocks. • PARAFAC analysis identified four different fluorescent components of the EEMs. • Sub-soil DOM was comprised of low molecular size constituents. [ABSTRACT FROM AUTHOR]

Organic matter (OM) oxidized by slightly alkaline KMnO 4 , termed permanganate-oxidizable carbon (POXC), has recently emerged as a standardized indicator of active, labile carbon within soil quality frameworks. Yet, qualitative information on POXC, particularly in semiarid drylands, is very scarce. The aim of this study was to characterize POXC within three long-term field experiments in Montana, USA: (i) across a wide range of edaphic (e.g., % clay) and management conditions (e.g., cropping intensity) ( n  = 148); and (ii) to identify the molecular composition of soil OM before and after KMnO 4 treatment using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The content of POXC was significantly greater under perennial (382–685 mg/kg) or annual cropping (404–607 mg/kg) than fallow-wheat (359–543 mg/kg) systems. Soil OM changes, however, were equally or better expressed when considering soil organic carbon (SOC) concentration. The occurrence of POXC paralleled SOC ( R  = 0.87; P  < 0.001) and total nitrogen (TN) ( R  = 0.82; P  < 0.001) concentrations, regardless of soil textural differences. The ESI FT-ICR MS analyses of aqueous soil extracts indicated that the KMnO 4 reaction oxidized dissolved OM of diverse molecular character. OM molecular composition after KMnO 4 treatment was enriched by strongly reduced chemical constituents (O/C < 0.4) at greater condensed aromaticity (AI > 0.67) and hydrogen saturation (aliphatic composition; H/C > 1.5) across all heterogeneous groups (C c H h N n O o S s ). Although POXC is a rapid assay widely used for characterizing soil OM dynamics, it may not provide a clear advantage over SOC concentration in semiarid drylands. The view of POXC as a merely labile, simple biodegradable OM fraction needs to be reconsidered. [ABSTRACT FROM AUTHOR]

Agricultural is essential to feed the human world but it can also degrade the physical world. Therefore, we need widely-accepted metrics to assess how prospective practices influence sustainability. We hypothesized that emergy and energy analyses considered together provide a robust, comprehensive measure of sustainability, and evaluated this hypothesis using findings from two field studies in the semiarid prairie region of Canada: a systems experiment including nine different 3-yr cropping rotation systems and a stubble experiment involving five preceding crop stubbles treatments with three nitrogen (N) addition levels. The grain yield emergy transformities of rotation systems with pulses, ranging from 0.68 to 0.83 E+05 sej J −1 , were 32% lower ( P < 0.05) than rotations without pulses. Significantly lower grain transformity of durum wheat grown on pulse stubbles than grown on durum wheat stubble were observed for both the systems and stubble experiments, suggested a higher crop production efficiency conferred by previous pulse crops. The emergy sustainability index (ESI) of Fallow-Durum wheat-Pea (F-D-P) rotation (1.94) was 1.3–2.2 times that of other rotations, while the continuous rotations increased ESI from 1.00–1.11 to ESI ΔQ of 2.00–2.21 by considering the storage increase (Δ Q ) of the system, i.e. soil organic carbon (SOC). The grain yield/energy input ratio (G/I) and energy output/energy input ratio (O/I) for F-D-P rotation (775 g MJ −1 and 12.9, respectively) were significantly ( P < 0.05) higher than those of all other rotations for its low energy input, which was obtained at the cost of huge SOC decrease. Modified energy use efficiency indices, G/I ΔSOC and O/I ΔSOC , were proposed in the present study to include the effect of SOC change (ΔSOC) in energy use efficiency by regarding ΔSOC as energy input where the system depleted SOC and as energy output where SOC accumulated. The G/I ΔSOC and O/I ΔSOC ratios for continuous rotations were significantly ( P < 0.05) higher than those of other rotations, indicating higher energy use efficiency in continuous rotation systems. Therefore, ESI ΔQ and O/I ΔSOC are recommended as sustainability indicators in emergy and energy analysis respectively, and we recommend that emergy and energy analysis should be done and considered together to have a more informative assessment of relative sustainability and efficiency of cropping systems. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) plays a critical role in the cycling of nutrients and long-term agricultural sustainability. The composition of DOM in soil is likely altered due to management, yet there is limited knowledge on the effect of long-term cropping on DOM chemical character. Here, we characterized water extractable DOM composition along a gradient of soil organic carbon (SOC) affected by differing cropping and tillage intensity in a semiarid climate of the northern Great Plains, USA. Soil samples (0–10, 10–20, 20–30 cm) were collected from conventional till-fallow winter wheat ( Triticum aestivum L.; F till -W), no-till spring pea/oilseed-wheat ( Pisum sativum L.; P g /O-W), and no-till continuous wheat (W-W) fields, and analyzed using UV/Vis absorbance and excitation-emission matrix fluorescence spectroscopy. The concentration of DOM decreased with depth and was significantly greater ( P < 0.05) under W-W or P g /O-W than F till -W. The absorbance at 254 nm (Abs 254 ), a proxy for DOM aromatic nature, indicated that aromaticity decreased with depth and lower biomass-C inputs (i.e. W-W ≥ P g /O-W ≥ F till -W). Multidimensional parallel factor (PARAFAC) analysis revealed humic-like (C1, C2), monolignol-like (C3), and protein/tannin-like (C4) components with varying fluorescence intensities as a function of cropping system and soil depth. DOM humification, indicated by the humification index (HIX), increased significantly with depth ( P < 0.05) and was higher for F till -W (2.95) than W-W (2.61) or P g /O-W (2.28). Overall, DOM became depleted of plant-derived constituents and was enriched by more decomposed, condensed substances in F till -W, as compared to W-W or P g /O-W soils. DOM composition is strongly affected by cropping intensity and such changes are important drivers controlling SOC accretion in arable soils. [ABSTRACT FROM AUTHOR]