There have been no systematic experiments conducted in Nevada's water-limited environment that examined the simultaneous benefits of soil health and feed value derived from cool-season cover cropping systems. The objective of this study was to determine the influence of different annual cool-season cover crop systems on above and belowground biomass production, plant tissue carbon and nitrogen, forage nutritive value (crude protein, acid, and neutral detergent fiber), relative feed value (RFV), and short-term soil health indicators under irrigation in a semi-arid environment. Treatments (cover crop systems) were a fallow (no cover crop), five monocultures of rye (Secale cereale L.), winter lentil (Lens culinaris Medik.), arrowleaf clover (Trifolium vesiculosum Savi), white sweetclover (Melilotus alba), forage kale (Brassica oleracea L.), and two three-species mixtures in 50-25-25 seeding ratios (CCM 1: rye, winter lentil, arrowleaf clover; CCM 2: rye, white sweetclover, forage kale). Cover crop systems were arranged in an RCBD with three replications. Plots were fall seeded in Reno, NV early October of each year (2020 and 2021) and terminated at the end of July of 2021 and 2022, respectively. Averaged across years, aboveground biomass production was lowest for the monoculture of winter lentil (4104 kg DM ha−1; SE = 1551) compared to all other cover crop systems (average = 7593 kg DM ha−1; SE = 1551). Biomass carbon produced was lowest for winter lentil (1717 kg ha−1; SE = 675) relative to all other cover crop systems (average = 3227 kg ha−1; SE = 675). The CCM 1 system had a greater C/N ratio (36.3) than CCM 2 and the monocultures of winter lentil, arrowleaf clover, and white sweetclover (average = 24.9). Belowground biomass did not differ among cover crop systems (average = 3161 kg DM ha−1; SE = 962). Crude protein concentration was similar among cover crop systems but the RFV was greatest for forage kale (RFV = 165; SE = 4.0) among all cover crop systems. Soil total N and organic carbon concentration did not differ among cover crop systems but soil K concentration was greatest under fallow (428 mg kg−1 soil; SE = 26) relative to all other systems (average = 345.6 mg kg−1 soil; SE = 26). Soil microbial community biomass was not altered by cover crop system or its interaction with year. While the short-term impact of the cover crop systems on soil health indicators was minimal relative to the fallow system, the overall results suggested that there is potential to integrate cover crops in Nevada's semi-arid environment under irrigation.

Weed seed persistence in soil can be influenced by many factors, including crop management. This research was conducted to determine whether organic management systems with higher organic amendments and soil microbial biomass could reduce weed seed persistence compared with conventional management systems. Seeds of smooth pigweed and common lambsquarters were buried in mesh bags in organic and conventional systems of two long-term experiments, the Farming Systems Project at the Beltsville Agricultural Research Center, Maryland, and the Farming Systems Trial at the Rodale Institute, Pennsylvania. Seed viability was determined after retrieval at half-year intervals for 2 yr. Total soil microbial biomass, as measured by phospholipid fatty acid (PLFA) content, was higher in organic systems than in conventional systems at both locations. Over all systems, locations, and experiments, viable seed half-life was relatively consistent with a mean of 1.3 and 1.1 yr and a standard deviation of 0.5 and 0.3 for smooth pigweed and common lambsquarters, respectively. Differences between systems were small and relatively inconsistent. Half-life of smooth pigweed seeds was shorter in the organic than in the conventional system in two of four location-experiments. Half-life of common lambsquarters was shorter in the organic than in the conventional system in one of four location-experiments, but longer in the organic than in the conventional system in two of four location-experiments. There were few correlations between PLFA biomarkers and seed half-lives in three of four location-experiments; however, there were negative correlations up to −0.64 for common lambsquarters and −0.55 for smooth pigweed in the second Rodale experiment. The lack of consistent system effects on seed persistence and the lack of consistent associations between soil microbial biomass and weed seed persistence suggest that soil microorganisms do not have a dominating role in seed mortality. More precise research targeted to identifying specific microbial functions causing seed mortality will be needed to provide a clearer picture of the role of soil microbes in weed seed persistence.

The health of the soil, recognized by its active role in the linked processes of decomposition and nutrient supply, is considered as the foundation of agriculture by the organic farming movement. Nutrient management in organically managed soils is fundamentally different from that of conventional agricultural systems. Crop rotations are designed with regard to maintenance of fertility with a focus on nutrient recycling. Where nutrients are added to the system, inputs are in organic and/or non-synthetic fertilizer sources that are mostly slow release in nature. Hence a greater reliance is placed on soil chemical and biological processes to release nutrients in plant-available forms. In this respect, nutrient availability in organically farmed soils is more dependent upon soil processes than is the case in conventional agriculture. The development and use of biological indicators of soil quality may therefore be more important in organic (and other low input) farming systems. The aim of this paper is to evaluate current evidence for the impact of organic farming systems on soil biological quality and consider the identification of appropriate biological indicators for use by organic farmers and their advisors. Organic farming systems are generally associated with increased biological activity and increased below-ground biodiversity. The main impacts on biological fertility do not result from the systems per se but are related to the amount and quality of the soil organic matter pool and disruptions of soil habitat via tillage. Even within the constraints of organic farming practices it is possible for farmers to make changes to management practices which will tend to improve soil biological quality. It is, however, by no means clear that distinct indicators of soil biological quality are needed for organic farming systems. It is important not only to identify the most appropriate indicators but also to ensure that farmers and land managers can understand and relate to them to support on-farm management decisions.

Soil microbial biomass (Cmic.) and is relation with soil carbon and nutrient contents in a tropical rain forest (Bawangling Nature Reserve, Hainan Island, P.R. China) were studied. Cmic. was determined by the substrate induced respiration (Sir) method; bacterial and fungal fractions were measured using a selective inhibition technique. For the A horizon, Cmic ranged between 350 and 700μgg-1 soil in April (beginning of the rainy season) and 250–600μg g-1 in October (end of the rainy season). Cmic. contents of the AB and B horizons were lower, ranging from 80 to 350 μg Cmic g-1 soil. On average, 75% of the biomass was bacterial, in the AB and B horizon this was slightly higher than in the A horizon. Cmic was closely correlated with Corg and N content. N and P contents as well as the respiratory response upon glucose addition indicated that towards the end of the rainy season compared with the start the soils were depleted in nutrients. These observations stress the importance of microbial biomass as a factor for nutrient retention in tropical forest ecosystems.

We studied the relationships between soil nutrient availability and microbial biomass and activity of two contrasting soil conditions in a tropical deciduous forest in western Mexico. Hilltops have higher pH, water, dissolved organic C, and ammonium concentrations than hillslopes. Our main hypothesis was that soil microbial biomass, microbial activity and bacterium species richness would be higher in soils with high availability of nutrients. Fifteen soil cores, 0–5 cm depth, were taken in the dry, early rainy and rainy season, from each of the ten replicate plots in hilltop and hillslope positions located on three contiguous small watersheds. We measured moisture, C, N and P availability, potential C mineralization, net nitrification, microbial biomass and culturable heterotrophic and nitrifying bacteria in composite samples from each plot. Microbial biomass, species richness of culturable heterotrophic bacteria and C mineralization were significantly higher on hilltops than on hillslopes. Net nitrification was, in contrast, significantly higher on hillslopes than on hilltops and counts of culturable nitrifying bacteria were also significantly higher in the rainy-season samples. Hilltops and hillslopes had low similarity in composition of culturable heterotrophic bacterial species, particularly during the rainy season. The results suggested that C and N availability and seasonal changes in soil moisture are important controlling factors for some soil culturable-bacterial species, which may affect both C mineralization and nitrification in these tropical deciduous forest soils.

A critical step in the quantification of soil quality (SQ) is the selection of SQ benchmarks. The benchmarks used in this study were SQ ratings made by 32 farmer collaborators representing a range of farming systems, scales of operation and geographic locations in the Mid-Atlantic region of USA. Soils from 45 pairs of sites identified by their farmers as having good and poor SQ were sampled over three seasons and analyzed for 19 soil parameters. Farmer judgments of SQ were based on many factors, most commonly soil organic matter, crop performance, soil water availability and erosion history. Selected individual soil parameters were normalized and integrated into an additive SQ index (SQI). Three additional indices were developed using discriminant analysis. The level of agreement between individual parameters, SQIs and farmer SQ ratings was evaluated using paired t-tests and mean percent difference values. The additive SQI was found to have the highest level of agreement with farmer SQ ratings (P<0.0001), demonstrating that a linear combination of soil parameters can be assembled that is more in agreement with holistic SQ criteria, such as farmer SQ ratings, than individual soil parameters. Extractable C from microwave (MW) sterilized soil (a measure of microbial biomass) was the individual parameter that best agreed with farmer SQ ratings (P<0.0001). Five additional soil C parameters, as well as aggregate stability, also agreed well with farmer SQ ratings (all P values <0.0005). The three parameters with the highest ratio of mean percent difference to coefficient of variation (an indication of parameter reliability) were extractable C from MW sterilized soil, anthrone reactive C and macroaggregate stability (14.2, 7.7 and 3.7, respectively). Mineral fertility parameters (pH, Ca, Ca:Mg ratio, P and K) were not significantly related to farmer SQ ratings (P values >0.05). The strong relationships observed between soil C parameters, soil structural parameters and farmer SQ ratings suggest that efforts to improve SQ in the study region should focus on monitoring and enhancement of soil C and soil structure.

The objective of this study was to investigate the effects of tree cover and season on soil N dynamics and microbial biomass in a semi-arid southern African savanna in Zimbabwe. We used a randomized complete block design with five blocks of 100 × 100 m, demarcated in a 10-ha pocket of Colophospermum mopane-dominated woodland protected from grazing and fire. In each block, we randomly selected three mopane trees with large canopies (8.3 m crown diameter) and another three with small canopies (2.7 m crown diameter). We determined soil organic carbon and nutrient concentrations, litterfall N and C inputs, microbial biomass and N transformations beneath large and small mopane trees as well as in the intercanopy areas. Soil organic carbon, microbial biomass, N, P and K were more than twice those beneath large trees than in the intercanopy areas. Rainy-season net mineral N accumulation rate in the surface soil (0–10 cm) ranged from 3.71 μg g−1 mo−1 in the intercanopy areas to 8.80 μg g−1 mo−1 beneath large trees; correspondingly, net nitrate accumulation rate ranged from 1.33 to 3.60 μg g−1 mo−1. Dry-season net mineral N and net nitrate accumulation rates were similar across sampling sites and did not exceed 2 and 0.4 μg g−1 mo−1, respectively. Litterfall N inputs were positively and significantly correlated with soil N availability, microbial biomass N and N transformations. At all sampling sites, microbial biomass and mineral N pools in the dry season were maximum when soil moisture (∼5%) and N transformations were minimum. In contrast, when soil moisture (9–13%) and N transformations were maximum in the rainy season, microbial biomass and mineral N pools were minimum. It is concluded that the improved soil conditions beneath isolated trees in semi-arid savannas may enhance herbaceous biomass yield especially of canopy shade-tolerant species.

Tropical livestock is often maintained on roughage-based diets deficient in N, and therefore requires supplementation with protein-rich substrates to achieve reasonable production levels. The optimum inclusion rate of a potential supplement is usually determined by in vivo feeding trials or by in vitro incubation of the diet components to estimate the feed value of the complete diet. The present work simulates a supplementation experiment in vitro, by incubating a pure roughage (barley straw), a pure supplement (Sesbania pachycarpa leaves) and mixtures of the two, with increasing inclusion levels of the supplement, in a short-term batch incubation system. Fermentation kinetics were followed by the release of fermentation endproducts (gas and short-chain fatty acids). Microbial biomass was estimated using ribosomal (r) RNA as internal marker for bacteria and eukaryotes separately. Cell-wall-degrading subpopulations were quantified by hybridisation with taxon-specific oligonucleotide probes targeting Chytridiomycetes, Fibrobacter spp., Ruminococcus albus and R. flavefaciens. Carboxymethylcellulase (CMCase) was assayed as an indicator for cell-wall-degrading activity. The addition of S. pachycarpa leaves stimulated fermentation in all cases. Gas production, and especially rRNA concentration, showed clear maxima at 40 % S. pachycarpa inclusion, rates that significantly exceeded the values interpolated from the incubations of the pure substrates. Short-chain fatty acid yield changed only slightly, but in the same way. The analysis of the microbial population structure showed that the positive effects were mainly mediated through enhanced growth of Ruminococcus spp. Increasing proportions of S. pachycarpa leaves in the diet led to a drastic decline in the total eukaryotic population. This points to a defaunation, which may also have added to the positive effects. The eukaryotic subpopulation of the rumen fungi were affected to a lesser degree. Although the cell-wall-degrading organisms showed positive responses to the supplementation, the CMCase activity was not affected significantly by the supplementation. The present work shows that it is possible to predict optimum inclusion levels for a new feed supplement in vitro and thus reduce in vivo experiments. It was also demonstrated that true supplementation effects occur particularly for the microbial biomass production, which is the primary source of amino acids for the ruminant animal. The analysis of microbial population structure in context with conventional metabolic measurements adds valuable information to interpret the observed effects on production-related variables.

A simple method of estimating changes in biologically active soil carbon (C) could help evaluate soil quality impacts of alternative management practices. Most reports of permanganate for active C determination use highly concentrated solutions (0.333 M) that are difficult to work with and tend to react with a large fraction of soil C that is not well distinguished from total organic C. We report on a highly simplified method in which dilute, slightly alkaline KMnO4 reacts with the most readily oxidizable (active) forms of soil C, converting Mn(VII) to Mn(II), and proportionally lowering absorbance of 550 nm light. The amount of soil C that reacted increased with concentration of KMnO4 used (0.01 to 0.1 M), degree of soil drying (moist fresh soil to air-dried for 24 hour) and time of shaking (1–15 minutes). Shaking of air-diy soil in a 0.02 M KMnO4 solution for 2 minutes produced consistent and management-sensitive results, both in the laboratory and with a field kit that used a hand-held colorimeter. Addition of 0.1 M. CaCl2 to the permanganate reagent enhanced settling of the soil after shaking, eliminating the need for centrifugaron in the field kit. Results from the laboratory and field-kit protocols were nearly identical (R2 = 0.98), as were those from an inter-laboratory sample exchange (R2 = 0.91). The active soil C measured by the new procedure was more sensitive to management effects than total organic C, and more closely related to biologically mediated soil properties, such as respiration, microbial biomass and aggregation, than several other measures of soil organic C.

To promote agricultural sustainability, there is a growing interest in developing soil quality indicators that can be used as early indicators of changes in management practices by growers, agricultural professionals, and researchers. A study was conducted on four commercial growers' fields and two research stations in western Oregon with treatments that had been started from 1 to 7 years prior to initiating the investigation. The primary comparison at each site was a winter cover crop and winter fallow in rotation with summer vegetable crops. The effects of these treatments on microbial biomass carbon (MBC), mineralizable N, soil enzyme activity (arylsulfatase and β-glucosidase), and cotton strip decomposition were analyzed to monitor changes in soil quality over a 2-year period. The cotton strip method was tested because of its simplicity (buried in soil for short periods and then assessed for tensile strength or weight loss) and potential as a soil biological indicator. Results showed that cover cropping significantly affected MBC and soil enzyme activity. Mineralizable N and CO2 respiration (laboratory incubation) did not respond to winter cover crop treatment. Cotton strip decomposition was relatively insensitive to field treatments. Because MBC and β-glucosidase activity responded quickly to field management treatment and were less variable than the other measurements, they showed the most potential as soil quality indicators. Total C (organic matter index) and extractable nutrients were not significantly affected by cover cropping (even after 7 years), indicating selected biological properties are superior to these chemical properties for detecting effects of soil management.

This paper summarizes data from previous and current studies on two adjacent farms, one organically managed and the other conventionally managed, in the Palouse region of eastern Washington. The 320-hectare organic farm has been managed without the use of commercial fertilizers and only limited use of pesticides since the farm was first plowed in 1909. The 525-hectare conventional farm, first cultivated in 1908, began receiving recommended rates of commercial fertilizers and pesticides in 1948 and the early 1950's, respectively. The organically-farmed Naff silt loam soil had significantly higher organic matter, cation exchange capacity, total nitrogen, extractable potassium, water content, pH, polysaccharide content, enzyme levels, and microbial biomass than did the conventionally-farmed Naff soil. Also, the organically-farmed soil had significantly lower modulus of rupture, more granular structure, less hard and more friable consistence, and 16 centimeters more topsoil. This topsail difference between farms was attributed to significantly greater erosion on the conventionally-farmed soil between 1948 and 1985. The difference in erosion rates between farms was most probably due to their different crop rotation systems; Le., only the organic farm included a green manure crop in its rotation, and it had different tillage practices. These studies indicate that, in the long-term, the organic farming system was more effective than the conventional farming system in maintaining the tilth and productivity of the Naff soil and in reducing its loss to erosion.