Build Soil Organic Matter Research Articles

Increased winter‐killed cover crop seeding rate may not increase soil health outcomes

AbstractImplementing soil conservation practices can begin to restore degraded soils, improve soil health, and increase overall ecosystem services. Cover cropping is an effective strategy to rebuild soil quality through decreased erosion and increased residue inputs, which can help build soil organic matter. Cover crop seeding rate may have a positive relationship with ecosystem services; however, it is unknown whether this is realized at or below the recommended cover crop seeding rate. The goal of this study was to identify the relationship between cover crop seeding rate and soil health biogeochemical measures across the growing season using five oat (Avena sativa L.)–pea (Pisum sativum L.) cover crop treatments of 0%, 25%, 50%, 75%, and 100% the industry standard seeding rate at the University of Massachusetts Amherst Research Farm. Soils were tested for soil carbon (C), nitrogen (N), and microbial measures at winter kill, spring thaw, post‐planting, and succeeding cash crop harvest. Soil measures did not vary among seeding rates, but total ground cover was consistent among treatments due to weed growth. Soil health measures vary seasonally reflecting soil microbial activity. Our study provides initial evidence that soil biogeochemical responses do not respond to increased seeding rate within one growing season when the resulting groundcover—cover crop biomass plus weeds—is consistent across seeding rates, but sampling date can influence the magnitude of soil biological and chemical soil health metrics.

Impacts of conservation agriculture on soil C and N stocks and organic matter fractions: comparing commercial producer fields with a long-term small-plot experiment in Brown Chernozems of Saskatchewan

Conservation agriculture (CA) is increasingly promoted to build soil organic matter (SOM) based on findings from predominantly small-plot long-term agroecosystem experiments (LTAEs), with minimal on-farm data. Using commercial producer fields ( n = 20) in the Brown Chernozemic soil zones of Saskatchewan, Canada, which were sampled before (1996) and after (2018) adopting direct-seeding and continuous cropping (1997), we examined changes in soil organic carbon (SOC) and soil total nitrogen (STN) stocks, along with C and N stocks in particulate (POM) and mineral-associated organic matter (MAOM), and compared them to an LTAE in the same soil zone. After 21 years, SOC and STN stocks (0–30 cm depth) increased by 13% and 21%, respectively, in commercial producer fields, and were more pronounced in finer- than coarser-textured soils. Conversely, there were no significant changes (0–30 cm depth) after 18 years (1998–2016) with CA (continuous wheat and pulse-wheat under no-tillage (PW-NT)) in the LTAE, except that STN stock for PW-NT decreased by 7.7%. The estimated rate of change to 30 cm depth was similar between the commercial fields and LTAE for SOC (0.28 and 0.16 Mg C ha−1 year−1, respectively), but not STN (0.04 and −0.03 Mg N ha−1 year−1, respectively). Changes were more evident in the MAOM than POM fraction in both cases. Although the impact of CA may be similar, as observed for SOC, actual on-farm changes will depend on site-specific factors, and specific CA practice. Therefore, on-farm monitoring studies are needed for more accurate assessments of SOM changes and C sequestration potentials.

Lead bioaccessibility and commonly measured soil characteristics in Detroit, Michigan

Historical and contemporary use of lead (Pb) in gasoline, paints, and industry have led to its concentration in urban soils, presenting a human health risk, with disproportionate impacts on children living in urban areas. Contaminated soil is one of the major contributors to child Pb exposure. While many residents practicing urban agriculture have their soil tested to determine the amount of soil total Pb present, this measure does not provide a direct indicator of soil Pb bioaccessibility (used to predict bioavailability). Because bioavailability is ultimately necessary to determine the exposure risk, we aimed to gain a more refined understanding of Pb risk using measurements commonly performed as part of typical agricultural soil tests. Accordingly, we sampled soils from 142 residential parcels located in Detroit, MI. Soils were evaluated for: pH, organic matter content, cation exchange capacity, phosphorus, sulfur, calcium, potassium, magnesium, and sodium and total and in-vitro bioaccessible (IVBA) Pb. Detroit soil IVBA Pb ranged from 4.5% to 81%, with a mean of 39%. Total Pb, organic matter (OM) content and soil pH were found to be the most important predictors of Pb bioaccessibility. Soils typically had a relatively low OM content (mean of 5%) however, samples with higher OM content had lower IVBA (e.g., the IVBA was 15.2% smaller in soils with 7.5% OM). Soils were typically slightly basic (mean of 7.8); however, samples with pH closer to neutral had lower IVBA (e.g., the IVBA was 11.6% smaller in soils with a pH of 7.3). The proximity of soil sampling locations to former smelter locations was also found to influence Pb bioaccessibility, with samples closer to former Pb smelter sites having a somewhat higher average IVBA. Results suggest increasing soil OM content in urban soils will reduce Pb bioaccessibility. Building soil OM would therefore improve both soil fertility and decrease soil Pb bioaccessibility, imparting a predicted decrease in exposure risks.

Carbon persistence of soils with long‐term biosolids amendments in California agroecosystems

AbstractBiosolids can build soil organic matter, but their ability to increase carbon and nitrogen in persistent fractions in deep soil is not well understood. We aimed to assess the mechanisms that influence soil carbon and nitrogen dynamics at three sites—Sacramento (irrigated, grazed grassland), Solano (rainfed, grazed grassland), and Merced (feed cropping system with alfalfa–corn rotation)—where soils were amended with biosolids for 20 years using density fractionations, organomineral extractions, and correlations between calcium and soil organic carbon at three depths (0–10, 30–50, and 75–100 cm). We found that amended soils had higher carbon and nitrogen content in the free‐ and occluded‐light fractions at all depths relative to the control in the Sacramento and Solano sites; however, the Merced site had a greater relative increase of carbon and nitrogen associated with the heavy fraction. Effect sizes show that biosolids increase carbon and nitrogen content in free‐ and occluded‐light fractions in the surface soil (0–10 cm), and in both light and heavy fractions in the deep soil layer (75–100 cm). Ratios of carbon to iron and aluminum show that chelation is an important mechanism of carbon stabilization in Sacramento and Solano sites throughout the soil profile. No (0–10 cm) to negative (75–100 cm) correlations were observed between calcium and soil carbon in the amended soils in the Merced site. Our results indicate that, while biosolids are typically incorporated at shallow depths, long‐term application of biosolids can increase the amount of free‐ and occluded‐light carbon fractions in deep soil.

Biochar and manure additions increased above‐ and belowground wood decomposition, and soil enzyme activities in a sandy loam soil

AbstractWhile biochar and manure can provide considerable benefits to soil properties, how these amendments may alter soil microbial activity and decomposition processes remains unknown. In a split‐split‐split‐plot experiment, we amended a sandy loam soil with three rates of manure (whole plot; 0, 3, 9 Mg ha−1) and biochar (split‐plot; 0, 2.5, 10 Mg ha−1), and installed three species of wood stakes (split‐split‐split plot; triploid poplar, Populus tomentosa Carr.; trembling aspen, Populus tremuloides Michx.; and loblolly pine, Pinus taeda L.) on the soil surface and in the mineral soil (split‐split plot) to serve as a substrate for microbial degradation. Wood stakes were sampled 3 years after installation to assess decomposition rates (mass loss), and changes in wood carbon (C) and nitrogen (N). In addition, soil extracellular enzyme activities at the 0–20 cm depth were examined. Biochar alone, especially 10 Mg ha−1, increased wood stake decomposition and moisture content on the soil surface and in the mineral soil. Manure at the rate of 9 Mg ha−1 increased soil N‐acetyl‐β‐D‐glucosaminidase, α‐glucosidase, and aryl sulfatase activities by 91%, 17%, and 48% respectively. Because of the synergistic benefits of biochar and manure, we suggest that, in this climatic regime and soil texture, 10 Mg ha−1 biochar can be used for soil C sequestration and soil quality improvement, and 9 Mg ha−1 manure can be used in combination with biochar to build soil organic matter in plantations.

Impact of Cover Cropping on Temporal Nutrient Distribution and Availability in the Soil

Cover cropping is a best management practice that can improve soil quality by reducing soil erosion, building soil organic matter (SOM), and improving soil nutrient availability. Southwest (SW) Florida citrus growers have the challenge of growing citrus in sandy soils characterized by low organic matter (<2%), extremely low water and nutrient-holding capacities, and high sand content (>90%), and therefore are looking for methods to improve SOM and nutrient retention and availability in sandy soils. A trial of two cover crop (CC) mixtures planted in the row middles (RM) of Huanglongbing-affected citrus ‘Valencia’ (Citrus sinensis (L.) Osbeck) orchards in sandy soils in SW Florida was conducted. This study explored how incorporating CCs in the RM of the orchards could affect soil ammonium (NH4+), soil nitrate (NO3−), exchangeable macronutrients, and SOM temporal availability. These parameters were measured under the tree canopy (UC) and within RM of two orchards: South Grove (SG) and North Grove (NG), both located in SW Florida. The two seeded CC mixtures were legume + non-legume (LG+NL) and non-legume (NL) and were compared to a control no-CC grower standard (GSC). Phosphorus, calcium, magnesium, and NH4+ were not statistically significantly different among treatments in either of the two sampling positions (UC and RM). Cover cropping significantly (p < 0.05) increased NO3−-N concentrations in the RM area of the citrus orchards after seven consecutive seasons (brassicas, legumes, and grasses) by 31% in the LG + NL and 29% in the NL with reference to the GSC. In addition to the significant increase in NO3−N, SOM significantly (p < 0.05) increased in the RM in the NG site only in both CCs treatments by 17% and 16% for LG + NL and NL treatments, respectively, compared with GSC.

Can N2 fixation by forage legumes build soil organic matter to rival fertilizer N in a tropical forest biome?

Fertilization of pastures with nitrogen (N) can increase animal productivity and may also increase the stocks of soil carbon (C). Recently stoloniferous forage legumes have been used to develop productive sustainable mixed pastures in the Atlantic forest biome. The objective of this study was to compare the impact over 24 years on soil C and N stocks of a productive N-fertilized pasture of Urochloa brizantha cv. Marandu with a mixed forage peanut (Arachis pintoi)-Marandu grass pasture introduced 8 years after an N-fertilized elephantgrass (Pennisetum purpureum) pasture. The pastures were rotationally stocked by Nellore cattle a green-forage allowance equivalent to 4% of body weight and animal performance was continuously monitored. Soil samples were taken at the start of the study and after 8 and 24 years of grazing and analyzed for total C and N and 13C abundance. In 8 years, the stocks of soil organic matter (SOM – 0-30 cm) increased by 4.4 Mg C and 0.58 Mg N ha−1 under the elephantgrass pasture and by 10.4 Mg C and 1.23 Mg N ha−1 under the Marandu grass pasture, both fertilized with 160 kg N ha−1 yr−1. Over the subsequent 16 years, SOM stocks under the Marandu grass fertilized with 120 kg N ha−1 and the mixed forage peanut-Marandu pasture which replaced elephantgrass attained similar stocks of soil C of 51.8 and 52.5 Mg C ha−1 respectively, approximately 12 Mg C greater than under the native vegetation. The 13C abundance of the soil samples indicated that the C4 grass roots made an insignificant contribution to soil C below 30 cm depth. The results show that the N2-fixing forage peanut was just as effective in accumulating SOM as an annual application of 120 kg N fertilizer ha−1 and indicated that after 24 years of these pastures there was little further SOM accumulation.

Soil management legacy interacts with wheat genotype to determine access to organic N in a dryland system

Organic nutrient management through the application of compost and/or cover crops provides mineralizable sources of nutrients for plants while often building soil organic matter (SOM) and various aspects of soil health. Variability in nutrient acquisition strategies between crop genotypes may confer advantages under different soil health contexts and could be important for crop selection and breeding, but crop response under field conditions remains unexplored. We investigated the ability of different genotypes of winter wheat (Triticum aestivum L.) to access nitrogen (N) from newly added cover crop residues in two soils with contrasting levels of SOM and biological activity. We planted three previously characterized wheat genotypes in a long-term dryland compost amendment field trial: 1) Byrd (modern, deep roots, low exudation), 2) Cheyenne (historic, drought susceptible, intermediate exudation), and 3) Snowmass (modern, drought-susceptible, high exudation). 15N-labelled cover crop residue was added to each plot and traced into wheat tissue. In the low SOM soil, the high exudate genotype Snowmass and historic genotype Cheyenne took up the most residue-derived N (6.4–8.1 kg N ha−1) compared to the low-exudate genotype Byrd (4.4 kg N ha−1), suggesting a strong exudate effect in the more carbon-limited soil. However, in the high SOM soil, the low-exudate, deep rooted genotype, Byrd, took up the most residue N (4.6 kg N ha−1 vs. 2.8 and 3.3 hg N ha−1 for Cheyenne and Snowmass, respectively), which indicated higher native N cycling activities and greater importance of drought resistance. Enzyme activity, inorganic N, and microbial communities were not influenced by genotype, though did show strong effects of compost application legacy. Our results show that belowground allocation strategies that favor microbial stimulation may be less successful under water limitation, especially when high native SOM and biological activity can support mineralization of residue N without added investment in root inputs. Increased soil health through SOM-building management likely enhances nutrient cycling, and may better support root strategies that invest less in microbial stimulation in favor of other limiting resources.

Economic trade-offs: analysis of hairy vetch (Vicia villosa) cover crop use in organic tomato (Solanum lycopersicumL.) high tunnel systems across multiple regions

AbstractHigh-tunnel (HT) systems have been shown to effectively improve yields, fruit quality and profitability. In order to maximize returns on investment, HTs are frequently planted successively with both winter and summer cash crops and may include >2 crop cycles per year in some climates. The intense cultivation strategies used in HT systems necessitate increased tillage and nutrient demands posing challenges for soil health, environmental quality and long-term economic sustainability, particularly among organic growers. Seasonal rotations that incorporate fertility-building cover crops, such as legumes and other green manures, have the potential to build soil organic matter, improve crop yield and reduce applications of animal manure and/or compost. The economic impact of cover crop use in HT production systems poses important implications for organic growers. In this study, we present three partial budget analyses to quantify the economic benefits from a leguminous winter cover crop–tomato cash crop rotation in HTs across three regions. Data used in the economic analysis come from multi-year organic HT field trials in Kansas (2016–2019), Kentucky (2016–2019) and Minnesota (2016–2020). Direct financial benefits from hairy vetch (Vicia villosa) cover crop N credits were observed but not sufficient to offset the direct and indirect costs of the cover crop practice. A winter cover crop used in organic HT vegetable systems results in negative financial benefits to producers even with conservation incentive payments. These results highlight challenges for organic growers who are required under the USDA National Organic Program to incorporate soil building practices as part of their rotation schedule. The findings will also be of interest to policy makers as they refine cost-share offerings and programming to incentivize cover crop adoption as a conservation strategy.

Using processed fertilizers or composted poultry manure results in similar yields but contrasting nutrient budgets in organic cabbage production

Certified organic farmers who grow mixed vegetables often rely on composted manure as their primary nutrient source to build soil organic matter and long-term fertility, but this can result in excessive phosphorus inputs relative to processed organic fertilizers. We established a two-year experiment to compare two certified organic fertilizers − 13-0-0 (derived from hydrolyzed feather meal, meat meal, and blood meal) and 10-2-8 (same components as 13-0-0 in addition to bone meal and sulfate of potash) – and composted chicken manure added to provide 112 kg plant-available N ha−1 in organic cabbage production of Northern Florida. Crown diameter was highest with processed fertilizers in both years, whereas SPAD readings were highest with 13-0-0 in 2020. In both years, sap nitrate measured during the growing season was generally higher with processed fertilizers relative to the composted manure treatment. Marketable yield was highest with processed fertilizers for both years and nutrient concentrations at harvest were similar among treatments, except for nitrogen concentrations that were highest with 10-2-8 in 2021. Nutrient export generally followed differences in yields and was comparable for processed fertilizers and composted manure. Using composted manure resulted in large nutrient surpluses, as opposed to smaller surpluses for 10-2-8 and deficits of phosphorus and potassium for 13-0-0. Our results confirm that poultry manure composted directly onsite can result in comparable organic cabbage yields relative to processed fertilizers, although this resulted in important phosphorus surpluses when applied to meet crop N demand.

Community Shade Tree Leaves: Beneficial Uses for Agriculture

Every autumn an abundance of leaves from various species of shade trees [e.g., oak (Quercus sp.), maple (Acer sp.)] are collected from urban landscapes. In 1988, shade tree leaves were banned from landfills and combustion facilities in New Jersey because it was an unsustainable practice. Composting and mulching leaves and using them as a resource was proposed. The purpose of this review is to summarize studies of mulching and amending soils with shade tree leaves and their potential to benefit agricultural production. Research sponsored by New Jersey Agricultural Experiment Station on soils and crops found that land application of shade tree leaves was beneficial for building soil organic matter content, protecting against erosion, and controlling weeds when used as a mulch. In general, crop yields and quality were improved with leaf mulch. Collected shade tree leaves on average have a relatively high carbon-to-nitrogen (N) ratio and the potential to cause a temporary deficiency of soil N availability. However, with good agronomic practices and well-timed N fertilization, crops perform well after shade tree leaves have been applied without increasing the recommended N fertilizer application rate.

Atmospheric dryness impacts on crop yields are buffered in soils with higher available water capacity

Atmospheric dryness has been recognized as a dominant driver for agroecosystem functioning due to its limiting controls on stomatal behavior, even under sufficient soil moisture. Due to its relative importance in influencing carbon and water fluxes, atmospheric dryness has emerged as an important element of global change, jeopardizing food security and agricultural profitability via negative impacts on crop yields. Although negative impacts of atmospheric dryness are well recognized at various scales, it is unknown how heterogeneity in soils’ ability to retain water for plant uptake affects crop yields’ response to increasing atmospheric dryness. To address this, we analyzed how soil available water capacity (AWC) affects the response of crop yields to space and time variation in summer (June-July-August) vapor pressure deficit (VPDJJA) across the conterminous U.S. (CONUS) during 1980–2020 using 77,701 and 51,190 county-year records for maize and soybean, respectively. A distinct co-distribution of VPDJJA and AWC regimes is experienced by maize and soybean acreage and is subject to significant yield variation. Accounting for entire AWC heterogeneity in CONUS, both crops showed a positive yield response to increasing VPDJJA until 0.8 kPa, thereafter showing a gradually increasing negative response to VPDJJA increase. Upon soil-specific investigation of yield response to VPD, the yield sensitivity parameter to VPDJJA became less negative as soil AWC increased, implying buffering of dryness impacts on yields as the ability of soils to retain water increased. For VPDJJA increase between 1.0 kPa and 1.4 kPa, mean VPDJJA impacts on maize yields in soils with 10 %<AWC < 12.5 % were buffered by one-half (50.6 %) as compared with 7.5 %<AWC < 10 % soils. Increasing AWC from 10 to 12.5 % class to 12.5–15 % class further buffered VPDJJA impacts on maize yields by 26.2 %. VPDJJA impacts on soybean yields in soils with 15 %<AWC < 17.5 % were buffered by 40 % as compared with 12.5 %<AWC < 15 % soils. Further increase in AWC (17.5–20 %) resulted in additional 15.5 % buffering of VPDJJA impacts on soybean as compared to impacts recorded for 15 %<AWC < 17.5 % soils. The greatest buffering of negative impacts from VPDJJA were found when AWC is>10 % and 15 % for maize and soybean, respectively. Possible physical mechanisms responsible for this buffering are improved plant physiological function and fulfilment of evaporative demand due to additional soil water resulting from higher AWC, given sufficient water supply. This empirical large-scale evidence of mediating role of AWC for crop yield impacts from a dryer atmosphere underscores the critical nature of soils to support climate-smart agricultural practices via building soil organic matter as well as providing co-benefits for improved crop performance to meet current and future population’s food and fiber needs.

Advancing the science and practice of ecological nutrient management for smallholder farmers

Soil degradation is widespread in smallholder agrarian communities across the globe where limited resource farmers struggle to overcome poverty and malnutrition. This review lays out the scientific basis and practical management options for an ecologically based approach to sustainably managing soil fertility, with particular attention to smallholder subsistence systems. We seek to change the trajectory of development programs that continue to promote inorganic fertilizers and other high input strategies to resource constrained smallholders, despite ample evidence that this approach is falling short of food security goals and contributing to resource degradation. Ecological nutrient management (ENM) is an agroecological approach to managing the biogeochemical cycles that govern soil ecosystem services and soil fertility. The portfolio of ENM strategies extends beyond reliance on inorganic fertilizers and is guided by the following five principles: (1) Build soil organic matter and other nutrient reserves. (2) Minimize the size of N and P pools that are the most susceptible to loss. (3) Maximize agroecosystem capacity to use soluble, inorganic N and P. (4) Use functional and phylogenetic biodiversity to minimize bare fallows and maximize presence of growing plants. (5) Construct agroecosystem and field scale mass balances to track net nutrient flows over multiple growing seasons. Strategic increases in spatial and temporal plant species diversity is a core ENM tactic that expands agroecosystem multifunctionality to meet smallholder priorities beyond soil restoration and crop yields. Examples of ENM practices include the use of functionally designed polycultures, diversified rotations, reduced fallow periods, increased reliance on legumes, integrated crop-livestock production, and use of variety of soil amendments. These practices foster soil organic matter accrual and restoration of soil function, both of which underpin agroecosystem resilience. When ENM is first implemented, short-term yield outcomes are variable; however, over the long-term, management systems that employ ENM can increase yields, yield stability, profitability and food security. ENM rests on a solid foundation of ecosystem and biogeochemical science, and despite the many barriers imposed by current agricultural policies, successful ENM systems are being promoted by some development actors and used by smallholder farmers, with promising results.

Abiotic and biotic filters determine the response of soil bacterial communities to manure amendment

Manure amendments are a common soil amendment in forage and row cropping systems used to provide plant-available nutrients, build soil organic matter, and enhance soil health. Many of the benefits of manure applications are thought to be driven via their impacts on soil microbial communities. However, manure amendments may also introduce potential undesirable microbes (pathogens, or those with antibiotic resistance elements) to soils. Despite the widespread use of manure amendments and their importance in agricultural systems, the forces governing the assembly of bacterial communities in soil in response to manure amendments are poorly characterized, limiting our ability to predict their impacts on soil communities. We constructed soil microcosms using five soils from different locations to investigate the impacts of liquid dairy manure on bacterial communities. Moreover, we used combinations of autoclaved liquid dairy manure and soils to determine the roles of abiotic and biotic factors in the response of indigenous soil communities to manure and the fate of manure-borne bacteria. Bacterial amplicon sequence variants (ASVs) that responded to manure amendment were largely dependent on soil origin. Initial shifts in soil communities after manure amendment were driven by the introduction of manure-borne taxa. However, introduced taxa died off rapidly while some indigenous taxa increased in relative abundance over time. Introduced taxa died off even in the absence of indigenous microbiota, suggesting that the soil abiotic environment is a strong barrier to colonization by manure-borne bacteria. Finally, autoclaved manure amended to soil elicited a similar response from indigenous soil microbes as did live manure, indicating that organic matter, nutrients, or other physiochemical factors associated with manure amendments are responsible for changes in indigenous soil populations.

Legume cover crop type and termination method effects on labile soil carbon and nitrogen and aggregation

AbstractGrowers use cover crops to provide nutrients for crops and build soil organic matter (SOM). Termination methods may alter the effects of cover crops on soil labile C and N. We examined how two cover crops and three termination methods affected soil microbes, soil aggregates, and C and N pools in an organic grain system. We compared crimson clover (Trifolium incarnatum L.) (CC), hairy vetch (Vicia villosa Roth) (HV), and a control together with disking, mowing, or a roller‐crimper for effects on hot‐water‐extractable carbohydrates, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN), potentially mineralizable C and N, and aggregation (quantified by mean weight diameter [MWD]). Disking comprised flail mowing plots and then cultivating. Roller‐crimping occurred via a roller with blades. Vetch soil contained 14% higher MBC than no cover crop pretermination, possibly because of enhanced rhizodeposition. Planting CC resulted in 44% higher MBC than no cover crop a week after termination, likely due to its higher biomass C/N ratio. Disking decreased MWD relative to flail mowing in no cover crop soils at 4 wk after termination across both years at 0‐to‐5‐cm depth. In addition, MWD was lower under CC than under no cover crop for both the flail mowed and roller‐crimped treatments at 4 wk after termination across both years from 0 to 5 cm. This is possibly due to enhanced desiccation of the soil in bare plots after termination. Our results indicate that quantity and quality of biomass of different legume species, rather than termination methods, dominated effects on labile C.

Soil Health and Nutrient Density: Beyond Organic vs. Conventional Farming

Controversy has long surrounded the question of nutritional differences between crops grown organically or using now-conventional methods, with studies dating back to the 1940s showing that farming methods can affect the nutrient density of crops. More recent studies have shown how reliance on tillage and synthetic nitrogen fertilizers influence soil life, and thereby soil health, in ways that can reduce mineral micronutrient uptake by and phytochemical production in crops. While organic farming tends to enhance soil health and conventional practices degrade it, relying on tillage for weed control on both organic and conventional farms degrades soil organic matter and can disrupt soil life in ways that reduce crop mineral uptake and phytochemical production. Conversely, microbial inoculants and compost and mulch that build soil organic matter can increase crop micronutrient and phytochemical content on both conventional and organic farms. Hence, agronomic effects on nutritional profiles do not fall out simply along the conventional vs. organic distinction, making the effects of farming practices on soil health a better lens for assessing their influence on nutrient density. A review of previous studies and meta-studies finds little evidence for significant differences in crop macronutrient levels between organic and conventional farming practices, as well as substantial evidence for the influence of different cultivars and farming practices on micronutrient concentrations. More consistent differences between organic and conventional crops include that conventional crops contain greater pesticide levels, whereas organically grown crops contain higher levels of phytochemicals shown to exhibit health-protective antioxidant and anti-inflammatory properties. Thus, part of the long-running controversy over nutritional differences between organic and conventional crops appears to arise from different definitions of what constitutes a nutrient—the conventional definition of dietary constituents necessary for growth and survival, or a broader one that also encompasses compounds beneficial for maintenance of health and prevention of chronic disease. For assessing the effects of farming practices on nutrient density soil health adds a much needed dimension—the provisioning of micronutrients and phytochemicals that support human health.

Defining and improving the rotational and intercropping value of a crop using a plant–soil feedbacks approach

AbstractCrop rotations and intercropping are an ever‐present sustainable practice across a diverse array of agroecosystems. These management practices can suppress weeds, reduce cycles of disease, build soil organic matter, and increase above‐ and belowground biodiversity, all of which improve the yield of a companion or subsequent crop. Here, we propose the terms ‘rotational’ and ‘intercropping value’ as a way to measure the overall effect of these benefits. Additionally, we articulate how to quantify different ecosystem services provided by rotational and intercrops including weed and disease suppression, enhancing microbial communities, and nitrogen fixation using a framework that accounts for how these services support other crops in agroecosystems. By providing a method of identifying and quantifying these rotational and intercropping traits, it may facilitate the breeding of better crops for rotations, for cover cropping, and for intercropping.

Response of soil properties and microbial indicators to land use change in an acid soil under Mediterranean conditions

Land use change (LUC) can alter the soil quality and lead to soil degradation or soil conservation depending on the management practices. In the Mediterranean region, the impact of LUC on soil quality has been well described on neutral or alkaline soils, which are the most common in the area. However, some areas in the west of the Iberian Peninsula are covered by Raña surfaces, a continental detritic formation associated with quartzitic ranges and characterized by very acid and weathered soil. Seven following land uses were selected for this study: cork oak climax vegetation (Cork Oak), pine afforestation (Pine), natural revegetated shrubland (Shrub) and grassland (Grassland) after land abandonment, tilled olive grove (Olive), tilled annual cropland for animal forage (Tillage) and the same annual cropland managed by no-tillage (No-Tillage). The two tree-based uses, Pine and Cork oak, accumulated the highest contents of carbon (C) and nitrogen (N) fractions. However, the further acidification and the C accumulation in labile forms of Pine could hinder the feasibility of Pine plantations to restore acid and degraded soils. Instead, the natural revegetation succession after land abandonment (first Grassland and then Shrub) were found as a suitable alternative able to increase the C content and restore the microbial activity in comparison with Tillage and Olive, the two land uses which showed the lowest C and N content and reduced microbial activity. Furthermore, the improved aggregate stability in Shrub, probably caused by root exudates of dominant plant species, could play a key role in soil restoration. Microbial biomass C and N, C decomposability and enzymatic activities were the most sensible microbial indicators to discriminate among the studied land uses. A clear pattern of lower microbial biomass and enzymatic activity was found with increasing human intervention and soil disturbance. In this respect, soil managed by no-tillage contained higher soil C and N contents when compared to Tillage and the microbial indicators were comparable with those obtained under Cork Oak. Our results demonstrate that soil tillage reduction is an essential step to mitigate soil degradation in Raña soils and highlighted the suitability of No-tillage as an alternative to traditional tillage, which can increase crop productivity while building soil organic matter content. In addition, the natural soil revegetation, including natural grasslands, shrublands and climax cork oak vegetation are more preferable for degraded soil improvement when compared to pine plantations.

Scenarios of climate adaptation potential on protected working lands from management of soils

Management of protected lands may enhance ecosystem services that conservation programs were designed to protect. Practices that build soil organic matter on agricultural lands also increase soil water holding capacity, potentially reducing climatic water deficit (CWD), increasing actual evapotranspiration (AET) and increasing groundwater recharge (RCH). We developed nine spatially-explicit land use and conservation scenarios (2001–2100) in the LUCAS land use change model to address two questions for California working lands (cropland and rangeland): How does land use change limit opportunities to manage soils for hydrologic climate adaptation benefits? To what extent and where can soil management practices increase climate adaptation on protected working lands? Hydrologic benefits [Σ(∆CWD, ∆AET, ∆RCH)] due to soil management were simulated in the Basin Characterization Model (a state-wide water balance model) for two Representative Concentration Pathway 8.5 climate models. LUCAS simulated land conversion and new conservation easements with potential for maximum hydrologic benefits. Climate drove differences in lost potential for water benefits due to urbanization (33.9–87.6 m3 × 106) in 2050. Conflict between development pressure and potential hydrologic benefits occurred most in Santa Clara County in the San Francisco Bay Area and Shasta County in Northern Sacramento Valley. Hydrologic benefits on easements were similar in magnitude to losses from development. Water savings from management of California Land Conservation (a.k.a. Williamson) Act contract lands were an order of magnitude greater, totaling over 460 m3 × 106 annually in a drier climate by 2050. Few counties provide most benefits because of soil properties, climate and land area protected. The increase in hydrologic benefits varies by agricultural practice and adoption rate, land use type and configuration, and terms of conservation agreements. The effectiveness of programs designed to improve climate adaptation at county to state scales will likely increase by taking this variability into consideration.

Building a botanical foundation for perennial agriculture: Global inventory of wild, perennial herbaceous Fabaceae species

Societal Impact StatementAgroecosystems are constantly evolving to meet the needs of a growing population in a sustainable manner. Concerns about ecological impacts of agriculture, including soil loss, have focused attention on crops that provide both agricultural products and ecological services. Perennial, herbaceous crops that live for multiple years and can be harvested mechanically produce large root systems that may reduce soil loss; however, these species are largely absent from agriculture. The diversity of wild, perennial, herbaceous legume species documented by the Perennial Agriculture Project Global Inventory (PAPGI) increases resources available to breeders of perennial, herbaceous legumes, and raises awareness about untapped wild plant diversity in future crop development.Summary Concerns about soil health and stability are focusing attention on crops that deliver both agricultural products and ecological services. Deep rooted, perennial plants that build soil organic matter, support diverse belowground microbial communities, and produce edible seeds are key components underpinning ecological intensification; however, few perennial, herbaceous crops have been domesticated for food. To facilitate development of edible, perennial, herbaceous crops, including perennial grains, we constructed an online resource of wild, perennial, herbaceous species—the Perennial Agriculture Project Global Inventory (PAPGI; http://www.tropicos.org/Project/PAPGI). The first component of this project focuses on wild, perennial, herbaceous Fabaceae species. We extracted taxonomic names and descriptors from the International Legume Database and Information Service. Names were added to PAPGI, a special project within the botanical database TROPICOS, where they link to specimen records and ethnobotanical and toxicological data. PAPGI includes 6,644 perennial, herbaceous Fabaceae species. We built a searchable database, a framework for the ongoing incorporation of more than 60 agriculturally important traits for perennial, herbaceous legumes. Here we highlight food and forage uses for 314 legume species, and toxicological data for 278 species. The novel contribution of PAPGI is its focus on wild, perennial herbaceous species that generally have not entered the domestication process but that hold promise for development as perennial food crops. By extracting botanical information relevant for agriculture we provide a dynamic resource for breeders and plant scientists working to advance ecological intensification of agriculture, and for conservation managers working to preserve wild species of potential agricultural importance.