Reduced Soil Disturbance Research Articles

Perennial crop legacy effects on nematode community structure in semi-arid wheat systems

The effects of diversifying wheat-based cropping systems in the Northern Great Plains (NGP) on soil chemical and physical properties is well documented: better soil tilth, improved water infiltration, and higher soil organic matter with crop rotations. However, the impact of crop rotations on soil biology is not as well understood. Nematode communities reflect soil quality and are directly observable, readily quantifiable, and occupy most of the consumer trophic levels in the soil food web. Within more humid climates, the community structure is better characterized to make associations with soil health and crop management strategies, but little is known about their community structure in semiarid regions such as the NGP. For this study, soils under contrasting cropping systems were sampled in the 15th year of a long-term study to quantify and assess the nematode community. Prior to planting, wheat-chemical fallow had a higher total nematode population than that of wheat-tilled fallow (P < 0.05). A wheat-pulse system with a history of crop perennation had a greater abundance of uncommon, omnivorous nematodes than a wheat-pulse system without a prior history of crop perennation. However, plant parasitic nematodes also were higher in abundance under the converted perennial system. Our results suggest that reducing soil disturbance and including a perennial component to cropping systems will foster a more diverse and balanced nematode community under semiarid dryland conditions, but potentially at the expense of increased plant parasitic nematode pressure.

Unintentional effects of environmentally-friendly farming practices: Arising conflicts between zero-tillage and a crop pest, the common vole (Microtus arvalis)

Common voles are a main European facultative, fossorial, farmland rodent pest that can greatly reduce crop yields during population outbreaks. Crop protection against common voles is a complex task that requires the consideration of a set of preventive and control measures within an integrated pest management strategy. A possible option could be to modify farming practices to reduce the availability of refuges for rodents and the damage to crops that they subsequently cause. Farming, however, must simultaneously meet multiple goals including the reduction of the carbon (C) emissions, soil erosion and water use, and the improvement of soil quality. Crop establishment through conservation agriculture strategies, like zero-tillage, would reduce crop management investment, but is also promoted in many regions to reduce C emissions and increase soil organic matter. It could, however, create favourable refuge habitats for fossorial rodent crop pests, like common voles, benefitting from reduced soil disturbance between crop rotations and thus increasing burrow persistence. Assessing the impact that tillage practices, their interaction with different crops and the influence of proximity to potential common vole sources, have on common vole occupancy could provide a valuable tool within an integrated management strategy. Using a 2-ha experimental field with 62 plots 180 m2 (each roughly matching common vole home range size) located experimental plots in north-western Spain, we tested how tillage practices, crop type (wheat, barley, vetch, Narbonne vetch, pea and fallow) and distances from possible colonization sources affect field use by common vole during low population density conditions. Our results show that tillage practices have more influence on common vole occurrence (zero tillage > reduced and conventional tillage) than other aspects such as crop type thus supporting the hypothesis that tillage practices play a key role in common vole habitat use.

The potential of common ragweed for further spread: invasibility of different habitats and the role of disturbances and propagule pressure

The infilling of existing suitable habitats within a landscape after establishment is of critical importance for the final outcome of a plant invasion, yet it is an often overlooked process. Common ragweed, Ambrosia artemisiifolia, is an invasive annual species in Europe causing serious problems due to its highly allergenic pollen and as an agricultural weed. Recent studies have modelled the broad-scale distribution of the species and assessed future invasion risk, but for predicting the expected outcome of ragweed invasion we also need a mechanistic understanding of its local invasion success. We conducted a field experiment to investigate the invasibility of eight common non-arable habitat types and the role of soil disturbance in central Hungary, in the hot spot of ragweed invasion in Europe. Seed addition alone resulted in negligible amount of ragweed biomass, except for sites where disturbance was part of the present management. Soil disturbance alone resulted in ragweed at those few sites where ragweed seeds were present in the seed bank, related to farming in recent decades. When disturbance and seed addition were combined, ragweed emerged in all habitat types and reached high biomass in all habitat types except for closed forests. As our experiment showed that most habitat types have high invasibility when disturbed, we conclude that ragweed has a high potential for further spread, even in this heavily infested region. Management should focus on preventing seed dispersal and eradicating establishing populations where ragweed is still absent, while reducing soil disturbance may be needed to avoid ragweed emergence in infested sites. This latter may require a reconsideration of land-use practices in infested regions.

Does minimum tillage improve the livelihood outcomes of smallholder farmers in Zambia?

Minimum tillage (MT) is a farming practice that reduces soil disturbance by limiting tillage only to planting stations. MT is an integral part of Climate Smart Agriculture aimed at raising agricultural productivity, improving farmer livelihoods and building climate resilient farming systems in sub-Saharan Africa. However, there are questions on its suitability for smallholder farmers in the region. This paper assesses the impacts of MT on crop yield and crop income using an endogenous switching regression (ESR) model applied to cross sectional data from 751 fields, of which 17% were under MT in Zambia. The ESR framework accounts for heterogeneity in the decision to adopt MT or not and consistently predicts the outcomes of adopters and non-adopters had they not adopted and adopted, respectively. The results suggest that adopting MT was associated with an average yield gain for maize, groundnut, sunflower, soybean and cotton of 334 kg/ha but it had no significant effects on crop income (from sales and for subsistence) of households in the short-term. These results are partly explained by partial adoption: even among adopters, only 8% of cultivated land was under MT. In these circumstances, although MT confers some yield benefits, the gains may be insufficient to offset the costs of implementation and translate into higher incomes and better livelihood outcomes in the short-term. Additional costs associated with MT include implements, herbicides, and labor for weed control and for land preparation. Assumptions of labor saving from preparing land in the dry season and cost savings by reduced fuel use and weed pressure are aspirational because of the prevalent customary land tenure and communal grazing systems, and because mechanization and the use of herbicides to control weeds remain low among smallholders. Nevertheless, if the longer-term productivity gains from MT are large enough, these may offset the higher implementation costs of MT due to economies of scale and may eventually result in improved incomes and food security. These findings may help to explain the perceived low uptake rates for MT in Zambia and call for lowering implementation costs through extension specific to MT and by adapting MT to local contexts.

Marginal cost to increase soil organic carbon using no-till on U.S. cropland

Recent global agreements on greenhouse gas emission reductions have reinforced the need to develop cost-effective offset programs that can be implemented to help augment emission reductions. One approach to offset carbon dioxide (CO2) emissions may be to increase soil organic carbon (SOC) stocks by reducing soil disturbance by changing from conventional tillage (CT) to no tillage (NT). In this analysis, the cost to increase SOC sequestration achieved on cropland by changing from CT to NT is estimated. The marginal cost of increasing SOC is determined by the amount SOC can be increased and the difference in profit of changing from conventional to no-till. Landowner costs and profit are derived from crop enterprise budgets, county yield data, and regional crop prices. A risk factor is also used to increase the cost of no-till adoption to account for the apparent reluctance of landowners to adopt no-till. The SOC sequestration potential on corn (Zea mays) and soybean (Glycine max) cropland combined is about 49.1 Tg CO2 year−1 (1 Tg = 1012 g) of which 47.6 Tg CO2 year−1 (nearly 97%) could be attained for less than $20-Mg−1 CO2 (1 Mg = 106 g). When the risk factor is included in the assessment, over 19.7 Tg CO2 year−1 could be attained for less than $20-Mg−1 CO2. The analysis demonstrates that SOC sequestration through changes from CT to NT on corn and soybean land could economically offset a portion of CO2 emissions.

Streaming Urea Ammonium Nitrate with or without Enhanced Efficiency Products Impacted Corn Yields, Ammonia, and Nitrous Oxide Emissions

Core Ideas Streaming urea ammonium nitrate resulted in 11% lower corn yields compared to injected urea ammonium nitrate.Ammonia volatilization (NH3) begins immediately after application for streaming urea ammonium nitrate.In 2015–2016, NH3 loss was 3.6 fold greater for streaming urea ammonium nitrate compared to injected urea ammonium nitrate.Urease and nitrification inhibitors did not increase corn yields with streaming urea ammonium nitrate.Streaming urea ammonium nitrate with a urease inhibitor increased N2O emissions by 18.7%. Surface streaming urea ammonium nitrate (UAN) into corn (Zea mays L.) at side‐dress (v4–v6) or later in the season (v12–v14) is an emerging N fertilizer application method as it is rapid, reduces soil disturbance, and allows for flexible application times. In 2013 and 2014, side‐dress N application (130 kg N ha−1) using three streaming UAN sources was evaluated for their ability to maintain grain yield, reduce ammonia (NH3) volatilization, and mitigate nitrous oxide (N2O) emissions. The products included streaming of urea ammonium nitrate (StrUAN), urea ammonium nitrate with a urease inhibitor (StrUAN‐UI), urea ammonium nitrate with urease inhibitor plus nitrification inhibitor (StrUAN‐UI+NI), and a control (no N). The efficacy of streaming relative to traditional shallow‐injected urea ammonium nitrate (InjUAN) was also assessed. Delayed NH3 sampling related to wind‐tunnel installation in 2013 and 2014 led to additional NH3 measurements in 2015 and 2016. Average yields from StrUAN were 11% lower relative to InjUAN. The use of inhibitors did not improve yields relative to StrUAN. Ammonia volatilization was not significantly different between StrUAN and InjUAN losing 14 and 20% of applied N (2‐yr average), respectively. However in 2015 and 2016, NH3 volatilization from StrUAN was 3.6‐fold greater than InjUAN when measurements were started immediately after application. Hence lower yields in 2013 and 2014 from StrUAN likely reflect N loss to rapid volatilization during or shortly after application. The StrUAN‐UI treatment increased 2‐yr average N2O emissions by 17.3 to 18.7% relative to StrUAN or StrUAN‐UI+NI. For humid‐temperate clay loam soil, UAN streaming with/without inhibitors was not effective for maintaining yields or reducing NH3 volatilization.

Soil displacement during ground-based mechanized forest operations using mixed-wood brush mats

The goal of this research was to examine the mitigating effect of brush mats on soil disturbance caused by off-road traffic of forest machinery, specifically how brush quantity affects rutting and soil displacement in a cut-to-length (CTL) harvesting operation. A field test was performed to analyze the effects of brush mats of varying quantities on the severeness of soil disturbance. At the project test site, located in a mixed-wood stand on silty soils in southern New Brunswick, Canada, two machine operating trails were covered with five different brush amounts (0, 5, 10, 15, and 20 kg/m2). A Logset F-series forwarder with a total loaded mass of 35,800 kg completed three traffic cycles (each consisting of one loaded and one unloaded pass) plus one additional empty pass to simulate the passage of a harvester. The resulting soil disturbance was assessed by determining the area of displaced soil in cross sections of trail segments covered with brush mats of 5, 10, 15, and 20 kg/m2. Results indicated that indent areas of individual tire tracks were between 0.0 and 0.6 m2 when covered by 15 kg/m2 brush mats and normally <0.2 m2 when covered with 20 kg/m2 mats. Relative to the no brush (0 kg/m2) treatment, 5, 10, 15, and 20 kg/m2 brush mats offered reductions of indent areas of 0.0, 14.3, 71.4, and 90.5%, respectively. ANOVA results indicated that brush mats of 15 and 20 kg/m2 along machine operating trails significantly reduced soil disturbance caused by timber harvesting equipment when compared to trail segments with no brush mat. Because regression trees were able to predict minimum indent area (0.0 m2) and rut depth (3.8 cm) based on soil moisture and brush amounts, extending CTL forest operations into soil moisture conditions beyond 50% is not being recommended in this study.

Agricultural management practices impacted carbon and nutrient concentrations in soil aggregates, with minimal influence on aggregate stability and total carbon and nutrient stocks in contrasting soils

Agricultural management practices can affect soil structure and soil organic carbon (SOC) and nutrient stocks, which are important for sustainable agriculture. There is however limited understanding of the long-term impact of management practices on SOC and total nitrogen (N), sulphur (S) and phosphorus (P) concentrations in aggregates from different soils, and consequent effects on SOC and nutrient storage in agro-ecosystems. Soils from long-term (16–46 years) management systems in semi-arid (Luvisol, at Condobolin, NSW), Mediterranean (Luvisol, at Merredin, WA) and sub-tropical (Vertisol, at Hermitage, QLD) environments in Australia were collected from 0 to 10 cm, 10 to 20 cm and 20 to 30 cm depths. Dry- and wet-sieving techniques were used to fractionate the soils into mega-aggregates (>2 mm), macro-aggregates (2–0.25 mm), micro-aggregates (0.25–0.053 mm), and silt-plus-clay particles, including micro-structures (<0.053 mm) i.e. “silt-plus-clay fractions”. Management practices in the Luvisols comprised conventional (CT) and reduced tillage (RT) under mixed crop–pasture rotation, no-till (NT) under continuous cereal–cover crop rotation, and perennial pasture (PP) at Condobolin, and stubble either retained (SR) or burnt (SB) under direct-drilled continuous wheat–legume rotation at Merredin. The practices in the Vertisol comprised a factorial combination of CT, NT, SR, SB, with either 0 (0N) or 90 kg urea-N ha−1 (90N) under continuous wheat–wheat rotation.In the Luvisol at Condobolin, the PP and NT had significantly (p < 0.05) higher soil aggregate stability than the CT and RT, with no impacts of management on SOC and total N, S and P stocks at all depths. The practices in the Luvisol at Merredin and Vertisol at Hermitage had no impact on soil aggregate stability, or on SOC and nutrient stocks at all depths, except the NT-SR-90N at Hermitage showed higher SOC (p < 0.10) and nutrient (p < 0.05) stocks than the other treatments at 0–10 cm only. The SOC and N concentrations were higher (p < 0.05) in the wet-sieved silt-plus-clay fractions and mega-aggregates than macro- and micro-aggregates in the PP and NT at Condobolin, and SR at Merredin, but were similar across aggregates in the CT and RT at Condobolin and SB at Merredin at 0–10 cm depth. Further, at Hermitage, SOC and N concentrations were similar among the aggregate-sizes across different treatments and depths. The only exception was the NT-SR-90N treatment, where SOC and N concentrations were higher (p < 0.05) in the silt-plus-clay fractions or micro-aggregates than in mega- and macro-aggregates, obtained by either dry- or wet-sieving. Total S concentration was in the order of macro- ≥ micro- > mega-aggregates across all the treatments and was higher in the PP at Condobolin (0–10 cm depth), and in the SR at Merredin (all soil depths) than the other corresponding treatments. Further, at Merredin, both SR and SB had higher P concentration in macro- and micro- than mega-aggregates. Across all the practices, SOC and N concentrations were higher in the dry- and wet-sieved silt-plus-clay fractions or micro- than mega- and macro-aggregates in both Luvisols, with no differences in the Vertisol. In summary, although the PP, NT, and SR (compared with other corresponding treatments at each site) had minimal impact on total SOC and nutrient stocks in bulk soils, these practices increased aggregate stability in some systems (i.e. Condobolin), and SOC and nutrient concentrations in the silt-plus-clay fractions or micro-aggregates in both Luvisols. These findings suggest that reducing soil disturbance and enhancing crop residue input in farming systems are important for SOC and nutrient storage, particularly in finer aggregate fractions.

Soil Organic Carbon Storage, &lt;i&gt;N&lt;/i&gt; Stock and Base Cations of Shade Coffee, Khat and Sugarcane for Andisols in South Ethiopia

In the Wondo Genet, Ethiopia, the common agricultural land uses include maize, shade coffee, khat and sugarcane. The objective of this study was to examine the impact of perennial land uses on soil organic carbon (SOC), soil N and base cations. Four sites having maize and one or two of perennial land uses and with similar site characteristics were identified for this study. Soils (0 - 30 cm) were sampled at corners of a plot (20 × 20 m2) placed in each land use at each site. Results indicated that the SOC storage of the shade coffee plantations were 86% and 125% higher compared with adjacent maize land uses with the absolute differences being 50.7 and 54.4 Mg&#183ha-1, respectively. The soil N stock was 109% and 126% higher for the shade coffee than the maize land use while the absolute differences were 5.7 and 4.7 Mg&#183ha-1 for the same sites. Among perennials, the higher SOC storage in the shade coffee is attributable to the increased litter input and reduced soil disturbance in the system. While the higher soil N in the shade coffee was attributed to reduction of leaching, N uplift, and the increased litter quality and input. The high relative increase in shade coffee in SOC and soil N at Finance site was ascribed to the finer soil texture and low SOC and soil N at the compared adjacent maize farm. Although not significant, the relative increase in SOC (34%) and soil N (43%) in the sugarcane at the Finance as well as the relative increase in SOC (7%) and soil N (9%) in khat at Gotu as compared to Chaffee site was attributed to mainly the management differences. The shade coffee has the greatest potential for SOC storage and for increasing N stock, while khat and sugarcane have the least potential.

Manejos do solo associados a telas de sombreamento no cultivo da cebolinha no verão

RESUMO Telas de sombreamento são amplamente utilizadas no sistema produtivo das hortaliças folhosas, todavia são desconhecidos os efeitos dessa tecnologia na cultura da cebolinha cultivada no verão. O objetivo desse trabalho foi avaliar a redução do preparo de solo, associado a telas de sombreamento, em cultivos sucessivos da cebolinha no verão. O experimento foi implantado no esquema de parcelas subdivididas com manejos do solo nas parcelas (1= grade aradora + grade niveladora + enxada rotativa encanteiradora e 2= grade aradora + grade niveladora) e manejos do ambiente nas subparcelas (1= tela preta 35%; 2= tela preta 50%; 3= tela prata 35%; 4= tela prata 50% e 5= pleno sol). As respostas da cebolinha ao uso de telas de sombreamento em relação ao pleno sol diferiram com as condições meteorológicas no verão. Em situação de altas temperaturas do ar e menor precipitação pluvial, a produtividade da cebolinha sob as telas foi equivalente ao pleno sol, todavia com incremento na precipitação e redução das temperaturas, o cultivo a pleno sol foi mais produtivo. Plantas cultivadas sob telas de sombreamento apresentaram incremento em altura. Efeito positivo das telas foi verificado na manutenção da umidade do solo, especialmente na superfície. O preparo do solo com grade aradora + grade niveladora apresentou maior retenção de água em todas as profundidades avaliadas, em relação ao manejo com grade aradora + grade niveladora + enxada rotativa encanteiradora, todavia houve decréscimo de produtividade de 21,7% (primeiro cultivo) e 14,9% (segundo cultivo) sem preparo de canteiro.

Supporting transition toward conservation agriculture: a framework to analyze the learning processes of farmers

Conservation agriculture (CA) is based on 3 principles, namely reduced soil disturbance, permanent soil cover, and more complex and legume-rich rotations; and multiple studies have shown its positive impacts. Because CA relies on a variety of ecological processes, it is more deeply rooted in a specific ecological context than conventional agriculture. The complexity of these processes makes it difficult to elaborate general recipes to be applied by farmers, who therefore need to learn to make their own choices adapted to their own agroecosystem. Consequently, helping farmers to move toward CA requires supporting them in learning to develop their own practices. Farmers’ learning remains poorly investigated at the individual level, with in particular very little work focusing on learning in CA. We hypothesize that the processes involved in learning to practice CA may differ from those involved in conventional agriculture: for instance, the current lack of detailed reference documents may induce farmers to experiment more. Against this background, we here aimed at describing how farmers experienced in CA learn, by qualifying their learning mechanisms and processes. To do so, we conducted five comprehensive interviews with farmers experienced in CA, and then inductively analyzed the data to explore the diversity of learning mechanisms involved, i.e. the elementary actions or cognitive activities which, organized together, constitute a learning process. We, thus, propose a descriptive framework of non-ordered and non-obligatory learning mechanisms that appear to be mobilized by farmersexperienced in conservation agriculture, as a first step toward a deeper analysis of their learning processes. We further emphasize the often unintentional aspect of learning, as well as the importance, for farmers who wish to implement CA practices, of developing new standards of comparison. A better understanding of these learning processes would help improving extension services and training for farmers.

Ecological intensification and arbuscular mycorrhizas: a meta‐analysis of tillage and cover crop effects

Summary Reliance on ecosystem services instead of synthetic, non‐renewable inputs is increasingly seen as key to achieving food security in an environmentally sustainable way. This process, known as ecological intensification, will depend in large part on enhancing below‐ground biological interactions that facilitate resource use efficiency. Arbuscular mycorrhizas (AM), associations formed between the roots of most terrestrial plant species and a specialized group of soil fungi, provide valuable ecosystem services, but the full magnitude of these services may not be fully realized under conventional intensively managed annual agricultural systems. Here, we use meta‐analysis to assess how reducing soil disturbance and periods without roots in agricultural systems affect the formation of AM and the diversity and community composition of arbuscular mycorrhizal fungi (AMF). We compiled data from 54 field studies across five continents that measured effects of tillage and/or cover cropping on AMF colonization and/or communities and assessed effects of management and environmental factors on these responses. Less intensive tillage and winter cover cropping similarly increased AMF colonization of summer annual cash crop roots by ∼30%. The key variables influencing the change in AMF colonization were the type of cover crop or the type of alternative tillage, suggesting that farmers can optimize combinations of tillage and cover crops that most enhance AM formation, particularly with no‐till systems and legume cover crops. Richness of AMF taxa increased by 11% in low‐intensity vs. conventional tillage regimes. Several studies showed changes in diversity and community composition of AMF with cover cropping, but these responses were not consistent. Synthesis and applications. This meta‐analysis indicates that less intensive tillage and cover cropping are both viable strategies for enhancing root colonization from indigenous arbuscular mycorrhizal fungi (AMF) across a wide range of soil types and cash crop species, and possibly also shifting AMF community structure, which could in turn increase biologically based resource use in agricultural systems.

The Effect of Conservation Tillage and Cover Crop Residue on Beneficial Arthropods and Weed Seed Predation in Acorn Squash.

Conservation tillage combined with cover crops or mulching may enhance natural enemy activity in agroecosystems by reducing soil disturbance and increasing habitat structural complexity. In particular, weed seed predation can increase with vegetation cover and reduced tillage, indicating that mulches may improve the quality of the habitat for weed seed foraging. The purpose of this study was to quantify the effects of tillage and mulching for conservation biological control in cucurbit fields. The effects of mulch and reduced tillage on arthropods and rates of weed seed loss from arenas were examined in field trials on sandy soils in 2014 and 2015. Experimental factors included tillage and cover crop, each with two levels: strip-tillage or full-tillage, and cover crop mulch (rye residue) or no cover crop mulch (unmulched). Arthropod abundance on the crop foliage was not affected by tillage or cover crops. Contrary to expectations, epigeal natural enemies of insects and rates of weed seed removal either did not respond to treatments or were greater in full-tilled plots and plots without mulch. Our study demonstrates the potential importance of weed seed predators in reducing weed seedbanks in vegetable agroecosystems, and suggests that early-season tillage may not be detrimental to epigeal predator assemblages.

Conservation agriculture: Systems thinking for sustainable farming

Outlook Conservation agriculture: Systems thinking for sustainable farming by Jeffrey Mitchell, Ron Harben, Garrison Sposito, Anil Shrestha, Daniel Munk, Gene Miyao, Randy Southard, Howard Ferris, William R. Horwath, Eric Kueneman, Judee Fisher, Monte Bottens, Phil Hogan, Robert Roy, Jim Komar, Dwayne Beck, Don Reicosky, Michelle Leinfelder-Miles, Brenna Aegerter, Johan Six, Tom Barcellos, Dino Giacomazzi, Alan Sano, Jesse Sanchez, Mike Crowell, John Diener, Darrell Cordova, Trevor Cordova and Jerry Rossiter C alifornia is an unquestioned global leader in the productivity of its farms and the diversity and quality of its crops. However, there are significant threats to the sustainability of the state’s agricultural systems. The scarcity of water has received great attention in recent years, but that is just one of many concerns. Fossil fuel use, carbon emissions, nitrate pollution of groundwater, labor cost and availability, air pollution and loss of soil fertility all present challenges to the long-term viability of farming in California. Conservation agriculture can help to address all of these issues. Fundamentally, conservation agriculture is about “kindly use” of the land, to quote farmer-essayist Wendell Berry. It is based on three principles: reducing soil disturbance (tilling less, or not at all), retaining crop residues on the soil surface year-round and fostering crop and soil biodiversity. By designing farming systems around these principles, our work has shown that farmers can save water, store more carbon in the soil, burn less fossil fuel, cut labor costs, lower dust emissions and increase profits. Despite conservation agriculture’s promise, how- ever, its adoption has been slow in California. In the Midwest and Great Plains regions, conservation ag- riculture is practiced on more than 30% of cropland, • Water: No-till, surface mulching practices and in- creases in soil organic matter can reduce soil wa- ter evaporation by 4 to 5 inches annually (Klocke et al. 2009; Mitchell, Singh et al. 2012; van Donk et al. 2010) and increase soil water storage ca- pacity by the equivalent of roughly 2 inches (Franzluebbers 2010; Hudson 1994). If applied on a significant amount of California’s roughly 8.5 million acres of irrigated lands, these measures could reduce statewide irrigation demand by millions of acre-feet. • Cost: By limiting tractor passes and other opera- tions, reduced-tillage practices cut production costs by $100 to $150 per acre across a range of crops grown in California (Mitchell, Carter et al. 2012; Mitchell, Klonsky et al. 2012). http://californiaagriculture.ucanr.edu • APRIL–JUNE 2016 53 Ron Harben In 2010, CASI held a public education event on cover crops for farmers and private sector, UC and NRCS participants at the UC ANR West Side Research and Extension Center in Five Points. compared with less than 5% of annual cropland in California. As founders and members of the Conservation Agriculture Sustainability Innovation center (CASI), we are partnering with California farmers and equipment makers to develop conser- vation agriculture practices and technologies that are effective and appropriate for the state’s produc- tion systems, and to build networks to help their adoption. The magnitude of the benefits possible with con- servation agriculture is striking. A few examples:

Heterogeneous preferences and the effects of incentives in promoting conservation agriculture in Malawi

There is a great deal of interest in increasing food security through the sustainable intensification of food production in developing countries around the world. One such approach is through Conservation Agriculture (CA), which improves soil quality through a suite of farming practices that reduce soil disturbance, increase soil cover through retained crop residues, and increase crop diversification. We use discrete choice experiments to study farmers’ preferences for these different CA practices, and assess willingness to adopt CA. Despite many long-term agronomic benefits, some farmers are not willing to adopt CA without incentives. Our results suggest that farmers perceive that CA practices interact with one another differently, sometimes complementing and sometimes degrading the benefits of the other practices. But our results also indicate that preferences are a function of experiences with CA, such that current farm level practices influence willingness to adopt the full CA package. Further, exposure to various risks such as flooding and insect infestations often constrains adoption. Providing subsidies can increase likely adoption of a full CA package, but may generate some perverse incentives that can result in subsequent disadoption.

Tillage and Fertilizer Effects on Crop Yield and Soil Properties over 45 Years in Southern Illinois

Reducing soil disturbance may limit erosion, but many still consider tillage essential for seedbed preparation, particularly on poorly drained soils. Our objective was to quantify tillage and fertilizer management effects after 45 yr {21 in continuous corn [Zea mays L.] [CC] and 24 in corn–soybean [Glycine max (L.) Merr.] [CS] rotation} on a somewhat poorly drained silt loam near Belleville, IL. Four tillage (moldboard plow [MP], chisel tillage [ChT], alternate tillage [AT], and no‐till [NT]) and five fertilizer (no fertilization, N‐only, N+NPK starter, NPK+NPK starter, and NPK broadcast) treatments were evaluated. With N, P, and K fertilizer, yields were similar for tilled and NT treatments, averaging 8.73 Mg ha−1 for CC and 11.93 Mg ha−1 and 3.70 Mg ha−1 for rotated corn and soybean. Below recommended soil‐test values resulted in NT yielding less than tilled treatments even though soil test P, K, and pH were similar. No‐till with N, P, and K increased soil organic matter (OM) to 27.6 g kg−1 (20.5 g kg−1 in all other treatments), with the greatest increase from 0‐ to 5‐cm. No‐till treatments showed stratification of P and K, but it had no effect on yield. No excessive pH stratification was observed. Overall, fertilizer management predominantly influenced crop yield and with complete NPK management non‐tilled yields were similar to tilled, even on flat, somewhat‐poorly drained soils. No‐till with NPK management therefore may allow farmers to maintain high yields while reducing soil and nutrient losses.

Conservation agriculture affects arthropod community composition in a rainfed maize–wheat system in central Mexico

As a system of practices involving crop rotations, reduced soil disturbance, and the retention of organic matter at the soil surface, conservation agriculture (CA) increases soil quality, reduces erosion, and provides a favorable habitat for beneficial soil-dwelling organisms which may provide improved pest control. To determine the effect of CA on generalist arthropod predators and pests, we assessed the ground-dwelling arthropod assemblage prior to crop planting and shortly after crop emergence in a long-term CA trial at the International Maize and Wheat Improvement Center (CIMMYT) in central Mexico. We used pitfall traps and in-field sentinel insect assay arenas to evaluate arthropod activity-density and predation, respectively, in a maize–wheat rotation, planted under CA (zero tillage, retention of residues) and conventional agriculture (tillage and no surface residue). In maize, activity-density of generalist predators (excluding ants) was higher in conventional agriculture treatments than in CA treatments prior to crop planting (P=0.03), but no significant differences were apparent in arthropod activity-densities at the treatment level at any other time. In multivariate analyses, the arthropod community was affected by tillage in maize at both sampling dates (P≤0.05), and by residue after crop emergence in wheat (P=0.03). Spiders trended toward a greater association with no-till treatments in maize and treatments with residue retained in wheat. In wheat, predation (biological control potential) was significantly lower in conventional compared with CA treatments (P≤0.05). According to multiple linear regressions, higher levels of soil cover significantly explained predation before and after planting in maize, and before planting in wheat (P≤0.05). Our results indicate that the type and amount of residue that remains at the soil surface may influence arthropod community dynamics. This first report of the effects of CA on arthropods in this long-term trial indicates that CA in central Mexico may contribute to conservation of certain arthropod predators and biological control of insect pests.

A cost-effective method for reducing soil disturbance-induced errors in static chamber measurement of wetland methane emissions

Static chambers used for sampling methane (CH4) in wetlands are highly sensitive to soil disturbance. Temporary compression around chambers during sampling can inflate the initial chamber CH4 headspace concentration and/or lead to generation of non-linear, unreliable flux estimates that must be discarded. In this study, we tested an often-used rubber gasket (RG)-sealed static chamber against a water-filled gutter (WFG) seal design that could be set up and sampled from a distance of 2 m with a newly designed remote rod sampling system to reduce soil disturbance. Compared to conventional RG design, our remotely sampled static chambers reduced the chance of detecting inflated initial CH4 concentrations (>3.6 ppm) from 66 to 6 % and nearly doubled the proportion of robust linear regressions (r 2 > 0.9) from 45 to 86 %. Importantly, the remote rod sampling system allows for more accurate and reliable CH4 sampling without costly boardwalk construction. This paper presents results demonstrating that the remote rod sampling system combined with WFG static chambers improves CH4 data reliability by reducing initial gas measurement variability due to chamber disturbance when tested on a mineral soil-restored wetland in Charles City County, Virginia, USA.

Microbial physiology and necromass regulate agricultural soil carbon accumulation

Strategies for mitigating soil organic carbon (SOC) losses in intensively managed agricultural systems typically draw from traditional concepts of soil organic matter formation, and thus emphasize increasing C inputs, especially from slowly decomposing crop residues, and reducing soil disturbance. However these approaches are often ineffective and do not adequately reflect current views of SOC cycling, which stress the important contributions of microbial biomass (MB) inputs to SOC. We examined microbial physiology as an alternate mechanism of SOC accumulation under organic (ORG) compared to conventional (CT) agricultural management practices, where ORG is accumulating C despite fewer total C inputs and greater soil tillage. We hypothesized that microbial communities in ORG have higher growth rates (MGR) and C use efficiencies (CUE) and that this relates to greater MB production and ultimately higher retention of new C inputs. We show that ORG had 50% higher CUE (±8 se) and 56% higher MGR (±22 se) relative to CT (p < 0.05). From in situ13C substrate additions, we show that higher CUE and MGR are associated with greater rates and amounts of 13C glucose and phenol assimilation into MBC and mineral-associated SOC pools in ORG up to 6 mo after field substrate additions (p < 0.05). ORG soils were also enriched in proteins and lipids and had lower abundances of aromatic compounds and plant lipids (p < 0.05). These results illustrate a new mechanism for SOC accumulation under reduced C inputs and intensive soil disturbance and demonstrate that agricultural systems that facilitate the transformation of plant C into MB may be an effective, often overlooked strategy for building SOC in agricultural soils.

SOIL QUALITY IN RELATION TO FOREST CONVERSION TO PERENNIAL OR ANNUAL CROPPING IN SOUTHERN BRAZIL

Many forested areas have been converted to intensive agricultural use to satisfy food, fiber, and forage production for a growing world population. There is great interest in evaluating forest conversion to cultivated land because this conversion adversely affects several soil properties. We examined soil microbial, physical, and chemical properties in an Oxisol (Latossolo Vermelho distrófico) of southern Brazil 24 years after forest conversion to a perennial crop with coffee or annual grain crops (maize and soybeans) in conventional tillage or no-tillage. One goal was to determine which soil quality parameters seemed most sensitive to change. A second goal was to test the hypothesis that no-tillage optimized preservation of soil quality indicators in annual cropping systems on converted land. Land use significantly affected microbial biomass and its activity, C and N mineralization, and aggregate stability by depth. Cultivated sites had lower microbial biomass and mineralizable C and N than a forest used as control. The forest and no-tillage sites had higher microbial biomass and mineralizable C and N than the conventional tillage site, and the metabolic quotient was 65 and 43 % lower, respectively. Multivariate analysis of soil microbial properties showed a clear separation among treatments, displaying a gradient from conventional tillage to forest. Although the soil at the coffee site was less disturbed and had a high organic C content, the microbial activity was low, probably due to greater soil acidity and Al toxicity. Under annual cropping, microbial activity in no-tillage was double that of the conventional tillage management. The greater microbial activity in forest and no-tillage sites may be attributed, at least partially, to lower soil disturbance. Reducing soil disturbance is important for soil C sequestration and microbial activity, although control of soil pH and Al toxicity are also essential to maintain the soil microbial activity high.