Conservation Agriculture Research Updates - May 2024

This article conducted a systematic review to compare crop yield from cropland with conventional management versus different CA practices, specifically reduced- or no-tillage, agroforestry, organic farming and cover crops. The data was first analyzed for different climate regions, soil textures, and cash crop types followed by how yield responses correlated with soil properties change under different CA practices. Their results showed that CA practices provided a mean increase of yield of 12% primarily with maize that had a 41% yield increase. Agroforestry increased crop yield by 66% and cover cropping by 11%, likely due to increases in soil water content and nutrient availability and decreases in erosion and surface runoff. However, other agricultural systems showed no significant increase after CA compared with conventional row cropping practices.

This paper looks at the role of cover crops in weed control either through direct competition, allelopathy or providing a physical barrier for emergence. However, they suggest that cover crop adoption remains limited by poor and/or unstable establishment in dry conditions, the weediness of cover crop volunteers in subsequent cash crops, and seed costs. This review looked at seed traits of various cover crops that would be helpful in selection of CC's for specific systems. They discuss how to improve CC establishment for 3 important CC families. Seed traits related to good germination were important with discussion on dormancy issues. The proper selection of cover crop cultivars and good establishment are vital in weed suppression.

This paper looks at organic agriculture using NT combined with rye cover crop in Japan. They looked at carbon footprint (CF) and energy efficiency in a soybean crop. There were 3 tillage treatments: Moldboard (MP), rotary tillage (RT) and no-till (NT). The two cover crop treatments were fallow and rye. Over 4 years, the NT had significantly lower energy input than MP or RT, but had lower yield of soybean. But using the rye CC resulted in mitigation of NT yield of soybean. NT-Rye increased SOC by 3.5%, less CO2 emissions and had the lowest CF. They recommend NT+RyeCC in organic agriculture. Note that NT without residues is often not as good as NT with residue cover. This study confirms this.

This paper starts by saying that although CA facilitates build-up of SOC, the sequestration potential of arable soils is affected by edaphic factors and is not well understood. The research used an on-farm approach with pairwise comparison of 21 conventional vs highly innovative ‘pioneer’ farms across a wide range of arable soil types and evaluated the leverage of site attributes and management practices such as crop diversity, reduced tillage, organic fertilization, cover cropping and inter cropping on the SOC sequestration potential. While most pioneer management practices proved beneficial for the sequestration of SOC – particularly cover cropping and crop diversity – our results clearly show that soil texture was the most significant shaping factor. Coarse-textured soils had a significantly higher potential for SOC accrual compared to medium- and fine-textured soils. The initial SOC content also had a significant effect on prevalent sequestration potentials. They conclude that carbon farming schemes need reconsideration within the state-of-the-art scientific framework of carbon saturation behavior in order to properly account for biophysical constraints when formulating soil-related climate change mitigation policies. 

Upland rainfed rice in Madagascar is usually planted on tilled soil as seed and not transplanted resulting in serious weed issues. This field experiment looked at a no-till system with the legume Stylosanthes (NT) managed as a living mulch and compared with the tilled (CT) system. In addition two fertilizer treatments were added; organic manure (F1) and organic combined with mineral fertilizer (F2). Weeds flora were documented and the affect of weeds on rice yield assessed by having weedy and weed-free plots. The effect of the cover crop on rice yield was also assessed using weed-stylosanthes-free plots. Results showed that NT suppressed the dominant grass weeds leading to a decrease in total weed biomass. Rice yield was significantly higher in NT than in CT. The living mulch reduced rice yield by 14% but it remained significantly higher in NT than in CT. The addition of mineral fertilizer to the organic manure had a positive effect on rice yield but only in weed-free conditions.

This study summarizes the results of physical and mechanical soil parameters obtained over the initial 10 years of different conservation management treatments (plowing versus reduced tillage with and without compost application) in an organic field trial conducted in central Germany that looked at the effects of soil conservation measures on soil's physical quality. Differences were mainly found in the topsoil with total porosity, and air capacity lower and bulk density higher in reduced tillage treatments compared to plowed ones. However, the mechanical stability was higher in reduced tillage systems with compost additions. They conclude that the reduced-tillage treatments did not exceed the critical physical values of the soil, nor affect the functionality of the soil (saturated hydraulic conductivity), thereby demonstrating its feasibility as a sustainable technique for organic farming. They also suggested that future studies should include measures to ameliorate compaction zones in reduced-tillage treatments by applying sub-soiling especially under dry soil conditions when reduced or no-tillage is first adopted. .

This study evaluated profitability of NT corn (Zea mays L.) in monoculture versus rotations with soybean (Glycine max L.) and cotton (Gossypium hirsutum L.) with or without winter covers from 2002 to 2017. Rotation interacted with phase to influence corn yield and net returns (NR), with positive rotation effects occurring in Phase IV. Covers influenced yields and NRs over 16 yr (p < .01). Vetch cover resulted in the highest corn yields, whereas wheat cover was the lowest. However, no cover plots produced NRs greater than any other cover. Enhanced yields or cost savings due to reduced fertilizer from covers did not offset cover costs. The study concluded that farmers may need subsidies to adopt conservation agriculture-based practices.

This long-term (18-years) study in France looked at soil microbial community changes in conventional (CON), conservation (CA), organic (ORG), and integrated (INT) cropping systems (wheat, pea and rapeseed). They looked at prokaryote, fungal and arbuscular mycorrhizal fungi (AMF) communities overwinter, crop growth and harvest. Species-rich prokaryote communities were most stable over the growing season. Cropping system exerted a greater effect on fungal communities, with alpha-diversity highest and temporal changes most stable under CA. CON was particularly detrimental for alpha-diversity in AMF communities, with AMF alpha-diversity and stability improved under all other cropping systems. 

This paper used a meta-analysis to evaluate crop productivity (wheat, rice, maize) and GHGs for 3 major soil conservation practices: no-till, manures, and biochar. None of the manures were able to reduce GHGs emissions. Use of biochar showed a strong coupling effect between reduction of GHGs  and the increase in crop productivity. Depending on crop type, all cereal crops showed varied degrees of GHGs mitigation under biochar application, with wheat responding most strongly due to the additional yield increment. No-tillage showed a significant reduction in CH4 and N2O emissions under rainfed and irrigated conditions. 

This review discusses the potential of soil and crop management practices such as minimum/reduced/no-tillage, use of organic manure, balanced and integrated plant nutrient application, precision land leveling, precision water and pest management, residue management, and cropping system optimization to maintain the C-equilibrium between soil and atmosphere and to enhance the C-sequestration in the long run. Results of meta-analysis show a potential 36% increase in soil organic C stock in the top 0–15 cm layer in this region. The authors conclude that there is an urgent need for scaling up and accelerated adoption climate resilient technologies to increase soil C-sequestration. Policies and programs need to be devised for incentivizing farmers to adopt more C-neutral or C-positive agricultural practices.

This is an interesting chapter 2 in a book entitled Advances in Organic Farming, that looks at recent findings, advantages, drawbacks, and opportunities for introduction of CA into Organic Farming. Advantages include less erosion and degradation due to improved soil structure, increase in soil carbon stock, diversity of macro- and micro-organisms, and reduction in nutrient loss through run-off and leaching. But since CA and OF have contrasting strategies there are difficulties that need to be overcome. These include weed control, soil compaction, slow mineralization rate, restricted choice of crops, unavailable equipment, low incentives and funding, and links to organic markets. 

This paper uses a long-term farming system experiment to evaluate and compare the agronomic, economic and ecological performance of the most common arable cropping systems in Europe: organic, conservation, and conventional farming. It contains data for 43 agroecosystem properties and determines overall multifunctionality. Organic production resulted in higher economic performance, thanks to higher product prices and additional support payments. Our results demonstrate that different cropping systems provide opposing services, enforcing the productivity-environmental protection dilemma for agroecosystem functioning.

The paper suggests that the increase in carbon sequestration under long-term NT and cover crop management is a sustainable agricultural system with an increase in SOC and soil respiration. This study looks at the addition of biochar on soil respiration in Japan. Long-term tillage practices, such as NT and moldboard plowing (MP), cover crops such as rye (RY) and fallow (FA), and biochar application such as with biochar (WB) and no biochar (NB) were applied to a split–split plot in a randomized complete block design with four replications. NT had higher respiration compared to MB. Rye had a higher respiration than fallow. Biochar significantly reduced respiration in the soybean and cover crop growing seasons but enhanced carbon sequestration. It reduced respiration by regulating the soil temperature, soil moisture and protect the SOC from decomposition. Biochar also increased SOC, decreased bulk density that improved soil porosity.

This article looks at regenerative agriculture, one of several sustainable narratives that have emerged as solutions for challenges facing agri-food systems. The paper uses 4 prominent narratives -- organic, CA, Sustainable intensification and agro-ecology -- and then discusses how RA fits in with these 4 narratives and what potential it has. They show that there are a number of differences and similarities that have coalesced to drive the emergence of RA. They suggest that regenerative agriculture risks inhibiting deeper agri-food system transformations that address both social and ecological challenges and is not the unifying sustainable agriculture narrative it claims to be. 

This is an interesting article that compares regenerative agriculture with CA in a Mediterranean climate that is characterized by poor quality soils, high climate variability, and resulting heavy agrochemical reliance. CA has helped with these issues and enhanced crop productivity and helped mitigate financial risk, but other issues including herbicide resistance, input costs rising, and increasing climate variability require attention. The aim of this review was to evaluate a set of agroecological practices that constitute a Regenerative Agriculture (RA) concept, for their potential to address these challenges from a soil quality, crop productivity and whole-farm economics perspective. Organic soil amendments from agro-wastes and multi-species cover crops subjected to adaptive multi-paddock (AMP) grazing as a phase within the crop rotation to reduce weed pressure, enhance soil multi-functionality, and resilience against environmental stresses were two interventions discussed. However, they recommend the need for more long-term and context specific research in the future to validate these technologies.

This study looked at different tillage systems (NT vs moldboard (CT)) with 4 fertilizer regimes (None (CON), NPK (MIN), Compost (ORG), & NPK + Compost (MIX) on SOC and microbial biomass 20 years later. The abundance of the microbial community and N-functional guilds within the soil profile (up to a depth of 60 cm) was also determined. SOC was higher in NT than CT at 0-10 cm depth. Organic fertilization increased SOC in both tillage treatments to 20cm. Microbial biomass decreased with depth due to a decrease in SOC, and, consequently, were higher in NT than in CT, in the top 20 cm soil for microbial biomass and bacterial abundance and top 10 cm for fungi and archaea. They conclude that their study provided  insights that can aid in development of effective strategies for steering soil microbiome responsible for N2O emissions.

This paper reviewed 92 empirical studies that investigated the effects of 17 regenerative farming practices across 11 broad categories of crops on SOC stock or content in Southeast Asia. They found that use of organic amendments like biochar, compost, and manure, as well as cover cropping, crop rotation, and conservation tillage to increase SOC. However, addition of compost and manure reported increases in greenhouse gas emissions like methane (CH4) and nitrous oxide (N2O), demonstrating that increases in SOC may be offset by increases in greenhouse gas emissions. Only a few studies measured both the changes in SOC stocks and greenhouse gas emissions and none of the studies completed full greenhouse gas inventories. 

This study from Spain, evaluates no-till, cover crops, and organic amendments as an alternative for conventional practices (CM) for rainfed cereal cropping on a calcareous soil based on the analysis of soil water retention curves (SWRC) and soil structure. The alternate treatment (AM) includes no-tillage (18 years continuous) after conventional tillage, crop rotation, use of cover crops and occasional application of organic amendments. CM involves continuous conventional tillage (chisel plow), mineral fertilization, no cover crops and a lower diversity of crops in the rotation. Their results showed more macropores under CM while mesopores and micropores were the same in both CM and AM. There were more stable macroaggregates in AM than in CM, as well as more organic C storage, greater microbial activity, and biomass. They also say that adoption of AM would not lead to a loss in yields.

This study looks at the impact of various soil management practices on soil microbial diversity in a no-till dryland soybean system in the USA. Treatments included cover crops and nutrient management including the use of poultry manure. Targeted amplicon sequencing of 16S rRNA and ITS2 genes was used to study the bacterial and fungal community composition. Poultry litter amendment and cover crops significantly influenced soil bacterial diversity. Fertilizer sources had different bacterial populations while cover crops influenced the fungal communities. Differential enrichment of advantageous bacterial (Proteobacteria, Actinobacteria and Acidobacteria) and fungal (Mortierellomycota) phyla was observed across the treatments. They propose a long-term study to provide more inferences on soil microbial community response to management changes.

This meta-analysis using 757 comparisons from 97 research articles looked at the impacts  on nitrogen and CA practices on SOC and N content. They found significant increases of SOC [21.39 % (CI = 15.16 to 28.64)] and TN [54.34 % (CI = 26.19 to 96.69)] stock with CA practices compared to conventional practices in the 0–15 cm soil depth. The impact of CA on SOC and TN is reduced in 0–60 cm depths compared to surface soil depths due to the limited input of crop residue deeper in the soil profile. Manure and manure mixed with mineral-N led to greater SOC sequestration than mineral-N alone. Where legume residue was used there was a decrease in C/N ratio.

This report from Spain in a semi-arid agro-ecosystem looked at different nutrient sources under minimum tillage. Organic amendments were compared with mineral fertilizes over a 5-year crop rotation using wheat. Wheat yield and biomass, and several soil properties were measured (pH, soil nutrients, soil organic matter  potentially mineralizable nitrogen, total microbial activity and heavy metals) throughout the 10-year study. Wheat yield was better under organic compared to mineral fertilizer. The application of organic amendments under MT resulted in a promising management agro-ecosystem compared to the mineral fertilized because crop nutrients came from organic wastes, no herbicides were applied while the yields were higher.

This is another interesting article of surface dwelling beetles that are important for biological pest control and organic matter decomposition. It looks at the beetle community responses to 6-years of tillage, crop residue use, rotation and soil fertility amendments. Reduced tillage increased beetle abundance  compared to inversion tillage. Crop residue also increased the incidence of some beetle species by 2-3 times. Another beetle increased by 628.6% in high fertilizer compared to manure + 60 kg N ha−1, manure + low fertilizer and the control. They conclude that reduced tillage, retention of crop residues on the soil surface and application of manure increase surface-dwelling beetle abundance and diversity.