1 Introduction
Conservation agriculture (CA) has its roots in the dramatic events which happened in the 1930s caused by wind erosion of agricultural soils, resulting from several years of severe drought on overtilled land in the central plains of the United States (southern Colorado, Kansas, Oklahoma, northern Texas), known as the Dust Bowl. This period was then marked by the destruction of grasslands and crops (covered in a few hours by a thick layer of fine soil), the ruin of farmers, the rural exodus of millions of people and the aggravation of the economic crisis. The direct consequence was the creation of the Soil Conservation Service (now named the Natural Resources Conservation Service). World Soil Day was established in 2014 to highlight the need to improve soil quality and to encourage action for the sustainable management of soil resources. Conservation agriculture (CA) has been proposed as a viable option to enhance soil health and long-term cropping system productivity. It relies on three fundamental principles: minimum soil disturbance (i.e., only the soil disturbance required to sow seeds into the soil), permanent soil cover with crops, cover crop, crop residues and live mulches, and crop diversification in space and time (), amongst complementary practices (e.g. appropriate nutrient management, enhanced groundcover with alternative organic resources) to enhance its functioning under the conditions of the global south (). Initiated primarily by farmers to reduce soil degradation and production costs, this crop management system now targets different goals and the simultaneous implementation of the three main CA principles intend to contribute to the delivery of multiple ecosystem services (; ): gradual improvements in soil health (); increased soil fertility (); reduced soil degradation caused by soil erosion (); improved soil structure (); enhanced water infiltration and available soil moisture (); reduced reliance on pesticide use through coherent crop diversification (Adeux et al.; ; ); mitigating climate change through carbon sequestration (; ); increasing returns on investment while reducing production costs (; ); enhancing farmers’ reconnection to their biotic and abiotic environment of production (). CA has been developed by pioneer farmers and its importance in the world is growing by 10M ha/year (). It is implemented on a wide array of pedoclimates and production systems primarily in field crops (but also vegetables, vineyard, fruit trees, etc.). However, depending on the region of the world, CA also faces different challenges limiting its development, adaptation, and widespread uptake.
Recent advances have highlighted how research and implementation of CA can benefit from the nexus between multiple disciplines including agronomy, ecology, social sciences, and economics among others. We have constructed this Research Topic to highlight new research avenues and practical actions to improve and promote CA worldwide. We have proposed to scientists who are conducted research on CA for years to bring together their expertise in a wide range of disciplines. Among the manuscripts from around the world that have been selected (Figure 1), several overarching themes emerged: (i) assessment of biological processes occurring in CA fields (Binacchi et al., Behnke et al.), (ii) multicriteria analysis of CA performance and identification of levers to increase adoption of CA (Adeux et al., Ngoma et al., Chaudhary et al., and Krishna et al.), and (iii) in situ or in silico experiments to improve CA-based practices in different contexts (Fonteyne et al., Krupnik et al., Pinnamaneni et al., and ).
Figure 1
2 Assessment of biological processes occurring in CA fields
Improving soil fertility is one of the key objectives targeting CA practices, either through increased biological nitrogen fixation by an increased proportion of legumes in the rotation or reduced N loss through leaching () or gas emission (). Binacchi et al. assessed the capacity of cowpea to biologically fix nitrogen in no-till systems with crop residue and cover intercropping with maize during 6 seasons in Kenya (Figure 1). They reported no positive effect of CA compared to conventional tillage-based plots and suggested future work should explore alternative spatial arrangement and variety selection to intercrop cowpea with maize. Behnke et al. assessed the effects of crop rotation, no-till, and cover cropping as a means to limit N losses, through their effect on microbes involved in the N cycle. They showed that maize monoculture increased nitrous oxide emissions by 44% compared to soybean monoculture mainly due to N fertilization (246 in maize vs 0 kg N/ha in soybean), that cereal rye/hairy vetch cover crop mixture reduced soil nitrate levels, but increased nitrous oxide emissions, likely due to the presence of legume in the cover crop mixture contributing to rapid nitrogen mineralization.
3 Multicriteria analysis of CA performance to increase adoption
It remains difficult and risky for farmers to give up ploughing which is a paradigm rooted in their cultural backgrounds () since we lack knowledge on conservation agriculture systems on some regions of the globe and particularly on its impacts on fuel and agrochemical use and economic profitability. Adeux et al. analyzed 13 indicators on a multicriteria basis across 3000 farms involved in the French DEPHY farm network in France to assess CA performance including environmental, economic and societal aspects (; ). Adeux et al. showed that CA required more herbicides (significant) but slightly less insecticides (even not significant), and decreased time of traction in the field, fuel consumption, as well as mechanization costs. However, CA tended to slightly decrease profitability due to slightly lower productivity but resulted in better profitability per hour of field traction. As in many studies, Adeux et al. encourage further investigation to identify the diversity of responses across a diversity of production situations and to track down the rare systems solving apparent trade-offs (i.e. increased profitability with reduced pesticide use while following CA principles). Ngoma et al. reviewed the evidences that CA is climate smart systems for Eastern and Southern African farming conditions. They identified the reasons why adoption rates by smallholders in this region remains low. They found that CA can contribute positively to productivity and resilience of the farming systems. However, they identified that the degree of success can considerably varies if implemented in farm or household.
Chaudhary et al. explored farmers experiences and the drivers of CA adoption in the Eastern Gangetic Plains of South Asia through 57 qualitative and semi-structured individual interviews. These farmers faced a variety of hurdles and adopted various strategies such as assuming the role of an educator by sharing their knowledge with other farmers in the community, changing mindsets for stover retention, adoption through self-investment. This led farmers to identify a range of benefits such as increased respect in the community, improved socio-economic conditions, and increased free time. Krishna et al. focused on the constraints to adopting zero tillage in rice and wheat irrigated farming systems of the Indo-Gangetic Plains. They showed that farmer adoption was low among smallholders (with less than 2 ha of land). Nevertheless, the benefits are the same for small and large farmers, both in terms of reduced variable costs and improved yields.
4 Improving CA-based practices in different contexts
CA systems combine a diverse set of farming practices, which may evolve since CA adoption (). In addition, to improve the benefits and limit the drawbacks of certain practices, research is required to adapt CA to changing climate () and pest pressure (). In other regions, CA acreage is increasing where soil erosion and degradation jeopardize the sustainability of agriculture. In Mexico, maize is the staple crop of the country Mexico and often produced by smallholder farmers on sloping terrains. Fonteyne et al. tested conservation agriculture and agroforestry practices, i.e. crop diversification through crop rotations, multicropping, relay cropping or agroforestry, in collaboration with local farmers in two states of Mexico (Figure 1). They showed that combining agroforestry with conservation agriculture resulted in a profitable and productive system that also reduced the economic risks for farmers by allowing them to obtain several crops per year. Pinnamaneni et al. tested the effect of a winter rye cover crop on soybean growth and yield, weed control, and profitability under no-till conditions in Mississippi, USA. They showed that CA-based soybean production with rye cover crops could be viable after the first year, since they found positive impact on soybean yield while potential for carbon sequestration and weed suppression. However, it has to be noticed that net returns were lower in year one. More importantly, they identified that conditions are required to succeed, such as deep planting of soybean seeds due to a thick layer of rye residue on the soil surface and additional effort in irrigation to avoid residue blocking water movement, particularly during the first irrigation.
Irrigation is indeed a facilitating practice for CA implementation and crop performance in certain regions of the globe, as mentioned by Krupnik et al. in Coastal Bangladesh. In this region, farmers are interested in growing a second crop in order to increase income and ensure food security following the predominant monsoon season rice crop. However, energy costs, labor, and investment constraints limit their ability to do so. Krupnik et al. concluded that both strip-tilled maize followed by unpuddled transplanted rice and strip-tilled maize followed by fully-tilled, puddled rice with residues retained can result in positive economic, agronomic and environmental outcomes compared to farmers’ practice or conventional full-tillage. However, discussions with farmers after the trials revealed that farmers remained more interested in their adapted practices than in the CA practices. The discussions revealed strong practical aversion to using the full suite of CA practices due to logistical constraints in negotiating the hire of laborers for unpuddled manual transplanting.
In order to explore a wider array of farming practices and combinations across different pedoclimates in France and Spain, Colbach and Cordeau investigated in silico how much tillage (type, depth and number of passes/year) reduces weed infestation and yield loss due to weeds, and which systems and weed species are the most affected by reductions in tillage. They showed that herbicide treatment frequency index increased when tillage frequency decreased, that no recorded no-till system was herbicide-free, and that long and diverse rotations and cover crops were associated with a reduction in tillage, herbicides, and yield loss. They concluded that no-till cropping systems must be more investigated to determine whether sustainable no-till herbicide-free systems are indeed feasible and sustainable.
Statements
Author contributions
SC, LG, MJ, CP, CT wrote and edited the article. All authors contributed to the article and approved the submitted version.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The handling editor EJ declared a past co-authorship with the authors.
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Summary
Keywords
no-till, direct seeding, cover crop, tillage, crop diversification, cropping system
Citation
Cordeau S, Gatere L, Jat ML, Pittelkow CM and Thierfelder C (2023) Editorial: Conservation agriculture: knowledge frontiers around the world. Front. Agron. 5:1177412. doi: 10.3389/fagro.2023.1177412
Received
01 March 2023
Accepted
09 May 2023
Published
20 June 2023
Volume
5 - 2023
Edited by
Eric Justes, Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), France
Reviewed by
Daniel Plaza-Bonilla, Universitat de Lleida, Spain
Updates
Copyright
© 2023 Cordeau, Gatere, Jat, Pittelkow and Thierfelder.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Stéphane Cordeau, stephane.cordeau@inrae.fr
†ORCID: Stéphane Cordeau, orcid.org/0000-0003-1069-8388; Lydiah Gatere, orcid.org/0000-0003-1664-2529; Mangi Lal Jat, orcid.org/0000-0003-0582-1126; Christian Thierfelder, orcid.org/0000-0002-6306-7670
Disclaimer
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.