Combining local knowledge and soil science for integrated soil health assessments in conservation agriculture systems

<p>Climate change challenges across sub-Saharan Africa require more resilient food production systems. To improve agricultural resilience, the Climate Smart Agriculture (CSA) framework has been proposed including Conservation Agriculture (CA). CA has three key principles; 1) minimum soil disturbance, 2) crop residue cover, 3) crop diversification. Current soil health studies assessing CA’s impact have focused on 'scientific measurements', paying no attention to local knowledge. Local knowledge however influences farmers’ land decision making and their evaluation of CA. In this study, a participatory approach to evaluate CA’s soil health impacts is developed and implemented using farmers’ observations and soil measurements on farm trials in two Malawian communities. The on-farm trials compared conventional ridge and furrow systems (CP), with CA maize only (CAM) and CA maize-legume intercrop systems (CAML). This approach contextualizes the CA soil health outcomes and contributes to understanding how an integrated approach can explain farmer decision-making.</p><p>Based on a stepwise integrated soil assessment framework, firstly farmers’ soil health indicators were identified as crop performance, soil consistency, moisture content, erosion, colour and structure. These local indicators were consistent with conventional soil health indicators for quantitative measurements. Soil measurements and observations show that CA leads to soil structural change. Both soil moisture (Mwansambo: 7.54%-38.15% lower for CP; Lemu 1.57%-47.39% lower for CP) and infiltration improve under CA (Lemu CAM/CAML 0.15 cms<sup>-1</sup>, CP 0.09 cms<sup>-1</sup>; Mwansambo CP/CAM 0.14 cms<sup>-1</sup>, CAML 0.18 cms<sup>-1</sup>). Farmers perceive ridges as positive due to aeration, nutrient release and infiltration, which corresponds with higher exchangeable ammonium (Lemu CP 76.0 mgkg <sup>-1</sup>, CAM 49.4 mgkg <sup>-1</sup>, CAML 51.7 mgkg <sup>-1</sup>), and nitrate/nitrite (Mwansambo CP 200.7  mgkg <sup>-1</sup>, CAM 171.9 mgkg <sup>-1</sup>, CAML 103.3 mgkg <sup>-1</sup>). This perspective still contributes to the popularity of ridges, despite the higher yield and total nitrogen measurements under CA. The perceived carbon benefits of residues, and ridge advantages have encouraged farmers to bury residues in ridges.</p><p>This work shows that an integrated approach provides more nuanced and localized information about land management. The stepwise integrated soil assessment framework developed in this study can be used to understand the role of soil health in farmers’ land management decision-making. Thereby supporting a two-way learning process for scaling agricultural innovations and broadening the evidence base for sustainable agricultural innovations.</p>

Improving soil health is necessary for increasing agricultural productivity and providing multiple ecosystem services. In the African Highlands (AH) where conversion of forests to cultivation on steep slopes is leading to soil degradation, sustainable land management practices are vital. Farmers’ awareness of soil health indicators (SHI) influences their choice of land management and needs to be better understood to improve communication between land managers and other stakeholders in agricultural systems. This study aims to collate and evaluate case study analyses of farmers’ awareness and use of soil health indicators in African Highlands. This is achieved by using a multi-method approach that combines a meta-summary analysis of AH’s SHI data from 24 published studies together with farmer interviews in the East Usambara Mountain region of Tanzania (EUM). Our findings show that farmers across the AH use observable attributes of the landscape as SHI. Out of 16 SHI reported by the farmers, vegetation performance/crop yield and soil colour were most frequently used across the AH. These were also the only two SHI that influenced farmers’ land management decisions in the EUM, where organic manure addition was the only land management option resulting from observed changes in SHI. Farmers’ use of only one or two SHI in land management decisions, as is the case in the EUM, seems to limit their choice and/or adoption of sustainable land management options, highlighting the need to increase awareness and use of more relevant SHI. This could be achieved by sharing SHI knowledge through learning alliances and agricultural extension service. Integration of farmers’ observation techniques and conventional soil testing in a hybrid approach is recommended for a more targeted assessment of soil health to inform appropriate and sustainable land management practices.

<p>Soil health is key to building resilience into agricultural and food systems in sub-Saharan Africa (SSA), where climate change presents a major challenge and unsustainable land management practices have exacerbated land degradation. A suite of interventions labelled climate-smart agriculture (CSA) such as conservation agriculture (cover cropping, mulching, crop rotation, intercropping, minimum/zero tillage, crop residue management), soil and water conservation (contour planting, terraces and bunds, planting pits, and irrigation) and agroforestry are promoted in SSA to improve soil health but adoption among smallholder farmers remains low. A strong evidence base on the impacts of CSA interventions on soil health in different agro-ecosystems in SSA is lacking. This contributes to weak policies and institutional support as well as conflicting messages that farmers receive about CSA impacts, which limit their adoption and lead to disadoption. Farmers’ knowledge of their soils influences their land management decisions and is an important factor in the uptake of CSA interventions. Using a multi-method approach that combines conventional soil testing and farmers’ visual techniques, we examined the impacts of soil and water conservation techniques on soil health indicators in the East Usambara Mountains of Tanzania. The link between farmers’ soil knowledge and their land management decisions was also explored in a wider review of lessons from the African Highlands. Farmers’ observed changes in selected soil health indicators, which influenced their land management decisions did not always match results of conventional soil testing, highlighting the need for integrating farmers’ observational techniques and conventional soil testing for a more targeted and comprehensive assessment of soil health. A hybrid approach to soil assessment is outlined that could foster greater uptake of sustainable land management practices including CSA by farmers in SSA and should be proactively pursued by soil scientists to ensure that their efforts translate to actions by land managers.</p>

Of late, intensive farming for higher food production is often associated with many negative implications for soil systems, such as decline of soil organic matter (SOM), increase in risks of soil erosion by wind and/or water, decline in soil biological diversity, increase in degradation of soil physical quality, lower nutrient-use efficiency, high risks of groundwater pollution, falling water tables, increasing salinization and waterlogging, in-field burning of crop residues, pollution of air and emission of greenhouse gases (GHG), leading to global warming, and decline in factor productivity. These negative implications necessitate an objective review of strategies to develop sustainable management practices, which could not only sustain soil health and ensure food security, but also enhance carbon sequestration, decrease GHG emissions, and offer clean and better ecosystem services. Conservation agriculture (CA), that includes reduced or no-till practices along with crop residue retention and mixed crop rotations, offers multiple benefits. Adoption of a system-based CA conserves water, improves and creates more efficient use of natural resources through the integrated management of available soil nutrients, water, and biological resources, and enhances use efficiency of external inputs. Due to apparent benefits of CA, it is increasingly being adopted and now covers about 180 million hectares (Mha) worldwide. However, in South Asia its spread is low (<5 Mha), mostly concentrated in the Indo-Gangetic Plains (IGP). In this region, one of the serious issues is “residue burning” with severe environmental impacts. A huge amount of crop residue left over after the combine harvest of rice has forced farmers to practice widespread residue burning (∼140 M tonnes) to cope with excessive stubble and also for timely planting/sowing of succeeding crops. In rice-wheat cropping systems, which cover more than 10 Mha in the IGP, CA practices are relatively more accepted by farmers. In these systems, any delay in sowing leads to yield penalty of 1–1.5% per day after the optimum sowing date of wheat. The strong adoption of CA practices in IGP is mainly to overcome delayed sowing due to the field preparation and control of weeds, timely planting, and also escape from terminal heat during the grain-filling stage. Major challenges to CA adoption in South Asia are small land holdings (<1 ha), low technological reach to farmers, nonavailability of suitable farm implements for small farm holders, and the staunch conventional farming mind-set. South Asia region consists of many countries of diverse agro-ecologies with contrasting farming systems and management. This region, recently known for rapid economic growth and increasing population, necessitates higher food production and also hot-spots for adoption of CA technologies. Therefore, in this review critically explores the possibility, extent of area, prospects, challenges, and benefits of CA in South Asia. HIGHLIGHTS Conservation agriculture (CA), consisting of reduced or no-tillage and crop residue retention, is a self–sustainable system which offers an alternative to crop residue burning. The CA approach improves soil health by increasing soil organic carbon (SOC) and aggregation and also conserves soil, water and energy than conventional farming systems. South Asian countries are suitable for adoption of CA practices but the area under CA remains low (<5 Mha) as compared to the global area (180 Mha). Adoption of CA in South Asia has skewed distribution, mainly in Indo-Gangetic Plains (IGP) in India, Pakistan, Nepal and Bangladesh in South Asia. Development of herbicide-resistant weed species and weed shift by continuous application of herbicides are the major challenges in adoption of CA. The traditional-farming mind-set, socio-economic conditions, small farm-holdings, weed and residue management, and non-availability of suitable machinery are key constraints to the low adoption of CA practices in South Asia.

Current gaps impeding researchers from developing a soil and watershed health nexus include design of long-term field-scale experiments and statistical methodologies that link soil health indicators (SHI) with water quality indicators (WQI). Land cover is often used to predict WQI but may not reflect the effects of previous management such as legacy fertilizer applications, disturbance, and shifts in plant populations) and soil texture. Our research objectives were to use nonparametric Spearman rank-order correlations to identify SHI and WQI that were related across the Fort Cobb Reservoir experimental watershed (FCREW); use the resulting rho (r) and p values (P) to explore potential drivers of SHI-WQI relationships, specifically land use, management, and inherent properties (soil texture, aspect, elevation, slope); and interpret findings to make recommendations regarding assessment of the sustainability of land use and management. The SHI values used in the correlation matrix were weighted by soil texture and land management. The SHI that were significantly correlated with one or more WQI were available water capacity (AWC), Mehlich III soil P, and the sand to clay ratio (S:C). Mehlich III soil P was highly correlated with three WQI: total dissolved solids (TDS) (0.80; P<0.01), electrical conductivity of water (EC-H2 O) (0.79; P<0.01), and water nitrates (NO3 -H2 O) (0.76; P<0.01). The correlations verified that soil texture and management jointly influence water quality (WQ), but the size of the soils dataset prohibited determination of the specific processes. Adoption of conservation tillage and grasslands within the FCREW improved WQ such that water samples met the U.S. Environmental Protection Agency (EPA) drinking water standards. Future research should integrate current WQI sampling sites into an edge-of-field design representing all management by soil series combinations within the FCREW.

Accurate assessment of the benefits of soil health building practices to soil function and crop performance requires region‐specific data and locally relevant indicators. In this study, we used a long‐term experiment to measure the effect of 25 yr of differing management on soil health and crop performance indicators in organic and conventionally farmed annual crops in a Mediterranean climate. We measured the strength and consistency of the relationships between several indicators and three functions of a healthy agroecosystem—C storage, net N mineralization, and yields—over two growing seasons and two crop types. Lastly, we used path analysis to test the hypothesis that healthier soils lead to healthier plants and higher yields. Organic plots had greater C stocks and net N mineralization compared with the conventional plots, but lower yields. The path analysis suggested that yields were limited by factors other than N deficiency. The relationships between soil health indicators and soil function were unaffected by crop type but were moderated by yearly changes in weather and operations timing. The indicators most strongly and consistently related to C stocks were permanganate oxidizable C and microbial biomass C, and to N mineralization were CO 2 mineralized from rewet soil and fluorescein diacetate hydrolysis. Our results highlight that (a) different indicators are appropriate for assessing different aspects of soil health, (b) using several years of data in developing robust ranges for indicator interpretation is important, and (c) links between soil and crop health must be assessed mechanistically within a given system.

Soil health and global sustainability: translating science into practice

Conservation agriculture and cover crop practices to regulate water, carbon and nitrogen cycles in the low-lying Venetian plain

Despite efforts to systemically disseminate Conservation Agriculture (CA) technology in Luapula Province of Zambia, the adoption rate remains limited. Furthermore, no empirical evidence has been presented on the factors influencing adoption of the technology or the extent to which farmers’ livelihood has been influenced due to uptake of the technology. This study therefore examined the adoption and impact of CA on crop productivity and income on farming households in the Province. Using the 2012 Rural Agricultural Livelihood Survey (RALS) data, the study employed a probit regression model to identify factors influencing adoption of CA among the smallholder farmers in the Province. The probit regression analysis showed that advice on CA and access to wetlands/dambos by households increased the probability to adopt CA. The study also adopted the Propensity Score Matching (PSM) approach to help match the adopters and non-adopters based on observable covariates in order to assess technology impact by providing consistent estimates of the Average Treatment Effect on the Treated (ATT). The results showed a small but insignificant positive impact of CA on crop productivity and income. This suggests that adoption of CA has the potential to generate an improvement in farming households’ livelihood in Luapula Province, Zambia. Therefore, adoption of CA in Luapula Province should be explicitly encouraged. This can be further enhanced by increased access to quality extension services that incorporates promotion of CA practices among the smallholder farming households in the area.

Conservation agriculture for sustainable intensification of rainfed semi-arid tropics

General ad hoc recommendations of fertilizer inputs do not only lead to lower nutrient-use efficiency but also result in poor soil health due to large spatial and temporal variability in soil nutrient-supplying capacity. Across the Indo-Gangetic Plains, the spatial variability in soil nutrient-supplying capacity further differs among contrasting conventional tillage (CT) and conservation agriculture (CA) systems. The success of CA is dependent on the development of component technologies such as water, weed, and nutrient management strategies to support this newly introduced form of agriculture. The nutrient management aspect under CA has remained less focused, even though it has a differential effect on crop productivity, and soil and environmental health. Like other agronomic practices (planting time, spacing, and weeding), suitable modifications to nutrient management practices are required for CA. The chances of success for CA will be limited unless the best nutrient management practices are acknowledged. Therefore, the adoption of CA can gain momentum through effective and efficient implementation of its fourth principle, i.e. nutrient management. In this chapter, the available information on nutrient transformations in soil and nutrient-use efficiency under CA, as well as opportunities for using precision nutrient management tools for efficient fertilizer nutrient usage based on scientific evidence are presented.

ContextThe rice-wheat (RW) system, spanning 13.5 million hectares in South Asia, is crucial for food security and livelihoods. However, intensive conventional tillage-based practices have harmed soil and environmental health, decreased productivity trends and increased greenhouse gas emissions. ObjectiveThis study aims to develop resilient, climate-smart cropping systems within the RW system, focusing on soil and crop productivity, economic viability, and reduced greenhouse gas (GHG) emissions. MethodsOver eight years, the study evaluated diverse parameters compared to farmer practices (FP) in seven scenarios (Sc), including one representing FP (Sc1) and six based on conservation agriculture (CA) principles. The study assessed system crop productivity, economic returns, soil quality (organic carbon; OC, nitrogen; N, phosphorus; P, potassium; K contents, bulk density; BD, soil aggregation, infiltration rates, microbial counts, and earthworm density), and GHG emissions. ResultsCA-based scenarios (Sc2 to Sc7) showed improved soil quality, lower bulk density, enhanced soil aggregation, and increased infiltration rates compared to Sc1. In the 0–15 cm layer, surface soil organic carbon (OC) and C stock were 63.7 % and 49.6 % higher, respectively, in CA-based scenarios. Additionally, available N, P and K contents in the surface layer increased by 10.2 %, 28.6 %, and 21.8 % under CA-based scenarios. Adoption of CA in intensified maize-based scenarios (Sc4 and Sc5) led to the increased system and economic yields, higher soil quality index (SQI), reduced GHG emissions and increased C stock compared to Sc1. ImplicationsThe study highlights that Conservation Agriculture (CA) practices and diversified crop rotations can address issues like falling crop productivity, reduced economic returns, soil degradation, and increasing environmental impacts in northwestern India's traditional rice-wheat system. However, widespread adoption requires government policies, including C credit payments and guaranteed markets with supportive pricing.

Conservation agriculture (CA) has been proposed as a viable strategy to enhance soil health and the resilience of farms to climate change, and to support the sustainability of agricultural production systems. While CA is a well-established approach, research results are lacking regarding its long-term impact on nitrogen (N) dynamics in the soil–plant system. In this study, a 20-year experiment was used to investigate the long-term effects of no-tillage in CA on soil organic carbon (SOC) and nitrogen (N) mineralization, plant N uptake, grain yields, and the grain quality of durum wheat. A CA system based on no-tillage (NT) was evaluated and compared with conventional tillage (CT) used for wheat/legumes biennial crop rotation. Results showed that soil samples from CA plots experienced significantly more N mineralization than those under CT, which was attributed to increased SOC and N. Topsoil sampled from the CA plots 20 years after the implementation of the experiment had 43% more absolute potentially mineralizable N (N0) than the CT plots, with no significant differences observed in deeper soil layers (15–30 cm and 30–45 cm). The absolute potentially mineralizable carbon (C0) in soils from the CA system was 49% and 35% higher than in soils from the CT system, at soil depths of 0–15 and 15–30 cm, respectively. Furthermore, CA resulted in higher amounts of remobilized N and higher rates of N uptake during the critical growth stages of durum wheat. The amount of N remobilized during the kernel-filling phase under CA was 59% higher than under CT. Total N uptake in wheat plants was 45% greater under CA compared to CT. The most significant differences in N uptake between the CA and CT systems were observed during two critical growth stages: late tillering to heading (1.7 times higher in CA than CT) and heading to anthesis (1.5 times higher in CA than CT). The most significant differences for N uptake were shown during the late tillering to heading stage and the heading to anthesis stage. The amount of N remobilized during the kernel filling phase under CA was 59% higher than CT. CA adoption resulted in 21% and 35% higher grain and straw yields, respectively, compared to CT. The grain and straw N yields were 21% and 51% higher, respectively, under CA than CT. Moreover, the CA system exhibited higher partial factor productivity of nitrogen fertilizer (PFP N) for both grain and straw yields. Thousand kernel weight (TKW) and hectoliter weight were also significantly higher under CA than CT. The grain protein content, wet gluten content, vitreousness, and falling number were similar between the CA and CT systems. These results highlight the benefits of long-term CA adoption to increase soil N mineralization, providing a substantial base for N uptake during the critical growth stages of durum wheat, thus leading to increased crop yield. The findings underscore the potential of CA systems in promoting sustainable agriculture and mitigating the impacts of soil degradation.

Conservation agriculture is seen as a potential solution to modern farming challenges. This paper elucidates its immediate impact by investigating the short-term dynamics of soil health, including the biological constituents, following the implementation of conservation agriculture. We hypothesised that implementing conservation agriculture would lead to changes in soil health. However, these changes will vary across the physical, chemical, and biological properties of the soil, given that each of these components is likely differently influenced by conservation agriculture. The study site was a multi-year trial in Ottosdal (South Africa) with different crop production systems, including maize monoculture, conservation agriculture (rotation of maize, sunflower, and cover crops), and an uncultivated grassland, which served as a natural reference system. Appropriate statistical methods were used to analyse soil health parameters and their interactions from samples collected during the three consecutive summer growing seasons. The study revealed significant soil health dynamics between the cultivated and uncultivated systems. Total available P, organic matter content, and microbial biomass were key indicators of soil health over the 3 years. Crop sequence influenced these dynamics, while a shift from abiotic to biotic factors was observed as primary system differentiators. Notably, crop rotation and soil structure significantly influenced soil microbial communities. These findings provide valuable insights into the interactions between soils and biota and the resulting effects on soil health dynamics. However, further research is required to fully elucidate the mechanisms involved and optimise sustainable farming practices for diverse environmental contexts.

Land degradation is a major problem in Ethiopia, as it contributes to climate change by releasing greenhouse gases (GHG) and slowing carbon sequestration rates. The objective of this review was to assess the role of conservation agriculture (CA) in climate change adaptation and mitigation in Ethiopia. The critical review method processes for identifying and synthesizing peer-reviewed research and review articles, reports, proceedings, and book chapters were followed, with materials obtained from relevant search engines. The findings of the various reports revealed that minimum tillage assists in soil moisture conservation when compared to conventional tillage. Conservation tillage maintains crop residue, reduces soil temperature significantly, and increases nutrient buildup in the surface soil layer, all of which lead to higher crop growth and production thus help as adaptation to climate change. Furthermore, agriculture and other land uses significantly contribute to greenhouse gas emissions; nevertheless, conservation agricultural methods improve soil organic carbon (SOC), soil aggregation, and carbon in aggregate, as well as soil health that contribute to climate changing mitigation. Several studies found that soil health indicators such as soil aggregation, soil organic carbon storage, soil enzymes, and microbial biomass improved under conservation tillage practices, potentially improving the carbon-nitrogen cycle, soil stability, and overall crop productivity. In terms of climate adaptation and mitigation, CA is one of the non-substitutable choices for reducing greenhouse gas emissions. Crop diversity, increased nitrogen consumption efficiency, crop rotation, improved soil carbon sequestration methods; crop residue retention, minimum soil disturbance, manure incorporation, and integrated farming systems are all important factors in minimizing GHG emissions. Moreover, factors impeding CA adoption include a lack of appropriate equipment and machinery, weed control methods, the use of crop residue for fuel wood and animal feed, a lack of awareness about the benefits of CA on soil health and sustainability, and a lack of government technical and financial support for smallholder farmers. Adoption and scaling up of CA practices are critical for ensuring a sustainable development goal and resilient future. Thus, relevant stakeholders should consider the aforementioned considerations while promoting the technology on a large scale through integration with enhanced technology.