Conservation Agriculture Research Updates - May 2024

This paper is based on two long-term experiments started in 2013 in Zimbabwe. There were 6 treatments: Conventional tillage (CT); CT plus rotation (CTR); No-tillage (NT); NT+ mulch (NTM); NT+ rotation (NTR); NT + mulch+rotation (NTMR). Maize was the main crop with treatments using rotation growing cowpea. SOC and soil bulk density (SBD) were taken from 9 depths from 0-100cm. Results show that SOC stocks were higher in NTM, NTR and NTMR treatments compared to NT and CT in the upper soil samples (0-5 and 0-10cm). NT alone had a small negative impact on upper SOC stocks. Cumulative SOC stocks were not significantly different between treatments in the whole 100cm soil profile. NTM enhances SOC stocks but only in the topsoil and showed the highest cumulative organic carbon inputs. Last, results showed thatat least 2 CA principles were needed to increase SOC stocks in these low-nitrogen-input cropping systems.

This article reports the results of evaluation of new wheat cultivars in on-farm conditions using different tillage systems. There were 7 wheat cultivars (3 bread wheat and 4 durum) and 3 tillage systems; conventional (CT), reduced (RT), and No-Till (NT) in two locations for 3 cropping seasons. Overall the CT treatment had the highest yield and NT the lowest. But maybe that was because there was no residue mulch or there were problems with the NT equipment or soil moisture at planting. NT needs a higher soil moisture at seeding that a CT soil. However, there were differences in yield between the different cultivars by tillage. Some cultivars had better yield under CT and others under NT. The experiment needs to look at cultivars by tillage with and without residue and plant the NT when the moisture is higher and not wait for the CT plots to be planted.

This article looks at humic acid (HA) quality and the clay-humus complex to provide information regarding soil carbon (C) and recalcitrant C under CA in a field experiment. No-till with and without residue was compared with conventional tillage without residue (CT) in a maize-wheat-pigeonpea system. Results showed that the NT+R treatment had more positive results than NT-R or CT in terms of humic acid quality and the clay-humus complex. NT+R also had higher yields than CT in both the cropping systems except in wheat crops in the M-W system. They conclude that ZT+R has the potential to enrich the organic carbon (C) quality in soil and increase the aromaticity of HA, leading to carbon stabilization in soils.

This a second paper from India that addresses the problem of surface residues by developing and using an attachment for the combine harvester. They developed a seeding attachment with a concave disc furrow opener that is attached to the combine that allows sowing of wheat at the same time rice is harvested. They evaluate the performance with 3 forward speeds, and three stubble heights in terms of wheat emergence, effective tillers, grain yield, fuel consumption, and the field capacity of the combine. The results showed that the total energy used for wheat crop establishment using the new seeding attachment was about 63% of the average energy demand from other methods.

This is another study of the impacts of CA but on permanent broad beds (PBB), narrow beds (PNB) and NT flat beds with residue retention on SOC protection within soil aggregates compared to conventionally tilled plots (CT). CA plots had a higher total SOC content than CT ones and improved soil physical properties. Plots under PBB + R, PNB + R and ZT + R had only ~11, 3% and 23% more SOC within silt + clay fraction, respectively, than CT plots (5.85 Mg ha−1). Thus, SOC stabilization within microaggregates inside macroaggregates was the major mechanism, and not the chemical stabilization within silt + clay, of C sequestration under CA. They conclude In this maize/cotton-wheat system that CA on beds or flat are viable options for carbon sequestration, water holding capacity and resistance to erosion.

This paper used a comprehensive database on the three main conservation agriculture practices (cover crops, diversified crop rotations, and no-till and/or reduced tillage (NT/RT)) to elucidate the effect of CA on N2O emissions and also identify the most important predictors of soil N20 emissions. Their analysis showed that NT/RT decreased soil N20 emissions compared to CT. The N20 reductions were w more common in humid climates and where the C level was less than 20g kg(-1). N20 emissions were variable using cover crops and different rotations. Cover crops were more likely to reduce soil N20 emissions in neutral soil pH and the lower C content listed above for tillage and N levels around 3g kg(-1). Diversified rotations tended in increase N20 emissions in temperate regions and neutral pH. They are able to describe the conditions where CA can contribute to mitigation of climate change.

This economics paper says that adoption of CA increases production while reducing GHG emissions but adoption in the developing World is low. They suggest it takes multiple years of continuous adoption for farmers to realize positive results. The paper uses an on-farm experiment in N. Ghana to identify how incentives and peer information affects adoption. They found no overall effect of peer information but found evidence that long-term adoption increased adoption especially if benefits included higher yields.

The author defines carbon farming as restorative land use, site specific best management to create a positive soil/ecosystem carbon budget. Essentially carbon sequestration of atmospheric carbon in soil and biomass. This can be above or below soil level. This paper describes the various attributes and ways to conduct carbon farming. He concludes that the overall objective of C farming is to grow C in land-based sinks and use it as a commodity to generate income while making agriculture a solution to climate change and restoring the environment.

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 paper looks at biological soil health for a long-term rice-wheat system using CA practices in India. The 6 treatments were 1) zero till direct seeded rice (ZTDSR)–zero till wheat (ZTW); 2) ZTDSR + wheat residue (WR) - ZTW + rice residue (RR),  3) ZTDSR + WR + sesbania brown manuring (SBM)–ZTW + RR, 4) ZTDSR–ZTW–zero till mungbean (ZTMB), 5) ZTDSR + mungbean residue (MR)–ZTW + RR-ZTMB + WR, 6)transplanted rice (TPR)-conventional till wheat (CTW)–conventional till mungbean (CTMB). Soil from 0-5 cm depth were analyzed for labile organic carbon pools, soil enzyme activities, and populations of bacteria, fungi and actinomycetes, and two microbial functions using qPCR methods. The results showed that the triple/double ZT plus crop residues caused an increase in the pools of carbon, enzymes, and microbial populations compared to the traditional system. Addition of mungbean and Sesbania improved nifH gene abundance compared to other treatments.

This paper looked at western corn rootworm (WCR) interactions with the soil microbiome are affected by a CA system - corn-soybean-wheat rotation with cover crops under no-till compared to a more traditional system - corn-soybean under mulch tillage and no cover crops when combined with transgenic Bt corn. They applied soil microbes from each system to two corn lines, one Bt and one non-Bt. They then reared Bt=-resistant and Bt susceptible WCR on inoculated seedlings to look at plant and insect changes in fitness. Bt was effective against susceptible larvae in both crop systems. However, Bt-resistant larvae were 20% smaller when reared where soil microbes came from CA systems. Comparing the microbial communities using 16S rRNA sequencing revealed that management practices influenced the microbiomes associated with the soil and the plant rhizosphere, but not WCR. They suggest that the value to  growers utilizing conservation management practices, is by bottom-up changes to plant–insect interactions via the soil microbiome.

This paper's objective was to identify suitable agricultural strategies with high yields, energy use efficiency (EUE) , and carbon use efficiency (CUE) for an array of different crops grown in India - cereals, legumes, oilseeds, and sugarcane in both rainfed and irrigated cropping systems. Irrigated systems had higher environmental impact (EI) and carbon footprint (CF) than rainfed systems. But rainfed crops had higher CUE than irrigated ones.  Adoption efficient irrigation strategies (micro irrigation), enhanced fertilizer use efficiency (site specific nutrient management or slow release fertilizer), conservation agriculture (conservation or reduced tillage) rice cultivation methods (SRI or Direct seeded rice) were some mitigation strategies identified.. 

This paper looks at how CA affects subtropical dryland farming systems in Pakistan. In a field experiment, fallow-wheat (farmers' practice) and the conservation tillage methods minimum tillage (MT), reduced tillage (RT), and zero tillage (ZT) were compared to conventional tillage (CT) in the main plots and the cropping systems sorghum-wheat (S-W) and mungbean-wheat (M-W) to fallow-wheat (F-W) in the sub-plots. They look at SOC, total organic carbon (TOC), microbial biomass carbon (MBC), particulate organic C (POC), and mineral associated organic C (MOC). They show that regardless of cropping system, cumulative CO2 flow was lowest in ZT plots. The CENTURY model confirmed that continuous use of tillage  is a major threat  to soil fertility and production.

This interesting paper looks at Agriculture as both the main cause of anthropogenic global warming and at the same time impacted by climate change. It is also a solution for climate change through sequestration of soil organic carbon (SOC) facilitated by CA. This paper assesses the actual capabilities of CA to mitigate climate change but also be a profitable management system for farmers. The paper elicits the economic profitability and environmental performance of CA from a field experiment in Northern Italy.

This article reviews the question "Can farmers in sub-Saharan Africa (SSA) increase yields and make food more available without using mineral fertilizer?" Supporters that say yes suggest that the principles of agroecology that rely on recycling, better efficiency and practices such as use of legumes and manure will mean more chemical fertilizer is not needed to raise yields. But this paper after extensive literature review suggests that more mineral fertilizer is needed in SSA. They put forward 5 reasons for this conclusion and can be found in this paper. They conclude there is a critical need for more mineral fertilizer in combination with the use of agroecological practices backed up by adequate policy support.

With the residue not being burnt and left as a mulch, there is a need for equipment to plant into this residue. This paper This paper describes a automatic control strip-till piece of equipment to overcome this problem in maize in China. The equipment has an air spring and electric linear actuator that controls the plowing depth straw width control that improves the stability of the equipment. Field tests showed that the straw clearing and soil crushing rates, tillage depth and breadth stability were above 90%. They conclude that the designed equipment would allow conservation tillage  for maize farmers.

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.

CA requires  utilization of residues as mulch and effective weed management. But these two important elements are more complex than just focusing on weeds and residues. This paper explores these two issues to provide answers and questions to these two items. One issue is free-range grazing of livestock on the residues after harvest. Another is burning of these residues. Without the residue soil cover, weed management cannot use the benefits of mulching. Herbicides can help but are costly and need farmer training. Several recommendations are made in this paper, but depend on the socio-economic status dynamics at farmer and community level.

Despite the introduction of CA to Southern Africa 3 decades ago, adoption has been low. This paper attempts to assess the effects of risk and impatience on the extent and intensity of adoption of CA in Zambia. Data was obtained from 646 households. 12% and 18% of the the smallholder respondents were impatient and risk averse, respectively. The paper discusses the reasons for these problems. They conclude that there is a need to include risk management, like crop insurance, when scaling sustainable agricultural practices to accelerate adoption.

This meta-analysis used 78 globally published papers that included 2005 comparisons with the goal to quantify the effects conservation tillage (CA?) on soil organic carbon (SOC) and extracellular enzyme activity (EEA). Results showed CA increased SOC and C, N, P and S related enzymes. Climatic, latitude and mean annual temperature, agronomic practices (fertilization and tillage), and soil depth, were identified as having direct effects on the EEA of the respective enzymes. They conclude from a global perspective, CA enhanced the activity of C-related enzymes, while the y of N-, P-, and S-related enzymes needs more research.