The conundrum of conservation agriculture and livelihoods in Southern Africa

Low crop productivity, food insecurity, hunger and malnutrition; inadequate farming knowledge and skills, implements and inputs are characteristic of smallholder agriculture in Southern Africa. Many researchers argue that conservation agriculture can guarantee higher crop productivity, food security, improved livelihoods and environmental protection, better than the unsustainable traditional systems of slash and burn practices. In this paper, we present the results of a meta-analysis of over 40 academic publications to review conservation agriculture’s role in influencing desired livelihood outcomes in Southern Africa. We conclude that the effectiveness of conservation agriculture towards better livelihood outcomes in Southern Africa remains debatable, especially when supportive government policies are lacking

Managing soil fertility diversity to enhance resource use efficiencies in smallholder farming systems: a case from Murewa District, Zimbabwe

Smallholder farms in sub-Saharan African exhibit substantial heterogeneity in soil fertility, and nutrient resource allocation strategies that address this variability are required to increase nutrient use efficiencies. We applied the Field-scale resource Interactions, use Efficiencies and Long-term soil fertility Development (FIELD) model to explore consequences of various manure and fertilizer application strategies on crop productivity and soil organic carbon (SOC) dynamics on farms varying in resource endowment in a case study village in Murewa District, Zimbabwe. FIELD simulated a rapid decline in SOC and maize yields when native woodlands were cleared for maize cultivation without fertilizer inputs coupled with removal of crop residues. Applications of 10 t manure ha-1 year-1 for 10 years were required to restore maize productivity to the yields attainable under native woodland. Long-term application of manure at 5 and 3 t ha-1 resulted in SOC contents comparable to zones of high and medium soil fertility observed on farms of wealthy cattle owners. Targeting manure application to restore SOC to 50–60% of contents under native woodlands was sufficient to increase productivity to 90% of attainable yields. Short-term increases in crop productivity achieved by reallocating manure to less fertile fields were short-lived on sandy soils. Preventing degradation of the soils under intensive cultivation is difficult, particularly in low input farming systems, and attention should be paid to judicious use of the limited nutrient resources to maintain a degree of soil fertility that supports good crop response to fertilizer applicatio

Effect of tillage practices on the soil carbon dioxide flux during fall and spring seasons in a Mediterranean Vertisol

In this study, we assessed the effect of conventional tillage (CT), reduced (RT) and no tillage (NT) practices on the soil CO2 flux of a Mediterranean Vertisol in semi-arid Morocco. The measurements focused on the short term (0 to 96 h) soil CO2 fluxes measured directly after tillage during the fall and spring period. Soil temperature, moisture and soil strength were measured congruently to study their effect on the soil CO2 flux magnitude. Immediately after fall tillage, the CT showed the highest CO2 flux (4.9 g m-2 h-1); RT exhibited an intermediate value (2.1 g m-2 h-1) whereas the lowest flux (0.7 g m-2 h-1) was reported under NT. After spring tillage, similar but smaller impacts of the tillage practices on soil CO2 flux were reported with fluxes ranging from 1.8 g CO2 m-2 h-1 (CT) to less than 0.1 g CO2 m-2 h-1 (NT). Soil strength was significantly correlated with soil CO2 emission; whereas surface soil temperature and moisture were low correlated to the soil CO2 flux. The intensity of rainfall events before fall and spring tillage practices could explain the seasonal CO2 flux trends. The findings promote conservation tillage and more specifically no tillage practices to reduce CO2 losses within these Mediterranean agroecosystems. (Résumé d'auteur

Meta-analysis of crop responses to conservation agriculture in sub-Saharan Africa

Conservation agriculture involves reduced or no-tillage, permanent soil cover and crop rotations to enhance soil fertility and crop yields. Conservation agriculture practices are increasingly promoted on smallholder farms in sub-Saharan Africa as a means to overcome continuing poor-profitability and soil degradation. In recent years a growing number of studies have been carried out in sub-Saharan Africa comparing conservation agriculture practices to conventional tillage-based practices. These studies have been conducted under a range of conditions (climate, soil, management, cropping system) gaining variable results on crop yield responses. The aim of this study is to compare and combine the results from different conservation agriculture experiments using meta-analysis in the hope of identifying patterns among study results, sources of disagreement among those results, or interesting relationships that may come to light in the context of the different studies

Методологічний підхід до вартісної оцінки асиміляційного потенціалу водойм на основі технології зворотного осмосу

Однією з причин, коли жителі залишають свої населені пункти, особливо шахтарські, є нестача або й відсутність води. Скидаючи шкідливі речовини у водойми, господарюючі суб’єкти привласнюють асиміляційний потенціал водного середовища (АПвс). Так, щорічно у водні об’єкти в Україні скидається до 800 млн. т різних стоків, третина яких є неочищеними. При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/3091

Limits of conservation agriculture to overcome low crop yields in sub-Saharan Africa

Conservation agriculture (CA) has become a dominant paradigm in scientific and policy thinking about the sustainable intensification of food production in sub-Saharan Africa. Yet claims that CA leads to increasing crop yields in African smallholder farming systems remain controversial. Through a meta-analysis of 933 observations from 16 different countries in sub-Saharan African studies, we show that average yields under CA are only slightly higher than those of conventional tillage systems (3.7% for six major crop species and 4.0% for maize). Larger yield responses for maize result from mulching and crop rotations/intercropping. When CA principles are implemented concomitantly, maize yield increases by 8.4%. The largest yield benefits from CA occur in combination with low rainfall and herbicides. We conclude that although CA may bring soil conservation benefits, it is not a technology for African smallholder farmers to overcome low crop productivity and food insecurity in the short term

Managing soil organic carbon in tropical agroecosystems: evidence from four long-term experiments in Kenya

In sub-Saharan Africa, maize is one of the most important staple crops, but long-term maize cropping with low external inputs has been associated with the loss of soil fertility. While adding high-quality organic resources combined with mineral fertilizer has been proposed to counteract this fertility loss, the long-term effectiveness and interactions with site properties still require more understanding. This study used repeated measurements over time to assess the effect of different quantities and qualities of organic resource addition combined with mineral nitrogen (N) on the change of soil organic carbon (SOC) contents over time (and SOC stocks in the year 2021) in four ongoing long-term experiments in Kenya. These experiments were established with identical treatments in moist to dry climates, on coarse to clayey soil textures, and have been conducted for at least 16 years. They received organic resources in quantities equivalent to 1.2 and 4 t C ha−1 yr−1 in the form of Tithonia diversifolia (high quality, fast turnover), Calliandra calothyrsus (high quality, intermediate turnover), Zea mays stover (low quality, fast turnover), sawdust (low quality, slow turnover) and local farmyard manure (variable quality, intermediate turnover). Furthermore, the addition of 240 kg N ha−1 yr−1 as mineral N fertilizer or no fertilizer was the split-plot treatment. At all four sites, a loss of SOC was predominantly observed, likely because the sites had been converted to cropland only a few decades before the start of the experiments. Across sites, the average decline of SOC content over 19 years in the 0 to 15 cm topsoil layer ranged from 42 % to 13 % of the initial SOC content for the control and the farmyard manure treatments at 4 t C ha−1 yr−1, respectively. Adding Calliandra or Tithonia at 4 t C ha−1 yr−1 limited the loss of SOC contents to about 24 % of initial SOC, while the addition of sawdust, maize stover (in three of the four sites) and sole mineral N addition showed no significant reduction of SOC loss over the control. Site-specific analyses, however, did show that at the site with the lowest initial SOC content (about 6 g kg−1), the addition of 4 t C ha−1 yr−1 farmyard manure or Calliandra with mineral N led to a gain in SOC contents. The other sites lost SOC in all treatments, albeit at site-specific rates. While subsoil SOC stocks in 2021 were little affected by organic resource additions (no difference in three of the four sites), the topsoil SOC stocks corroborated the results obtained from the SOC content measurements (0–15 cm) over time. The relative annual change of SOC contents showed a higher site specificity in farmyard manure, Calliandra and Tithonia treatments than in the control treatment, suggesting that the drivers of site specificity in SOC buildup (soil mineralogy, soil texture, climate) need to be better understood for effective targeting management of organic resources. Farmyard manure showed the highest potential for reducing SOC losses, but the necessary quantities to build SOC are often not realistic for smallholder farmers in Africa. Therefore, additional agronomic interventions such as intercropping, crop rotations or the cultivation of crops with extended root systems are necessary to maintain or increase SOC.</p

Effects of Conservation Agriculture and manure application on maize grain yield and soil organic carbon: a comparative analysis

In southern Africa, most farming systems exhibit a close integration of crop and livestock components, with an output of one component being an input of the other. The allocation of crop residues for livestock feed meets two out of three critical objectives; it ensures feed during the dry season (De Leeuw, 1996), improves quantity and quality of manure to restore soil fertility (Murwira et al., 1995) but does not ensure permanent soil cover required under conservation agriculture (CA). Thus under CA, there are strong trade-offs for either allocating crop residues for livestock feed or using the crop residues directly for mulch thereby reducing the amount and quality of manure available and compromising the condition of livestock. The objective of this study is to perform a comparative analysis of maize grain yield and soil organic carbon (SOC) changes in CA systems versus conventional tillage systems with manure application. Crop residue retention and reduced tillage are options that are expected to increase SOC in the long-term, in a similar way to manure application. Therefore, it is necessary to perform a comparative analysis to quantify the differences and to identify the most sustainable system. Crop yield is important for ensuring food security and income, and SOC is an important determinant of soil fertility, productivity and sustainability (Lal, 1997)

Estoques de carbono do solo após 20 anos de adoção em cronosequências de plantio direto na região de Rio Verde/Montividiu, Goiás.

O objetivo deste trabalho foi estimar o sequestro de carbono (C) em áreas sob Sistema sob plantio direto (SPD) na região de Rio Verde e Montividiu, Estado de Goiás, consideradas representativas da agricultura sob SPD na região do Cerrado