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Appropriate tillage and crop diversifications can improve soil quality leading to yield sustainability. Our objective was to quantify tillage, crop rotation and mineral fertiliser application effects on carbon sequestration, aggregation and soil water movement after two cropping cycles in the smallholder sector of Zimbabwe. Two split-plot experiments were set up at four sites on sandy, loamy and clayey soils. At experiment 1, crop rotation (maize-soya bean; continuous maize) was the main plot and mineral fertiliser ((NPKS (180 N + 30P2O5+30K2O+6.5SO3 kg ha−1); control (no fertiliser added)) was the sub-plot. At experiment 2, tillage (reduced, conventional) was the main plot and mineral fertiliser (NPKS; control) was the sub-plot. Soil samples collected from 0 to 0.2 m and 0.2–0.4 m layers were analysed for soil organic matter (SOM) content, bulk density and proportion of water stable aggregates. Saturated hydraulic conductivities (Ks), steady state infiltration rates (is) and soil sorptivities (Sp) were estimated from fitting field infiltration data into the Phillip model. SOM stocks (mean = 3.483 Mg ha−1) were significantly increased by reduced tillage at the sandy site and higher (p

The application of insufficient amounts of mineral fertiliser, coupled with unreliable precipitation, has caused a drastic reduction in the yield of sorghum in the smallholder-farming areas of Zimbabwe. This calls for innovative interventions to improve production under changing climatic conditions. This study evaluated the effect of contour-based rainwater-harvesting methods and the use of cattle manure + N nutrient amendment on sorghum yield. A split-split plot experiment was conducted where rainwater-harvesting practice, sorghum variety, cattle manure + N and distance from rainwater-harvesting structure were treatment factors. The results showed that the yield of sorghum was significantly higher under the tied contour and infiltration pits than standard contour at all distances from rainwater-harvesting practices and seasons. In all seasons sorghum varieties Macia and Sc Sila showed higher yield under the tied contour and infiltration pits than standard contour. However, regardless of the distance from rainwater-harvesting practice and season the sorghum variety, Macia showed a higher grain yield than Sc Sila. At each incremental level of N application to cattle manure, Macia had a higher grain yield than Sc Sila, and no significant grain yield benefits were shown in each variety at N application to cattle manure above 50 kg N ha−1. [ABSTRACT FROM AUTHOR]

Surface-dwelling beetles offer ecosystem services in agro-ecosystems including biological pest control and organic matter decomposition. This study was conducted to investigate beetle community response to six years of tillage, crop residue application, crop rotation and soil fertility amendments (low fertiliser, high fertiliser, manure, manure + low fertiliser and manure + 60 kg N ha−1) treatments. Reduced tillage increased beetle abundance by 4.6% relative to soil inversion tillage. Crop residue application increased the abundances of Platynus assimilis, Zophosis boei and total beetles by two to three times. Meanwhile, Renatiella reticulata increased by 628.6% in high fertiliser compared to manure + 60 kg N ha−1, manure + low fertiliser and the control. In crop rotation + crop residue retention plots, application of sole manure at 10 t ha−1 increased the Shannon index by 360–365% relative to manure + 60 kg N ha−1 and manure + low fertiliser. Based on the findings in this study, it can be concluded that reduced tillage, retention of crop residues on the soil surface and application of manure increase surface-dwelling beetle abundance and diversity. [ABSTRACT FROM AUTHOR]

Understanding drivers of weed density and diversity is essential for the development of weed management strategies. Here, we compared temporal changes in weed density and diversity under no‐till (NT) and conventional (CONV) tillage systems in cotton–maize rotations on loam, clay loam and sandy loam soils immediately after transition to NT in Kadoma, Zimbabwe. The effect of tillage system on weed density varied through the growth season and was dependent upon soil type and species composition of the weed community. Although weed responses to tillage system varied amongst species, we identified general trend effects on weed density on specific soils. At 3 weeks after crop emergence (WACE), weed density on loam soils was 76% and 96% higher in NT than in CONV during the 2009/2010 and 2010/2011 seasons, respectively, and on clay loam soils it was 37% and 33% higher in NT than CONV, respectively. Weed densities in NT and CONV were similar across all soil types at 6 WACE during the 2009/2010 and 2010/2011 seasons and at 9 WACE in 2009/2010. Tillage system did not affect weed density during the growth season on sandy loam soils. Weed diversity (Shannon index) was at least 75% higher in NT than CONV on loam and clay loam soils at 3 WACE during both seasons. It is likely these increases in weed densities following conversion to NT will exacerbate already prevalent weed management problems in the smallholder sector. Earlier weeding is recommended to suppress weed emergence and reduce likely associated crop yield losses. [ABSTRACT FROM AUTHOR]

Highlights • Early planting had the lowest risk of crop failure. • False season start plus N fertiliser application increased the risk of yield reduction. • Yield benefits resulted when planting coincided with the N flush with first rains. • High risk of complete crop failure in normal season experienced when no fertiliser was applied. Abstract Although rainfed cropping in semi-arid areas is risky due to frequent droughts and dry spells, planting early with the first rains is often expected to result in yield benefits. We hypothesised that planting early leads to yield benefits if the planting coincides with a mineral N flush at the start of the season but leads to crop failure if there is a false start to the cropping season. The effects of different management options, including tillage (ploughing and ripping), mulch (two levels 0 and 2 t ha−1) and fertility amendments (five levels: 0; 20 and 40 kg N ha−1; 5 t manure ha−1 and 5 t ha−1 manure + 20 kg N ha−1) on grain yields were simulated using the calibrated and tested APSIM model over a 30-year period (1984–2015). Yields were simulated and compared across seven planting date scenarios (1 November, 15 November, 30 November, 15 December, 31 December, 15 January and planting when cumulative rainfall of 20 mm was received in three consecutive days). Planting with the first rains with manure + 20 kg N ha−1 resulted in the best average yield of 2271 kg ha−1 whilst the poorest average yields of 22 kg ha−1 were observed with planting on 15 January with no fertility amendment (0 kg N ha−1). Planting early (1 Nov to 15 Nov) and with the first rains resulted in exceeding the food self-sufficiency threshold of 1080 kg ha-1 in 40–83 % of the cases if fertility amendments are applied, as well as a low probability of complete crop failure, ranging from 0 to 40%. Grain yield penalties due to a false start followed the trend: ripper + mulch > plough + mulch > ripper (no mulch) averaging 256, 190 and 182 kg ha-1 respectively across all the fertility treatments. The model was able to simulate the occurrence of the mineral N flush with the first rains. Its coincidence with planting resulted in average yield benefits of 712, 452, 382 and 210 kg ha-1 for the following respective planting dates: 1 Nov, 15 Nov, 30 Nov, variable date when >20 mm rainfall was received. Early planting, in combination with reduced tillage, mulch and N containing fertility amendments is critical to reduce risk of crop failure in the smallholder cropping systems of semi-arid areas of southern Africa and achieve the best possible yields. [ABSTRACT FROM AUTHOR]

Intercropping cereals with legumes can potentially enhance productivity and soil fertility. There is limited experimental evidence on the mechanisms underlying benefits or risks in intercropping systems and below-ground interactions in intercrops remain largely unstudied. Such understanding can inform strategies towards maximising returns to investments, particularly in poor fertility soils on smallholder farms in semi-arid areas of sub-Saharan Africa. Additive intercropping experiments were established covering several seasons (2010/11–2014/15) and different conditions (on-station and on-farm) to determine effects on soil chemical variables, root dynamics and yield of intercrops. Maize was planted with the first effective rains and received either no fertiliser or 40 kg N ha −1 . Cowpea was planted on the same date as maize or three weeks after planting maize in intercrops or sole stands and received no fertiliser. End-of-season available N was highest ( P < 0.05) under the late planted intercrop with 40 kg N ha −1 treatment in 2013/14. Addition of 40 kg N ha −1 significantly increased maize grain yield by 500–1100 kg ha −1 in the 2013/14 season. There was generally greater productivity and over-yielding in the intercrops compared with the sole crops; most intercrops had a land equivalent ratio >1. Intercropping, however, resulted in compromised cowpea yields especially under the relay intercrop compared with the sole cowpea stands whilst maize yield was either not affected or improved. We attributed this to the lack of below-ground niche differentiation in root distribution between maize and cowpea. Maize–cowpea intercropping with low doses of N fertiliser resulted in over-yielding compared with monocropping. Intercropping proved to be a robust option across seasons and soil types, confirming that it is a promising option for resource-poor smallholders. [ABSTRACT FROM AUTHOR]

An understanding of the contribution of manure applications to global atmospheric NO loading is needed to evaluate agriculture's contribution to the global warming process. Two field experiments were carried out at Dufuya wetland (19°17′S; 29°21′E, 1260 m above sea level) to determine the effects of single and split manure applications on emissions of NO from soil during the growing seasons of two rape and two tomato crops. Two field experiments were established. In the first experiment the manure was applied in three levels of 0, 15, and 30 Mg ha as a single application just before planting of the first tomato crop. In the second experiment the 15 and 30 Mg ha manure application rates were divided into four split applications of 3.75 and 7.5 Mg ha respectively, for each of the four cropping events. Single applications of 15 and 30 Mg ha manure once in four cropping events had higher emissions of NO than those recorded on plots that received split applications of 3.75 and 7.5 Mg ha manure at least up to the second test crop. Thereafter NO emissions on plots subjected to split applications of manure were higher or equal to those recorded in plots that received single basal applications of 30 Mg ha applied a week before planting the first crop. Seasonal split applications of manure to wetland vegetable crops can reduce emissions of NO at least up to the second seasonal split application. [ABSTRACT FROM AUTHOR]

Crop water productivity is often regarded as indicating the water use efficiency of crops, an important aspect, particularly under erratic rainfall conditions. This study investigated the effects of cattle manure and mineral-N fertilizer application on maize (Zea mays L.) water productivity (MWP) on clay and sandy soils in a smallholder farming area of Zimbabwe. Four fields previously exhibiting heterogeneous fertility were managed under the following treatments: control (no amendment) and cattle manure (5, 15, and 25 Mg ha-1) + 100 kg ha-1 mineral-N fertilizer for 7 yr. Thereafter, the effects of fertility treatment on MWP were expressed as actual maize grain yield produced per unit of seasonal transpiration modeled using AquaCrop. Furthermore, the relationship of MWP to physical soil properties was determined using principal component analysis. The MWP significantly (P < 0.05) improved with an increase in cattle manure plus mineral-N fertilizer application over control on both soils ranging between 0.5 and 1.7 kg m-3 and between 0.24 and 1.1 kg m-3 on clay and sandy soils, respectively. The MWP was significantly correlated (P < 0.05) with the steady-state infiltration rate on the clay soil and with soil organic C on the sandy soil. We concluded that cattle manure and mineral-N fertilizer application is key to MWP improvement in rainfed smallholder cropping systems and is closely coupled with improvements in physical soil properties on clay soil than sandy soil. Therefore, the observations attest to the importance of site-specific management that could contribute to efficient resource use in resource-constrained farming areas. [ABSTRACT FROM AUTHOR]

Wetlands are major natural sources of greenhouse gases (GHGs). In central and southern Africa, one of the most extensive wetlands are dambos (seasonal wetlands) which occupy 20–25% of land area. However, there are very little data on GHG methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) emissions from dambos, and this study presents the first estimates from dambos in Zimbabwe. The objective was to evaluate the effects of catena positions; upland, dambo mid-slope and dambo bottom, on GHG emissions along an undisturbed dambo transect. Methane emissions were −0.3, 29.5 and −1.3 mg m−2 hr−1, N2O emission were 40.1, 3.9 and 5.5 µg m2 hr−1, while CO2emissions were 2648.9, 896.2 and 590.1 mg m−2 hr−1for upland, mid-slope and bottom catena, respectively. Our results showed that uplands were important sources of N2O and CO2, and a sink for CH4, while the dambo mid-slope position was a major source of CH4, but a weak source of CO2and N2O. Dambo bottom catena was weak source GHGs. Overall, dambos were major sources of CH4and weak sources of N2O and CO2.We concluded that, depending on catenal position, dambos can be major or minor sources of GHGs. [ABSTRACT FROM AUTHOR]

Agricultural soils are a primary source of anthropogenic trace gas emissions, and the subtropics contribute greatly, particularly since 51% of world soils are in these climate zones. A field experiment was carried out in an ephemeral wetland in central Zimbabwe in order to determine the effect of cattle manure (1.36% N) and mineral N fertilizer (ammonium nitrate, 34.5% N) application on N2O fluxes from soil. Combined applications of 0 kg N fertilizer + 0 Mg cattle manure ha−1(control), 100 kg N fertilizer + 15 Mg manure ha−1and 200 kg N fertilizer + 30 Mg manure ha−1constituted the three treatments arranged in a randomized complete block design with four replications. Tomato and rape crops were grown in rotation over a period of two seasons. Emissions of N2O were sampled using the static chamber technique. Increasing N fertilizer and manure application rates from low to high rates increased the N2O fluxes by 37–106%. When low and high rates were applied to the tomato and rape crops, 0.51%, 0.40%, and 0.93%, 0.64% of applied N was lost as N2O, respectively. This implies that rape production has a greater N2O emitting potential than the production of tomatoes in wetlands. [ABSTRACT FROM PUBLISHER]

Seasonal wetland (dambo) cultivation in smallholder farming areas is important because it improves household food security. However, most farming practices, such as burning of vegetation and conventional tillage in dambo gardens, may reduce soil organic carbon (SOC) and nutrient dynamics. We evaluated the effects of simulated burning, vegetation clearing and clipping, and conventional tillage in dambo gardens on SOC, nutrient contents and biomass production over a 3-year period. The results showed that clearing and clipping of vegetation and conventional tillage reduced SOC, soil nutrient contents and biomass yields, while burning increased SOC and soil nutrient contents. For the 0–10 cm depth, conventional tillage, clearing and clipping resulted in a 37%, 34% and 18% decrease in SOC, respectively, after three seasons, burning resulted in a 25% increase in SOC, while there were no changes in the control after 3 years. For the 0–40 cm depth, the average change in SOC was 32%, 25% and 16% for conventional tillage, clearing and clipping, respectively. Locally and regionally, conventional tillage, clearing and clipping reduce SOC, nutrient contents and biomass production in dambos. Though annual burning increased SOC and nutrient contents in the short term, the long-term effects are uncertain, hence there is a need for long-term studies. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Reduced tillage plots planted 12–18 days earlier than conventional tillage plots. [•] Weeding frequency was 42.1–58.9% higher in reduced tillage plots. [•] Labor demand was 119.7% higher under reduced tillage. [•] Returns to investment were 42.7% higher under reduced tillage. [ABSTRACT FROM AUTHOR]

Abstract: The study was carried out to evaluate the impact of tillage system in combination with different herbicides on weed density, diversity, crop growth and yields on 18 farms in Kadoma, Zimbabwe. Experiments were set up as a split plot design with three replications on each farm. Tillage was the main plot (Conservation Tillage (CT), Conventional Tillage (CONV)) and weeding option (hand weeding, cyanazine, atrazine, glyphosate only and mixture of cyanazine + alachlor and atrazine + alachlor) as the sub-plots. Due to the heterogeneous nature of farmers' resource base, the farms were grouped into three farm types: high (Type 1), medium (Type 2) and poorly resourced farmers (Type 3). The hand hoe weeded treatments had 49 percent higher total weed densities in CT relative to CONV, and was statistically similar to the glyphosate treatment. The mixed pre-emergence herbicides reduced the diversity indices by 69 and 70 percent when compared to the hand hoe weeded treatment under CT in cotton and maize, respectively. The effectiveness of all pre-emergence herbicides were not influenced by tillage but were affected by farmers resource endowments with pronounced effect in Farm Type 1. Maximum plant heights of 85 and 238 cm were recorded for mixed pre-emergence herbicides under CT for cotton and maize, respectively. Minimum plant heights of 75 and 217 cm were recorded for the respective hand hoe weeded treatments. The hand hoe weeded treatments resulted in average cotton lint yield of 1497 and 2018 kg ha−1 for maize. The mixed pre-emergence herbicides treatments gave yields of 2138 and 2356 kg ha−1 of cotton and maize, respectively. The higher weed densities in CT under hand weeded treatments underscored the need for other weeding options. Similarly, a mixture of cyanazine + alachlor in cotton and atrazine + alachlor in maize is recommended for suppressing broad and grass weed populations and enhancing yields in CT systems. [Copyright &y& Elsevier]

A study was conducted from November 2000 to February 2001 to establish causes of poor protea plant growth in the Juliasdale and Norton-Darwendale commercial farming areas of Zimbabwe. Soil and leaf samples from farmer-perceived "deficient" and "normal" areas were analyzed. Soils perceived by farmers to be deficient had lower levels of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) compared with the normal soils. In Juliasdale, all cultivars from perceived-deficient samples had lower levels of zinc (Zn) in leaves compared with normal leaves. Leucospermum cultivar 'Tango' and Protea cultivar 'Moonshine' also had low levels of P and Zn in the deficient plants compared with the normal plants. In Norton-Darwendale, the Protea cultivar 'Moonshine' had lower levels of nitrogen (N), P, K, and boron (B) in perceived-deficient samples compared with normal samples. Soil-analysis data were generally comparable to leaf-analysis data, indicating the potential use of leaf analysis to determine nutritional requirements of proteas. [ABSTRACT FROM AUTHOR]

Climate change has been posited as the biggest threat to crop productivity in agro-systems, yet its impact on the water footprints of crop production for many regions remains uncertain. This study sought to determine evidence of historical climate change (1980–2010) and its resultant impact on the blue water footprint of winter wheat production in Zimbabwe. The analysis involved assessing the impact of climate change on wheat yield and crop water requirements, the key factors determining the blue water footprint. The CROPWAT model and the global water footprint assessment (WFA) standard were used to calculate the blue water footprint. Multiple linear regression was used to correlate climate variables to wheat yield, crop water requirements and the blue water footprint. Results show a significant (p < 0.05) warming of temperatures in the country's main wheat growing areas. Crop water requirements for winter wheat decreased by 4.88%, due to positive and negative trends in humidity and wind speed respectively. Between 1980 and 2000 the coupled effects of solar radiation at anthesis and maximum temperatures in July, August and September reduced wheat yields by 6.65%. The cumulative effects of climate change on crop water requirements and wheat yields increased the blue water footprint by 4%. The results of the study suggest that climate change and agricultural management factors might be equally responsible for the increase in the blue water footprint. Unlabelled Image • Climate change in Zimbabwe's wheat growing areas assessed using Mann-Kendall test. • Statistical modelling of climate variables and blue water footprint (WF) of wheat. • Climate change reduced wheat water requirements by 4.88% between 1980 and 2010. • Climate change reduced wheat yields by 6.65% between 1980 and 2010. • Blue WF increased by 4% due to climate impacts on yields and water requirements. [ABSTRACT FROM AUTHOR]

Abstract: Many farmers in central Mozambique intercrop maize with grain legumes as a means to improve food security and income. The objective of this study was to understand the farming system, and to evaluate the suitability of maize–legume intercropping to alleviate the biophysical and socio-economic constraints faced by smallholder farmers in Ruaca and Vunduzi villages, central Mozambique. To achieve this we characterised the farming systems and measured grain yields, rainfall infiltration, economic returns and acceptability of maize–legume intercrops under different N and P application rates. Two intercropping strategies were tested: (a) an additive design of within-row intercropping in which legume was intercropped with alternating hills of maize within the same row; maize plant population was the same as sole crop maize, and (b) a substitutive design with distinct alternating rows of maize and legume (local practice). Fertiliser treatments imposed on all treatments were: (i) no fertiliser, (ii) 20kgPha−1, (iii) 20kgPha−1 +30kgNha−1, and (iv) 20kgPha−1 +60kgNha−1. Intercrops were relatively more productive than the corresponding sole crops; land equivalent ratios (LER) for within-row intercropping ranged between 1.1 and 2.4, and between 1.0 and 1.9 for distinct-row intercropping. Average maize yield penalty for intercropping maize and pigeonpea in the within-row was small (8%) compared with 50% in the distinct-row design; average (season×fertiliser) sole maize yield was 3.2tha−1. Intercropping maize and cowpea in within-row led to maize yield loss of only 6%, whereas distinct-row intercropping reduced maize yield by 25% from 2.1tha−1 of sole maize (season×fertiliser). Cowpea yield was less affected by intercropping: sole cowpea had an average yield of 0.9tha−1, distinct-row intercropping (0.8tha−1) and the within-row intercropping yielded 0.9tha−1. Legumes were comparatively less affected by the long dry spells which were prevalent during the study period. Response to N and P fertiliser was weak due to poor rainfall distribution. In the third season, maize in rotation with pigeonpea and without N fertiliser application yielded 5.6tha−1, eight times more than continuous maize which was severely infested by striga (Striga asiatica) and yielded only 0.7tha−1. Rainfall infiltration increased from 6mmh−1 to 22mmh−1 with long-term maize–legume intercropping due to a combination of good quality biomass production which provided mulch combined with no tillage. Intercropping maize and pigeonpea was profitable with a rate of return of at least 343% over sole maize cropping. Farmers preferred the within-row maize–legume intercropping with an acceptability score of 84% because of good yields for both maize and legume. Intercropping increased the labour required for weeding by 36% compared with the sole crops. Farmers in Ruaca faced labour constraints due to extensification thus maize–pigeonpea intercropping may improve productivity and help reduce the area cultivated. In Vunduzi, land limitation was a major problem and intensification through legumes is amongst the few feasible options to increase both production and productivity. The late maturity of pigeonpea means that free-grazing of cattle has to be delayed, which allows farmers to retain crop residues in the fields as mulch if they choose to; this allows the use of no-tillage practises. We conclude that maize–legume intercropping has potential to: (a) reduce the risk of crop failure, (b) improve productivity and income, and (c) increase food security in vulnerable production systems, and is a feasible entry point to ecological intensification. [Copyright &y& Elsevier]

Abstract: Controversy surrounds the promotion of conservation agriculture (CA) in smallholder farming systems in sub-Saharan Africa. The introduction of CA is a profound change in farm management. Benefits in reduced erosion and stabilized crop production may be obtained, but technical performance at field level is but one of the determinants of adoption. For various reasons, all of the CA principles are not always fully implemented by farmers and results not as favourable as expected. As with other approaches to increasing agricultural productivity, the production constraints, farmers’ objectives, and the expected benefits and costs of implementing CA are important aspects that influence adoption. At farm and village levels, trade-offs in the allocation of resources become important in determining how CA may fit into a given farming system. At a regional level, factors such as the market conditions, interactions among stakeholders and other institutional and political dimensions become important. At each level, opportunities or difficulties emerge that enhance or impede development, adaptation and adoption of CA. The ex-ante identification of situations for where CA (and which form of CA) is appropriate demands research from a multi-stakeholder, multi-level, and interdisciplinary perspective. Recommendations are made where research is required to address key knowledge gaps. [Copyright &y& Elsevier]

In complex mixed crop-livestock systems with limited resources and biomass scarcity, crop residues play an important but increasingly contested role. This paper focuses on farming systems in the semi-arid areas of Zimbabwe, where biomass production is limited and farmers integrate crop and livestock activities. Conservation Agriculture (CA) is promoted to intensify crop production, emphasizing the retention of surface mulch with crop residues (CR). This paper quantifies the associated potential economic trade-offs and profitability of using residues for soil amendment or as livestock feed, and explores alternative biomass production options. We draw on household surveys, stakeholder feedback, crop, livestock and economic modeling tools. We use the Trade-Off Analysis Model for Multi Dimensional Impact Assessment (TOA-MD) to compare different CR use scenarios at community level and for different farm types: particularly the current base system (cattle grazing of maize residues) and sustainable intensification alternatives based on a CA option (mulching using maize residues ± inorganic fertilizer) and a maize–mucuna ( Mucuna pruriens ) rotation. Our results indicate that a maize–mucuna rotation can reduce trade-offs between CR uses for feed and mulch, providing locally available organic soil enhancement, supplementary feed and a potential source of income. Conservation Agriculture without fertilizer application and at non-subsidized fertilizer prices is not financially viable; whereas with subsidized fertilizer it can benefit half the farm population. The poverty effects of all considered alternative biomass options are however limited; they do not raise income sufficiently to lift farmers out of poverty. Further research is needed to establish the competitiveness of alternative biomass enhancing technologies and the socio-economic processes that can facilitate sustainable intensification of mixed crop-livestock systems, particularly in semi-arid environments. [ABSTRACT FROM AUTHOR]