Smallholder Cropping Systems Research Articles

Smallholder Cropping Systems Contribute Limited Greenhouse Gas Fluxes in Upper Eastern Kenya

The contribution of smallholder farming systems to the National greenhouse gas (GHG) budget is missing in most developing countries, including Kenya. Data on the contribution of smallholder cropping systems to the GHG balance is essential for realising Sustainable Development Goal 13 on climate action, i.e., on nationally determined contributions (NDCs) and in compliance with the Paris Agreement. Do smallholder farming systems act as nature-based solutions for greenhouse gas emissions reduction? This study evaluated GHG emissions from cropping systems under on-farm smallholder farming conditions. We had five cropping systems on two smallholder farms: sole maize, maize-bean intercrop, coffee, banana, and agroforestry. Gas samples were collected using three static chambers per cropping system. The gas samples were analysed using gas chromatography (GC) fitted with a 63Ni-electron capture detector (ECD) for N2O and flame ionisation detector (FID) for CH4 and CO2 using N as carrier gas. Cumulative annual fluxes of (CH4, N2O, and CO2) varied significantly in farms one and two across the cropping systems. The cumulative soil GHG fluxes ranged from -1.34 kg CH4-C ha−1 yr−1 under agroforestry to -0.77 kg CH4-C ha−1 yr−1 under banana for CH4, 0.30 kg N2O-N ha−1 yr−1 to 1.23 kg N2O-N ha−1 yr−1 for N2O and 5949 kg CO2-C ha−1 yr−1 to 12954 kg CO2-C ha−1 yr−1 for CO2. The maize grain yields ranged from 0 to 3.38 Mg ha−1. The N2O yields scaled emissions ranged from 0.10 to 0.26 g kg−1 maize and 0.68 to 1.30 g kg−1 beans. Smallholder farmers in Upper Eastern Kenya contribute a limited amount of soil GHG emissions and thus could act as a nature-based solution for lowering agricultural emissions.

The Use and Impact of Multi-Nutrient Fertilizers in Kenyan Smallholder Cropping Systems

Despite the documented advantages to multi-nutrient fertilizer application their use remains low across smallholder cropping systems in Kenya. A better understanding of the key influences that foster (and restrict) their use can chart a path for new ways to encourage innovation on-farm.

Immediate and residual-effects of sole and intercropped grain legumes in maize production systems under rain-fed conditions of Northern Tanzania

Intercropping of maize with grain-legume crops predominates on smallholder farms in East Africa. However, the growth and development of crops and their interaction with fertilizer in intercropping systems are not well understood. We sought to answer the questions: (i) what are the effects of fertilizer on the growth and development of maize-pigeonpea and maize-lablab intercropping systems under variable agroecological conditions? (ii) what are the residual effects of two seasons of sole and intercrops of maize, pigeonpea and lablab on a succeeding maize crop? We studied pure stands of maize, long-duration pigeonpea, medium-duration pigeonpea and lablab, and additive intercropping combinations on eight farms in Babati, Tanzania. The intercropping combinations studied were: maize with long-duration pigeonpea, maize with medium-duration pigeonpea and maize with lablab. Three fertilizer levels were applied: no fertilizer; 40 kg P ha −1 ; and 90 kg N ha −1 + 40 kg P ha −1 . The P was applied at planting in the form of triple superphosphate to both maize and legumes, thus in intercrops the 40 kg P ha −1 was shared between maize and legume. The N was spot-applied in the form of urea in three equal splits, only on maize. The trials were implemented for two consecutive cropping seasons (2017/2018 and 2018/2019), without changing treatments and plot locations. To evaluate the residual effect of grain legumes, we planted a sole crop of maize in the third season (2019/2020) in all plots, with no addition of fertilizer. Maize and pigeonpea were sown simultaneously, while lablab was relay-planted one month after maize. Maize dry matter (DM) and grain yield were not significantly affected by the presence of legumes, but were about twice as large in 2017/2018 as in 2018/2019 season, likely due to the considerably higher rainfall in the 2017/2018 season. Legume productivity was more consistent across the two seasons. Legume crops in the intercrops produced significantly less DM and grain yield than in their respective pure stands, but maize yield did not differ significantly between sole and intercrops. The productivity of maize was significantly increased by N fertilization, but the legumes responded positively only to P fertilizer in the 2017/2018 season. Land-equivalent and area-time-equivalent ratios of intercropping systems were consistently greater than one. The DM and grain yield of maize following two seasons of legumes was consistently larger than in plots where maize was grown continuously. The P-fertilizer applied in the preceding seasons had significant residual effects on the yield of the succeeding maize crop. The temporal niche complementarity of pigeonpea and lablab with maize minimized competition in the intercrops, although intercrops are clearly more demanding in labor at planting and harvest. Overall, our results showed the superior performance of maize-legume intercropping over sole maize, both in terms of additional grain yield within a season and the residual effects in the succeeding season. We did not observe biotic constraints in the succeeding maize crop. Maize-legume intercropping with fertilizer application was effective in enhancing the productivity of smallholder cropping systems.

Profit efficiency in family-owned crop farms in Eastern Cape Province of South Africa: a translog profit function approach

BackgroundFarm productivity on smallholder family-owned crop farms remains low despite several interventions to transform agriculture especially in developing countries. Farmers in rural areas face serious constraints that impede their productive capacities for the principal dietary staple, notably maize. Smallholder farmers have access to unprofitable markets that in turn make their enterprises less profitable. Efforts to commercialise smallholder maize production have not yielded desired results. This study, therefore, estimates profit efficiency and its determinants in the smallholder cropping systems in the Eastern Cape Province of South Africa.MethodologyA random sample of 158 smallholder maize farmers was selected. A normalised translog profit function was then fitted by means of a one-step estimation of technical efficiency and its determinants using the STATA software.ResultsThe results indicate that cost of fertiliser and area under cultivation for maize were the positive drivers of profitability. Complementarities among resources were very important determinants of profit.ConclusionThe study concludes that family-owned farms have a positive effect on crop production. Farm profits rise with cultivated area in maize farms. Therefore, the study recommends that policy favouring smallholder commercialisation would improve farm profits.

Tradeoffs and Economic Impacts of Replacing Tobacco with Alternative Crops in Smallholder Cropping Systems in Hoima District, Uganda

Tradeoffs and Economic Impacts of Replacing Tobacco with Alternative Crops in Smallholder Cropping Systems in Hoima District, Uganda

Nitrous Oxide Emissions from Smallholders’ Cropping Systems in Sub-Saharan Africa

Increased concentration of atmospheric nitrous oxide (N2O), a potent greenhouse gas (GHG), is of great concern due to its impact on ozone layer depletion leading to climate change. Ozone layer depletion allows penetration of ultraviolet radiations, which are hazardous to human health. Climate change culminates in reduced food productivity. Limited empirical studies have been conducted in Sub-Saharan Africa (SSA) to quantify and understand the dynamics of soil N2O fluxes from smallholder cropping systems. The available literature on soil N2O fluxes in SSA is limited; hence, there is a pressing need to consolidate it to ease mitigation targeting and policy formulation initiatives. We reviewed the state of N2O emissions from selected cropping systems, drivers that significantly influence N2O emissions, and probable soil N2O emissions mitigation options from 30 studies in SSA cropping systems have been elucidated here. The review outcome indicates that coffee, tea, maize, and vegetables emit N2O ranging from 1 to 1.9, 0.4 to 3.9, 0.1 to 4.26, and 48 to 113.4 kg N2O-N ha-1 yr−1, respectively. The yield-scaled and N2O emissions factors ranged between 0.08 and 67 g N2O-N kg−1 and 0.01 and 4.1%, respectively, across cropping systems. Soil characteristics, farm management practices, and climatic and environmental conditions were significant drivers influencing N2O emissions across SSA cropping systems. We found that site-specific soil N2O emissions mitigation measures are required due to high variations in N2O drivers across SSA. We conclude that appropriate fertilizer and organic input management combined with improved soil management practices are potential approaches in N2O emissions mitigation in SSA. We recommend that (i) while formulating soil N2O emissions mitigation approaches, in SSA, policymakers should consider site-specific targeting approaches, and (ii) more empirical studies need to be conducted in diverse agroecological zones of SSA to qualify various mitigation options on N2O emissions, yield-scaled N2O emissions, and N2O emission factors which are essential in improving national and regional GHG inventories.

The role and impact of oil palm plantations in landscape management in South Tapanuli District, North Sumatra, Indonesia

This study was conducted in South Tapanuli District, which is one of the two oil palm centres implementing the landscape management project. Data collected from Regional Plan documents and 169 smallholder samples and analysed with Cross Tabulation and Compare Means Test. The results show that landscape management has been implemented through Regional Planning and various regulations. However, many institutions are authorized to manage landscape, which occasionally result in confusing and contradictory decisions. Through regulations, the Government has limited the expansion of oil palm plantations by specifying Forest and Food Regions. Intensification and diversification approaches are also considered as alternatives for balancing land allocations among sectors and commodities. Intensification is taught through the Sustainable Oil Palm Field School Program, which can improve smallholder knowledge and implementation of landscape management. However, smallholders with larger plantation areas are less interested in participating in the program. Diversifications were indicated through the smallholder cropping system, which is focused on potential commodities such as rubber, coffee or cacao. Smallholders perceive other commodities as less profitable because most of their agribusiness systems are less developed than the palm oil agribusiness system. Therefore, improvement in every potential agribusiness system is recommended to optimize landscape management in South Tapanuli.

Combined effects of landscape composition and pesticide use on herbivore and pollinator functions in smallholder farms

BackgroundLandscape composition has the potential to foster regulating ecosystem services such as pollination and biocontrol in temperate regions. However, most landscape studies do not take pesticide use into account even though it is the main control strategy worldwide and has negative impacts on beneficial insects. Moreover, few studies have explored these combined effects in smallholder cropping system with diverse landscapes and small cultivated fields.MethodsWe assessed the effect of semi-natural cover and pesticide use on pollinator and herbivore abundances and functions in 9 fields in the Ecuadorian Andes through participatory experiments with smallholder farmers. We performed a path analysis to quantify the effects of landscape and pesticide use on herbivory, pollination and ultimately yield.ResultsPesticide use significantly reduced pollinator abundance but had no significant effect on pest abundance. Similarly, we found non-significant effects of landscape composition on either herbivory and pollination. The study also provides new information on understudied Andean lupine’s pests and pollinators, whose application for small farmers is discussed. Finally, we hypothesize that peculiarities of tropical smallholder cropping systems and landscapes could explain the non-significant landscape effects on insect-based processes, which calls for more research in places outside the well-studied temperate region.ConclusionsLandscape composition did not show any significant effect on pest and pollinator while pesticide use decreased the abundance pollinators, but with no significant effect on yield. This study also provides information about Andean lupine reproduction and overcompensation mechanisms that could be of interest for local farmers and researchers of this understudied crop.

Estimation of Maize (Zea mays L.) Yield Per Harvest Area: Appropriate Methods

Standardization of crop yield estimation methods at various levels of farming helps to obtain accurate agricultural statistics as well as assessing the suitability of agricultural practices under various production conditions. The current paper reviews various maize yield estimation methods, taking into account available yield parameters, and it also analyses the yield gap between maize potential and attainable yield. The easiest and more reliable methods of yield estimation are based on yield parameters collected from the field. However, farmer estimation methods are cheaper and faster compared to any other method of yield estimation from farmers’ fields. This paper also elaborates on the importance of the use of more complex methods for yield estimation, such as remote sensing and crop modelling. These complex methods are more accurate and can predict yield before field harvest with less deviation from the exact harvest yield. However, they are very expensive and not efficient for small plots of land (less than 1 ha). Factors that contribute to the gap between potential and actual yield include poor implementation of agricultural policies, strict regulation of fertilizer inputs, vulnerability of smallholder cropping systems to adverse climatic conditions, occurrence of biotic and abiotic constraints, as well as unavailability of seeds and labor.

Energy-efficient, sustainable crop production practices benefit smallholder farmers and the environment across three countries in the Eastern Gangetic Plains, South Asia

Abstract In the Eastern Gangetic Plains of South Asia current agronomic practices are energy-intensive, and this contributes to higher cropping system production costs and CO2-equivalent greenhouse gas emissions. Increasingly uncertain and scarce resources, together with an increasingly variable and changing climate, make conventional crop production vulnerable and unsustainable. We hypothesized that replacing traditional crop management with conservation agriculture based-sustainable intensification practices would reduce energy requirements and CO2-equivalent emissions while increasing energy use efficiency. Across three major cropping systems (rice-wheat, rice-maize and rice-lentil) we tested improved management practices against a conventional baseline on over 400 on-farm trials. Improved management practices significantly reduced the total energy used in rice-wheat cropping systems, from 30,045 MJ ha−1 under traditional baseline practice to around 26,500 MJ ha−1. Similar savings in total energy used were observed in rice-maize and rice-lentil cropping systems; additionally, energy use was significantly more efficient under improved management in all three cropping systems. CO2-equivalent emissions were reduced by around 10% under cropping systems with improved management compared to emissions from baseline systems. For all cropping systems the rice-equivalent yield and net income were inversely proportional to the specific energy of the system under improved management but not under traditional practice. This study demonstrated that high cropping system yields under improved management practices increased energy use efficiency while reducing CO2-equivalent emissions. Our research enables farmers in the Eastern Gangetic Plains to produce more food, more sustainably, under increasing climate variability and change. These results are applicable across the Eastern Gangetic Plains region of over 450 million people and also have broader application for smallholder cropping systems in developing and emerging-economy countries globally.

Short-term influence of biochar and fertilizer-biochar blends on soil nutrients, fauna and maize growth

Use of inorganic fertilizers in smallholder cropping systems in Africa is often becoming inefficient due to increasing unresponsiveness to fertilizer application. A study was conducted for 2 years (four seasons) to assess the effects of biochar made from Prosopis juliflora (Sw.) DC. biomass on nutrients, fauna abundance and subsequent influence on maize planted in a nitisol. There were 12 amendments comprising: (i) biochar applied alone at a rate of 5 and 10 Mg ha−1; (ii) three fertilizer types applied separately (di-ammonium phosphate (18:46:0), urea (46:0:0) and composite NPK (23:23:0)); (iii) six fertilizer + biochar blends of the three fertilizer types and two biochar rates (0.05 and 0.1 Mg ha−1); and (iv) a control with no inputs. Treatments were replicated four times in a randomized complete block design. The amendments were applied in the first two seasons, while the last two were used to assess residual effects. At the end of the first two seasons, total C and N were higher in soils where biochar or fertilizer + biochar was applied, with more than 15.0 g C and 1.9 g N kg−1, compared to 10.4 g C and 1.0 g N kg−1 in control plots. Available P and exchangeable K were over 200% and 100% higher in biochar or fertilizer + biochar amended than control soils, respectively. Application of biochar had no effects on macrofauna such as beetles, centipedes, millipedes, termites and ants, but attracted earthworms. Soil that received 10 Mg biochar ha−1 recorded twice the number of earthworms (207 individuals m−2) compared to soil with 5 Mg biochar ha−1 (105 individuals m−2) and control (97 individuals m−2). Soils which received biochar, with or without fertilizer, had higher taxonomic richness (7.0 species) compared to soils which received DAP (2.8) or NPK (3.8). Nematodes, particularly bacterivorous groups, decreased by more than eight times with biochar application. In the first and second seasons, 5.6 Mg maize grain yield ha−1 was obtained from plots amended with biochar (without fertilizer), which was about six times higher than that harvested from unfertilised control at 0.9 Mg ha−1. Yield differences in plots where fertilizer was applied with or without biochar were not significant. Yield in the third and fourth seasons declined to 3.2 and 1.5 Mg ha−1, irrespective of fertilizer type or biochar amounts.

Maize–lablab intercropping is promising in supporting the sustainable intensification of smallholder cropping systems under high climate risk in southern Africa

AbstractIdentifying options for the sustainable intensification of cropping systems in southern Africa under prevailing high climate risk is needed. With this in mind, we tested an intercropping system that combined the staple crop maize with lablab, a local but underutilised legume. Grain and biomass productivity was determined for four variants (i) sole maize (sole-maize), (ii) sole lablab (sole-lablab), (iii) maize/lablab with both crops sown simultaneously (intercropped-SP) and (iv) maize/lablab with lablab sown 28 days after the maize crop (intercropped-DP). Soil water and weather data were monitored and evaluated. The trial was conducted for two seasons (2015/2016 and 2016/2017) at two sites in the Limpopo Province, South Africa: Univen (847 mm rainfall, 29.2 °C maximum and 18.9 °C minimum temperature average for the cropping season over the years 2008–2017) and Syferkuil (491 mm rainfall, with 27.0 °C maximum and 14.8 °C minimum temperature). Analysis revealed three key results: The treatment with intercropped-SP had significantly lower maize yields (2320 kg ha−1) compared with maize in intercropped-DP (2865 kg ha−1) or sole-maize (2623 kg ha−1). As expected, maize yields in the El Niño affected in season 2015/2016 were on average 1688 kg ha−1 lower than in 2016/2017. Maize yields were significantly lower (957 kg ha−1) at Univen, the warmer site with higher rainfall, than at Syferkuil. In 2015/2016, maximum temperature at Univen exceeded 40 °C around anthesis. Furthermore, soil water was close to the estimated permanent wilting point (PWP) for most of the cropping season, which indicates possible water limitations. In Syferkuil, the soil water was maintained well above PWP. Lablab yields were low, around 500 ha−1, but stable as they were not affected by treatment across season and site. Overall, the study demonstrated that intercropped-DP appears to use available soil water more efficiently than sole maize. Intercropped-DP could therefore be considered as an option for sustainable intensification under high climate risk and resource-limited conditions for smallholders in southern Africa.

Partnerships for Progress in a Smallholder Cropping System

Partnerships for Progress in a Smallholder Cropping System

Learning from the soil’s memory: Tailoring of fertilizer application based on past manure applications increases fertilizer use efficiency and crop productivity on Kenyan smallholder farms

Abstract The large uncertainty in yield response to fertilizer application within smallholder cropping systems in sub-Saharan Africa (SSA) limits efforts aimed at intensifying crop production based on increased fertilizer application. We assessed the key field-scale cause of variability in maize (Zea mays) grain yield response to fertilizer nitrogen (N), phosphorus (P) and potassium (K) in the Sidindi area of Western Kenya based on past manure application, distance from the homestead, and clay and silt contents. We used data from nutrient omission trials conducted on 23 farms over seven consecutive cropping seasons covering the period 2013–2016, without changing treatments or plot location. Treatments included a control and PK, NK, NP and NPK. Accounting for past manure application increased the explained variability in maize yield, and yield response to N, P, and K application. Mean treatment maize grain yield in the control, PK, NK, NP and NPK treatments were 1.0, 2.2, 1.5, 2.9 and 4.5 t ha−1 at 88% dry matter respectively in fields without past manure application, and 2.4, 2.7, 4.4, 4.9 and 5.4 t ha-1 in fields which had received animal manure in at least two out of three seasons prior to the start of the trials. Mean maize yield response to N, P and K application was 2.3, 3.0 and 1.6 t ha−1 respectively in fields without past manure application, and 2.8, 1.1 and 0.6 t ha−1 in fields with past manure application. In the seventh cropping season, past animal manure application contributed a fertilizer equivalent of 28.3, 29.8 and 31.5 kg ha−1 of N, P and K, respectively. At both the onset and at the start of the last season, fields with past animal manure application had on average higher contents of SOC, available P and exchangeable K, yet differences were not always significant within treatments. Accounting for past animal manure application reduces crop fertilizer requirements for P and K as well as decreasing uncertainty in yield response to fertilizer. We conclude that the strong influence of past animal manure application on yield response to fertilizer application merits the inclusion of past manure application as a co-variate in analysis of yield response data from smallholder cropping systems of SSA.

Risk management options in maize cropping systems in semi-arid areas of Southern Africa

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.

Effect of Land related Factors on Smallholder Cropping Systems in Rural Sri Lanka

There are marked differences between the Wet and Intermediate Zones of Sri Lanka in the type of crops selected and cropping practices used by smallholder farmers. This study was specifically geared to i) identify the major smallholder cropping systems in the study area, ii) analyze the relationship between land size and cropping intensity, and iii) to determine how land size, land ownership, proximity to land from the homestead influences the selection of different cropping systems. Data and information were collected from a sample of 96 households in the four selected villages representing each from Kalutara, Kegalle, Moneragala and Hambanthota districts using semi structured interviews, direct observations, case studies and farm sketches. Data were analyzed using a variety of statistical methods including chisquare and general linear model. The study found that the allocation of land for the selected crops was lower in the villages of Kegalle and Kalutara districts compared to the Moneragala and Hambanthota. The study also ascertained that an increase in land size resulted in a decrease in the number of crops grown and cropping intensity in home gardens and rubber smallholdings. Also lower priority was given to intercropping of rubber smallholdings by farmers owned with more than 2 acre of land available, and vice versa. The income level of the household had a considerable influence on several factors including, selection of cropping systems, size of land holding, and allocation of land to different crops. Variation in land ownership between villages had a significant effect on the establishment of crops (p<0.001) i.e. owner-cultivated smallholdings comprised a mixture of many short term and permanent crops while tenant cultivated smallholdings consisted solely of short-term crops. Distance of the land from the homestead had a significant effect on the selection or non-selection of cropping systems. Consequently, crops with less risk and maintenance were grown further out from homestead (e.g. citronella) and rubber compared to banana and tea. Similarly, the form of land smallholdings consisted of a mixture of intercrops (including other permanent crops), and soil protection methods were practiced, whereas tenanted farms had seasonal intercrops with less attention paid to soil protection and improvement. KEYWORDS: Land ownership, Proximity, Land size, Smallholders, Cropping systems

Comparative fertilization effects on maize productivity under conservation and conventional tillage on sandy soils in a smallholder cropping system in Zimbabwe

Components of conservation agriculture (CA) are being widely promoted in southern Africa as one of the strategies to increase food security and mitigate rural poverty, despite there being scarce empirical evidence on their efficacy on degraded soils. On-farm trials were established in Eastern Zimbabwe to assess the effects of tillage systems on maize grain yields under rain-fed conditions across a soil organic matter gradient. The study compared the effects of a) conventional tillage (CT), b) basins-based CA (B-CA), and c) furrow-based CA (F-CA) on sandy soils with contrasting soil organic carbon (SOC). Fields had SOC ranging from 0.18 to 0.89% and clay content from 60 to 150 g kg−1. A nutrient omission trial using nitrogen (N), phosphorus (P), potassium (K), cattle manure (M) and their combinations was set up on twenty farms each with two fields selected by the host farmer as either poor or rich in soil fertility in Study 1, and ten farms in Study 2, each with two fields selected as in Study 1. Fields selected by farmers as poor fields had SOC <0.4%, were more acidic, had lower amounts of exchangeable bases (Mg, Ca, K), available P and total N. These lab-based results corroborated well with farmers’ local rating of soil fertility. For Study 1, nutrient management significantly increased maize yields across the three years (P < 0.001) but there were no significant tillage effects observed. Grain yields increased from 0.3 Mg ha−1 for unfertilized control to 4.1 Mg ha−1 for the NPKSM treatment. Yield response to N was consistently larger than for P or K, irrespective of soil fertility status. Response to N increased with increase in soil fertility, suggesting higher N use efficiency for soils with higher SOC. Except for NPKSM, no significant yield differences were observed under the residual and additive plots for treatments, when N was added each year. At productivity levels of <4 Mg ha−1, there was no yield gain in applying both P and K for consecutive years, suggesting that nutrient investments by resource constrained farmers for Year 2 could target only N application. For Study 2, maize grain yields were significantly higher under B-CA compared with both F-CA and CT in the second year (P < 0.01). The consistently larger NPKSM yields highlight the importance of integrated nutrient management, combining mineral and organic sources of nutrients to ensure maize productivity on poor soils in agro-ecologies receiving unreliable rainfall.

Cultivar mixtures: a meta-analysis of the effect of intraspecific diversity on crop yield.

Extensive research has shown that greater plant community diversity leads to higher levels of productivity and other ecosystem services, and such increased diversity has been suggested as a way to improve yield and agricultural sustainability. Increasing intraspecific diversity with cultivar mixtures is one way to increase diversity in agricultural systems. We examined the relationship between intraspecific diversity and yield in cultivar mixtures using a meta-analysis of 91 studies and >3,600 observations. Additionally, we investigated how environmental and management factors might influence this relationship, and if the yield stability of cultivar mixtures differed from that of monocultures. We found that the yield increased by 2.2% overall in cultivar mixtures relative to their monoculture components. Mixtures with more cultivars and those with more functional trait diversity showed higher relative yields. Under biotic stressors, such as disease pressure, and abiotic stressors, such as low levels of soil organic matter and nutrient availability, this diversity effect was stronger, resulting in higher relative yields. Finally, cultivar mixtures generally showed higher yield stability compared to monocultures, especially in response to annual weather variability at a site over time. This practice of mixing cultivars can be integrated into intensified cropping systems where species monocultures dominate, as well as in smallholder cropping systems where low-cost improvements are in demand. Overall, these results suggest that cultivar mixtures are a viable strategy to increase diversity in agroecosystems, promoting increased yield and yield stability, with minimal environmental impact.

Quantifying Fertilizer Application Response Variability with VHR Satellite NDVI Time Series in a Rainfed Smallholder Cropping System of Mali

Soil fertility in smallholder farming areas is known to vary strongly on multiple scales. This study measures the sensitivity of the recorded satellite signal to on-farm soil fertility treatments applied to five crop types, and quantifies this fertilization effect with respect to within-field variation, between-field variation and field position in the catena. Plant growth was assessed in 5–6 plots per field in 48 fields located in the Sudano-Sahelian agro-ecological zone of southeastern Mali. A unique series of Very High Resolution (VHR) satellite and Unmanned Aerial Vehicle (UAV) images were used to calculate the Normalized Difference Vegetation Index (NDVI). In this experiment, for half of the fields at least 50% of the NDVI variance within a field was due to fertilization. Moreover, the sensitivity of NDVI to fertilizer application was crop-dependent and varied through the season, with optima at the end of August for peanut and cotton and early October for sorghum and maize. The influence of fertilizer on NDVI was comparatively small at the landscape scale (up to 35% of total variation), relative to the influence of other components of variation such as field management and catena position. The NDVI response could only partially be benchmarked against a fertilization reference within the field. We conclude that comparisons of the spatial and temporal responses of NDVI, with respect to fertilization and crop management, requires a stratification of soil catena-related crop growth conditions at the landscape scale.

Fertilizer micro-dosing increases crop yield in the Sahelian low-input cropping system: A success with a shadow

ABSTRACTOver the years, a scarcity of information on nutrient gains or losses has led to overemphasis being placed on crop yields and economic income as the direct benefits from fertilizer micro-dosing technology. There is increasing concern about the sustainability of this technology in smallholder Sahelian cropping systems. This study was designed in the 2013 and 2014 cropping seasons to establish nutrient balances under fertilizer micro-dosing technology and their implications on soil nutrient stocks. Two fertilizer micro-dosing treatments [2 g hill−1 of diammonium phosphate (DAP) and 6 g hill−1 of compound fertilizer Nitrogen-Phosphorus-Potassium (NPK) (15-15-15)] and three rates of manure (100 g hill−1, 200 g hill−1 and 300 g hill−1) and the relevant control treatments were arranged in a factorial experiment organized in a randomized complete block design with three replications. On average, millet (Pennisetum glaucum (L.) R.Br.) grain yield increased by 39 and 72% for the plots that received the fertilizer micro-dosing of 6 g NPK hill−1 and 2 g DAP hill−1, respectively, in comparison with the unfertilized control plots. The average partial nutrients balances for the two cropping seasons were −37 kg N ha−1yr−1, −1 kg P ha−1yr−1 and −34 kg K ha−1yr−1 in plots that received the application of 2 g DAP hill−1, and −31 kg N ha−1yr−1, −1 kg P ha−1yr−1 and −27 kg K ha−1yr−1 for 6 g NPK hill−1. The transfer of straw yields accounted for 66% N, 55% P and 89% K for removal. The average full nutrient balances for the two cropping seasons in fertilizer micro-dosing treatments were −47.8 kg N ha−1 yr−1, −6.8 kg P ha−1 yr−1 and −21.3 kg K ha−1 yr−1 which represent 7.8, 24.1 and 9.4% of N, P and K stocks, respectively. The nutrient stock to balance ratio (NSB) for N decreased from 13 to 11 and from 15 to 12 for the plots that received the application of 2 g DAP hill−1 and 6 g NPK hill−1, respectively. The average NSB for P did not exceed 5 for the same plots. It was concluded that fertilizer micro-dosing increases the risk of soil nutrient depletion in the Sahelian low-input cropping system. These results have important implications for developing an agro-ecological approach to addressing sustainable food production in the Sahelian smallholder cropping system.