Productivity and profitability of maize-legume cropping systems under conservation agriculture among smallholder farmers in Malawi

A study was conducted from 2014 to 2017 in Malawi to elucidate the short-term effects of maize-legume intercropping and rotation systems under conservation agriculture (CA) and conventional tillage (CT) on crop productivity and profitability. Twelve farmers hosted on-farm trials per district, in three districts, with each farmer having six plots. The design of the study was randomised complete block design arranged in a split plot fashion with tillage as main plot and cropping systems as sub-plots, with each farmer acting as a replicate. CA had 1400 and 3200 kg ha−1 more maize grain yield in the second and third seasons, respectively compared with CT. In the first two seasons, CT had 310, 180 and 270 kg ha−1 more cowpea, soybean and pigeon pea grain yields in Salima, Mzimba and Mangochi districts, respectively, compared with CA. Similarly, CA had 1100 and 950 kg ha−1 more groundnut grain yields than CT in Salima and Mzimba districts in the second and third seasons, respectively. Over the three-year study period, partial land equivalent ratio for maize ranged from 0.78 to 1.24. Largest net returns were achieved by intercropping maize with pigeon pea in Mangochi and rotating maize and groundnut in Mzimba and Salima districts

Productivity of pigeon pea and maize rotation system in Balaka District, Southern Malawi

In Malawi, some parts of the country, such as Balaka District in Southern Malawi, are particularly prone to erratic rains with poor soil productivity. In the 2015/2016 rainy season some learning centres (LCs) focusing on pigeon-pea (Cajanus cajan) – maize (Zea mays L) rotations were established in four sections of Ulongwe Agriculture Extension Planning Area (EPA) in Balaka District to enhance soil fertility, nutrition and income diversification for increased resilience to production under erratic rain condition. Up to 132 plots of pigeon were established in 2005/2016 season. Of these 44 fields were sampled for yield, biomass, plant stand and 32 sites for soil data. In the second season of 2016/17, a maize fertilizer response trial with five rates of NPKS (0, 23:21:0+4S, 46:21:0+4S, 69:21:0+4S, and 92:21:0+4S) was super-imposed in the 44 fields, where farmers incorporated pigeon pea residues, a parallel study conducted in a nearby, adjacent field. In the first season, rainfall was low and erratic. Three dry spells (>10 non-rainy days) were recorded in two of four rain gauge stations, and two dry spells in one station. The soil test results showed low P, K and N status. Pigeon pea plant stand was low, with an average of 2.22 plants m-2 compared to an expected 4.44 plants m-2. Grain yields and stover weights were quite variable with a mean of 442 and 1698 kg/ha, respectively. In the second season maize yields grown in both old pigeon pea or continuous maize plots gave a linear response to fertilizer. The gains from pigeon rotation averaged 620, 308, 496 and -1072 for Chibwana Nsamala, Hindahinda, Mulambe and Chitseko sections respectively. The highest recorded yield was 4049 kg/ha from Hindahinda

Maize response to macronutrients and potential for profitability in sub-Saharan Africa

The final publication is available at Springer via http://dx.doi.org/10.1007/s10705-015-9717-2Sub-Saharan Africa (SSA) is plagued by low productivity and little research is available on the attainable responses and profitability to applied nutrients under variable environments. The objective of this study was to determine the attainable maize grain response to and potential of profitability of N, P and K application in SSA using boundary line approaches. Data from experiments conducted in SSA under AfSIS project (2009–2012) and from FAO trials database (1969–1996) in 15 countries and constituting over 375 different experimental locations and 6600 data points are used. Both response to fertilizer and value cost ratio (VCR) are highly variable and no more than 61 % cases for N, 43 % for P and 25 % for K attain VCR of 2 or more. Also, based on the recent AfSIS data, VCR exceeds 1 in just 67 % (N), 57 % (P) and 40 % (K) of the cases, even when best management practices are applied on a research farm, and interest rates are zero. Chances for profitability are highest when soil organic carbon is 1–2 % and control maize grain yield is 1–3 t ha−1 but also depends on relatively static soil properties (primarily texture and mineralogy) that are not under farmer control. We conclude that return on investment of macronutrient fertilizer is highly variable and can be substantially increased by helping farmers decide where to apply the fertilizers. Consequently, farmers need access to information on factors influencing economic returns of fertilizer use in order to make the right decisions

Productivity and profitability on groundnut (Arachis hypogaea L) and maize (Zea mays L) in a semi-arid area of southern Malawi

In many parts of Malawi, including Balaka district in Southern Malawi, are prone to erratic rains with poor soil productivity and famer practices. A research and outreach project was initiated in October 2015 to establish learning centres (LCs) of groundnut: maize rotations as an entry point to diversify nutrition and income base of smallholder farmers, while building up on soil fertility for increased resilience to production under climatic variation. Some 132 plots of groundnut were established in 2015/2016 in four sections of Ulongwe Extension Planning Area (EPA) in Balaka district. Of these, 44 fields were sampled for yield, biomass, plant stand and soils data. In the second season of 2016/2017, a maize fertilizer response trial (five rates of NP2O5K2O; 0, 23:21:0+4S, 46:21:0+4S, 69:21:0+4S, and 92:21:0+4S) was super-imposed in plots where farmers incorporated groundnut residues, in comparison with continuous maize from adjacent own field. In the first season, rainfall was below average and erratic, with 10-day dry spells recorded in two of four recording stations. The soils were generally poor, with test values below threshold for many variables including organic matter, nitrogen and phosphorus. Groundnut average yields and standard deviation were 754 (±186) kg/ha, respectively. Plant stands were poor, with up to 24% of the 46 LCs attaining ≤50% of targeted plant stand of 8.88 plants m-2. Poor plant stand is suggested as a major contributor to low yields. Results from the 2016/2017 fertilizer response trials showed linear response of maize to fertilizer application. Yields ranged from an average of 1.47 t/ha without fertilizer application to 4.0 t/ha at 92:21:0+4S. It is concluded that the poor soil fertility, low field plant densities, and dry spells are the main causes of low yields. Gross margins were positive for groundnut yield of 1,000 kg/ha and fertilizer rates on maize of 46:23:0+4S and above

Agronomic biofortification of leafy vegetables grown in an Oxisol, Alfisol and Vertisol with isotopically labelled selenium (77Se)

Selenium biofortification of crops is a proven technology for improving dietary nutrition. This study used isotopically labelled selenate (>99% enriched 77Se) to assess uptake and Se availability to two green vegetables, Brassica napus L (B. napus) and Amaranthus retroflexus L (A. retroflexus) grown in three contrasting Malawi soils: a Vertisol (calcareous), Alfisol (moderately acidic) and Oxisol (acidic). Plants were grown under glasshouse conditions (4 replicates; 6 kg soil per pot) following application of 77Se-enriched selenate at rates equivalent to 0, 10 and 20 g ha−1. Leaves were harvested at fortnightly intervals and the plants were then allowed to re-grow, to simulate cultivation practice. Leaf samples were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) for selenium isotopes (77Se and 78Se). The isotopic data were processed to quantify the contribution to plant Se concentration from the fertilizer and the soil. Both concentration and uptake of the fertilizer 77Se declined sharply with sequential harvests due to progressive fixation of 77Se in the soil rather than exhaustion (by uptake) of the Se applied. Initially the bioavailability of fertilizer Se was three orders of magnitude greater than the soil Se but this declined to the same order of magnitude by the end of the trial. Application of 77Se had no effect on uptake of soil-derived Se. There were marked differences between the three soils studied. The relative bio-availability of the fertilizer Se followed the sequence (Vertisol > Alfisol > Oxisol) but the two crops showed the same trend in decline of fertilizer Se uptake. Thus, fixation of selenium in the soils studied was sufficiently rapid that Se biofortification of green vegetables subject to several harvests would require multiple applications during the growing season

Agronomic iodine biofortification of leafy vegetables grown in Vertisols, Oxisols and Alfisols

Iodine deficiency disorders (IDD) in sub-Saharan African countries are related to low dietary I intake and generally combatted through salt iodisation. Agronomic biofortification of food crops may be an alternative approach. This study assessed the effectiveness of I biofortification of green vegetables (Brassica napus L and Amaranthus retroflexus L.) grown in tropical soils with contrasting chemistry and fertility. Application rates of 0, 5 and 10 kg ha−1 I applied to foliage or soil were assessed. Leaves were harvested fortnightly for ~ 2 months after I application before a second crop was grown to assess the availability of residual soil I. A separate experiment was used to investigate storage of I within the plants. Iodine concentration and uptake in sequential harvests showed a sharp drop within 28 days of I application in all soil types for all I application levels and methods. This rapid decline likely reflects I fixation in the soil. Iodine biofortification increased I uptake and concentration in the vegetables to a level useful for increasing dietary I intake and could be a feasible way to reduce IDD in tropical regions. However, biofortification of green vegetables which are subject to multiple harvests requires repeated I applications

Selenium biofortification of crops on a Malawi Alfisol under conservation agriculture

Biofortification with selenium (Se) may rely on rapid uptake by crops, following application, to offset progressive fixation into unavailable organic forms of Se in soil. A biofortification study was conducted on an Alfisol within a long-term conservation agriculture (CA) field trial at Chitedze Research Station, Malawi. The aim was to assess the dynamics of selenium bioavailability to a staple cereal (Zea mays) and a range of legumes (cowpeas, groundnuts, pigeon peas and velvet beans) under CA management, as well as residual Se effects in the year following biofortification. Isotopically labelled selenate (>99% enriched 77SeVI) was applied to each plot, in solution, at a rate of 20 g ha−1, at maize flowering (75 days after planting), in February 2017. Samples of grain and stover from maize and legumes, and topsoil, were collected at harvest in May 2017 and May 2018. Plant and soil samples were analyzed by ICP-MS for selenium isotopes (77Se and 78Se). The concentration of 77Se in the grain of maize and single-cropped legumes exceeded 200 µg kg−1 in all the treatments. This would contribute approximately 56–64 µg day−1 to the Malawi diet, as refined maize flour. The fertilizer derived Se concentration ratio of maize grain-to-stover Se were >1 in 2017 but <1 in 2018; which followed the same trend as the native soil-derived Se in the residual year. In legumes the grain-to-stover concentration ratio was consistently <1 in both years, except for the velvet beans. Differences in CA management had minimal influence on 77Se concentration in plant grain but the low yield in the single conventional treatment reduced 77Se uptake. Residual 77Se in the soil (35% of the applied) measured at harvest in 2017 was still present at harvest in the residual year (2018) but was completely unavailable to any of the crops. Almost none of the remaining 77Se was present in soluble or phosphate-extractable forms and virtually all was present in the ‘organic’ (TMAH-extractable) fraction. Thus, annual Se applications to maize would be necessary to maintain concentrations which could improve dietary supply and reduce current Se deficiency in Malawi

Selenium deficiency risks in sub-Saharan African food systems and their geospatial linkages

Selenium (Se) is an essential element for human health. However, our knowledge of the prevalence of Se deficiency is less than for other micronutrients of public health concern such as iodine, iron and zinc, especially in sub-Saharan Africa (SSA). Studies of food systems in SSA, in particular in Malawi, have revealed that human Se deficiency risks are widespread and influenced strongly by geography. Direct evidence of Se deficiency risks includes nationally representative data of Se concentrations in blood plasma and urine as population biomarkers of Se status. Long-range geospatial variation in Se deficiency risks has been linked to soil characteristics and their effects on the Se concentration of food crops. Selenium deficiency risks are also linked to socio-economic status including access to animal source foods. This review highlights the need for geospatially-resolved data on the movement of Se and other micronutrients in food systems which span agriculture–nutrition–health disciplinary domains (defined as a GeoNutrition approach). Given that similar drivers of deficiency risks for Se, and other micronutrients, are likely to occur in other countries in SSA and elsewhere, micronutrient surveillance programmes should be designed accordingly