Forage and maize yields in mixed crop-livestock farming systems

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Forage and maize yields in mixed crop-livestock farming systems Enhancing forage and maize yields in mixed crop-livestock systems under conservation agriculture in sub-humid Zimbabwe E.F Mutsamba*, I. Nyagumbo, W. Mupangwa CIMMYT, P.O. Box MP163, Mount Pleasant, Harare, Zimbabwe

A R T I C LE I N FO

A B S T R A C T

Keywords: Cropping systems Gross margins Intercropping Rotations Sole maize

In mixed crop-livestock farming systems, smallholder farmers face the challenge of insufficient dry season livestock feed whilst crop production is mainly constrained by poor soil fertility and erratic rains. Conservation agriculture (CA) which is premised on three main principles namely minimal soil disturbance, crop rotations and mulching is being promoted as a potential solution to declining soil productivity. However, farmers implementing CA in mixed crop-livestock systems are conflicted by the use of crop residues either as livestock feed or as mulch under crop production. A study was carried from 2012/13 to 2014/15 season in Murehwa, a subhumid region of Zimbabwe, to evaluate the effects of maize-legume cropping systems on forage, maize grain yield and gross margins. In this context, forage refers to the plant material/biomass harvested for livestock feeding. The cropping systems involved one conventional tillage practice with continuous sole maize (CT), four CA treatments consisting of continuous sole maize, maize-mucuna intercrop, maize-cowpea intercrop and maizegroundnut/soybean rotations. The experiment was replicated on eight farmers’ fields with each farmer treated as a replicate. Maize-mucuna (4 134 kg ha-1) and maize-cowpea (3 999 kg ha-1) intercrop systems significantly increased forage yield compared to CA sole maize (3 646 kg ha-1) and CT sole maize (3 076 kg ha-1). Among the rotations, maize-soybean rotation system performed better than the maize-groundnut system with respect to forage yield and maize grain. Intercropping and sole cropping systems however showed no significant maize grain yield difference. The highest and lowest gross margins/ha were obtained from the maize-mucuna intercrop (US$1395) and maize-soybean rotation system (US$507), respectively. The study thus suggests that farmers can grow legumes as intercrops with maize without any loss in maize grain yield. Maize-mucuna intercropping was the best of the tested cropping systems with respect to forage yield and gross margins in mixed crop-livestock systems of Murehwa.

1. Introduction The farming systems in the communal areas of Zimbabwe are mainly based on integrated crop and livestock production (Rufino et al., 2011). Crop production in these smallholder farming systems provides food and generates income at subsistence level. However, crop production is negatively affected by recurrent droughts, exorbitant input prices and inherently poor soil fertility among other constraints (Kindu et al., 2014). Livestock are a source of income, act as social security and are a status symbol in these rural communities. In times of distress, livestock can be converted into cash for buying food in drought years, paying health and education services and dowry (Homann-Kee et al., 2015). Livestock also provide draught power and manure to the cropping systems (Baudron et al., 2015). The residues from crops are often ⁎

fed to livestock during the dry season, thus an integrated/mixed croplivestock system is established (Rufino et al., 2011). However, in mixed crop-livestock farming systems, smallholder farmers face the challenge of insufficient dry season livestock feed (Mutsamba et al., 2012). Furthermore, in such mixed systems, crop residues are multi-purpose because they are required for livestock feeding, mulching, energy, construction and as source of cash (Jaleta et al., 2015). Crop residues are therefore an important resource, yet the crop biomass produced on smallholder farms is limited largely due to poor soil fertility and erratic rains. Maize (Zea mays) yields in the smallholder farming systems of Zimbabwe are as low as 0.5 t ha-1 against a yield potential of 12 t ha-1 (ZimVAC, 2017). In order to restore and improve soil fertility, various strategies employing both organic and inorganic fertilizers are critical

Corresponding author. E-mail address: [email protected] (E.F. Mutsamba).

https://doi.org/10.1016/j.njas.2019.100317 Received 5 June 2018; Received in revised form 6 November 2019; Accepted 7 November 2019 1573-5214/ © 2019 Royal Netherlands Society for Agricultural Sciences. Published by Elsevier B.V. All rights reserved.

Please cite this article as: E.F Mutsamba, I. Nyagumbo and W. Mupangwa, NJAS - Wageningen Journal of Life Sciences, https://doi.org/10.1016/j.njas.2019.100317

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legumes grown in Zimbabwe are soybeans (Glycine max (L.) Merr), groundnuts (Arachis hypogea L.) and cowpeas (Vigna unguiculata (L.) Walp) (Waddington et al., 1998). Groundnuts normally occupy the largest proportion of land amongst the legume crops grown by smallholder farming communities in Zimbabwe because of its importance as food protein source. On the other hand, soybean is important for income generation, as a protein source for both livestock and humans, and for its diverse by-products such as milk, flour and chunks (Chiukira and Juru, 2012). Cowpea is also grown and consumed by more than 200 million people in Africa (Kayinamura and Murwira, 2003). Cowpea leaves are consumed as relish whilst the grain is consumed as boiled grain. Forage legumes that could improve crop-livestock farming systems such as mucuna/velvet bean (Mucuna pruriens L.), lablab (Lablab purpureus L.) and sunn hemp (Crotalaria juncea L.) have been screened in Zimbabwe (Nyoka et al., 2004). Mucuna is mainly used as a green manure (Mhlanga et al., 2015) and for cattle feed (Jiri, 2003) to increase milk production and body score (Murungweni et al., 2004). Due to its high forage production rate, mucuna is increasingly becoming a viable option to supply supplementary feed for the smallholder farmers’ livestock (Gwiriri et al., 2016). Feeding livestock with forage legumes reduces the cost of producing milk and increases income by 50 % compared to where commercial feeds are used (Murungweni et al., 2004; Chakoma et al., 2016; Gwiriri et al., 2016). Forage legumes increase the viability and availability of quality supplements during the dry months of the year, which usually coincides with poor feed quantity and quality (Gwiriri et al., 2016; Descheemaeker et al., 2018). The various forage legumes and plant parts contain different crude protein levels. For example, mucuna plant (13.9 %), mucuna seed (21 %), soybean plant (30 %), cowpea plant (14 %) and groundnuts plant (14 %) compared to maize dry stover with 3.7 % (Chakoma et al., 2016; Gwiriri et al., 2016). Previous studies on forage legumes were mainly conducted under conventional tillage systems except recently where they were used as cover crops in CA systems. In this context, forage refers to the plant material/biomass which is fed to livestock. In Zimbabwe, there is limited information on the productivity of different maize-legume associations under CA in mixed crop-livestock farming systems. There is a knowledge gap on the quantities of forage biomass produced under CA and the potential period during which livestock can be fed with home grown feed products during the dry season. The broad objective of this study was to evaluate the performance of maize-legume (groundnuts, soybeans, cowpeas and mucuna) cropping systems with and without manure under CA in north-eastern Zimbabwe. Specifically, the study sought to determine (i) grain and forage yield from maize-mucuna and maize-cowpea intercrops; and maize-groundnut/soybean rotation systems with or without manure under CA (ii) the potential of generating supplementary dry-season livestock feed from maize, groundnuts, soybeans, cowpeas and mucuna biomass and (iii) the gross margins of the maize-mucuna and maize-cowpea intercrops; and maize-groundnut/ soybean rotations systems with or without manure under CA in subhumid Zimbabwe.

for the smallholder farming sector (Sanginga and Woomer, 2009; Rusinamhodzi et al., 2012; Vanlauwe et al., 2015). Smallholder farmers are encouraged to practice cereal-legume cropping systems and use organic or inorganic fertilizers in order to improve soil productivity. Various combinations of mineral fertilizer and organic nutrient sources have been tested under different socio-economic and biophysical conditions of the smallholder sector of southern Africa (Zingore et al., 2007; Chivenge et al., 2009). However, inorganic fertilizer use has remained below the quantities required to sustain crop production. Livestock manure is a low cost option for soil fertility maintenance in smallholder crop production as it supplies macro and micro nutrients, raises soil pH, increases soil organic matter content hence increasing water holding capacity. Livestock manure also reduces water and wind erosion, improves soil aeration and promote beneficial microorganisms thereby improving soil health (Sanchez, 2002; Mutiro and Murwira, 2003; Ncube et al., 2009). However, livestock manure production at farm level has remained insufficient for optimum application to all cropped fields (Zingore et al., 2007). In addition, manure from smallholder farming areas of Zimbabwe are generally of poor quality (low N) as they mineralize their N slowly (Murwira et al., 2004). Besides using organic and inorganic fertilizers, smallholder farmers in Zimbabwe and the southern Africa region are also implementing conservation agriculture (CA) in order to improve soil fertility and crop productivity (Nyamangara et al., 2014; Mupangwa and Thierfelder, 2013; Nyagumbo et al., 2015). CA is premised on three main principles namely minimal soil disturbance, permanent/semi-permanent soil cover using live cover or dead plant material and crop rotation as full rotations or as inter/ or relay crops (Hobbs, 2007). Minimal soil disturbance is recommended since tillage-based conventional agriculture leads to a decline in soil organic matter, increased water runoff and soil erosion, and other manifestations of physical, chemical and biological soil degradation (Thierfelder and Wall, 2009; Nyamangara et al., 2014). On the other hand, minimal soil disturbance promotes soil biological activities (Mutema et al., 2013) and improves soil physical structure (Chivenge et al., 2007; Nyamangara et al., 2014). Minimal soil disturbance allows farmers to plant early, as the number of operations, time and energy required to prepare the land are reduced (FAO, 2004). Delayed planting from the first planting opportunity reduces crop yields due to a combination of factors (Mugabe and Banga, 2001; Nyagumbo et al., 2017). Although CA is beneficial (Thierfelder and Wall, 2009; Mutema et al., 2013; Nyamangara et al., 2014), its major set-backs apart from residues competition with livestock for soil cover and weeds include lack of appropriate equipment, failure by farmers to implement recommended rotations (farmer crop preferences may not match recommendations), prohibitive inputs such as herbicides and generally lack of awareness (Baudron et al., 2015). To some farmers in Zimbabwe, growing a crop without ploughing is unheard of as the local word for growing a crop ‘kurima’ is synonymous with ploughing. Minimal soil disturbance thus results in more weeds under CA compared to conventional ploughing leading to the need for chemical weed control through use of herbicides in CA systems (Muoni et al., 2014). Inclusion of legumes in intercropping and rotations under CA has the advantage of fixing nitrogen into the soil, improving soil conservation, weed, pest and disease control (Waddington et al., 1998; Rusinamhodzi et al., 2012; Gebru, 2015). This consequently increases crop yield and better economic returns. Legumes can be classified as grain legumes, green manure cover crops (GMCC) and forage legumes. Grain legumes are often preferred by smallholder farmers to GMCC because they ensure food security, improved diets and income (Giller, 2001; Rusinamhodzi et al., 2012) through their multi-purpose nature (food, fodder and soil fertility). In Zimbabwe, farmers practice crop rotations in conventionally tilled cropping systems (e.g. maizegroundnut or maize-cowpea rotation). Rotations and intercropping diversify farmers’ incomes and spread the risks of complete crop failure (Thierfelder et al., 2012). The most common multi-purpose grain

2. Materials and methods 2.1. Study sites The study was carried out in Murehwa district (17043’S, 31039’E, 1 300 m above sea level), located in Mashonaland East province of Zimbabwe. Murehwa lies in agro-ecological region II receiving annual rainfall range of 750−1000 mm from November-April. The soils are dominated by low fertile inherent granitic sandy soil (Lixisols: FAO, 2014). The soil pH (CaCl2) prior to establishment of the experiment averaged pH 4 (Table 1). Major food crops grown are maize, groundnuts, cowpeas and sweet potatoes (Ipomea batatas L.) whilst major livestock include cattle (Bos indicus L.) and goats (Capra hircus L.). 2

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Table 1 Soil characteristics prior to trial establishment, December 2012. meq/100g Farmer name

Rep

pH

N ppm

P2O5

Chigama Garwe* Hakata Chidawaya* Chikwerekwere Mahwamba Dzingai* Chimani* Av. soybean fields Av. groundnuts fields p-value Cv (%)

1 1 2 2 3 4 3 4

3.7 4.1 6.5 4.0 3.1 3.0 4.0 3.0 3.78 4.08 NS 29.1

25 26 41 34 16 39 42 20 30.50 30.20 NS 32.9

12 17 39 19 15 16 13 30 19.80 22.50 NS 46.9

ppm

K

Ca

Mg

Texture

Colour

0.10 0.18 0.07 0.15 0.06 0.08 0.19 0.07 0.15 0.08 NS 47.0

0.65 1.10 0.67 0.57 0.37 0.46 1.10 0.41 0.80 2.60 NS 43.3

0.29 0.44 0.50 0.21 0.23 0.28 0.30 0.28 0.31 0.33 NS 31.7

Mg Mg Mg Mg Mg Mg Mg Mg

PB B PB PB PB PB PB PB

S S S S S S S S

Key: B = brown or brownish; P = pale; mg = medium grained; S = sand. *are farmers who grew soybeans and the remainder grew groundnuts in rotation systems. NS indicates that means in the same column were not significantly different from each other at P ≤ 0.05 probability level.

applied as mulch at 2.5 t ha-1 in CA treatments at the beginning of each rainy season. Maize seed was planted at 90 cm inter-row and 25 cm in row spacing with one plant per station giving a plant population of approximately 44 000 plants ha-1. Mucuna and cowpeas were relayed in between maize rows at 90 cm inter-row spacing and in row spacing of 25 cm for mucuna and 12.5 cm for cowpea, with 1 seed per planting station. Soybeans and groundnuts were planted at 45 cm between rows and in-row spacing of 5 and 15 cm, respectively, with one plant per station. Soybean seed was inoculated with rhizobia just before planting. Gypsum (20 % Ca, 17.5 % S), was applied to groundnuts four weeks after planting. Manure was banded in furrows in CT plots and on maize rip line soon after planting in CA plots at 5 t ha-1 on dry weight basis. Cattle manure from communal areas of Murehwa contains an average of 0.74 % N, 0.12 % P and 0.69 % K (Mugwira and Murwira, 1997; Murwira et al., 2004; Dunjana et al., 2012; Makonya, 2014). Basal compound D (7N:14P2O5: 7K2O) was applied at a rate of 240 kg ha-1 at planting whilst top dressing of ammonium nitrate (34.5 % N) was applied at 200 kg ha-1. Top dressing was split applied to maize only at three-four weeks after planting and two weeks after the first application. Mucuna and cowpea did not receive any soil fertility amendment. Initial weed control in CA plots was done by applying Glyphosate (480 g l-1 active ingredient) at 2.5 l ha-1 soon after planting and thereafter weeding was done manually using hand hoes. In CT treatment, all weeding operations were done manually using a hand hoe.

2.2. Experimental design and layout The experiment was laid out in a randomized complete block design and was run at eight farmer’s fields for three seasons from 2012/ 13–2014/15. Prior to the experiment, all fields were under conventional mouldboard tillage (CT) and had maize during the 2011/12 season. Each farmer was treated as a replicate with a set of six treatments testing five cropping systems where one system was CT and the other four systems were under CA. The six treatments were: i ii iii iv v vi

CT + sole maize continuous CA + sole maize continuous CA + maize + cowpea intercropping CA + maize + mucuna intercropping CA + maize + soybean/groundnut rotation (maize phase) CA + soybean/groundnut + maize rotation (legume phase)

All the eight farmers hosted sole and intercrops (treatment i-iv) for three seasons. However, four of the farmers had CA maize-soybean rotation system (maize-soybean farmers) whilst the other four hosted the CA maize-groundnut rotation system (maize-groundnut farmers). It was farmers’ choices on which legume (groundnut or soybean) to rotate with maize. Soil parameters were similar for farmers who practised maize-soybean and maize-groundnut rotation systems (Table 1). During the 2012/13 and 2013/14 seasons, basal fertiliser (compound D) only was applied at planting in each plot measuring 40 m x 10 m (400 m2). Each plot was further split into two during the 2014/ 15 season; where half of the plot received manure + basal fertiliser and the other half received basal fertiliser only at planting. When manure was added, the experimental layout was considered as a split-plot where cropping systems were considered as main treatments and fertility (manure or no manure) as sub treatments.

2.4. Data collection 2.4.1. Soil samples Soil samples were collected from each farmer’s field for initial field characterization. Soils were randomly collected from eight points in each farmer’s field at a depth of 0−20 cm before planting. Samples from each farmer’s field were thoroughly mixed to make a composite sample that was submitted to the laboratory for analyses. Soil texture analysis was done through the hydrometer method, soil pH was determined by the CaCl2 method, total nitrogen (%N) by the Kjeldahl method, the K and Ca concentrations were determined by flame photometry, and plant available P using the Bray method (Anderson and Ingram, 1993).

2.3. Establishment and management of trials An animal drawn Fitarelli direct seeder (Brazilian made) was used for opening planting furrows, seeding and basal fertilizer application at once in CA plots. In CT treatment, an ox-drawn mouldboard plough was used for land preparation (tilling the soil and opening planting furrows) while seed dropping, fertilizer application and covering of the seed were done manually by hand. Mucuna and cowpea were planted between the maize rows using hand hoes. Crop residues were fed to livestock as they freely graze during the dry season whilst some farmers stored the residues on raised platforms and fed them to their livestock as supplement feed during the dry seasons. Hypharennia grass was

2.4.2. Rainfall data Daily rainfall was recorded using a rain gauge mounted at each farmer’s field. In 2012/13, rainfall was recorded from mid-December when the project started whilst in the other seasons, rainfall was 3

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margin analysis. Forage yield was calculated in intercropping and rotation systems respectively as: 1. Forage yield, intercropping (kg/ha)= Maize stover + legume stover + mucuna grain 2. Forage yield, rotation (kg/ha)= (Maize stover + legume stover)/2 The forage yield under rotation system was divided by two since there were two plots under this system, one plot under the cereal phase, and the other plot under the legume phase. To get the output from this system, an average from the legume plot and cereal plot was calculated to get the effective yield per hectare. We assumed that there are no farmers who would put their whole field under legume but would rather split it into legume and cereal field.

Table 2 Costs of inputs ha-1 used to calculate gross margins across seasons in Murehwa. Commodity

Type of commodity

Price (US$ ha-1)

Seed

Maize seed Mucuna seed Cowpea seed Soybean seed Groundnuts seed Compound D fertilizer Ammonium nitrate fertiliser Manure Gypsum Grass Glyphosate Carbaryl

57.50 40.00 15.00 180.00 100.00 135.00 125.00 300.00 27.00 250.00 17.50 17.50

Fertilizers

Herbicides Pesticides

2.4.4. Land equivalent ratio (LER) The advantage of maize intercropping compared to sole cropping was calculated using the Partial Land Equivalent Ratio (LER) as:

recorded from November when the first rains were received.

LER = Yi /Yii Where Yi is the maize grain or maize biomass yield from either maizemucuna or maize-cowpea intercrop under CA and Yii is the maize grain or maize biomass yields from the continuous CA sole maize crop.

2.4.3. Crop yields Cowpea was harvested at the end of February each year, whilst maize; soybeans and groundnuts were harvested at the beginning of May. Mucuna was harvested towards the end of May before livestock started free grazing. All crops were harvested at full maturity except for mucuna which was harvested soon after flowering since crops were planted late in the season during the 2012/13 season. Maize, cowpea and mucuna grain and stover (biomass) yields were measured from net plots (area) of 2 rows x 5 m long whilst the net plots for groundnuts and soybeans consisted of four rows that were 5 m long. Six net plots were harvested per each main treatment. Maize grain yield was adjusted to 12.5 % moisture content and expressed to a hectare basis. Biomass measurements were also collected from the same net plots where grain yield was determined. Plant stalks in each net plot were cut at ground level and weighed. One stem from each net plot was taken, making six stalks from each treatment and these stalks were later cut into pieces and a sub-sample of about 500 g was taken, weighed exactly to the nearest 0.1 g and oven dried at 480C for 48 h. The dried subsamples were re-weighed using a precision scale. The moisture content was calculated as the weight between wet and dry sample divided by the wet mass. The calculated biomass moisture content was then used to calculate dry biomass weight from each plot and expressed on a per hectare basis. Mucuna grain yield was incorporated in the forage yield calculation whilst all other legumes’ grain yields were only used for the gross margin analysis as they were taken for home consumption. Stover from all crops was measured and used in forage yield calculations and gross

2.4.5. Gross margin analysis The profitability of the cropping systems was determined using the gross margin analysis as: Gross Margin = Total Revenue - Total Input Costs Where: Total Revenue = [(Ylegume × P) + (Ymaize × P) + (N2 x P) + (legume stover x P) + (maize stover x P)], Y is the crop (grain) yield; N2 is the estimated residual nitrogen from biological nitrogen fixation by the legume; stover is the quantity of either legume or maize biomass; P is the market price for each respective commodity prevailing at the period of the research. The amount of N fixed through biological nitrogen fixation was estimated for cowpea, mucuna, soybean and groundnuts at 27, 34, 53 and 55 kg/ha respectively (Giller, 2001; Njira et al., 2012). The N fixed from cowpea and mucuna was relatively low since these legumes were intercropped and they had half recommended plant population. Input costs included cost of inputs such as inorganic and organic fertilizers, seeds, pesticides, labour manure, mulching grass and herbicides. Labour was estimated at $3/labour day. The costs of inputs per hectare were obtained from actual costs/receipted prices during purchasing period (Table 2). Labour costs incurred by farmers were mainly due to land preparation, mulching, planting, weeding, fertilizer, manure and pesticide applications and harvesting (Table 3). The labour costs were calculated according to standard labour rates per acre prevailing in the area at the time of the study whilst labour

Table 3 Amount of labour for each field operation (labour days). Treatment

CT Mz

CA Mz

Mz/Cw Int

Mz/Mc Int

Mz/Sy Rot

Sy/Mz Rot

Mz/Gnt Rot

Gnt/Mz Rot

Land clearing Land preparation Sowing Basal fertiliser Mulching Manuring Herbicide application Pesticide application Weeding Top dressing Harvesting Threshing maize Total labour days Labour unit price (USD) Labour costs

0.6 4 2.5 1.47 – 3.0 – – 13.0 0.6 4.0 7.47 36.65 3 109.95

0.7 – 2.4 – 8.0 3.0 0.8 – 7.33 0.77 4.0 7.3 34.3 3 102.9

0.7 – 4 – 8.0 3.0 0.8 0.97 7.33 0.77 6.0 6.35 37.92 3 113.76

0.7 – 4 – 8.0 3.0 0.8 0.97 7.33 0.77 6.0 7.98 39.54 3 118.62

0.7 – 2.4 – 8.0 3.0 0.8 – 7.33 0.77 4.0 7.21 34.2 3 102.6

0.7 – 2.4 – 8.0 3.0 0.8 – 6.2 – 4.0 1.51 26.61 3 79.83

0.7 – 2.4 – 8.0 3.0 0.8 – 7.33 0.77 4.0 6.17 33.16 3 99.48

0.7 – 2.4 – 8.0 3.0 0.8 – 5.8 – 4.0 3.69 28.39 3 85.17

CT = conventional tillage; CA = conservation agriculture; Mz = maize; Mc = mucuna; Cw = cowpea; Sy = soybean; Gnt = groundnuts; Int = intercropping; Rot = rotation. 4

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ha-1) was achieved in 2012/13 season compared to the other two seasons (4 006 and 4 232 kg ha-1) (Fig. 2). From the farmers who implemented the maize-groundnut rotation system, the least forage yield was achieved from the rotation system (2 331 kg ha-1) whilst the highest forage yield was from the maize-mucuna (3 566 kg ha-1) and maize-cowpea intercrops (3 479 kg ha-1). For the farmers who implemented the maize-soybean rotation system, the rotation system (3 332 kg ha-1) and conventional systems (3 484 kg ha-1) had the least forage yield whilst maize-mucuna intercrop (4 668 kg ha1 ) and CA sole maize (4 464 kg ha-1) systems had the highest output (P = 0.011). Maize-soybean rotation also yielded higher (P < 0.05) forage by 30 % compared to the maize-groundnut system. When manure was applied, intercropping systems had higher forage yield than the sole systems (P = 0.018) (Table 4). From the maizegroundnut farmers, there was no significant difference among all cropping systems when manure was added. For the maize-soybean farmers, rotation system (3 720 kg ha-1) had lower forage yield compared to the other three systems under CA (5 001–5 723 kg ha-1) at P < 0.05. Overall, maize-mucuna intercropping with manure resulted in forage yield of 4 600 kg ha-1. The mean forage yield (P = 0.12) under manured fields was 4 137 kg ha-1 whilst non-manured fields had 3 543 kg ha-1. However, significant differences (P = 0.014) were observed between fields with and without manure when rotations were excluded.

requirements were obtained by averaging the actual time taken to do each operation in each of the eight fields taking into account number of people working, gender, estimate age and time taken. This data was supported by information from people who hire out labour who were asked on how much they would charge if hired to weed the plot and the time they will take. 2.5. Statistical analyses A combined analysis of variance (ANOVA) across fields was conducted using Genstat 11 Statistical Package (2008). The effects of different cropping systems on forage and maize grain yield were analysed across three seasons. Data was pooled for combined ANOVA analysis whenever the interaction between fields, cropping system and season was not significant. The manure effect was analysed using a split-plot design with cropping systems as main treatments and fertility levels (manure or no manure) as sub treatments. Each farmer was considered as a replicate. The least significant difference (LSD) method at P ≤ 0.05 was used to separate means. Standard errors were calculated, and standard error bars were used to distinguish means presented in bar graphs. 3. Results 3.1. Seasonal rainfall

3.3. Maize and legume grain yield under different cropping systems The rainfall amount received during the 2012/13 (704 mm) and 2014/15 (720 mm) seasons was below the expected range of 750-1 000 mm while the seasonal rainfall received during 2013/14 cropping period was within the expected range (Fig. 1). During the 2012/13 and 2014/15 seasons, some mid-season dry spells were experienced in early January and mid-March. During the 2013/14 season, effective planting rains started in November 2013 and the daily rainfall was dominated by rainfall events of 20−40 mm per day.

Season and cropping system interaction had no significant effects on maize grain yield. Across the eight experimental fields, intercropping maize with mucuna and cowpea had no significant influence on maize grain yield (P = 0.961) compared to sole maize under CA and CT systems (Table 4). For the maize-groundnut farmers, maize grain yield from the maize-groundnut rotation system (2 704 kg ha-1) was higher (P = 0.03) compared to the other systems (1 574 – 1 981 kg ha-1). However, for the soybean farmers, there were no significant maize grain yield differences between all the cropping systems. A comparison of the two rotation systems showed that maize-soybean rotation yielded higher (P < 0.05) maize grain by 30 % compared to the maizegroundnut system. When manure was applied, intercropped maize had lower (P = 0.012) maize grain yield than sole maize crops (Table 4). From the maize-groundnut farmers, the highest maize grain yield was achieved in the rotation system (2 064 kg ha-1) and the least from the maize-cowpea intercrop (1 060 kg ha-1). For the maize-soybean farmers, rotation system had 18 % higher maize grain yield compared to the intercrops

3.2. Forage yield under different cropping systems Cropping systems and seasons had significant effects on forage yield (P < 0.05). Both maize-mucuna (4 134 kg ha-1) and maize-cowpea (3 999 kg ha-1) intercropping systems under CA had significantly higher forage yield compared to maize sole systems under conventional (3 076 kg ha-1) tillage system (Table 4). Forage yield analysis showed a LER of 1.133 and 1.097 for the maize-mucuna and maize-cowpea intercrop, respectively. The maize-mucuna and maize-cowpea intercropping systems had similar forage yields. The least forage yield (2 905 kg

Fig. 1. Seasonal rainfall pattern across the farmers’ fields used in Murehwa from 2012 to 2015 seasons. 5

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Table 4 Forage and maize grain yields (kg ha-1) from intercropping and sole systems from 2012/13–2014/15 seasons. Forage yield Treatments

Maize grain yield

2012/13-2014/15 no manure a

CT + sole maize continuous CA + sole maize continuous CA + maize + cowpea intercropping CA + maize + mucuna intercropping P value Lsd0.05 (n)

2014-15 with manure a

3 565 4 115a 4 820b 4 481b 0.018 796 8

3 076 3 646b 4 134c 3 999bc 0.014 460 8

2012/13-2014/15 no manure

2014-15 with manure

2 670 2 729 2 565 2 623 0.961 NS 8

2 878b 2 847b 2 280a 2 394a 0.012 433 8

Means with different letters within the same column are significantly different (P < 0.05); NS - not significant at P < 0.05; Lsd is least significant difference at 5 %, n is number of replicates.

Fig. 2. Forage yield achieved in different seasons across the eight farms used for experimentation in Murehwa.

soybean rotation had the least GM compared to both intercropping systems and maize-groundnuts rotation system (Fig. 3a). All treatments in the 2014/15 season with a combination of manure and fertilizer (F + M) had relatively lower gross margins compared to treatments with fertilizer only (Fig. 3b).

Table 5 Effects of manure on maize yield (kg ha-1) in Murehwa during the 2014/15 season. Treatment

*F + M *F only P value Lsd0.05 (n)

Grain yield (kg ha-1) All farmers (excluding rotations)

Groundnut farmers (all treatments)

Soybean farmers (all treatments)

2 795 2 404 0.014 306 8

1 704 1 201 0.04 493 4

4 035 3 851 0.38 423 4

4. Discussion 4.1. Forage yield and the potential of producing livestock supplementary feed under different cropping systems The maize-mucuna and maize-cowpea intercropping systems under CA were more productive compared to sole maize, maize-groundnut and maize-soybean rotation systems. The increase in productivity of the intercrops was attributed to exploitation for nutrients from different soil layers by the cereal and legume crop mixtures without competing with each other (Dahmardeh et al., 2010). Intercropping is reported to increase light interception, reduce water evaporation and improve soil moisture conservation compared to sole crops (Ghanbari et al., 2010). Legumes also fix atmospheric nitrogen, which may be utilized by the host plant or may be excreted from the nodules into the soil and be used by other plants growing nearby during or in the following season (Giller et al., 2011). Ngongoni et al. (2007) also showed that forage yield increased when maize was intercropped with a legume under conventional tillage. The LER of 1.1 for both intercropping systems means the sole maize require more land to equal the same total productivity as the intercrops, hence maize plus either mucuna or cowpea is more productive than continuous sole maize under CA on the granitic sands. The results therefore suggest that intercropping systems can reduce the conflict on

*F only means inorganic fertilizer only applied as basal soil fertility amendment whilst F + M means inorganic fertilizer plus cattle manure added as basal soil fertility amendment at planting, n is number of replicates.

(P = 0.025). The effects of manure on sole maize yield under minimum and conventional tillage showed no significant interaction between the tillage and fertility (manure application). However, overall results showed that manure + fertilizer resulted in higher (P = 0.014) maize grain yield (2 795 kg ha-1) compared to where fertilizer only was applied (2 404 kg ha-1) (Table 5). The average grain yield for cowpeas, soybean, groundnuts and mucuna over the three seasons were 326, 1 122, 1 269 and 1 510 kg ha1 respectively. 3.4. Gross margin (GM) analyses CA treatment with maize-mucuna intercrop yielded the highest gross margin compared to the other treatments whilst the maize6

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Fig. 3. Gross margins of cropping systems tested from a) 2012/13–2014/15 seasons without manure and b) 2014/15 season with manure (F + M) and without manure (F only) across 8 farms in Murehwa. Vertical bars represent standard error (n = 8). Gnuts = groundnuts.

legume intercropping systems will reduce the need for farmers to buy commercial feed concentrates (Chakoma et al., 2016). Sole cropping under CA produced more forage yield compared to CT, reflecting the benefits of minimum soil disturbance and mulching compared to conventional sole maize. Tillage-based conventional agriculture leads to soil organic matter decline, water runoff and soil erosion (Thierfelder and Wall, 2009). Mutsamba et al. (2012) also showed higher maize yield under CA compared to CT, concurring with our study results. The significantly higher forage yield from 2013/14 and 2014/15 seasons compared to 2012/13 season could have been due to early planting done in the second and third seasons. During the 2012/13 season, planting was delayed due to late disbursement of project funds. Delays in planting by more than 21 days reduced maize grain yields by 32 % in sub-humid Zimbabwe (Shumba et al., 1989; Nyagumbo et al., 2017). The reduction in crop yields due to late planting can be attributed to the omission of the nitrogen flush due to mineralization at the beginning of the season which is activated by the first rains (FAOREOSA, 2010). Late planted crops tend to be subjected to more periods of moisture stress during critical flowering and grain filling stages as the probability of moisture stressed pentads increases as the season progresses in Zimbabwe (Mupangwa et al., 2011). The study also shows that manure application generally resulted in higher forage yield compared to where no manure was applied. Manure supplies soil nutrients, raises soil pH, increases soil organic content, increases water holding capacity and promote beneficial microorganisms (Mugwira and Murwira, 1997; Dunjana et al., 2012).

use of crop residues in mixed crop-livestock systems as livestock feed or for soil cover (Rusinamhodzi et al., 2015). The legume will act as a cover crop during the wet season, whilst its biomass will be fed to livestock during the dry season. A LER greater than 1.0 has been reported also with maize-cowpea intercrop (Rusinamhodzi et al., 2012). The greater LER of the intercrops could have been due to a greater resource use such as light, nutrients and water (Dahmardeh et al., 2010). Assuming the farmer feeds cattle at 5 kg per day/animal (Chakoma et al., 2016) and has five cattle (Mutenje et al., 2014), 25 kg of feed are required for the five cattle. If the farmer harvests 4 600 kg of forage, enough feed is therefore available for 184 days (about six months). From intercropping systems, the farmer has enough feed for at least five months during the dry season which stretches from May to November in Murehwa. From the sole cropping results, farmers can feed their livestock for about four months but the feed is less nutritious as there is less protein from maize stover only compared to a mixture of maize and legume stover from intercrop systems (Jiri, 2003). Livestock feed from intercrops have additional crude protein from the legumes (Chakoma et al., 2016; Gwiriri et al., 2016; Descheemaeker et al., 2018). Dahmardeh et al (2010) showed that maize and cowpea intercrops gave higher total forage dry matter digestibility than maize or cowpea sole crops and led to increased feed quality (crude protein and dry matter digestibility concentration). Consequently, the nutritious livestock feed will then result in manure of high quality (Murwira and Kirchmann, 1993) thereby improving soil fertility (Mugwira and Murwira, 1997; Waddington et al., 1998). Since most smallholder farmers are resource constrained (Mutenje et al., 2014), nutritious livestock feed from maize-

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legumes do not require top dressing are factors contributing to higher gross margin on maize mucuna-intercrop. Weeding labour was reduced under maize-mucuna intercropping system due to weed suppression, a result that agrees with Mhlanga et al. (2015) who reported that cover crops can be used as an alternative to herbicide application or weed suppressors. Segun-Olasami and Bamire (2010) also reported that maize-cowpea intercropping was more profitable than the sole maize under conventional tillage. Overall, the maize–soybean rotation system had the least gross margins due to the low forage yield from the soybean crop, an effect we attribute to ineffective inoculation from the applied Rhizobium inoculant that resulted in poor soybean yields. All treatments in the 2014/15 season with a combination of manure and fertilizer (F + M) had lower gross margins compared to treatments with fertilizer only due to an additional cost of manure at 5 t ha-1 despite the yield increase noticed. Farmers also cited an increase in labour for digging, transporting and applying the manure as well as weeding since manure carries a high concentration of weed seeds. Chivenge et al. (2009) showed that 65 % of farmers in Murehwa leave their manure open, thus lose some N through volatilization. The returns from the manure are not adequate to upset their costs due to the poor quality. Quality of manure is also affected by quality of feed, age and species of animal, ambient temperature, moisture levels and duration of storage (Murwira and Kirchmann, 1993; Mugwira and Murwira, 1997). Manure obtained from animals foraging on low nutritive quality veld and manure contaminated with sand soil does not significantly improve crop production (Murwira and Kirchmann, 1993). Therefore, farmers need to feed their animals on nutritious feed and cure manure in order to enhance the quality of manure and make the costs of manure application worthwhile.

4.2. Maize grain yield under different cropping systems Similar maize grain yields from intercropping and sole systems imply that smallholder farmers, characterized by low agricultural productivity and land constraints, can practice maize-legume intensification. Maize-legume intercropping offers opportunity for farmers to diversify sources of income and spread the risk of total crop failure in case of drought (Thierfelder et al., 2012). On the contrary, maize–legume intercrop options were relatively more productive than the corresponding sole crops and this can be attributed to N-transfer from legumes as suggested by Rusinamhodzi et al. (2012). This N-transfer occurs through root excretion, decomposition of biomass and leaf fall (Fujita et al., 1992). In this study, the mucuna sometimes climbed on the maize plants leading to maize lodging, hence maize yield was suppressed to similar levels as in the sole crops. Maize-groundnut rotation system had higher maize grain yield compared to sole and intercropping systems. Nambiar et al. (1983) suggest that N contributions in intercrops are usually lower than those from sole legumes because intercrops occupy less land area and are subject to competition for production resources, particularly for light from the taller cereal crop. Rotation system thus enabled the subsequent maize crop to make use of more residual N compared to intercrop systems under CA. Crop rotation resulted in highly positive effects on maize yields in other CA studies (Thierfelder et al., 2012; Nyagumbo et al., 2015). Thierfelder et al. (2012) showed that maize yield from intercropping was lower than from rotation and argued that full rotation take complete advantage of space and natural resources whilst intercropping sometimes entails competition between the component crops. Despite the benefits of rotations (Thierfelder et al., 2012; Nyagumbo et al., 2015), farmers in areas with land constraints prefer intercropping than rotations because they believe that the overall yield penalty and loss of area dedicated to maize would be minimal (Thierfelder et al., 2012). A 30 % maize yield increase from maize-soybean rotation system compared to the maize-groundnut system was also reported by Nyagumbo et al. (2015) who showed that soybean and groundnut rotation systems increased maize yield by 20 and 54 %, respectively. However, it could not be conclusively established why on average farmers who implemented the maize-soybean rotation had higher yields than their maize-groundnut counterparts. A possible explanation to this is that since farmers chose their rotation legume crop voluntarily, it could have been that those who preferred soybean were cash-crop oriented producers with better field management skills than those who preferred groundnuts. However, all the eight farmers had similar soils (Table 1), planted on similar dates, received similar rainfall amounts and applied same fertilisers at similar rates. The application of both manure and fertilizer resulted in higher maize grain yield compared to where fertilizer only was applied. The study thus shows the need for supplementing soil fertility through manuring in order to improve and sustain crop production since mineral fertilizers alone, at current levels used by farmers, are insufficient to achieve crop yields required for household food security (Vanlauwe et al., 2015). The study therefore confirms the need for smallholder farmers to produce fodder legumes so as to increase manure quantity, hence improving crop yields. However, when manure was applied, intercropped maize had lower grain yield than sole crops. Manure improves soil fertility (Mugwira and Murwira, 1997), thus, intercropping systems resulted in high vegetative growth leading to high forage yields but suppressed maize grain yield to similar levels as sole crops.

4.4. Feasibility of the tested options for smallholder farmers 4.4.1. Mulching with hypherennia grass The dry above ground biomass of hypherennia grass was harvested from field edges, nearby fallow land and forests, and contour drain channels. It is envisaged that depletion of grass was limited since it had shed its seeds by the time of cutting the grass for mulching. However, cutting and carrying mulching materials require labour to import it to the field and this may promote transportation of weed seeds from forests to the field (COMESA, 2010). Mupangwa et al. (2018) showed that hypherennia grass did not suppress maize yields when sufficient mineral N was added in the cropping system. In-situ mulch production and use of green manure cover crops are other options to grass or crop residues for mulching (Mhlanga et al., 2016; Mupangwa et al., 2016). 4.4.2. Mechanised CA Mechanised CA through animal traction is a feasible proposition for smallholder farmers because 30–50% of the farmers in the study sites own draft animals and the use of oxen pulled ploughing is a traditional practice. Additionally, over the last 10 years, some CA equipment was distributed by government and non-governmental organisations in these communities thereby exposing farmers to the technologies. Local equipment manufacturers then followed suite by manufacturing relevant and appropriate CA equipment such as rippers, hand planters and direct seeders. A significant number of farmers purchased their own equipment (COMESA, 2010). Use of herbicides is also a viable and popular option for farmers given limited labour often experienced during the peak cropping period (Muoni et al., 2014). However, proper training and guidance is required prior to use of herbicides.

4.3. Gross margin analyses

4.4.3. Cattle manure use Cattle manure is an important soil fertility replenishment practice among cattle owners. On average, farmers broadcast manure at 5 t ha-1 and application is often to a small part of their fields. Manure application is rotated between different fields over time due to insufficient quantities (Zingore et al., 2007). In this study, manure was banded

The highest gross margins from the maize-mucuna intercropping systems observed in this study are due to more forage yield obtained from the same piece of land than under rotation system. The relatively higher price of mucuna grain compared to maize grain and the fact that 8

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along the planting furrow, which is a more efficient and precise application method compared to the common broadcasting practice. CA smallholder farmers usually practice manure banding or spot application, leading to creation of a fertile micro-environment within the planting stations or basins.

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4.4.4. Crop rotations and intercropping Smallholder farmers are already practicing rotations and intercropping, and these systems can be adopted with limited challenges in Murehwa and similar environments. However, crop rotations are often hindered by preference for the staple maize crop, lack of legume seed and unattractive market incentives (Thierfelder et al., 2012). In addition, smallholder farmers are hesitant to rotate maize with crops of no immediate economic benefit such as green manure cover crops. Nevertheless, if non-food legumes are produced for forage use, the uptake is promising because farmers are able to sell the produce as grain, hay bales or use it to feed their own livestock, which consequently, improves milk production or body score for beef production (Chakoma et al., 2016). 5. Conclusion Maize–mucuna and maize-cowpea intercrops significantly increased biomass output, hence increased forage yield compared to sole maize systems. Intercropping is thus well suited to integrated crop-livestock farming systems on the sandy soils in Murehwa district and similar environments. Forage yield results show that intercropping systems involving mucuna can enable farmers to generate both food and dry season livestock feed lasting up to five months per household, assuming they have five cattle, and each is fed 5 kg per day. The insignificant differences between maize grain yield from intercrops and sole maize crops means there is no maize yield penalty from intercropping while at the same time generating some quality forage from the legume. This therefore gives an opportunity to farmers with limited land, but would want to grow legumes to practice maize-legume intercropping for improved food and livestock feed production. The study also showed that manure use on granitic sands enhances system productivity in crop-livestock systems but depressed gross margins in the short term. The gross margin analyses showed that maize-mucuna intercropping system is more profitable compared to sole cropping, maize-cowpea intercrop and rotation systems involving maize with either soybean or groundnuts. Declaration of Competing Interest All authors have participated in designing the study; analysis and interpretation of the data; drafting and revising the article, till approval of the final version. This paper is an original contribution that has not been published or accepted for publication and is not under consideration at another journal. Acknowledgements The authors hereby acknowledge financial support received for the project ‘Integrating Crops and Livestock for Improved Food Security and Livelihoods in Rural Zimbabwe (ZimCLIFS)’ from the Australian Center for International Agricultural Research (ACIAR), project number CSE/2010/022. The authors also acknowledge the input from the two anonymous reviewers who helped to improve this paper. Many thanks also go to implementing partners, extension staff and farmers of Murehwa district for their tireless efforts during the study period. References Anderson, J., Ingram, J.S.I., 1993. Tropical Soil Biology and Fertility: A Handbook of

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