Evaluation of cereal-legume intercropped forages for smallholder dairy production in Zimbabwe

N T Ngongoni, M Mwale^*, C Mapiye^*, M T Moyo^**, H Hamudikuwanda and M Titterton

Animal Science Department, University of Zimbabwe, P.O. Box MP 167 Mt. Pleasant, Harare, Zimbabwe
^*Department of Livestock and Pasture Science, Faculty of Science and Agriculture, University of Fort Hare,
Private Bag X1314, Alice 5700, South Africa
^**Department of Livestock and Wildlife Management, Midlands State University, P. Bag 9055, Gweru, Zimbabwe
mukudzeishe@yahoo.com

Abstract

Total herbage yields were significantly higher on the clay than sandy soil, with yield ranging from 8.0 to 11.0 t/ha Dry matter (DM) and 1.0 to 5.6 t/ha DM, respectively. On intercrops legumes contributed 14-69 % of the total herbage yield for sandy soils (P < 0.05). On clay soil, legume contribution was low ranging from 3-30 %. The dry matter yield for cereals grown on the sandy soil was 22-34 % of clay soil yields. Cowpea, lablab and sunnhemp sandy soil yields ranged from 44-60 % of the clay soil yield. Soybean performed poorly on the sandy soil whilst lupin did so in both sites. Sandy soil forage tended to have significantly higher DM, Water soluble carbohydrate (WSC) and fibre contents and low Crude protein (CP) contents than those grown on clay soil. Maize and Jumbo had higher yields than Pan 888 and Sugargraze (P < 0.05). Cowpea, lablab and sunnhemp had higher yields than lupin and soybean (P < 0.05).

Intercropping of cereals and legumes is commendable for the increase of nutrient quality particularly the crude protein content of cereals on clay soils. However, the matching has to be thoroughly done to avoid mixing forages that may hinder each other from the access of nutrients, chiefly sunlight. Therefore, farmers are recommended to use cereal-legume intercrops especially maize or sorghum and cowpea and or lablab to enhance dry season feed availability.

Key words: Cereal, intercrop, legume, nutritive quality, persistence, yield, Zimbabwe

Introduction

The problem of the unavailability and purchased protein concentrates relative to the producer prices of milk in Zimbabwe makes the practice of protein supplementation a non-viable option (Ngongoni et al 2006). In Zimbabwe ruminant livestock are grazed largely on native pasture, that is usually in short supply and of poor nutritive value during the prolonged dry season (Muchadeyi 1998). Protein supply is critical, particularly in the dry season. Increasing rural resettlement has led to a rapid and general decline in the areas of grazing lands available to smallholder farmers (Nyoka et al 2004). Therefore, the need to intensify and optimise both crop and livestock production is the major challenge being faced by smallholder farmers.

Technologies aiming at increasing productivity of crops and livestock, while enhancing well-being of farmers and minimising resource degradation, must be developed (Mapiye et al 2007). Intercropping cereals with ley (dual-purpose) legumes is a potential technology (Maasdorp and Titterton 1997; Muchadeyi 1998). Apart from the direct contribution to livestock production through the provision of protein-rich fodder, ley legumes can improve the productivity of cereal crops by increasing the amount of nitrogen available for uptake (Giller 2001). Legumes offer a possible lower-cost alternative to nitrogen fertilisers and purchased protein supplements for improving smallholder dairy production (Mapiye et al 2006). Successful utilisation of cereals ley legumes in intercropping systems depends on the selection of locally adapted (climate and edaphic) species with good associative ability (Mapiye et al 2007). Therefore, the objective of this study is to assess the establishment, persistence, yield and nutritive quality of cereal and ley legumes sole crops and cereal-legume intercrops on sandy and clay soils in Zimbabwe.
 

Materials and methods

Study site

The project was conducted at Henderson Research Station in Mazoe, Zimbabwe. Henderson Research Station lies about 32 km to the North of Harare. The research station lies in Mazoe valley at an altitude of 1200m above sea level. Henderson Research Station characterized by mean annual rainfall of 880 mm and mean annual temperature that ranges from 20-30 ^oC (Henderson Research Station 2005). Effective rainfall is normally distributed during the summer months of November through to March with small amounts in October and April. Rainfall affects animal production mainly through its effects on growth of grass and the availability of crop products as animal feed. The forages were grown on two soil types, grey sandy and red clay soils.

Soil sampling and analysis

Ten soil samples were collected from each experimental site (soil type). The samples from each experimental site were mixed thoroughly before a sub-sample was taken. The sub-samples were analysed for pH, nitrogen, potassium and phosphorus exchangeable cations (Table 1).

Land preparation

At each experimental site an area of 0.8 ha was ploughed and disced during the dry season in the months of October and November in 1995. The area was disced again in December to incorporate lime at the rates of 600 and 2 000 kg/ha at the sand and clay soils respectively, as recommended after soil analysis.

Forages used

Forages used comprised of four cereals and five legumes. The cereal forages used were maize (SC 401, short season maize hybrid) and sorghum varieties; Pan 888 (local sorghum variety), Jumbo (late flowering sorghum x sudan hybrid) and Sugargraze (sweet sorghum x sweet sorghum hybrid). The legume forages were Lablab purpureus, (Lablab), Vigna unguiculata (Cowpea; trailing type), Crotalaria juncea (Sunnhemp), Glycine max (forage soybean) and Lupinus albus (White/bitter Lupin).

Experimental design

The experimental layout was a 2 x 4 x 5 factorial in a split-split plot design with soil type as the main plot factor, cereal as the sub-plot factor and legume as sub-sub-plot factor. The experiment was replicated four times. The design was chosen so that the legumes sole crop treatment yields would not be confounded by the shading effect of the cereal in adjacent sole or intercropped plots.

Planting

The forages were planted between the 27^th of December 1995 and 5^th of January 1996. All the crops were planted with compound D [Nitrogen (N): Phosphorus (P): Potassium (K) = 8:14:7) at the rate of 300 kg/ha and 400 kg/ha for the sandy and clay soils, respectively. The fertilizer was applied in bands along the rows with cereals in the intercropped plots and in all rows in the pure legume plots. Maize was planted in rows with 90 cm inter-row and 17 cm intra-row spacing to achieve plant population of 65 360 plants/ha. The sorghums were in rows with 90 cm inter-row spacing to achieve a population of 250 000 to 300 000 plants/ha. The legumes (forage soyabean, cowpea, lablab and lupin) were planted in rows with 30 cm inter-row spacing in the pure crop and 45 cm inter-row spacing in the intercropped plots to achieve plant population of 300 000 and 100 000 plants/ha, respectively. Sunnhemp was planted in the same rows but to achieve plant populations of 660 000 and 220 000 plants/ha in the sole and intercropped treatments respectively. In all cases 10 to 15 % more seed was planted to ensure good plot establishment.

The legume seed was inoculated with the appropriate Rhizobium strains on the day of planting. Forages were planted in such a way that the rows were oriented in the east-west direction; this was done to minimize legume growth retardation due to shading by the tall-growing cereal crops. The shade would then fall within the row. In the legume plots, plot size was increased from 25.2 to 29.0 m² to increase the area to be discarded so as to reduce shading effect of cereal plants in adjacent plots. For the clay soil type, supplementary irrigation was done to aid emergence, which was being impeded by soil capping.

Crop management

Plant emergence was monitored through plant counts in the plots, from week 1 to week 4 after planting. Mean emergence was calculated as a percentage of the intended plant population. Within the first 4 weeks, replanting and thinning of forages was done. The crops were weeded at 4 weeks after emergence and given a top dressing of ammonium nitrate of 300 and 400 kg/ha for sand and clay soils respectively. The second weeding was done during the eighth week. Scouting for diseases and pests was done regularly throughout the growth phase up to 13 weeks, and remedial action taken when required.

Plant growth monitoring and harvesting

Harvesting was done when forages were 13 weeks old. The forage was harvested from a net plot comprising of two rows of cereal and two rows of legume in the intercrop. In sole plots the net plot comprised of 2 rows of cereal and in legumes sole plots the harvesting was done in a net plot of 9.46 m². In the intercrop cereal and legume yields were determined separately by harvesting each component separately and composting harvested forages to get total yield from each plot. Samples of 250 g weight were obtained by taking a sub-sample of chopped herbage in order to determine the dry matter (DM) content, yield and nutrient composition of the forages.

For nutrient quality evaluation, the herbage was harvested at 6 weeks. In each plot 3 to 5 random sampling points were selected and herbage was cut from 1 m row at each sampling point. The herbage was weighed fresh and two samples of 100 and 250 g separated from the bulk sample. The 100 g sample was dried at 102 °C for 2 hours (Goering and Van Soest 1970) and was used for the determination of water-soluble carbohydrates. The 250 g sample was dried in a forced draught oven at 60 °C for 72 hours. The dried samples were ground to pass through a 2 mm sieve and retained for crude protein (CP), Neutral detergent fibre (NDF) and Acid detergent fibre (ADF) determinations. Harvesting of the samples continued at 2-week intervals until final harvesting at 13 weeks. Throughout the growth period the crops were monitored for growth and development by scoring for vigour, flowering, pod development and maturity.

Chemical analysis

Samples were collected and oven dried at 65 °C for 72 hours for DM determination and subsequent DM yield determination. The dry samples were ground to pass through a 2 mm screen and were analysed for CP, NDF and ADF. Crude protein was determined through Macro-kjeldhal digestion with sulphuric acid and distillation with sodium hydroxide and collection of ammonium ion over boric acid and titration with hydrochloric acid. NDF was determined by digestion and refluxing method with NDF solution (Goering and Van Soest 1970). ADF component was determined by digestion and refluxing method with ADF solutions (Goering and Van Soest 1970).

Water-soluble carbohydrate (WSC) content was determined by extracting sugars from 0.2 g of dried sample using 200 ml of distilled water. The sample was shaken for an hour and filtered through a Whattman No. 1 filter paper. The filtrate was retained for determination of WSC contents using the anthrone method (Deriaz 1961). The concentration of soluble sugars was determined spectrophotometrically based on the blue-green complex formed by boiling soluble carbohydrates with anthrone in 76 % concentrated sulphuric acid. The WSC content was determined by reading off the content from a standard graph using glucose standard solutions.

Statistical analyses

Analyses of variance were performed on the data using the general linear model (GLM) procedure of the Statistical Analysis System (SAS 1998). Least square means and Pdiff statistics were used to detect differences between means. The model fitted the effects of soil type (sandy soil and clay soil), cereal (maize SC 401 and sorghum varieties; Pan 888, Jumbo and Sugargraze), legume (Lablab purpureus, Vigna unguiculata, Crotalaria juncea, Glycine max and Lupinus albus) and their interactions. The analysis was carried out on the record of dependent variables that included establishment, persistence, yield and nutritive quality.
 

Results

Establishment and persistence of forages

Legumes germinated within the first week of planting. All legumes on the clay soil germinated with ease (Table 2). Soybean, lablab and lupin had over 80 % germination emergences on sandy soils while cowpea and sunnhemp had poor emergence (Table 2). Among the cereals Pan 888 had less than 50 % emergence rate on clay soil.

The trends were similar for the sandy soil (Table 2). From initial emergence to four weeks after emergence on sandy soils, the cereal populations for Jumbo and Sugargraze declined, but more than 50 % of targeted population was maintained. At 4 weeks among the cereals only maize reached the targeted plant population. Pests attacked the rest of the cereals and hence their growth and establishment was compromised.

Yield and nutrient quality for sole planted forages

Fungal diseases in most sorghum varieties compromised yield. Within the sandy soil for sole cropped cereals, the total yield was not significantly different across the cereals (P > 0.05). Jumbo and Pan 888 had the highest DM content followed by Sugargraze and then Maize (Table 3).

Although the DM content of the cereals was high the dry matter (DM) yields of forages grown as sole crops were low on the sandy soil (P < 0.05). The CP, NDF, ADF and hemi-cellulose contents were not significantly different across cereals (P > 0.05). For the water-soluble carbohydrates (WSC) PAN 888 had the highest value followed by Sugargraze and maize, while Jumbo had the least content (P < 0.05) (Table 3). On sandy soils, sunnhemp had the highest DM yield (5071 kg/ha) and DM content (334 g/kg) compared to other legumes (P < 0.05) (Table 4). Crude protein, ADF, NDF and hemi-cellulose were not significantly different across legumes grown on sandy soils (P > 0.05) (Table 4). On sandy soils, lablab had the highest WSC content followed by cowpea (P < 0.05) (Table 4).

Yield was significantly different between the cereals (P < 0.05), with maize having the highest yield (12 253 kg/ha) followed by Jumbo (8723 kg/ha), Sugargraze (6329 kg/ha) and Pan 888 (4501 kg/ha) having the least yield, on the clay soil. On clay soils, CP ADF, NDF, WSC and hemi-cellulose were not significantly different (P > 0.05). Sunnhemp yield was the highest (8314 kg/ha) on clay soils, followed by lablab (6547 kg/ha), soybean, (5366 kg/ha) and lupin (4037 kg/ha) while cowpea had the least yield (3 693 kg/ha) (P < 0.05). Crude protein, NDF, hemi-cellulose and WSC values were not significantly different across the legumes (P > 0.05) (Table 5). ADF content of sunnhemp (442 g/kg DM) and lupin (430 g/kg DM) were significantly different from that of lablab (382 g/kg DM), cowpea (372 g/kg DM) and soybean (300 g/kg DM) (P < 0.05).

Yield and quality of cereal-legume forages grown on a sandy soil

Due to the large number of comparisons made on yield and quality components the results were centered on yield and quality of the four cereals across legume treatments. Lupin dried out before harvesting and chemical analysis on herbage was not done for all the experiments. The legume contribution towards the total yield was higher in lablab and cowpea combinations than in lupin, soybean and sunnhemp combinations (P < 0.05). There was a significant improvement in cereal CP content in cowpea and lablab combinations as compared to sole sorghum (Jumbo) (Table 5). The legume yield and proportion was significantly higher in lablab, sunnhemp and cowpea combinations than in soybean and lupin (Table 5).

For maize based mixed forages, high total yields were realized in combinations with lablab (4254 kg/ha), sunnhemp (4217 kg/ha) and cowpea (3610 kg/ha) compared to maize sole crop (2932 kg/ha) (P < 0.05). The legume yield and proportion was significantly higher in lablab (2203 kg/ha; 0.52), sunnhemp (2092 kg/ha; 0.50) and cowpea (1747 kg/ha; 0.49) combinations than in soybean (355 kg/ha; 0.15) and lupin (P < 0.05). Legume inclusion improved the CP content of maize-legume intercrops (64-100 g/kg DM) compared to maize sole crop (54 g/kg DM) (P < 0.05). No significant differences in NDF and ADF were detected, but were lower in legume combinations than in sole cropped maize. The WSC content of sole cropped maize (126 g/kg DM) was significantly higher than that of maize-legume combinations (84-89 g/kg DM).

In Pan 888 and Sugargraze legume combinations, the yield and quality followed the same trends as in Jumbo and maize. However, in lablab, cowpea and sunnhemp forages, the legume contribution was close to or higher than 55 % of total yield (P < 0.05). There were significant differences in legume yield component of the intercrop (P < 0.05). All legumes had significantly higher CP content than cereals intercropped with them. Soybean had significantly higher CP than all other legumes (P < 0.05).

Yield and quality of cereal-legume forages grown on a clay soil

The yield of maize and Jumbo were consistently higher (P < 0.05) than those of either Sugargraze or PAN 888 for all cereal-legume combinations. The legume contribution in the cereal-legume forages was quite low ranging from 0.03-0.15 of total DM yields compared to 0.20-0.50 % on the sandy soil. The DM content of forages ranged from 0.14-0.25 with most forage combinations falling in the range of 180-200 g/kg. Total cereal yields were highest where cereals were intercropped with lablab or cowpea (P < 0.05). When grown alone maize had higher DM yield than the sorghum varieties (P < 0.05).

The crude protein content of forages was lower in cereals grown alone and in cereal-legume forages than in legumes alone (P < 0.05). There was a tendency for CP content of maize and Jumbo (98-114 g/kg DM) based combinations to be lower than that of Pan 888 and Sugargraze (104-138 g/kg DM) combinations. However, the CP content of cereals grown on the clay soil was high (P < 0.05). There was no particular pattern in changes in fibre content of forages for each cereal-legume treatment.
 

Discussion

Establishment and persistence

The decline in plant population was mainly due to pest attack, wild ungulates and waterlogged conditions in the case of lupin. The decline in population indicates a serious pest problem and therefore suggests that disease and pest control in forages should be done to optimize yield and quality. Fodder yield losses can be as high as 28.8 and 37.5 % for cowpea and sorghum, respectively (Shri and Gupta 1988) due to pests attack. Shri and Gupta (1988) suggests that chemical methods and cultural methods be integrated in pest and disease control in forages. Maize stalk borer and aphids were noted at about 4 weeks and spraying with carbaryl effectively controlled the aphids in maize and sorghum cereal crops.

Fungal diseases in most sorghum varieties compromised yield. Infestation of Sugargraze by the fungus elmintosporium turcicum depressed yields despite the high plant population. The prevalence of fungal diseases is much more when plant populations are high and when the environment is humid. The season when forages were grown (1995/96) had high rainfall with humid conditions prevalent for most of the growing season, particularly in the clay soil. Control of diseases through use of fungicide provides opportunity to avoid losses but may not be feasible in forages due to the high cost/benefit ratio (Ahmad 1988). Treatment with chemicals may also present toxicity problems to livestock. Breeding or use of resistant cultivars is a useful strategy that can improve pest/disease control for most forage species.

Intercropping and total yields

The improvement of total forage yield by intercropping on sandy soils yield is in agreement with findings reported in a review by Tripathi and Gill (1988). In some cases there maybe a total yield reduction accompanied by an improvement in total protein yield (Maasdorp and Titterton 1997; Jingura et al 2001). The low contribution of the legumes especially soybean and lupin to DM yield may be attributed to establishment and persistence problems caused by waterlogging and foraging by wild animals. In addition to this, the yield of these legumes in the intercrop may have been compromised by their erect growth habit. This growth habit makes them susceptible to shading which leads to lengthening of the internodes accompanied by the reduction in the number of flowers per plant and number of pods/plant (Jiang and Egli 1993). As the pods and seed contribute about 50 % to total herbage in these plants (Rodney and Albrecht 1994) reduction in the seed component tends to reduce the yield and quality contribution of these legumes in the intercrop. Intercropping of such legumes with tall cereal plants may reduce nitrogen fixation through reduction in nodule number and activity (Jiang and Egli 1993). This implies that for such forages sole cropping and mixing at ensiling may give an opportunity to produce adequate quantities of legume to meet the required proportions for improved forage quality.

Redfearn et al (1999) purported that although forage quality of intercrop soybean is greater than mono-crop soybean, intercropping forage-type soybean with tall-growing forage does not appear to be practical because of the decrease in dry matter accumulation. Lupin was a total failure on the sandy soil primarily due to  conditions, which prevailed soon after emergence and throughout the growing season. This suggests that lupin is unsuitable for use in areas subjected to excessive wetness.

The higher contribution of cowpea and lablab the water-logging compared to that of lupin and soybean could have been enhanced by their twining growth habit that allows the plants to entwine around the cereal plants. This growth habit allows access to light and ensures that photosynthesis and in due course substantial nitrogen fixation by these plants still occur under intercropping (Jiang and Egli 1993).

Sunnhemp yields were enhanced by its competitive ability. Sunnhemp and cereal heights were similar and hence the legume was competitive for light and managed to sustain yields. The relatively high dry matter content of sunnhemp as compared to other legumes may also have contributed to its high contribution to the total intercrop yields. Generally, legume contribution towards total yield was higher on the sandy soils than on the clay soils. The legume proportion was also higher in the sorghum varieties Pan 888 and Sugargraze than in maize and Jumbo. This may have been as a result of legume growth being impeded by the taller cereal plants through shading and thereby the photosynthetic activity of the plants.

Nutrient quality of intercropped forages

Intercropping at both sand and clay soil sites improved the quality components of the forages particularly crude protein content, as compared to sole cereal crop protein yields. However, the protein concentration of most of the cereals on the sandy soil was below the critical 60g to 80 g/kg DM (Humphreys 1991). The legume improved the protein content to meet maintenance requirements and production in the case of cowpea, lablab and sunnhemp (71-100 g/kg DM). This increase in protein content implies that a reduction in protein concentrate use is possible if such forages are conserved for the dry season feeding of dairy animals. There was also a considerable decline in fibre component of the intercropped forages particularly where cowpea was used. This can have implications on the intake and digestibilities of such forage mixtures as these may be influenced by the fibre content of forages (Van Soest 1987; Maasdorp and Titterton 1997).

On the clay soils, though the yield was high there was a depression in protein concentration in forages where Jumbo was the cereal of choice. Research reports a decline in protein concentration of soybean intercropped with sorghum where protein content of sorghum was reduced despite the 2.64 times more nitrogen fixation by soybean plants grown with sorghum (Humphreys 1991; Jiang and Egli 1993). Carruthers et al (1998) reported that intercropping corn with legumes is an alternative to corn monocropping and is a possible way to reduce the use of inputs, such as herbicides, while maintaining current weed control levels. In addition, due to increased total yields, total protein yield may be superior to that of cereal forages alone. In addition the inter-seeded non-legume forages produce bountifully in legume forages while minimizing costs and conserving soil-without commercial nitrogen fertilizer.
 

Conclusion

Among the cereals grown on sandy soils, the sorghum varieties, especially Jumbo yielded in the same range as maize. This suggests that sorghum can substitute maize under such environments. Total herbage yields were significantly higher on the clay than sandy soil, with yield ranging from 8.0 to 11.0 t/ha DM and 1.0 to 5.6 t/ha DM, respectively. Changes in nutrient quality were more pronounced in cereals-legume intercrops than in sole cropped cereals on sandy soils. However, persistence and growth of some forages particularly soybean and lupin were affected by the growth habit, waterlogging conditions and diseases and pests. Thus, soybean and lupin use as forage may be limited by susceptibility to pests.

Cereals have to be combined with legumes that do not have an erect growth habit but trailing growth habit. Apart from increase in nutrient composition and bountiful production, intercropping assists in minimizing protein concentrate costs and conserving soil-without commercial nitrogen fertilizer. Lablab, cowpea and sunnhemp have potential to be used for forage production on both sandy and clay soils, and in intercropping systems. Therefore, farmers are recommended to use cereal-legume intercrops especially maize or sorghum and cowpea and or lablab to enhance dry season feed availability. These intercropped forages can be harvested during the rain season or during winter if they are irrigated and conserved as silage for dry season feeding to enhance viability and sustainability of smallholder dairy production in Zimbabwe.

Acknowledgements

Authors are indebted to Danish International Development Agency (DANIDA) for the financial support of this project.
 

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Received 13 March 2007; Accepted 27 April 2007; Published 5 September 2007

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