Yield and quality of Brachiaria Sp.cv Mulato-forage perennial peanut (Arachis pintoi) mixture in the Highlands of Madagascar

Volatsara B Rahetlah, Jean Marc Randrianaivoarivony, Blandine Andrianarisoa*, Lucile H Razafimpamoa and Vololona L Ramalanjaona

Centre de Développement Rural et de Recherche Appliquée, BP 198, Antsirabe 110, Madagascar
volats@yahoo.fr
* Laboratoire de Biotechnologie et Microbiologie, Faculté des Sciences, Université d’Antananarivo, BP 196, Antananarivo 101, Madagascar
blandine@andrianarisoa.net

Abstract

High quality forage shortage is a major constraint to dairy cattle productivity enhancement in the Highlands of Madagascar. The present study aimed to determine the effect of intercropping Brachiaria Sp. cv Mulato with forage perennial peanut at the ratio of 1:1 on sustainable improvement of yield and quality of forage.

Total dry matter and crude protein yields for three consecutive years were 9,3 and 12,4% higher in mixture  compared with pure stand of brachiaria, respectively. The highest land equivalent ratio value (LER) for dry matter yield of the mixture attained 1,41. Slight increase of protein digested in the small intestine when rumen-fermentable nitrogen is limiting (PDIN) content and total ash content were obtained from mixture compared with pure stand of brachiaria. Five years after establishment, soil phosphorus, potassium, carbon and nitrogen contents were 39, 20, 13, and 6% higher under intercropping compared with pure stand of brachiaria, respectively.

Key words: biomass, competition, manure, persistence, productivity, resource, soil

Introduction

Dairy farming is an important source of income for small-scale crop-livestock farmers in the central Highlands of Madagacar (Rakotondramanana 1999 ; Raharimalala 2002). Livestock development efforts over the past four decades have led to significant increase of the global milk production which is mainly attributed to dairy farming extension rather than dairy productivity enhancement. Milk yield per cow remain low averaging 2500 litres per year (CIRAD et al 2008).  

Feed shortage and particularly, high quality forage availability is one of the major limiting factors to dairy productivity improvement (Lecomte et al 2008). Low quality forage consisted of natural pasture and crop residues are found in the diet in large quantities. Livestock feed shortage is aggravated by regular decrease of crop production and productivity related to degrading farming circumstances. In fact, on-farm crop production and productivity are declining as a result of soil fertility losses due to soil erosion and deforestation practices and to the decrease or the abandon of mineral fertilizers use (Vågen et al 2006). This situation is also exacerbated by the negative impacts of climatic variations and climatic change (FAO 2006).

Brachiaria species and particularly, the cultivar Mulato of the hybrid brachiaria (Brachiaria ruziziensis x Brachiaria brizantha) are among the most cultivated forage grasses in the Highlands of Madagascar (CIRAD et al 2008). They are well adapted to the agro-ecological zones and give high biomass yields (FIFAMANOR 2007).  Perennial peanut (Arachis pintoï) is a forage legume adapted in the Highlands of Madagascar mainly used as a cover crop (CIRAD et al 2008).  

The present study aimed to determine the effect of intercropping Brachiaria Sp. cv Mulato with forage perennial peanut, in single alternate row (1:1) on sustainable improvement of yield and quality of forage.

Materials and methods

Experimental site  

The experiment was conducted over three consecutive years from the third year (2008-2009) to the fifth year (2010-2011) after establishment at the research station of FIFAMANOR (Centre for Rural Development and Applied Research) in the Vakinankaratra region (19° 18' S-47°07' E ; 1591m), in the Highlands of Madagacar. The climate is tropical altitude with a warm and rainy season extending from November to April with mean rainfall of 1300mm and a dry and cool season extending from May to October. Mean rainfall and mean temperature recorded at the experimental site during the experiment are presented in Figure 1.  

Experimental design 

The experiment was laid out in a randomized complete block design with three replicates.  Plot size was 3 x 3m and buffer zones between and within blocks were 0,5 and 1m, respectively. Treatments consisted of pure stands of hybrid Brachiaria (Cv Mulato) and forage perennial peanut and their mixture in single alternate row (1 :1).

Pure stands and mixture were established during the rainy season of 2006-2007 through vegetative multiplication at the spacing of 0.3 x 0.3m. Basal fertilizer composed of 33 N, 66 P₂O₅ and 48 K₂O kg ha^{-1 in the form of NPK (11-22-16) composite fertilizer and 20 tonnes of cattle manure ha-1} were evenly applied to all treatments at the planting time. The same amount of cattle manure was applied to all treatments at the beginning of the third and the forth year after an uniformization cut of the herbage. By contrast, no fertilizer was applied to all plots at the beginning of the fifth year.

 Sampling and chemical analysis

Pure stands and mixture were cut three times during the third and the fourth year, respectively and two times during the fifth year. Cutting interval was 6 to 8 weeks.  Green matter yield was estimated by cutting herbage from two quadrats of 1m² in the inner rows of each plot. Forage samples (800 to 1000g wet weight) of all treatments were taken for laboratory analysis. 

Forage samples were then cut into pieces of 5cm and oven-dried at 60°C for 72 hours for dry matter determination. Dried samples were ground to pass through a 1mm sieve for proximate analysis and a 2mm sieve for rumen degradation study (AOAC 1990). Forage quality in terms of total ash (TA), crude fibre (CF), crude protein (CP), energy feed unit (milk feed unit, UFL), protein digested in the small intestine when nitrogen is limiting (PDIN) and protein digested in the small intestine when energy is limiting (PDIE) contents were evaluated.  Total ash content was determined by incinerating dried samples in a muffle furnace at 550°C for six hours. Crude protein and crude fibre contents were determined by the Kjeldhal and the Weende methods, respectively. Milk feed unit, PDIN and PDIE contents were determined according to the nylon bag method (AOAC 1990). Dry matter and protein digested in the small intestine (PDI) yields were then calculated. 

Biological competition

Land equivalent ratio (LER) index is used to evaluate the efficiency of intercropping in using the resources of the environment compared with pure stands (Wiley 1979 ; Mead et al 1980). If the value of LER is exceeding unity, intercropping favours the growth and the yield of species in mixture. By contrast, LER values lower than unity indicate negative effect of intercropping on the growth and yield of combined species. Land equivalent ratio is calculated as follows : LER = {Lg+Ll} ; Lg = (RMSg / RMSgg) Ll = (RMSl / RMSll) where Lg et Ll are the land equivalent ratio of individual crops, RMSg and RMSl are the individual intercrops yields and  RMSgg and RMSll are the individual pure stand yields.

Soil chemical analysis

At the end of the experiment, soil samples were taken in all plots, at the horizons of 0 to 15cm. Soil carbon, nitrogen, phosphorus, potassium and exchangeable bases contents as well as soil cationic-exchange capacity (CEC) and pH were measured.

Statistical analysis

The recorded data were subjected to analysis of variance (ANOVA) and means were separated according to the least significant difference (LSD) method (p<0.05) using Genstat software packages (Buysse et al 2004).

Results and discussion

Dry matter and protein digested in the small intestine yields  

Dry matter (DM) and protein digested in the small intestine (PDI) yields over the experiment were affected by year, cropping system and their interaction (Table 1). The highest DM and PDI yields were recorded in the third year after establishment (2008-2009) while the lowest in the fifth year after establishment (2010-2011). Dry matter yield was probably related to rainfall pattern, clumps ageing and manure application effect. In fact, mean rainfall recorded for the third year was superior compared to the subsequent years (Figure 1).  Correlations between dry matter yields of different grass species and grass-legume mixtures and rainfall patterns have been reported by Ramírez de la Ribera et al (2008) and Ibrahim and Mannetje L’t (1998), respectively. However, Pholsen et al (2005) reported 47 to 118% increase of dry matter yield of the cultivar Basilik of Brachiaria decumbens over three consecutive years after application of 3 to 25 tonnes ha^-1 of cattle manure.  

Averaged over three years, mean DM and PDI yields of mixture were slightly higher than those of the pure stand of brachiaria (Table 2). Total DM and PDI yields of mixture for a three years period were 9,3 et 9,4% higher than those of the pure stand of brachiaria (Table 3).  Lobo and Acuña (2004) reported 18,5% higher mean dry matter yield over three consecutive years for Brachiaria brizantha-Arachis pintoi mixture compared with pure stand of Brachiaria brizantha. 

During the third year (2008-2009), the highest dry matter yield (20,35 t ha^-1) was obtained from the mixture (Table 1). Mixture produced 30 and 233% more dry matter yield than pure stands of either species, respectively.  In addition, PDI yield of the mixture is 24% higher compared with pure stand of brachiaria. Higher DM yields of mixtures compared with pure stands have been reported by Njwe et al (1990) and Valentim et al (1987) on Brachiaria ruziziensis-legume and grass-Arachis glabra mixtures, respectively.

Dry matter yield increase in mixture compared with pure stand of brachiaria is probably associated with increased productivity of intercropped species due to inter-specific complementary effects for efficient use of environmental resources such as space, nutrients, water and light.  In fact, mean dry weight of clump was 33% higher in mixture compared with pure stand of brachiaria (Table 4). Further, mean clump diameter and mean plant height of brachiaria plant were superior in mixture compared with pure stand (Table 4). Moreover, higher biomass yields of mixture at the two first cuts indicate higher regrowth capacity compared with pure stand of brachiaria (Figure 2). Berdahl et al (2001) reported higher dry matter yields of ryegrass-alfalfa mixtures compared with pure stands at each cutting date.  

Figure 2 : Dry matter yield (t/ha) of pure stands and mixture at cutting dates (2008-2009)

 During the fourth year (2009-2010), the highest DM (17,9 t ha^-1) and PDI (1,23 t ha^-1) yields were obtained from the pure stand of brachiaria but differences were not significant compared with mixture (Table 1). However, during the fifth year (2010-2011), DM and PDI yields of mixture were slightly higher than those of pure stand of brachiaria (Table 1). Improved persistence of mixtures compared with pure stands has been reported by Berdahl et al (2001) and Ibrahim and Mannetje (1998).

Forage quality 

Mean total ash (TA), crude fibre (CF), crude protein (CP), milk feed unit (UFL) and protein digested in the small intestine when energy is limiting (PDIE) contents were not affected by treatments. The highest TA (10,7% of DM), CP (20,8% DM), UFL (0,8 units kg^-1 DM), PDIE (98,5 g kg^-1 DM) and protein digested in the small intestine when nitrogen is limiting (PDIN) (149,9 g kg^-1 DM) were recorded for the pure stand of forage perennial peanut (Figure 3). This result indicates relative high nutritive value of this legume, which is in accordance with the findings of Ngome and Mtei (2010) and Sinclair et al (2007). Total ash, CF, CP and PDIN contents in mixture were 8,5%, 13,6%,  2,8% and 11,6% higher compared with those of the pure stand of brachiaria. Njwe et al (1990) reported no significant difference of CP content between mixture of Brachiaria ruziziensis-Desmodium sp and pure stand of Brachiaria ruziziensis. 

Figure 3 : Mean forage nutritive value over the experiment

Biological competition indices 

The highest land equivalent ratio (LER) of mixture in terms of dry matter yield was obtained in the third year (Table 5). Hence, LER value exceeding unity (1,41) indicates yield advantage of intercropping over pure stands. In addition, 41% more areas would be required by pure stands to achieve the same dry matter yield as mixture. Forage perennial peanut rate in dry matter yield was 4,5%.  This low contribution of forage perennial peanut to dry matter yield could be associated with the lack of significant forage quality improvement in mixture compared with pure stand of brachiaria. Grof (1985) and Hernández et al (1995) reported 8, 20 and 44% proportions of forage perennial peanut in dry matter yields of mixtures with brachiaria species, respectively.

 Soil chemical analysis 

Chemical analysis of soil samples taken from all plots at the end of the fifth year, revealed increased phosphorus (39%), potassium (20%), carbon (13.5%) and nitrogen (6%) contents under intercropping compared with pure stand of brachiaria (Table 6). These results suggest better resources exploitation by the intercropping system. Improved soil chemical properties could be associated with the increased productivity of species in mixture. Higher phosphorus uptake by Brachiaria dictyoneura pure stand compared with mixture with Arachis pintoi or Centrosema macrocarpum has been reported by Gómez-Carabalí et al (2010). However, Dahmardeh et al (2010) stated that intercropping maize with legume could increase soil nutrient (N, P, K) contents and improve soil fertility conservation compared with sole cropping.  

Conclusions

Results from this study show that intercropping of hybrid brachiaria (Cv Mulato) with forage perennial peanut at the ratio of 1:1 has the potential to:

• Increase total dry matter and protein yields over three consecutive years by 9% ;
• Increase dry matter productivity up to 41% compared with pure stands ;
• Improve forage quality through protein digested in the small intestine when nitrogen is limiting (PDIN) content enhancement ;
• Improve soil chemical properties compared with pure stand of brachiaria by increasing phosphorus, potassium, carbon and nitrogen soil contents.

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Received 16 August 2012; Accepted 27 August 2012; Published 1 October 2012

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