MATERIALS AND METHODS

The field experiment was carried out on the University of Zabol farm, Iran (61° 41’E, 30° 54’N, above sea level 483 m), average 30 years rainfall was 49 mm.

Table 1:	Monthly average temperature, relative humidity and wind speed recorded at Zabol, Iran location during the 2007 growing seasons (Agricultural Climatology Research Station of Zahak)

Table 2:	Soil characteristics of the experiment area during the 2008 growing seasons (Agricultural Research Center of Sistan)

Table 3:	The description of experimental treatments

The experiment was carried out during 2007 growing season (Table 1) on a sandy-loam soil (Table 2). All phosphorus (150 g m^-2) and potassium (100 g m^-2) and half nitrogen (50 g m^-2) were applied at sowing, while balance of nitrogen was applied at stem elongation stage. All other cultural practices including (irrigation, thinning and weeding) were kept normal and uniform for all the treatments.

The treatments were compared in a factorial design with eight levels of planting ratios 100:100 (M:C), 50:100 (m:C), 100:50 (M:c), 50:50 (m:c), 75:25 (M":c"), 25:75 (m":C"), 0:100 (C) and 100:0 (M) and two levels of maturity stages (milky stage and doughy stage) in four replication. The treatments used for this experiment is shown in Table 3. The treatment comprising the individual plot size was (7x4 m) 28 m². Maize variety K.s.c 704 and cowpea (Vigna unguiculata L.) variety cv 29005 was sown on year 2007. For this experiment, the density of maize and cowpea are expressed, sole crop densities being 20 and 8 plant m^-2 maize and bean, respectively. Inter-row spacing was 25 and 10 cm in the sole crops of maize and bean were used with a between-row spacing of 50 cm. Initially 2-3 seeds were sown per hill. Twenty five days after sowing (25 March) at seedling were thinned to retain one healthy seedling per hill. Three hand weeding procedures were applied 20, 30 and 40 days after sowing. Quality parameters like CP (Crude Protein), ADF (Acid Detergent Fiber), NDF (Neutral Detergent Fiber), WSC (Water Soluble Carbohydrate), DMD (Dry Matter Digestibility) and Ash (Ashes) were determined using the NIR (Near Infra-red Spectrophotometer) Model 8600, PERTEC Co (Roberts et al., 2004).

Statistical analysis: The data on growth, yield and quality parameters were analyzed by Fisher’s analysis of variance technique and Duncan test at 0.05 probability level to compare the treatment means (Steel and Torrie, 1984). Data analysis were conducted using of SAS (SAS Institute, 2004) as a Factorial Experiment 8x2 with four replicates.

RESULTS

Maximum economical yield for maize (9.0 kg/10 m²) was recorded in plots where M^’c^’ were sown. Minimum economical yield for maize (2.2 kg/10 m²) was recorded in plots of maize and bean sown ratio m^’C^’ (Table 4), Maximum biological yield for maize (19.6 kg/10 m²) was recorded in plots where MC but maximum biological yield for bean (14.8 kg/10 m²) was recorded in plots where mC were sown. The highest LER (Land Equivalent Ratio) was obtained by sowing the crop in additive design in a ratio of MC (2.26) and the lowest LER was obtained by sowing the crops in replacement design of mc (1.27).

LER (Land Equivalent Ratio) values were greater than one in all intercropping systems with different planting ratios which indicated yield advantage of intercropping over sole cropping of maize. Bean (HF 465) LER increased with increases in bean population (Luiz and Willey, 2008). This might be attributed to the fact that bean plants possibly benefited from the nitrogen applied to maize rows. The results indicated that intercropping of maize+bean gave higher land use efficiency than mono cropping of maize. Various experiments have documented the best time to harvest corn f or silage to optimize yield and quality (Philippeau and Michalet Doreau, 1997; Bal et al., 1997). Total biomass yield of intercropped maize per unit area tended to increase with increasing maize population (Luiz and Willey, 2008). Grain yield per unit area of intercropped beans decreased as maize population increased (Mutungamiri et al., 2001). The cowpea sown alone produced the lowest green fodder (37.9 kg/10 m²). Similar results have been reported earlier by Khandaker (1994). The data in Table 5 revealed that green fodder yield and quality forage were significantly affected by planting ratios and harvest time. DMD was significantly (p<0.01) affected by the harvest time. The highest DMD was achieved at H₁ (61.5%) that which was greater than at H₂. DMD was affected (p<0.01) by planting ratios. The intercrops Mc (100% maize+50% cowpea) produced the highest of DMD (62.5%) and the intercrop m’C^’ (maize 25%+cowpea 75%) produced the lowest of DMD.

Table 4:	Mean values of economical and biological yield and LER of maize and cowpea as influenced by different planting ratios and harvest time based on Duncan test
Any two Mean values not sharing a common letter differ significantly from each other at 5% probability; LER: Land Equivalent Ratio, CV: Coefficient of variation

Table 5:	Means of green fodder yield and quality parameters as influenced by different planting ratios and harvest time of intercropping maize and bean based on Duncan test
Any two Mean values not sharing a common letter differ significantly from each other at 5% probability; DMD: Dry Matter Digestibility, NDF: Neutral Detergent Fiber, ADF: Acid Detergent Fiber, WSC: Water Soluble Carbohydrate, CP: Crude Protein, Ash: Ashes, CV: Coefficient of variation

The DMD of the intercrop was between the sole maize and higher than that for sole cowpea (Table 5).

The increase in mixed green forage yield compared to maize grown alone mainly ascribed to more production of vegetation and biomass of component legume crops. DMD was greatly (p<0.01) affected by the harvest time. The mean of DMD over the harvest time at H₁ (61.5%). The intercrops Mc (100% maize+50% cowpea) produced the highest of DMD (62.5%) and the intercrop m’C^’ (maize 25%+cowpea 75%) produced the lowest of DMD (Table 5). The production of crude protein was also affected significantly by planting ratios and harvest time of maize and bean. The results (Table 5) revealed that an increased proportion of bean in seed mixture increased the crude protein contents. The bean sown alone produced more crude protein (19.65%). Maize sown alone produced minimum crude protein (12.11%). Primitive effect of legume intercrops on protein concentration of main crop has also been reported by Mpairwe et al. (2002) and Azraf-ul-Haq et al. (2007).

Maximum crude protein (15.2%) was obtained in H₁ and minimum crude protein (12.3%) was obtained in H₂. Crude protein has previously been shown to decline with increasing maturities (Shepherd and Kung, 1996). Armstrong et al. (2008) reported that intercropping climbing beans with corn increased CP in the mixture, but also increased neutral detergent fiber concentration and decreased digestibility compared to monoculture corn. Dawo et al. (2007) reported that CP concentration increased 22% in the mixture when corn proportion in the mixture decreased by 50%. The results are in agreement with other studies where legumes also increased CP concentration when in mixture with corn (Anil et al., 2000; Dawo et al., 2007). Maximum ADF (31.85%) was recorded by sowing maize alone. Harvest time was also affected significantly on ADF; Maximum ADF was recorded by H₁. A decline in fiber concentration with increasing maturity can be attributed to the dilution effect created by the increasing content of grain as corn matures (Coors et al., 1997 ). Maximum WSC was recorded Maize sown alone and bean sown alone produce minimum WSC. In maize WSC in H₁ lowest content and H₂ was highest content.

An increase in WSC with increasing maturity can be attributed to the dilution effect created by the increasing content ratio of grain to fodder as corn matures. Johnson and McClure (1968) reported increased soluble carbohydrate in stalks from tasseling to the milk stage and a decline thereafter plots were established at the University Of Wisconsin Ag- with advancing maturity. Decrease in the ash concentration with maturity could results from dilution of minerals within increased the DMD.

DISCUSSION

Obtained results shown that an increased proportion of bean in intercrops increased the crude protein contents. Primitive effect of legume intercrops on protein concentration of main crop has also been reported by Mpairwe et al. (2002) and Azraf-ul-Haq (2007). The mean intercrop CP concentration, across H₁ and H₂, were (15.2 and 12.3%) for this experiment. These were greater than maize but less than cowpea, similarly results have been given for maize. Maximum crude protein percentage (15.2%) was obtained in milky stage and minimum crude protein (12.3%) was obtained in doughty stage, the decrease of CP content with maturity reported by Ghanbari and Lee (2003). Crude protein has previously been shown to decline with increasing maturities (Shepard and Kung, 1996). Armstrong et al. (2008) reported that intercropping climbing beans with corn an increased of neutral detergent fiber concentration and decreased digestibility compared to monoculture corn. Dawo et al. (2007), reported that CP concentration increased 22% in the mixture when corn proportion in the mixture decreased by 50%. Present results are in agreement with other studies where legumes also increased CP concentration when in mixture with corn (Anil et al., 2000; Dawo et al., 2007). Reduction in NDF and ADF concentration of forage from H₂ compared with H₁ can be attributed to increasing of grain to whole biomass ratio. Harvest time was also affected significantly on ADF; maximum ADF was recorded by milk stage. A decline in fiber concentration with increasing maturity can be attributed to the dilution effect created by the increasing content of grain as corn matures (Coors et al., 1997). WSC concentration increased in intercrops compared with that in sole cowpea. The highest WSC was recorded for sole maize and sole crop of cowpea produce the lowest WSC and dry matter digestibility. Johnson and McClure (1968) reported increased soluble carbohydrate in stalks from tasseling to the milk stage and a decline thereafter Plots were established at the University Of Wisconsin Ag-with advancing maturity. Decrease in ash concentration with maturity could results from dilution of minerals as crop mature and agree with Ghanbari and Lee (2003).

CONCLUSION

This study has thus clearly brought out the beneficial effects of maize-cowpea intercropping for forage yield and quality. As a conclusion, intercropping is more productive than sole cropping. Maize-cowpea intercropping increasing green fodder yield and forage quality of maize. Therefore, it can conclude that this initial investigation show results of maize/climbing cowpea mixture were advantageous compared to both sole crops of maize and cowpea.

ACKNOWLEDGMENT

This project was financed by the University of Zabol, Iran. We would like to thank the staff of Research Centers of Zabol.