Growth and Yield Performance of Black Gram (Vigna mungo L.) under Malabar Neem (Melia dubia) Plantations in Western Zone of Tamil Nadu

Agroforestry is a dynamic and ecological based natural resource management system, through which the combination of trees/woody perennials in farm and rangelands, diversifies and sustains production for increased social, economic and environmental benefits (Sureshbhai et al., 2017). The intercropping of pulses with commercial tree species in initial stages of establishment is desirable for replenishment of soil fertility by legumes and additional income to the farmers. Spatial arrangement of trees in plantation plays an important role in growth and yield of agricultural intercrops as well as trees. In order to utilize the interspaces in early stages in closer spacing and wider spacing even in later stages of plantation development, the selection of the crops for intercropping is important. The intercropping of agricultural crops not only gives additional income to farmers but also improves the soil condition due to different intercultural practices and fertilizer application and weeding during crop period (Bhusara et al., 2018). The current supply of raw materials for industries like pulpwood, plywood and furniture and biomass energy in the country is far behind the demand. Not only is the forest wealth of the country is poor but its productivity in terms of Mean Annual Increment (MAI) is also one of the lowest. The average MAI of Indian Forest is 0.5-0.7 m³ ha^-1 compared to the global average of 2.1 m³ ha^-1 (Srivastava, 2005). It is estimated that the demand for timber is likely to grow from 58 million cubic meters in 2005 to 169 million cubic meters in 2025 (Goswami et al., 2020; Saravanan et al., 2014).
        
Black gram (Vigna mungo L.) also known as urd bean in India is one of the most important cultivated pulse crops of the ‘Vigna’ group and cultivation from ancient times (Pandey et al., 2019). It is an important rainfed short duration legume crop of India and occupying an area of 44.93 lakh ha with 29.26 lakh tonnes production and 651 kg/ha productivity. It is grown in various agro-ecological conditions and cropping systems with diverse agricultural practices, both in rainy (kharif) and post rainy (rabi) seasons (Singh and Ahlawat, 2005). It is grown in summer and winter and accounts for 28 per cent of world grain legume production. In Tamil Nadu, black gram is considered as an important pulse crop and it is grown in an area of 3.72 lakh hectares with a production of 1,262 lakh metric tonnes and productivity of 645 kg/ha (Veeramani, 2019).
        
Melia dubia (Malabar neem) is a fast growing indigenous industrial wood species which belongs to the family Meliaceae. It is one of the most important multipurpose trees with a straight cylindrical trunk attaining a height of 20-25 m with a spreading crown and a straight bole of 9 m length and 1.2-1.5 m girth. M. dubia is predominantly growing in Southern India whose cultivation has now expanded to whole of the country (Parthiban et al., 2009). It is a short rotation and multi utility tree, mainly used as a raw material for various woods based industries like plywood, pulp and paper production and in packing case, matches splints etc. (Sarvade et al., 2014). The tree girth obtained more than 40 cm is saleable at the minimum rate of Rs 2000 to Rs. 7500 per ton for match, veneer and pulp industry. It is an ideal species for plywood and pulpwood industry apart from being extensively used in afforestation (Partiban et al., 2009; Priyanka et al., 2019). It is a promising tree highly suitable for agroforestry or farm forestry with a life cycle of 8 to 12 years is gaining economic importance both in domestic and global markets and its grows up to 40 feet within two years of planted tree yielding up to 40 tons of biomass on an average per acre per annum of 10 year old plantation. The minimum cultivation period is six years and it can be allowed up to 8 years for good economic value. About 400 trees can be planted in an acre which fetches Rs. 10-12 lakhs in 6-8 years (Goswami et al., 2020; Yadav et al., 2019). Considering its fast growing ability and multipurpose uses, it is also accepted as an ideal agroforestry species. Large scale plantations of M. dubia have been raised by various state forest departments and private entrepreneurs in Southern India (Chauhan and Kumar, 2014; Kumar et al., 2017).
        
M. dubia is one of the emerging industrial agroforestry plantations in Southern India intercropped with various agricultural crops in large scale plantations for pulpwood and paper industry. To maximize the land utilization, an agroforestry trial was laid to investigate the performance of black gram varieties under different spatial arrangements of 1.5 year old Melia dubia plantation.

Details of the experimental site
 
A field experiment was conducted during the year of 2019-20 (Kharif and Rabi season) at Vanavarayar Institute of Agriculture, Pollachi, Tamil Nadu (10.66°N and 76.88°E with an altitude of 198 m above MSL). The maximum and minimum temperature ranged from 29.0 to 32.7°C and 19.2 to 23.7°C, respectively. With regard to relative humidity, there was a fluctuation from 77.5 to 94 per cent (07 22 hours) and from 49.6 to 77.3 per cent (14 22 hours). There was a total rainfall of 742 mm was received in 117 rainy days. The evaporation and bright sunshine hour’s day^-1 ranged from 2.8 to 6.2 mm and 3.1 to 7.2 hours, respectively.
        
The initial analysis of the soil of the experimental site revealed that the soil was slightly alkaline (pH= 7.85) with low in soluble salts (EC= 0.42 dSm^-1), medium in organic carbon content (0.58 per cent), medium in available N (264 kg ha^-1), medium in P₂O₅ (16.7 kg ha^-1) and high in K₂O (426 kg ha^-1). The irrigation water was found to be neutral in reaction (pH= 7.6) with medium level of the soluble salts (EC= 1.18 dSm^-1). Detailed soil physico-chemical characteristics of the soil are presented in Table 1.
 

 
Experimental details
 
The experiments designed for intercropping of two black gram high yielding varieties viz., CO 6 - V₁ and VBN 6 - V₂ sowing at two different seasons like Kharif and Rabi season with Melia dubia variety of MTP 1 which was planted in 2016 with three spacing of S₁ (3 × 1.5 m), S₂ (3 × 3 m) and S₃ (4 × 4 m) while S₀ as open field (Sole crop of black gram). Experiment is designed in randomized block design (RBD) with eight treatments and three replications.
 
The treatments for black gram crop includes-
T₁- S₀V₁ = Black gram variety CO 6 sole crop.
T₂- S₀V₂ = Black gram variety VBN 6 sole crop.
T₃- S₁V₁ = M. dubia (3 × 1.5 m) + black gram variety CO6.
T₄- S₁V₂ = M. dubia (3 × 1.5 m) + black gram variety VBN 6. 
T₅- S₂V₁= M. dubia (3 × 3 m) + black gram variety CO 6.
T₆- S₂V₂ = M. dubia (3 × 3 m) + black gram variety VBN 6.
T₇- S₃V₁ = M. dubia (4 × 4 m) + black gram variety CO6.
T₈- S₃V₂= M. dubia (4 × 4 m) + black gram variety VBN 6.
 
        
The treatments of Melia dubia includes, T₁ (S₁), T₂ (S₂), T₃ (S₃), T₄ (S₁V₁), T₅ (S₁V₂), T₆ (S₂V₁), T₇ (S₂V₂), T₈ (S₃V₁) and T₉ (S₃V₂). Character of the black gram variety CO 6 and TNAU (black gram) VBN 6 was furnished in Table 2.
 

        
The recommended doses of N, P₂O₅, K₂O were 25, 50, 25 kg ha^-1, respectively. Full dose of nitrogen, phosphorus, potassium in the form of urea, DAP, MOP were applied basal as per treatments. In addition to gypsum 20 kg ha^-1 and soil application of 25 kg ZnSO₄ ha^-1 were applied. All other agronomic practices were adopted as per needs of the crop.
        
Growth and yield attributes as black gram height, number of branches, number of leaves and number of flowers was recorded before final harvest by randomly selecting 5 plants in each replication and treatment. The maximum plant height was measured from the base of the stem to the tip of the longest trifoliate leaf. Number of pods in individual selected plant was counted at every picking and finally these were added to obtain the mean number of pods per plant. Yield per plot (10 sq. m) was worked out for respective plots and expressed in kg. Yield per hectare was calculated by plot value × 1000 expressed in tonne. With respect of Melia dubia, growth attributes viz., tree height (m) and diameter (cm) were documented at two months interval. Data were analyzed statistically using Fisher’s analysis of variance techniques and least significant difference (LSD) test at 5 per cent probability level was employed to test the significance among treatment’s means.

The data of growth and yield parameters of black gram as sole crop and under different spatial arrangements of M. dubia for both the season of study (Kharif and Rabi) and pooled analysis are shown in Table 3, 4 and 5.
 

 

 

 
Growth attributes
 
Growth attributes of black gram in pooled analysis of both season like plant height (49.96 cm), number of branches (3.76), number of leaves (259.75), number of flowers (53.44) and number of pods (22.85) are recorded significantly high in T₂- S₀V₂ i.e. open condition as compared to with M. dubia based agroforestry model. Further, wider agroforestry tree spacing played an important role in M. dubia (4 × 4 m) on growth attributes compared to closer spacing 3 × 1.5 m in T₃ (S₁V₁). It might be due to less availability of light under different spacing of trees compared to open condition as sole crop. The similar reduction in growth attributes of intercrops in agroforestry was recorded by Rani et al., (2015), Rajalingam et al., (2016). Green gram and lentil are shade sensitive which results poor branching and pod settings in pulses (Nandal and Singh, 2001).
 
Yield parameters
 
In terms of yield parameters of black gram showed that the maximum yield for variety VBN 6 in the open condition as compared to the different spacing of M. dubia as maximum yield of seed per plant (g/plant) and seed yield (tonne/ha). black gram reported the highest seed yield in T₂ (sole cropping with variety VBN 6) as 5.38 g/plant and 0.82 tonnes/ha while in intercropping maximum yield was recorded with T₇- (variety VBN 6 with M. dubia at 4 × 4 m spacing) as 5.24 g/plant and 0.80 tonnes/ha. The yield reduction in pulses in intercropping with trees also reported by Bhusara et al., (2018), Pandey et al., (2019) and Nandal and Hooda (2005). Faidherbia albida with pulses reported that grain yield is black gram in lower canopy density than the monocrops and higher canopy density, which support that if canopy is properly managed the yield reduction in intercropping with trees can be reduced (Korwar and Pratibha, 1999).
 
Growth attributes of Melia dubia with intercropping
 
The tree height of Melia dubia in black gram agroforestry model recorded an increasing trend before intercropping as well as after harvesting of the intercrops. The results revealed that the tree height varied from 3.88 m to 6.89 m and 4.23 m to 8.09 m before sowing and after harvesting of the intercrops respectively and also exhibited significant difference in height increment. Among the different spacing arrangements, maximum height increment in the tree component was recorded under M. dubia (3 × 1.5 m) + CO 6 (1.57 m) in Kharif season and the lowest was reported under Melia (4 × 4 m) + VBN 6 (0.34 m) when compared to controls (Table 6). Significant difference was observed in diameter at breast height among different spacing and black gram variety combinations under agroforestry model before sowing and after harvesting of the intercrops. The results revealed that diameter at breast height ranged between 10.54 cm and 20.73 cm before sowing and 10.85 cm to 23.04 cm after harvesting the intercrops in combination of two seasons. Similar results for higher productivity of crop combination with Ailanthus excelsa was reported by Rajalingam et al., (2016). Better growth performance of guava + wheat compared to sole crop of wheat (Dalal et al., 2016). Growth attribute of Pungam based agroforestry system, seed source of Pongamia pinnata (MAP111) + Soybean ecorded higher productivity compared to sole crop (Parthiban and Fernandaz, 2017; Rao et al., 2017). The growth and yield of annual crops were found to be less in intercrop compared to sole crop, while the volume of trees and growth rate improved when planted along with intercropping of pluses (Ashalatha et al., 2015). Similarly, the competitive effect of trees on yield attributes and yield of black gram and mustard was observed tree spacing many influence the growth rate of both crops under agroforestry model. The light intercepted by under storey crops was more when the trees were pruned up to 70 per cent this has been directly influenced the crop height and gaining maximum seed yield and the trees were allowed to grow normally (Newaj et al., 2005). Patil and Channabasappa (2008), reported that when adaptation of closer spacing were reduce the seed yield of black gram and wider spacing may increase the light intensity to understory crops. Similarly, various agricultural crops growing under Acacia auriculiformis based agroforestry system viz., maize, sorghum, sunflower and groundnut adjoining to tree line were observed lesser yield compared with the wider tree spacing (Nagagouda, 1990; Solaimalai et al., 2005).
 

        
The M. dubia trees performed better in intercropping than in sole plantations (Fig 1-4) in both the season of observations. The maximum average increment of height was in T₄- S₁V₁ as 1.39 m in both seasons while maximum DBH increment was in T₉- S₃V₂ as 2.09 cm. Hence, the maximum tree height was exposed in closer spacing and highest DBH shows at wider spacing with black gram based agroforestry system. Thus intercrops favouring the growth of M. dubia probably due to application nutrients and irrigation to crops are also utilized by the trees.
 

 

 

 

Intercropping of  pulses with fast growing trees provide maximum returns to the farmers as compared to sole plantation or sole cropping. In the present study, the intercropping of black gram varieties with Melia dubia plantations in different spacing were the highest under sole cropping compared to intercropping. The growth and yield parameters of M. dubia were found maximum with intercrops than sole plantation irrespective of the spatial arrangement.
        
The average maximum seed yield of black gram with intercropping reported in T₈- (variety VBN 6 with M. dubia at 4 × 4 m spacing) as 0.80 tonnes/ha which shows marginal reduction of 0.02 tonnes/ ha in yield than sole cropping. Hence wider spacing of S₃ (4 × 4 m) can be suggested for intercropping under M. dubia plantations in initial 4 years. If we consider the economic return from the tree crop at the stage of harvesting, the financial benefits were more in the intercropping systems as compared to the sole cropping systems. It may also reduce the risk of crop failure and compensate the return from the trees. The interaction of trees and crops can be utilized for maximum gain by technological interventions and good agricultural practices.