Pulses play an important role in human diet as a major protein source, three times more than cereals and rich in sulphur, calories and vitamins especially B-complex, as well as in farm economy of our country. They are integral component of sustainable crop production, especially in rainfed areas. Blackgram [
Vigna mungo (L
.) Hepper], a highly prized pulse crop of Leguminosae family, is spread in Indian subcontinent and popularly known as “Urad dal”. It is cultivated in Bangladesh, Afghanistan, Myanmar and Pakistan. Most suitable climate for blackgram is 27-30°C, moderate rainfall and loamy soil with high water holding capability. Blackgram is third most important pulse crop grown under rainfed, rice fallow, irrigated conditions and during
kharif,
rabi and summer seasons, which matures in 90-100 days and it, enriches soil with nitrogen. India is major producer and consumer of blackgram
(Raju, 2019). It is used for preparation of different food preparations like
Idli,
Dosa and non-fermented foods
(Sivasubramanian et al., 2015), with rice flour.
The mineral composition includes calcium (286 mg), iron (15.67 mg), magnesium (553 mg), phosphorus (785 mg), potassium (2035 mg), sodium (79 mg), zinc (6.93 mg), copper (2.031 mg), manganese (3.161 mg) and protein (52.18 g) and Vitamins like Vit. A (2.14 1 mg), C (2.62 mg), B1 (0.273 mg), B2 (0.254 mg), B3(1.447 mg), B6 (0.906 mg), B9 (0.281 mg), B12 (216 mg) and vitamin B15 (0.906 mg)
(Suneja et al., 2011). It holds 341 calories of energy and provides 25.21 g of protein per 100 g. This crop itself is a mini-fertilizer factory because it has unique characteristics of maintaining and restoring soil fertility through fixing atmospheric nitrogen in symbiotic association with rhizobium bacteria present in root nodules. It is used as a nutritive fodder especially for milch animals (
Tiwari and Shivhare, 2016) and also used as a green manure crop. It possesses very good root system which binds soil particles and thus prevents soil erosion.
The review work was carried out at Department of Agronomy, Agricultural College and Research Institute, Tamil Nadu Agricultural University, Madurai, Tamil Nadu, India. Nearly six months from September, 2019 to February, 2020 had been spent in collecting literature which includes 2 months for manuscript writing. About 200 scientific papers were screened, shortlisted and 88 papers used to prepare this manuscript. For searching of research papers various data bases such as TNAU e library, ARCC journals, google scholar, research gate and scopus were used.
Importance of pulses
Pulses are an excellent source of vegetable protein and a wide range of vitamins and minerals. Every class of Indian society invariably includes pulses in their daily diet and traditionally it is consumed with cereals, which are relatively rich in sulphur containing amino acids. A good quality protein is obtained in dishes prepared using pulses with cereals. The human body utilizes between 32 and 78% of protein from pulses ingested. Dietary allowance for adult male is 60 g/day and for adult female 55 g/day (
Directorate of Pulses Development, 2016) but per capita availability is only 42 g/day in India.
Iriti and Varoni (2017) stated that pulses represent the most important food grain to prepare staple food extensively to cover basic protein and energy needs throughout the history of humanity. Further, in India, government sector provides all assistance to promote pulse production besides offering minimum support price (MSP) for food grains produced by farmers. A relook into enhanced MSP (Fig 1) for blackgram by 32% from 2015 price indicates growing significance of blackgram.
Challenges for low productivity in blackgram
Mostly pulses are grown under rainfed, low fertile, problematic soils and unpredictable environmental conditions in India with a high degree of risk and often face many constraints.
Climatic constraints
A group of scientists [
Ali and Gupta (2012),
Reddy, (2009) and
Singh and Singh, (2008)] identified that late sowing of blackgram lead to reduction in growing period and suffering from cold injurious at early stages of growth, causing arresting of biological activities for a long period. Later, a sudden rise in temperature attracts incidence of diseases and pests. The changing climate may drastically affect yield and alter incidence of pest and diseases.
Soil constraints
A neutral soil pH is preferred for blackgram
(Singh et al., 2013a) and is sensitive to acidic, saline and alkaline conditions. The Eastern and North Eastern India has acidic soil which affects availability boron, molybdenum and sulphur which are essential for blackgram. On contrary, semi-arid regions has salinity and alkalinity problem.
Agronomic constraints
Ramakrishna et al., (2000) and
Reddy (2009) were of the opinion that improper sowing time and method, low seed rate, insufficient irrigation, inadequate intercultural operation are concerns for low productivity. Further, sowing under
utera cropping system with poor management leads to decline in blackgram yield in rice fallow condition.
Varietal constraints
Vasanthakumar et al., (1987) viewed that, non-availability of suitable varieties and poor quality of seeds limited blackgram yield. Decades later, the same factors were also stressed by
Singh et al., (2013a) and
Ramakrishna et al., (2000). However, in recent times this constraint has been addressed by pulse breeders across the country.
Storage constraints
During
kharif, coincidence of harvest time with monsoon rains led to yield loss and poor grain quality and hence, proper closed threshing floor and storage facility were essential (
GOI, 2013) and due to inadequate storage facilities in rural areas, farmers lose a substantial quantity of harvested produce as observed by
Singh et al., (2013b).
Marketing constraints
The delayed return of rupee invested for cultivating blackgram is another important concern for farmers. Farmers have to arrange required finance for input purchase, wages for labourers; they put in lots of efforts for these.
Narayan and Kumar (2015) observed that, technology inadequacy and non availability of essential inputs are the real challenges for farmers.
National and Tamil Nadu scenario
The trends in area, production and productivity of blackgram during 2010 to 2018 of Tamil Nadu and India are discussed hereunder. It indicated that production, area under blackgram grew steadily over years to reach 52.79 lakh ha during 2017-2018. The productivity ranged from 542 kg/ha to 662 kg/ha. In 2016-2017, there was a sudden rise in area, production, productivity due to promotion and support by Government of India during International year of pulses. In Tamil Nadu state, area under blackgram fluctuated between 3.19 and 4.26 lakh ha, so did production, fluctuated from 1.27 to 3.01 lakh tonnes. The productivity ranged from 398 kg/ha to 707 kg/ha (Fig 2).
Opportunities for enhancing blackgram productivity
Genetic advancements made and varieties evolved for specific situations besides, technological information for enhancing the productivity of blackgram have been reported.
I). Seedbed preparations
It is vital for ensuring easy and uniform germination as well as good growth and development of plants besides, ensuring increased water use efficiency and availability of nutrients to crops. Suitable seedbed preparation method facilitates absorption and storage of soil water resulting in better crop growth.
Elankavi et al., (2019) and
Kalpana and Selvi (2008) stated that ridges and furrows provides ideal environment for aeration, microbial activity and drainage and for yield attributes and yield but raised bed method was ideal for semi-arid conditions of Uttar Pradesh during
kharif (Tomar et al., 2016), by providing favourable rhizosphere conditions, lowering bulk density (30%), higher infiltration rate (5%)
(Kumar et al., 2015). However,
Rathore et al., (2010) claimed broad beds were superior for growth and yield, under water logged areas also
(Ghosh et al., 2014).
A recent study
(Surya et al., 2020) indicated that, for rice fallow blackgram, broadcasting of 37.5 kg of blackgram after harvest of rice and practicing tiller (9 Tyne) ploughing 1 or 2 days after sowing is novel and ideal method for higher grain yield (713.5 kg/ha). For machine seeding,
Vallalkannan (2019) while comparing broadcasting with multi-crop planter (Turbo seeder) both in flat bed and raised bed (90 cm) found raised beds is suitable, which had higher plant population, branch number, number of seeds and seed yield (2.61 g/plant).
II). Zero-budget (non-monetary) input management
a) Genotype selection
Improved and suitable varieties for different agro-climatic conditions and seasons and varieties tolerant to various biotic and abiotic stresses have been developed. The maturity of blackgram varieties ranges from 60 to 85 days with yield potential of 800 to 2000 kg/ha and it is cultivated in
kharif, rabi and summer seasons (Table 1). A few special varieties included bold seeded (MDU1, DU 1, VBN 9), mutants (TAU 2, TU 94-2)
(Reddy and Dhanasekar, 2007); Summer irrigated (VBN 8,
Indira Urd Pratham, DU 1), rice fallow (LBG-648, LBG-402, LBG-22, LBG-611) and summer rice fallows (LBG-20, WBG-26, LBG-623, PU-31 (RARS, Tirupati); Synchronized flowering (VBN 8,VBN 10, KKM 1. For intercropping under coconut garden, mutant variety TAU-2 is suitable in Kerala (www.kau.in).
Rice fallow varieties
In delta regions of Tamil Nadu, Andhra Pradesh, Karnataka and Odisha, different varieties of mungbean and urdbean are grown in rice fallows
(Sanjeev et al., 2016) by utilizing residual soil moisture
(Behera et al., 2014).
Resistant varieties
In recent years, blackgram varieties developed are generally tolerant to resistant in nature to various diseases
(Prasanthi et al., 2010); Cercospora leaf spot and rust resistant variety is LBG-648 and wilt resistant varieties are LBG-402, LBG-648, LBG-611, LBG-22, LBG-645, LBG-685 (RARS, Tirupati). Trombay varieties TU68, TU80, were found less susceptible to pulse beetle compared to other genotypes
(Gopalaswamy et al., 2016).
b) Time of sowing
Sowing at optimum time plays a key role in obtaining high seed yield
(Dubey and Singh, 2006). In summer irrigated blackgram,
Kandasamy and Kuppuswamy (2007) studied interactions between genotypes (T9, ADT3, ADT 5, VBN2, CO5) and dates of sowing at weekly intervals (January 12
th, 19
th, 26
th and Feb. 2
nd) in Cauvery delta zone of Tamil Nadu and found that genotype ADT 3 recorded higher yield parameters, yield (831 kg/ha) when sown on 19
th January.
Narinder et al., (2016) experimented genotype (T-9, PU-19, PU-35) vs. dates of sowing (August 5
th, 15
th and 25
th) in
kharif blackgram, and concluded that PU-35 variety gave maximum yield (11.11 q/ha) when sown on August 15
th. In scarce rainfall zone of Andhra Pradesh,
Reddemma et al., (2019) studied genotypes (TBG-104, LBG-787, GBG-1 and PU-31) with dates of sowing (October 1st fortnight, October, 2
nd fortnight, November 2
nd fortnight) and found that sowing PU-31 on October 1
st fortnight gave high seed (856.42 kg/ha) and haulm yield (2473 kg/ha).
For
kharif blackgram in vertisol,
Subbulakshmi (2019) explained, by studying three dates of sowing (39, 41, 43 Standard weeks) with four genotypes (CO5, CO6, VBN4, VBN5), that sowing CO5 during 39
th standard week had registered highest growth, yield parameters and yield. For the same season, August 9
th was the best
(Tiwari et al., 2018) with maximum plant population (25) while lowest plant population was obtained under delayed sowing on August 27
th. For rice fallow blackgram,
Maruthupandi et al., (2017) suggested that sowing of seeds 10 days before rice harvest was the best cultivation method for getting higher CGR, RGR, NAR and yield.
c) Method of planting
Under rice fallow pulse system, among various methods of planting tested, line dibbling was ideal as reported by
Maruthupandi et al., (2017). But,
Kumar et al., (1992) were of the opinion that dibbling seeds immediately after harvest of rice recorded higher seed yield than broadcasting of seeds in standing crop of rice.
III). Low-budget management techniques
a) Seed treatments
Seed treatment, a low-budget agronomic management technique, refers to application of physical, chemical or biological agents to seeds prior to sowing in order to control and reduce infection and infestation, besides promoting growth and development of plant. Biological seed treatments will be increasing in near future (
Sharma et al., 2015). Further, Pre-sowing seed hardening facilitates seed germination; minimize risk of stand establishment under varied environmental conditions and good crop growth
Subjecting blackgram cv. VBN4 seeds to various treatments and evaluating under laboratory and field conditions revealed that seeds fortified in the order of MgSO
4<polykote<Carbendazim<dimethoate<
Pseudomononas fluorescens<Rhizobium<Azophos<DAP recorded higher seed yield and other parameters when compared to control
(Sathiyanarayanan et al., 2015).
Hydrating seeds with GA3 50 ppm and 12 hours surface drying at room temperature hastened germination and seedling emergence and improved plant dry weight at harvest
(Gangaraju et al., 2019).
Seed dry dressing with botanicals (fenugreek seed powder, custard apple, moringa leaf powder at 2, 3, 4 g/kg of seeds), shaking for 1, 2, 3 hours exposed, seeds treated with 3 g/kg of fenugreek seed powder with 1 hour shaking had increased physiological parameters in fresh and aged seeds, followed by custard apple leaf powder 4 g/kg treatment
(Sathish and Bhaskaran, 2013).
As molybdenum is essential for nodulation and leghaemoglobin, studies by
Anwarulla and Shivashankar (1987) with blackgram and green gram revealed that seed treatment with sodium molybdate at 12 g/kg and foliar nutrition at 1·2 kg/ha was superior for nodule number, dry weight and leghaemoglobin content with increased dry matter and pod yield
b) Foliar nutrition
Among fertilizer application practices, foliar application of nutrients is a low-budget, yet effective method. Foliar nutrients usually penetrate into leaf cuticle or stomata, enter the cells and facilitate nutrients entry. It is credited with rapid absorption and complete utilization of nutrients and the only way to mitigate nutrient stress and to maximize blackgram yield (Table 2).
IV). Integrated Nutrient Management (INM) practices
INM principle encompasses on adding fertilizer in right amount, at right time with right combinations including other cheaper, eco-friendly natural materials which can supply nutrients to restore soil health. Accordingly the findings of various research studies are presented in (Table 3). A perusal of research findings, indicated besides N,P,K, blackgram needs secondary nutrient like sulphur. Among micronutrients, Fe, Mo, Zn are critical for growth and development of blackgram. Organic resources like vermicompost, FYM and biofertilisers, favour nutrient uptake and improved crop yields.
V). Weed management
For irrigated blackgram, pre-emergence herbicide pendimethalin @ 1 kg/ha and alachlor 1.5 kg/ha; for post-emergence, acifluorfen sodium(16.5%) + clodinafop propargyl (8% EC) @ 187.5 g/ha and Imazethapyr 0.075 kg/ha were effective in controlling weeds and higher yield as reported by
Jagadesh et al., (2018) and
Srinivasaperumal and Kalisudarson (2019) respectively.
Devaraju and Senthivel (2018) reported pendimethalin 1 kg/ha followed by Imazethapyr (50 g/ha) was effective.
For non-chemical weed control, mulching with sugarcane trash decreased weed density in blackgram
(Sivakumar et al., 2020), they also reported that pendimethalin @ 1 kg a.i/ha) at 3 DAS fb quizalofos-p ethyl @ 50 g/ha on 25 DAS had minimum weed density, maximum weed control efficiency (97%) at 45 DAS and 97% at 60 DAS.
VI). Integrated pest management
Adoption of a IPM module consisting of components (Table 4) like seed treatment, erection of bird perches, installation traps against pest, use of bio rational pesticide, mechanical management and need based insecticide, was best for blackgram to control pod borer and pod bug damages
(Gajendran et al., 2006).