INTRODUCTION Green manures have become popular in the present day as a result of the growing issues in agriculture, such as climate change, extreme weather events, soil deterioration, and land contamination due to the overuse of agricultural chemicals. Growing green manure crops on farmland has shown to be a viable and cost-effective way to ensure the long-term productivity of cultivated areas by preparing the soil for succeeding harvests. The green manure crops are grown and incorporated into the soil in order to restore the land's productivity. Green manures are a gift from nature since they improve the physical, chemical, and biological qualities of the soil while also lowering the nitrogen fertilizer requirements for the following crop. Unreliability of green manure performance, nonavailability of seeds, and labor intensive operations are the major agronomic constraints (Ramanjaneyulu et al., 2021). Socio-economic factors like the cost of land, labor, and mineral N fertilizer are seen to determine the cost-effectiveness and thereby farmers' adoption of sustainable green manure technology (Becker et al., 1995). According to Mishra and Nayak (2004), dhaincha, sunhemp, mung bean and guar grown during kharif season as green manure crops contributed 8-21 tons of green matter and 42-95 kg of N ha-1. Similarly, khesari, cowpea and berseem grown during rabi season contributed 12-29 tons of green matter and 67-68 kg N ha-1. The green manure crops are generally selected based on the location specific edaphoclimatic conditions, rainfall pattern, irrigation facility and turn-around time (Thimmanna et al., 2014). Further, short duration legume green manure crops can be explored to get some additional income through seed production and then incorporating the green manure crop residues after taking the harvest. This may ensure green manure seed availability for the next season sowing besides enriching the soil through residue incorporation. Seed yield of 4-5 q ha-1 under rainfed conditions and 12.5-15.0 q ha-1 under limited irrigation conditions (1-3 irrigations depending on soil, climate and crop) is possible (Ramanjaneyulu et al., 2021). Most of the green manure crops are fitted into rice-based cropping systems during pre-kharif system. In those regions where most of the times the fields are kept fallow following the kharif crop, rabi legume green manures can be grown to improve the soil quality along with providing seed as well as income. With this concept, the current research was designed to investigate the performance of legume green manure crops during rabi for their suitability in the Southern Telangana Zone. MATERIAL AND METHODS The research trial was conducted during rabi, 2020-21 at College farm, College of Agriculture, Rajendranagar, Hyderabad and was laid out in a randomized block design (RBD) and replicated thrice with seven green manure crops viz., green gram, black gram, horse gram, cowpea, sunhemp, dhaincha and pillipesara. The clay loam soil of the experimental site was alkaline in reaction with low organic matter and soil available nitrogen and high soil available phosphorous and potassium. All the crops were sown in the second fortnight of November. The mean maximum temperature varied from 26.4°C to 38.1°C and the mean minimum temperature varied from 11.1°C to 18.9°C during the period of crop growth. The relative humidity at morning (RHI) stretched from 75.3 to 95.7 per cent, where it was 22 to 60 per cent in the evening. The bright sunshine hours (BSH) fluctuated between 5.1 to 14.8 hrs. The wind velocity ranged from 2.5 to 4.7 kmph during the growing season. The pan evaporation ranged from 2.4 to 6.8 mm. Recommended dose of fertilizers and seed rate for respective green manure crops are mentioned in the Table 1. The objective of the research was to study the performance of the selected green manure crops in terms of their yield and economics. The data concerning to the yield attributes and yield was recorded at harvest. Plants that were randomly selected in the main plot at the first phase of recording the observations were used to record the yield attributes. The total cost incurred in the cultivation of green manure crops was expressed as cost of cultivation per hectare (` ha-1). The price of inputs prevailing at the time of their use was taken into consideration to work out the cost of cultivation. The yields of the green manure crops were converted into the equivalent yield of cowpea based on the price of the produce. RESULTS AND DISCUSSION Yield performance of green manures during rabi Yield attributes. Yield attributes are the desirable traits of a crop that are directly related to the yield. The yield parameters of the green manure crops studied in the present investigation are - pods per plant, seeds per pod, and test weight and are presented in Table 2. The number of pods per plant were the highest for sunhemp (50) and the lowest for pillipesara (11) while the number of seeds per pod were the highest for dhaincha (17) and least for horse gram (5). The difference in seed sizes of the green manure crops was reflected in their 100 seed weights. Cowpea with bold seeds weighed 7.34 g per 100 seeds while due to the small seed size, the 100 seed weights of sunhemp, dhaincha, and pillipesara ranged from 1.57 to 1.86 g. The yield attributes reported by the green manure crops during rabi were pursuant to their inherent morphological and physiological traits; and their relative adaptability to low-temperature conditions. Yield. Yield is one of the most important and complex traits in crops. It is both regulated by genes known as quantitative trait loci and influenced by external environmental factors (Wang et al., 2012; Zeng et al., 2017; Zhang et al., 2017). In general, yield in legume crops is determined by indirect traits like plant height, no. of branches, leaf area as well as direct traits like pods per plant, seeds per pod, and 1000-grain-weight (Moldenhauer and Nathan, 2004; Sakamoto and Matsuoka, 2008; Huang et al., 2013). The yield obtained by the green manure crops in the present study was an amalgamation of both direct and indirect traits as mentioned above. The cowpea in accordance with the higher pod number, seed size, and seed weight displayed highest grain yield of 2128 kg ha-1. The sunhemp with a yield of 1579 kg ha-1 stood next best to cowpea. Conversely, the lowest yield among the green manure crops was reported by pillipesara (201 kg ha-1). The yield obtained by all the green manure crops in the study is far less than their potential yields under favorable conditions. However, the yields of green manure crops presented in this study reflected their adaptability and suitability during rabi. The yield of short-statured legumes viz., green gram (483 kg ha-1), black gram (389 kg ha-1), horse gram (305 kg ha-1), and pillipesara (201 kg ha-1) remained very low during rabi owing to their poor growth with lesser plant heights, leaf area, and dry matter production. Stalk yield. Reportedly the stalk yield of the green manure crops varied significantly during rabi and is presented in Table 2. The stalk yield of the green manure crops ranged from 670 kg ha-1 to 7522 kg ha-1. The best among the green manure crops with the highest stalk yield was sunhemp (7522 kg ha-1). Cowpea stood next best to sunhemp with a stalk yield of 4990 kg ha-1. Apparently, taller stalks with higher biomass might have resulted in exceedingly higher stalk yields of these crops (sunhemp and cowpea) compared to the others The lowest stalk yield, on the other hand, was represented by pillipesara (670 kg ha-1). Harvest index. Globally, the harvest index of grain legumes is variable, while in cereals, it is generally considered to be relatively stable (McKenzie, 1987). Legumes may have more variable harvest indexes than cereals for a number of reasons. Wet and dry seasons (Hernandez, 1986), N application, sowing date, shade, irrigation (Verghis, 1996; Anwar et al., 1999), and lodging (McKenzie et al., 1985) may all be reasons for harvest index variability. The harvest index of the green manure crops in the study ranged from as low as 17.4 in sunhemp to 34.1 in green gram. Cowpea with a harvest index of 29.9 followed green gram. More biomass can give increased pod bearing structures, and result in more seed yield and a high harvest index (Ayaz, 2001). However, the results from the present study indicated poor translocation of photosynthates to achieve higher yields and therefore, lower harvest index values. This can be confirmed from the yields of green manure crops in this study which are exceptionally lower than their potential yields. The extended period of vegetative growth causing a period of ineffective flowering in the cool winter environment might have reduced the harvest index in sunhemp (Saxena, 1984). Cowpea equivalent yield of green manure crops. The yield comparison of the green manure crops in the study was done by converting the yields of individual green manure crops to the cowpea equivalent yields (Table 2). The cowpea equivalent yield of different green manure crops indicated the superiority of cowpea in achieving higher yield (2128 kg ha-1) during rabi and its advantage to be used as a grain cum green manure crop. This was followed by sunhemp (1880 kg ha-1). The lowest cowpea equivalent yield on the other side was noted with pillipesara (359 kg ha-1). Economics. Economic profitability is the prime force that drives any scientific technology from research field to the actual area of concern i.e., farmers’ field. Hence, the scientific practice that is ecologically promising and economically appealing would be sustainable in long-run (Sudhanshu Sudhakar, 2013). Cost of Cultivation. The cost of cultivation of green manure crops did not vary much (Table 3). It ranged from ` 14237 and ` 15487 ha-1. The cost of cultivation incurred was maximum with cowpea (` 15487 ha-1). While sunhemp with cost of cultivation of ` 14925 ha-1 followed cowpea. The difference in cost of cultivation of green manure crops was majorly due to the cost incurred on seed rate, which varied with the seed size of the crops. The different fertilization schedules for these crops also caused changes in the cost of cultivation of the green manure crops. Gross returns. The differences in the grain and stalk yields of the green manure crops had brought about significant variation in the gross returns. The gross returns obtained by the cultivation of green manure crops were presented in Table 3. The gross returns of the green manure crops ranged from ` 15075 ha-1 to ` 89376 ha-1. The highest returns of `89376 ha-1 were reported by cowpea, while the lowest (` 15075 ha-1) was given by pillipesara. The sunhemp with gross returns of `78950 ha-1 stood next best to cowpea. Though the unit price of cowpea is the least (`42 kg-1) among the green manure crops, the overall better growth of the crop has resulted in higher grain yield which in turn fetched maximum returns. A comparably higher yield of sunhemp due to equivalent performance as that of cowpea has realized higher gross returns next to cowpea. However, the difference between cowpea and sunhemp remained significant. On the other side, in spite of the higher unit cost of the crops - black gram, horse gram, green gram, and pillipesara ranging from ` 60 to 75 ha-1, the gross returns of these crops were low and have ranged from ` 15075 ha-1 to `34776 ha-1 due to their lowest yields as observed in Table 2 of this article. Net returns. Owing to significant differences in the gross returns, the net returns from the green manure crops also varied significantly. The data on the net returns of green manure crops were presented in the Table 3. The net returns of the green manure crops ranged from ` 500 ha-1 to ` 73889 ha-1. Cowpea fetched the highest net return (`73889 ha-1), while pillipesara fetched the lowest (` 500 ha-1). Maximum gross returns even at a higher cost of cultivation have resulted in higher net returns in cowpea (` 73889 ha-1) and sun hemp (` 64025 ha-1) compared to the other crops. However, the cowpea and sunhemp remained significantly different with cowpea getting higher net returns than sunhemp. Returns per rupee investment. The returns per rupee investment also were significantly different among the green manure crops during rabi. The data on returns per rupee investment were given in Table 3. The returns obtained per rupee invested due to green manure crops ranged from `1.03 to 5.77. A maximum return of ` 5.77 per rupee invested was obtained from cowpea, while the minimum of ` 1.03 per rupee invested was obtained from pillipesara. The sunhemp with ` 5.30 benefit per rupee invested proved to be the next best to cowpea. Exceedingly higher growth of cowpea and sunhemp during rabi than the other green manure crops might have incurred more profit per rupee invested. However, the difference between cowpea and sunhemp was significant with cowpea giving higher benefit per rupee invested than the sunhemp.