Yield and yield attributes of Mungbean (Vigna radiata L.) cultivars as affected by phosphorous levels under different tillage systems

Two mungbean cultivars, Swat-1 and NM-98, four levels of phosphorous (0, 20, 40, and 60 kg ha−1) in the form of TSP, and four tillage systems, zero tillage (no tillage), minimum tillage (2-time), conventional tillage (4-time), and maximum tillage (6-time) were used. Results divulge that plant height, number of pods plant−1, number of seeds pod−1, biological yield, seed yield, 1,000 seed weight, harvest index, and protein content were significantly affected by mungbean cultivars, various phosphorous levels, and tillage systems. Cultivar swat-1 stands first in term of growth and yield. Highest thousand seed weight, seed yield, biological yield, and harvest index % were produced by P at the rate of 60 kg ha−1, while maximum plant height, number of pods plant−1, number of seeds pod−1, and protein content were given by P at the rate of 40 kg ha−1 at par with P at the rate of 60 kg ha−1. Among different tillage systems, maximum number of pods plant−1, 1,000 seed weight, biological yield, seed yield, and protein content were observed in maximum tillage system. In case of interaction between P × T, maximum pods plant−1, 1,000 seed weight, biological yield, seed yield, and protein content were produced by 60 kg P ha−1 + maximum tillage system. Subjects: Agriculture & Environmental Sciences; Bioscience; Environment & Agriculture; Soil Sciences


PUBLIC INTEREST STATEMENT
Mungbean has high nutritive value, and due to this, has advantage over the other pulses known as king of the pulse crop. The seed contains 24.20% protein content, 1.30% fat, and 60.4% carbohydrates; calcium (Ca) is 118 and phosphorus (P) is 340 mg per 100 g of seed. Pulses are known as poor man's meat and cheap source of vegetable protein containing 20-25% protein.
Its production is very low in many regions due to miss management of the inputs. Therefore, if farmers implement more number of tillage practices as compared to conventional, so the crop nutrients demand will be fulfilled by the leached and adsorbed nutrients, away from root zone by pulverizing the soil with more number of tillage, whereas the productivity of the soil will also increase with soft soil, promote root density, and will result in more number of nodules having more nitrogen fixation.

Introduction
Mungbean (Vigna radiata L.) is an important conventional pulse crop of Pakistan and commonly known as green gram. It has high nutritive value, and due to this, has advantage over the other pulses. The seed contains 24.20% protein content, 1.30% fat, and 60.4% carbohydrates; calcium (Ca) is 118 and phosphorus (P) is 340 mg per 100 g of seed, respectively (Imran et al., 2015). It fixes atmospheric nitrogen through Rhizobium species. Rhizobium species in the presence of phosphorus not only fix more nitrogen through increased number of nodules but the protein contents, dry matter, and seed yield of various legume crops also increased to considerable extent. Pulses are known as poor man's meat and cheap source of vegetable protein containing 20-25% protein. The Mungbean (Vigna radiata) is esteemed among the entire pulse species because it is an easily digestible pulse. Production of mungbean has remained static during the last decade; as a result, the gap between supply and demand is widening (Imran et al., 2015). Its average yield in Pakistan is 461.5 kg ha −1 and total seed production is 91.2 thousand tones (Anonymous, 1998), which is much lower the harvested potential of our existing varieties. Area under cultivation of mungbean in Pakistan is 197.6 thousand hectares. Therefore, it is necessary to advance the weak chains of crop production lays emphasis on the judicious use of artificial/commercial fertilizer to ensure a rich crop harvest. Mungbean is naturally nodulation crop to some extent and the degree of nodulation varies with the area and culture being used. Being a legume crop, it necessitates less nitrogen but phosphorus application is an important input for higher yields per unit area. Energy storage and transfer are the most essential functions of P in plant growth. It is an important structural component of a wide variety of biochemicals, including nucleic acid, nucleotides, phosphor-proteins, phospholipids, and sugar phosphate (Havlin, Beaton, Tisdule, & Nelson, 2004). Various levels of applied P significantly affected the growth and yield components of mungbean (Khan, Asif, Hussain, & Aziz, 2003). Sharma and Singh (1993) reported that phosphorus applications increased green gram seed yield and protein content (Sharma & Singh, 1993). Tillage is the mechanical manipulation of the soil. Tillage operations are done to prepare seedbed for sowing, improve soil physical structure, and to control weed. Conventional tillage system is used to prepare seedbed. It requires more energy as fuel and consumes more time. But the concept of zero tillage and minimum tillage requires less fuel, preserves moisture, and saves time for timely cultivation. In zero tillage system, the soil is left undisturbed from harvest to seeding and seeding to harvest (Thiagalingam et al., 1996). Zero tillage and minimum tillage system may have beneficial impact on seed yield and minimize the environmental degradation such as soil erosion (Armstrong, Millar, Halpin, Reid, & Standley, 2003). Mungbean sown with zero tillage and adequate vegetative mulch on the soil surface gave high yield comparable with, or even higher than those obtained under conventional tillage (Thiagalingam et al., 1996). Keeping in view the above facts, therefore, present study was designed to evaluate the response of mungbean cultivars to different levels of phosphorus and different tillage systems for realizing the maximum yield potential under the agro-ecological conditions of swat valley.

Materials and methods
To study the response of mungbean cultivars to various phosphorous levels under different tillage system, field experiments were consecutively conducted at Agriculture Research Institute, (N) Mingora Swat, Pakistan, during summer 2012 and 2013 (two-years consecutive study). The experimental design used was randomized complete block (RCB) design with three replications. Two mungbean cultivars Swat-1 and NM-98, four levels of phosphorous (0, 20, 40, and 60 kg ha −1 ) in the form of triple super phosphate (TSP), and four tillage systems, zero tillage (no tillage), minimum tillage (2-time), conventional tillage (4-time), and maximum tillage (6-time) were used. A plot size of 5 × 3 m was used. Subplot was consisted of six rows having 50 cm row-to-row distance with row length of 5 m. Nitrogen in the form of urea was applied at the rate of 25 kg ha −1 as a starter dose during seedbed preparation. All the recommended agronomic practices like weeding, hoeing, irrigation, and other cultural practices were followed. Data were recorded on plant height, number of pods plant −1 , number of seed pod −1 , biological yield, seed yield, 1,000 seed weight, harvest index %, and protein content. Plant height was measured at the harvesting stage. Plant height from the ground level to the apex of the five randomly selected plants in each subplot was measured through measuring tape and averaged. After threshing, data on thousand seeds weight (g) were recorded from three seed lot and weighted with the help of electronic balance. Four central rows in each subplot were harvested, sun dried, and threshed. Seed weight was taken with the help of electronic balance and then converted into kg ha −1 using the following formula: Biological yield was calculated using the following formula: Harvest index was calculated using the following formula: Collected data were analyzed statistically through statistical package (statistix 8.1) according to the procedure relevant to three factorial RCB design. Least significant difference (LSD p ≤ 0.05) test was used for mean comparison to identify the significant components of the treatment means (Jan, Shah, Hollington, Khan, & Sohail, 2009).

Plant height (cm)
Perusal of the data indicated that cultivars, P levels, and tillage systems significantly affected the plant height. Interaction between P × T significantly affected the plant height, while other interactive effects between C × P, C × T, and C × P × T were found non-significant. Mean value showed that the maximum plant height was recorded in cultivar Swat-1 (54.6 cm) followed by NM-98 (52.6 cm) during the year 2012. In next year (2013), both cultivars were statistically at par having 53.3 and 53.4 cm plant height. In case of P levels, the maximum plant height was recorded in plot received P at the rate of 60 and 40 kg ha −1 (54.8 and 54.7 cm), while minimum plant height was noted in the control plot in the year 2012, while during next year (2013), the same results were noted again and the highest plant height was recorded in plots treated with 60 and 40 kg P ha −1 , but the results were statistically at par with 20 kg and 60 kg P ha −1 . This might be due to more uptake of P which enhances root penetration and density with the results of more BNF and used by the plant for self-sustainability and development. These findings are with conformity of those reported by Iqbal, Khan, and Shaheen (2012) and (Imran et al., 2015); they observed that the maximum plant height was recorded in the plot treated with 90 kg P ha −1 having at par with 60 kg ha −1 . Similarly, tillage system significantly affected the plant height, and the maximum plant height was noted in conventional tillage, which was statistically at par with maximum tillage system (54.6 and 54.7 cm), while minimum plant height was recorded in minimum tillage system having at par with the control plot (51.7 and 52.3 cm). In the next year experiment (2013), the maximum plant height was found in maximum tillage followed by conventional tillage but having statistically at par value (55.3 and 53.8 cm). Shortest plant height was observed in no tillage practice plots having at par with minimum tillage (52.3 and 51.6 cm), respectively. The reason could be better soil physical condition and well-pulverized soil for root penetration to uptake optimum nutrients. The findings of these results are connected with those of Yusuf, Siemens, and Bullock (1999) and (Imran et al., 2015) who described that plants grown with conventional tillage are taller than zero tillage. In case of interaction, conventional tillage with P at the rate of 60 kg ha −1 gave the highest plant height (59.8 cm), whereas the minimum plant height was recorded in minimum tillage system with no P application (50.3 cm). These results are with conformity of those of Iqbal et al. (2012); they stated that conventional tillage + 90 kg P gave the highest plant height.

Number of pods plant −1
Analysis of the data showed that cultivars, P levels, and tillage systems significantly affected number of pods plant −1 . Interaction between P × T significantly affected number of pods plant −1 , while × 100 other interactive effects of C × P, C × T, and C × P × T were found non-significant. Mean value of the data divulges that maximum pods plant −1 produced by cultivar Swat-1 (19.2) followed by NM-98 (17.8) during 2012, while in next year cultivar, swat 1 produced 19.4 pods plant −1 followed by NM-98 having 18.2 pods plant −1 . This might be due to genetic superiority. P levels significantly affected pods number in the year 2012 and maximum pods plant −1 produced by the plot treated with 60 kg ha −1 having at par with 40 kg P ha −1 treated plot (20.6 and 20.0), whereas minimum pods plant −1 were recorded in the control plot (16.0). In the year 2013, maximum pods plant −1 (20.8) were recorded in plots treated with P at the rate of 60 kg ha −1 followed by 40 kg ha −1 (19.3). Increase in pods number with P application was also reported by Iqbal et al. (2012) and Balachandran and Sasidhar (1991) who observed increase in pods number with P levels. In case of tillage system, maximum pods plant −1 were observed in maximum tillage (6- 2012); they described that conventional tillage gave maximum pods plant −1 . The interaction between P × T was found highly significant. Maximum numbers of pods were observed in maximum tillage with the application of 60 kg P ha −1 (28) followed by conventional tillage with the application of 60 kg P ha −1 (25.5), whereas minimum pods were recorded in zero tillage + no P (control) having 13.6 pods plant −1 . These results are agreed with those of Shafiq, Hassan, Ahmad, and Rashid (1994), Imran et al. (2015), and Iqbal et al. (2012); they stated that maximum number of pods plant −1 and other yield contributing parameters can be obtained with the application of optimum fertilization and better tillage practices.

Number of seeds pod −1
Analyzed data divulge that number of seeds pod −1 significantly affected by cultivars, P levels, and tillage system, whereas all the interaction was non-significant in this order. The data showed that highest seeds pod −1 were noted in cultivar swat-1 (11.1) followed by the other sown cultivar NM-98 (9.2) in the year 2012. In the next year, seeds pod −1 varied in both cultivars, and 12.16 seeds pod −1 were recorded in cultivars Swat-1 and 11.6 in NM-98 in the year 2013. The reason could be genetic superiority having high yielding characteristics. P levels significantly affected the number of seeds pod −1 , and the maximum seeds pod −1 were recorded in 60-kg P ha −1 -treated plots (10.9) having at par value with 40 kg P ha −1 having (10.8) number of seeds pod −1 during the first year, while maximum (11.2) seeds pod −1 were noted again in the next year in plots treated with 60 kg P ha −1 followed by 40 kg P ha −1 (10.9 seeds). Minimum seeds pod −1 (9.1) were counted in the control plot having at par value with 20 kg P ha −1 . These results are agreed with conformity of Dubey, Sinha, and Yadva (1993) and Iqbal et al. (2012); they described that number of seeds pod −1 was increased with increase in P levels. Similarly, in case of tillage system, during 2012, maximum number of seeds pod −1 was noted in maximum tillage (11.3 seeds) but statistically at par with conventional tillage system having (10.7) seeds pod −1 , while minimum seeds pod −1 was recorded in zero tillage (8.8 seeds). The same position was seen again during 2013, and maximum seeds (11.4) were retained by maximum tillage-practiced plot followed by at par (10.8) conventional tillage-practiced plot, whereas minimum seeds pod −1 (8.9) were counted in zero tillage-practiced plots, respectively. These findings are also reported by Zamir (2006) who concluded that number of seeds pod −1 was enhanced with conventional tillage system.

Biological yield (kg ha −1 )
Perusal of the data indicated that cultivars, P levels, tillage, and interaction between P × T significantly affected biological yield, while interaction of C × P, C × T, and C × P × T was non-significant. The result showed that cultivar Swat-1 produced maximum biological yield (3,441.5 kg ha −1 ) followed by the other sown cultivars NM-98 (3,235.7 kg ha −1 ) in the year 2012, whereas the same cultivars Swat-1 produced 3,510.7 and NM-98 3,285.9 kg biological yield in the year 2013. Among P levels, maximum biological yield in the year 2012 was observed with 60 kg P ha −1 (3,642.3 kg ha −1 ) followed by 40 kg P ha −1 (3,432.3 kg ha −1 ), whereas minimum biological yield was recorded in the control plot (3,097.4 kg ha −1 ) but statistically at par with 20-kg P ha −1 -treated plot having 3,182.3 kg ha −1 biological yield. In the year 2013, the same position was sustained and maximum (3,710.8 kg) biological yield was recorded in plots treated with 60 kg P ha −1 followed by 40 kg P ha −1 application. The results are closely associated with those of Shafiq et al. (1994) and Jamshidian and Khajehpour (1999); they reported substantial result of P on biological yield of mungbean. Correspondingly, tillage systems also significantly affected biological yield in the year 2012 and in 2013. Highest biological yield was noted in maximum tillage-practiced plot (3,680.3 kg ha −1 ) followed by conventional tillage (3,405.0 kg ha −1 ), whereas minimum biological yield was recorded in zero tillage system (3,086.5 kg ha −1 ) but statistically at par with minimum tillage having (3,182.5 kg ha −1 ) biological yield.
In the year 2013, a linear increase was noted in biological yield with fluctuation in tillage systems, and maximum biological yield (3,684.4 kg) was recorded in maximum tillage, followed by conventional tillage system (3,399.9 kg) and minimum tillage (3,183.4 kg), respectively. These results are against with those of Zamir (2006) and Iqbal et al. (2012); they described that conventional tillage and minimum tillage systems gave at par-valued biological yield. In case of interaction between P × T, maximum biological yield was observed in treatment of maximum tillage with 60 kg P ha −1 followed by conventional tillage with 60 kg P ha −1 (4,341.3 and 3,880.0 kg ha −1 ); however, lowest biological yield was noted in treatment zero tillage with no P application (3,041.7 kg ha −1 ). The findings of these results are related with conformity with those of Zamir (2006) and Iqbal et al. (2012); they stated that conventional tillage + P level at the rate of 90 kg ha −1 and minimum tillage systems + 90 kg P gave at par-valued biological yield.

Seed yield (kg ha −1 )
Seed yield showed that cultivars, P levels, tillage, and interaction between P × T significantly affected seed yield, while interaction of C × P, C × T and C × P × T was non-significant in term of seed yield. Mean value of the data showed that in the year 2012, maximum seed yield was recorded in cultivar Swat-1 (1,075.4 kg ha −1 ) followed by the other sown cultivar NM-98 (962.6 kg ha −1 ), while in the next year, seed yield enhanced in both cultivars. Cultivar Swat-1 produced 1,140.3 kg seed yield ha −1 and NM-98 produced 987.4 kg seed yield ha −1 . Among P levels, maximum seed yield was noted in the year 2012 and in 2013 with 60-kg P ha −1 -treated plot (1,182.8 kg and 1,227.9 kg ha −1 ) followed by 40-kg P ha −1 -treated plot (1,045.8 kg and 1,057.2 kg ha −1 ) but statistically at par with 20 kg P ha −1 (998.8 kg and 1,014.7 kg ha −1 ), while minimum seed yield was noted in the control plot (848.6 kg and 847.9 kg ha −1 ). The results are associated with conformity of Khan et al. (2003); they divulge that seed yield was enhanced with enhancement in the P levels. Results showed that tillage system significantly affected seed yield. Maximum seed yield was recorded in maximum tillage (1,221.8 kg ha −1 ) followed by conventional tillage (1,071.0 kg ha −1 ) although minimum seed yield was noted in zero tillage (839.5 kg ha −1 ) during the first year experiment. In the year 2013, a linear increase was recorded in seed yield with increase in tillage operations. Maximum seed yield (1,242.7 kg) produced by maximum tillage-practiced plot followed by conventional and minimum tillage practices (1,075 kg and 947.7 kg), while minimum seed yield was noted in no tillage practice plot (841.4 kg), respectively. This finding of the results supported by Imran et al. (2015) and Iqbal et al. (2012) who reported that tillage system had significant effect on seed yield of mungbean. Interaction between P × T divulges that highest seed yield was given by maximum tillage + 60 kg P ha −1 (1,493.0 kg ha −1 ) followed by conventional tillage + 60 kg P ha −1 (1,259.2 kg ha −1 ). Minimum seed yield was noted in zero tillage with no P application (741.7 kg ha −1 ). These results are closely associated with those of Shafiq et al. (1994), Imran et al. (2015), and Jamshidian et al.; they perceived that seed yield was enhanced with conventional tillage with the application of 90-kg P ha −1 -treated plot.

Thousand Seed weight (gm)
Perusal of thousand seed weight indicated that cultivars, P levels, tillage systems, and interaction between C × T and P × T significantly affected 1,000 seed weight. Mean data indicated that cultivar swat-1 attained maximum 1,000 seed weight than cultivar NM-98 (50.5 and 48.7 gm) in the year 2012, whereas in the year 2013, both cultivars produced statistically at par-valued thousand seed weight (50.4 and 49.8 gm) having no statistical differences, respectively. P levels result showed that maximum 1,000 seed weight was recorded in plot treated with 60 kg ha −1 (52.4 gm) followed by 40 kg P ha −1 but statistically at par with the control plot and 20 kg P ha −1 (47.7 and 49.1 gm). In the year 2013, maximum 1,000 seed weight (51.6 g) was recorded in plots treated with 60 kg P ha −1 , while lowest 1,000 seed weight (46.96 gm) was noted in the control plot, respectively. Increase in seed weight with P levels shows a direct positive contribution of P toward seed formation and development. These results confirmed by the finding of Khan et al. (2003); they determined that 1,000 seed weight increased with P levels. Similarly, tillage system divulges that in the year 2012, maximum 1,000 seed weight was observed in maximum tillage system (52.5 gm) followed by conventional tillage (49.1 gm), while minimum 1,000 seed weight was observed in minimum tillage system (47.2 gm), while in 2013, maximum 1,000 seed weight was recorded in maximum tillage practices (53.0 gm) followed by at par the other rest tillage practices having no statistical difference among them in respect of thousand seed yield (49.3, 48.2, and 49.5 gm). The results are in line with those of Iqbal et al. (2012). Interaction between C × T showed that cultivar swat-1 gave minimum 1,000 seed weight in zero tillage (51.5 gm) and cultivar NM-98 (47.5 gm), while maximum 1,000 seed weight in maximum tillage system gave by cultivar swat-1 (53.0 gm) and NM-98 (52.1 gm), respectively. In conventional tillage system, cultivar NM-98 gave maximum 1,000 seed weight than that of cultivar Swat-1 (50.0 and 48.3 gm). Interaction between P × T divulges that highest 1,000 seed weight was given by treatment maximum tillage + 60 kg P ha −1 followed by conventional tillage + 40 kg P ha −1 (56.8 and 51.5 gm). Thousand seed weight of conventional tillage system + 60 kg P ha −1 was statistically at par with that of maximum tillage + 40 kg P ha −1 (51.8 and 51.5 gm). Minimum 1,000 seed weight was observed in zero tillage + no P application (45.5 gm). These findings also reported by Iqbal et al. (2012); they testified that 1,000 seed weight was enhanced with tillage system and P levels.

Harvest index (%)
Analysis of the data showed that cultivars, P levels, and tillage systems significantly affected H.I %, whereas all the interaction was found non-significant. The data divulge that supreme H.I was recorded in cultivar swat-1 in the year 2012 and also in 2013 (30.9 and 31.4%) followed by the other sown cultivar NM-98 (29.4 and 29.2%). In case of P levels, maximum H.I was recorded in 60 kg P ha −1 -treated plot (32.1%) followed by 20 kg P ha −1 having at par value with 60 kg P ha −1 and 40 kg P ha −1 (31.

Protein content (%)
Data regarding protein content (%) showed that cultivars, P levels, tillage system, and interaction between P × T significantly affected protein content. Data of protein content divulge that concentrated protein content was recorded in cultivar swat-1 (22.8%) followed by cultivar NM-98 (22.4%) in the year 2012, while having at par valued in the year 2013 (23.4 and 23.1%), respectively (Tables 1  and 2). Among P levels, maximum protein content was recorded in both years with 60 and 40-kg P ha −1 -applied plots having statistically at par (