Productivity of Groundnut + Pigeonpea Relay Intercropping System as Influenced by Weed Management Options

The most feasible approach to enhance crop yield is sowing and growing crops from beginning of monsoon season to post-monsoon season by adopting concept of relay intercropping system (AICRP, 2002-07). Groundnut contributes about 40 per cent to the total oilseeds production in the country (Sathyapriya et al., 2013). It is a leguminous crop, which fixes atmospheric nitrogen and covers the soil. While on the other hand, pigeonpea is a fast-growing crop with its extensive root system. Its deep tap root system allows optimum utilization of soil moisture and soil nutrients and can be an ideal crop in groundnut relay intercropping system and both the crops complement each other. Pigeonpea is used as a most preferred pulse crop by Indian rural and urban communities. Groundnut + pigeonpea is dominant cropping system, which helps to maintain the sustainability and profitability which form the major goals in the present world. Pigeonpea was sown a month after the groundnut crop was sown to reduce the competition between the crops and this may help increase of the yield. This practise is advocated and encouraged by the Pulses Research Station, JAU, Junagadh because of the erratic and scanty rainfall recived in the Saurashtra region making groundnut cultivation risky.

Weed management is an important agronomic aspect in crop production, as weed cause the highest percentage of damage to the crop and especially in dry regions where they compete with the crops for water, nutrients, CO₂ and light, ultimately reducing the crop yields to tune of 31%- 59% (Singh et al., 2020). The traditional practices of weed management i.e., manual weeding is difficult to adopt in the present scenario with the growing labour scarcity and increasing labour wages. Mechanical weeding is difficult in intercropping as the intercrops may be damaged. Hence to reduce the risk and cost, chemical practices can be adopted along with the traditional practice of manual hand weeding. Thus, the crop may be put to advantage supressing the growth of weeds. This not only increases the yield but also reduces the cost of cultivation by decreasing the cost on additional labour utilised for manual weeding. The energy required for the crop production can also be reduced with the appropriate use of weed management practices. Finally, the productivity per unit land can be increased which increases the national income and accelerates the development of the nation. Thus, the proposal of doubling the farmers’ income can be made true in a sustainable manner through crop intensification and diversification approach. Groundnut + pigeonpea relay intercropping system is the dominant intercropping system in Saurashtra region of Gujarat. But not much work has been done in the weed management aspect of groundnut + pigeonpea cropping system and especially in the relay intercropping of these crops. 

A field experiment was conducted at Instructional Farm, Department of Agronomy, College of Agriculture, Junagadh Agricultural University, Junagadh (Gujarat) during kharif seasons of year 2019-20 and 2020-21. The soil of the experimental plot was clayey in texture, medium in organic carbon (0.62%), slightly alkaline in reaction with pH (8.32) and EC (0.286 dS m^-1). The soil was low in available nitrogen (270.20 kg ha^-1), medium in available phosphorus (28.2 kg ha^-1) and medium in available potash (251.7 kg ha^-1).

Additive series of intercropping in 2:1 ratio was adopted, wherein the main/base crop is groundnut and intercrop is pigeonpea. “GG 20” was groundnut variety used for this study as base crop, pigeonpea variety “GJP-1” as intercrop. The experiment was laid out in RBD with ten treatments, which were replicated thrice. The treatments comprised pendimethalin 0.9 kg ha-1 as PE fb IC+HW at 45 DAS (T₁), pendimethalin 0.45 kg ha^-1 + oxyfluorfen 0.09 kg ha^-1 as PE fb IC+HW at 45 DAS (T₂), IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as POE (T₃), IC+HW at 15 DAS fb quizalofop-p-ethyl 40 g ha^-1 at 45 DAS as POE (T₄), IC+HW at 15 DAS fb propaquizafop 70 g ha^-1 at 45 DAS as POE (T₅), pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as POE (T₆), pendimethalin 0.9 kg ha^-1 as PE fb quizalofop-p-ethyl 40 g ha^-1 at 45 DAS as POE (T7), pendimethalin 0.9 kg ha^-1 as PE fb propaquizafop 70 g ha^-1 at 45 DAS as POE (T₈), weed free (T₉) and unweeded control (T₁₀). The practices were adopted in accordance to the proposed treatments. Interculture in combination with hand weeding was carried in treatments 3, 4 and 5 at 15 DAS while in treatment 1 and 2 it was conducted at 45 DAS of groundnut. Pre emergence herbicide viz., pendimethalin 30% EC and oxyfluorfen 23.5% EC was applied on the next day of sowing of groundnut and post emergence herbicides, quizalofop-p-ethyl, propaquizafop and sodium-acifluorfen + clodinafop-propargyl were applied at 45 DAS after intercultivation. The weed free was maintained clean with regular intercultivation and manual weeding. The unweeded control was left unweeding allowing the continuous growth of weeds. The spacing adopted was 60 cm × 10 cm for groundnut and 120 cm × 20 cm for pigeonpea to accomadate the row ratio of 2:1 and groundnut variety is semi spreading. The growth and yield attributes were recorded at harvest.

Groundnut

Plant height

The weed free treatment (T9) was found to be significantly superior in plant height (53.33, 54.57 and 53.95 cm in 2019-20, 2020-21 and pooled results, respectively) at harvest, which was statistically on par with treatments comprising IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₃) and pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₆) in the year 2019-20, 2020-21 and pooled results. On the contrary, the unweeded control (T₁₀) recorded significantly the lowest plant height (36.63 cm, 39.70 cm and 38.17 cm in 2019-20, 2020-21 and pooled results, respectively) (Table 1).



Dry matter per plant
 
The weed free treatment (T9) was noticed to be statistically superior in dry matter per plant at harvest (31.5, 30.1 and 30.8 g in 2019-20, 2020-21 and pooled results, respectively), which was on par with IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₃) and pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₆) in 2019-20 and pooled results. In the second year, the weed free treatment (T₉) was found to be at par with treatments T₃ (IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE), T₆ (Pendimethalin 0.9 kg ha-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha-1 at 45 DAS as PoE), T₁ (Pendimethalin 0.9 kg ha^-1 PE fb IC+HW at 45 DAS) and T₂ (Pendimethalin 0.45 kg ha^-1 + oxyfluorfen 0.09 kg ha-1 PE fb IC+HW at 45 DAS). The unweeded control (T₁₀) recorded significantly the lowest dry matter per plant (17.2, 15.5 and 16.3 g) in 2019-20, 2020-21 and pooled results (Table 1).
 
Pigeonpea
 
Plant height
 
At harvest, significantly taller plants (202.4, 191.4 and 196.9 cm in 2019-20, 2020-21 and pooled results, respectively) were recorded with the weed free treatment (T₉) in both  2019-20, 2020-21 and pooled results and was statistically on par with IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha-1 at 45 DAS as PoE (T₃), pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₆) during the year 2019-20. Treatment T₉ (Weed free) was noticed to be statistically at par with T₃ and T₆ during 2020-21 and pooled results (Table 1). The unweeded control (T₁₀) recorded significantly the lowest plant height (128.5, 107.2 and 117.8 cm in 2019-20, 2020-21 and pooled results, respectively) in both years as well as pooled results.
 
Dry matter per plant
 
At harvest, the weed free treatment (T₉) recorded significantly greater crop dry matter per plant (64.5, 60.9 and 62.7 g  in 2019-20, 2020-21 and pooled results, respectively) and was at par with IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha-1 at 45 DAS as PoE (T₃) and pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₆) during 2019-20, 2020-21 and pooled results. In 2019-20 and 2020-21, treatments T₃ (IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE) and T₆ (Pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE) were found to be at par with pendimethalin 0.9 kg ha^-1 as PE fb IC+HW at 45 DAS (T1) and pendimethalin 0.45 kg ha-1 + oxyfluorfen 0.09 kg ha^-1 as PE fb IC+HW at 45 DAS (T₂). Significantly lower crop dry matter per plant (35.5, 32.4 and 34.0 g in 2019-20, 2020-21 and pooled results, respectively) was recorded with the unweeded control (T₁₀) during both years and pooled data (Table 1).

Groundnut

Number of mature and immature pods per plant

The data on number of mature and immature pods per plant in groundnut are furnished in Table 2.


 
Number of mature pods
 
Significantly more number of mature pods per plant (11.86, 10.98 and 11.42 in 2019-20, 2020-21 and pooled results, respectively) was recorded with the weed free treatment (T₉) and it was at par with IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₃) and pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₆) during both the years along with pooled results. However, treatments T3 and T6 were statistically on par with pendimethalin 0.9 kg ha^-1 PE fb IC+HW at 45 DAS (T₁) and pendimethalin 0.45 kg ha^-1 + oxyfluorfen 0.09 kg ha^-1 as PE fb IC+HW at 45 DAS (T₂) during 2019-20 and 2020-21. Significantly lesser number of mature pods (6.29, 5.78 and 6.04 in 2019-20, 2020-21 and pooled results, respectively) was observed with the unweeded control (T₁₀) due to the heavy weed competition.
 
Pod yield
 
Significantly higher pod yield (1956, 1735 and 1846 kg ha^-1 in 2019-20, 2020-21 and pooled results, respectively) was acquired by the weed free treatment (T₉), which was statistically on par with treatments viz., IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₃) and pendimethalin 0.9 kg ha^-1 PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₆) in the year 2019-20, while in the second year and pooled data, the weed free treatment (T₉) was found to statistically at par with only T₃. However, T₃ was on par with T₆, T₁, T₂ during both the years as well as the pooled data. Conversely, the unweeded control (T₁₀) recorded significantly the lowest pod yield (585, 436 and 510 kg ha^-1 in 2019-20, 2020-21 and pooled results, respectively).
 
Haulm yield
 
In the both the years (2019-20 and 2020-21) and pooled data, the weed free treatment (T₉) registered significantly higher groundnut haulm yield (3593, 2950 and 3271 kg ha^-1 in 2019-20, 2020-21 and pooled results, respectively). The weed free treatment (T₉) was at par with IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₃), pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₆) during 2019-20, 2020-21 and pooled results and in turn the treatment T3  was at par with T₂ (Pendimethalin 0.45 kg ha^-1 + oxyfluorfen 0.09 kg ha^-1 as PE fb IC+HW at 45 DAS) and T₁ (Pendimethalin 0.9 kg ha^-1 as PE fb IC+HW at 45 DAS). The unweeded control (T₁₀) recorded significantly the lowest haulm yield (1150, 823 and 987 kg ha^-1 in 2019-20, 2020-21 and pooled results, respectively).

The effect of rainfall faded at the end of cropping season and clear-cut difference among the treatments was noticed in yield attributes and yield. The superior values in number of mature pods per plant, pod yield, haulm yield and lower values of number of immature pods per plant were registered with the weed free treatment, which was statistically at par with treatments T₃ and T₆. The zero competition from weeds under the weed free conditions might have resulted in the luxurious growth of the groundnut crop. The higher values of yield and yield attributes under herbicidal treatments could be attributed to increase in growth characters like plant height and dry matter per plant due to proper integration of weed management practices, which resulted in lower dry weight of weeds which is negatively correlated to the yield ultimately reducing the weed competition favouring the crop growth and productivity. The better plant growth and improved yield attributes finally led to higher dry pod, kernel and haulm yields. The effective weed control in critical crop growth period of 2-8 weeks (Tewari et al., 1989) was observed especially in these treatments leading to enhanced photosynthetic activity and partitioning of assimilates, resulting in improved yield attributes and yield. The sowing of pigeonpea crop for every two lines of groundnut helped to remove the prevailing weeds in those lines and slow growth of the pigeonpea facilitated the good growth of the groundnut.

The lowest values of the yield attributes (number of mature pods per plant), pod yield, haulm yield were registered with the unweeded control (T₁₀). This might be due to the shorter plant height, lower number of branches and lower dry matter per plant owing the competition faced by the crop for moisture, light, nutrients and CO₂ due to the uncontrolled weeds. The results of the present investigation strongly support the findings of Reddy and Reddy (2004); Kushwah and Vyas (2005); Dutta et al., (2005); Madhavi et al., (2008); Kalhapure et al., (2013); Yadav et al., (2014); Dixit et al., (2016); Haque et al., (2016) and Vora et al., (2019).

Pigeonpea

Number of pods per plant

Significantly higher number of pods per plant (223.2, 201.5 and 212.3 in 2019-20, 2020-21 and pooled results, respectively) in pigeonpea was recorded with the weed free treatment (T₉) and it was statistically equivalent to IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₃) and pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T6) in both the years along with pooled results. During 2019-20, the weed free treatment (T9) was also statistically at par with pendimethalin 0.9 kg ha-1 PE fb IC+HW at 45 DAS (T₁). Treatments T₃ and T₆  were statistically at par with pendimethalin 0.9 kg ha^-1 PE fb IC + HW at 45 DAS (T₁) and pendimethalin 0.45 kg ha^-1 + oxyfluorfen 0.09 kg ha^-1 as PE fb IC+HW at 45 DAS (T₂) during 2019-20, 2020-21 and pooled results. Significantly lower number of pods per plant was recorded with the unweeded control (111.2, 81.5 and 96.3 in 2019-20, 2020-21 and pooled results, respectively) during 2019-20, 2020-21 along with pooled results.

Seed yield

The weed free treatment (T₉) registered significantly higher seed yield (2023, 1861 and 1942 kg ha^-1 in 2019-20, 2020-21 and pooled results, respectively), which was observed to be statistically on par with IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₃), pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₆) and pendimethalin 0.9 kg ha^-1 as PE fb IC+HW at 45 DAS (T₁) during the first year, while in the second year and pooled data, it was statistically at par with T₃ and T₆. However, T₁ was statistically on par with second best treatment, T₃ during 2020-21 and pooled results. On the other hand, the unweeded control (T₁₀) recorded significantly lowest seed yield (522, 423 and 472 kg ha^-1 in 2019-20, 2020-21 and pooled results, respectively).

Stalk yield

The weed free treatment (T₉) registered significantly higher stalk yield (3549, 3080 and 3314 kg ha^-1 in 2019-20, 2020-21 and pooled results, respectively) and was at par with IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₃), pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₆) during 2019-20, 2020-21 and pooled data. Pendimethalin 0.9 kg ha^-1 as PE fb IC+HW at 45 DAS (T₁) and pendimethalin 0.45 kg ha^-1 + oxyfluorfen 0.09 kg ha^-1 as PE fb IC+HW at 45 DAS (T₂) were found to be statistically at par with T₃ and T₆ during 2019-20 and 2020-21. The unweeded control (T₁₀) recorded significantly the lowest stalk yield (1201, 1027 and 1114 kg ha^-1 in 2019-20, 2020-21 and pooled results, respectively).

The crop under weed free conditions attained optimum growth possibly due to elimination of weeds from inter and intra rows besides better aeration due to manipulation of surface soil and thus, more space, moisture, light and nutrients were available for the better growth and development, which resulted into superior yield attributes and consequently the highest seed and stalk yields. Among the herbicidal treatments, application of pendimethalin as pre-emergence curbed the establishment of initial flush of weeds and initial interculturealong with hand weeding at 15 DAS removed all the established weed flora and maintained a clean environment around the crop. Application of the ready-mix herbicides at 45 DAS helped to control the mixed weed flora providing a competitive advantage to the crop. The sowing of pigeonpea crop in between the rows of groundnut also helped in removal of the weeds and the groundnut crop acted as a mulch for pigeonpea crop in the later stages curbing the weed growth. 

Significantly the lowest values of the yield attributes pod yield, haulm were recorded with the unweeded control (T₁₀). The severe competition due to unrestricted growth of weeds in this treatment might have inhibited the growth of the crop leading to the inhibited yield attributes, seed and stalk yields. Similar findings were obtained by Srivastava et al., (2004); Singh (2007); Shete et al., (2009); Murali et al., (2013); Goud and Patil (2014); Malik and Yadav (2014); Harithavardhini et al., (2016); Kathirvelan (2017) and Sai and Tigga (2018).

Groundnut pod equivalent yield

The data on groundnut pod equivalent yield are presented in Table 3. The weed free treatment (T₉) was significantly superior in groundnut equivalent pod yield 4261, 3856 and 4058 kg ha^-1 in 2019-20, 2020-21 and pooled results, respectively) during both the years as well as pooled results. It was found to be statistically at par with IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₃) and further, this treatment (T₃) was statistically equivalent to pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₆) in 2019-20, 2020-21. In pooled data, the weed free treatment (T₉) was significantly superior over all other treatments and T₃ and T₆ were at par with each other which were found to be the next best treatments. The unweeded control (T₁₀) due to heavy weed competition recorded significantly the lowest groundnut pod equivalent yield (1179, 918 and 1049 kg ha^-1 during 2019-20, 2020-21 and pooled results, respectively).



Groundnut haulm equivalent yield

Significantly higher groundnut haulm equivalent yield (3593, 2950 and 3271 kg ha^-1 in 2019-20, 2020-21 and pooled results, respectively) was recorded with the weed free treatment (T₉) during both the years as well as pooled results. IC+HW at 15 DAS fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₃) and pendimethalin 0.9 kg ha^-1 as PE fb sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS as PoE (T₆) were statistically equivalent with each other and also with T₉ (Weed free) during 2019-20, 2020-21 and pooled data. Pendimethalin 0.9 kg ha^-1 as PE fb IC+HW at 45 DAS (T₁) and pendimethalin 0.45 kg ha^-1 + oxyfluorfen 0.09 kg ha^-1 as PE fb IC+HW at 45 DAS (T2) were recorded to be statistically at par with T₆, T₃ in the three cases. The unweeded control (T₁₀) due to heavy weed competition recorded significantly the lowest groundnut haulm equivalent yield (1300, 952 and 1126 kg ha^-1 in 2019-20, 2020-21 and pooled results, respectively).

Under weed free conditions, both the crops might have had a luxuriant growth supplementing each other by their nitrogen fixing capacity and hence, ultimately resulting in superior yield of both crops and also groundnut equivalent yield. In weed management treatments, it might be due to timely and effective control of weeds right from germination of crops by intercultivation coupled with post-emergence herbicides which provided weed free environment to the groundnut and pigeonpea resulted in higher yields than other treatments (Bhagyashree et al., 2018). The sowing of the pigeonpea in between the lines of groundnut after a month had mulching effect along with removing the weeds in those lines. The results of this study confirmed the earlier findings of Tomar et al., (2004); Singh et al., (2005); Pardeshi et al. (2008); Kumawat (2013) and Khazi et al., (2018).

On the basis of the results obtained from the two-year field investigation, it could be concluded that higher yield along with effective weed management in kharif groundnut + pigeonpea relay intercropping under South Saurashtra Agro-climatic Zone can be achieved by IC+HW at 15 DAS followed by sodium-acifluorfen 16.5% + clodinafop-propargyl 8% (Premix) 1 kg ha^-1 at 45 DAS without any phytotoxic effect on both the crops.