Residual Effect of Weed Management Practices Executed in Preceding Maize on Succeeding Greengram

Maize is the major cereal crop denoted as Queen of Cereals after rice and wheat contributing to food security and farm income in India. Maize followed by summer pulses is the predominant cropping system in many places in our country. In India, there is substantial scope of summer green gram after harvesting of winter crops due to its short duration, deep root system and it can be grown with residual moisture and limited irrigation. Weeds were probably the most ever present class of crop pests and cause massive crop failures over vast areas. Weeds, being hardier in nature compete with crop plants for nutrients, moisture, sunlight and space during entire vegetative and early reproductive stages of crop growth and their relative density plays a significant role in reducing the yield of crops (Dash et al., 2018). Hand weeding and mechanical operations were still widely adopted to keep the crop weed free during the critical period, but these are more expensive and at times not possible due to acute shortage of labour. Therefore, the use of pre and post emergence herbicides is an ideal means to tackle the problem of weeds. Application of herbicides at recommended rates may collapse within a few days or weeks and inflict no limitations on cropping options in the next season or year. However some herbicides do not degrade quickly even at suggested doses of application and can remain in the soil for weeks, months or years after treatment and may inhibit the growth of succeeding crops (Singh et al., 2012). Field studies on persistence and effect of new generation herbicide molecules on succeeding crop are lacking. Keeping the above facts in view, an investigation was carried out to study the effectiveness of herbicides for broad spectrum weed control in maize and their residual effect on succeeding greengram.

Field experiment was conducted during the two consecutive rabi and summer seasons of 2017-18 and 2018-19 at Wetland Farm of Sri Venkateswara Agricultural College, Tirupati Campus of Acharya N.G. Ranga Agricultural University, Andhra Pradesh to study the performance of new generation herbicides and their combinations in maize and the residual effect of herbicides on succeeding greengram. The farm is geographically situated at 13.6°N latitude and 79.3°E longitude, at an altitude of 182.9 m above the mean sea level. The soil of the experimental site was sandy clay loam in texture, neutral in soil reaction, low in organic carbon (0.25%) and available nitrogen (174 kg ha^-1), medium in available phosphorus (20.5 kg ha^-1) and potassium (186 kg ha^-1). The experiment consisted of ten treatments viz., atrazine @ 1.0 kg a.i. ha^-1 as pre emergence fb one HW at 30 DAS (T₁), atrazine @ 1.0 kg a.i. ha^-1 as pre emergence fb tembotrione @ 120 g a.i. ha^-1 as post emergence (T₂), atrazine @ 1.0 kg a.i ha^-1 as pre emergence fb topramezone @ 30 g a.i. ha^-1 as post emergence (T₃), atrazine @ 1.0 kg a.i. ha^-1 as pre emergence fb halosulfuron methyl @ 67.5 g a.i. ha^-1 as post emergence (T₄), atrazine @ 1.0 kg a.i. ha^-1 as pre emergence fb 2,4-D amine salt @ 580 g a.i. ha^-1 as post emergence (T₅), atrazine @ 1.0 kg a.i. ha^-1 as pre emergence fb tembotrione @ 60 g + 2,4-D amine salt @ 290 g a.i. ha^-1 as post emergence (T₆), atrazine @ 1.0 kg a.i. ha^-1 as pre emergence fb topramezone @ 15 g + 2,4-D amine salt @ 290 g a.i. ha^-1 as post emergence (T₇), atrazine @ 1.0 kg a.i. ha^-1 as pre emergence fb halosulfuron methyl @ 34 g + 2,4-D amine salt @ 290 g a.i. ha^-1 as post emergence (T₈), hand weeding twice at 15 and 30 DAS (T₉) and weedy check (T₁₀), laid out in a randomized block design with three replications. The pre emergence herbicide was applied on the next day after sowing and early post emergence herbicides were applied at 21 DAS, when the weeds are at 2-3 leaf stage in maize. Greengram seeds of variety IPM-02-14 was sown in undisturbed layout of the experimental plots as a residual crop after ploughing the field with rotovator, at a spacing of 30 cm × 10 cm to observe the residual effect of pre and post emergence herbicides applied to rabi maize on 24th and 08th March and harvested on 25^th and 23^rd May during summer, 2018 and 2019 respectively. The gross plot size is 5.4 × 4. 6 m.  A uniform basal dose of 20 kg N and 50 kg of P₂O₅ ha^-1 was applied through urea and single super phosphate to all the plots. Weeding was not performed in greengram plots since the crop was raised to study the residual effect of herbicides applied to maize crop. All other recommended management practices were followed to raise the crop.
       
A total rainfall of 105.6 mm was received in 6 rainy days as against the decennial average rainfall of 101.0 mm received in 5 rainy days during the greengram growth period during summer 2018, whereas during summer 2019, a total rainfall of only 24.0 mm was received in 4 rainy days as against the decennial average rainfall of 86.4 mm received in 6 rainy days.
       
Weed sampling was done at random by placing a quadrant of 1 m × 1 m in each plot and the number of weeds species were counted and expressed as no. m^-2 and dry weight of total weeds was recorded after drying to a constant weight at 65°C and expressed as g m^-2. In view of larger variation in the recorded values of density and dry weight of weeds, the corresponding data were subjected to square root transformation √x + 0.5 and the corresponding transformed values were used for statistical analysis as suggested by Gomez and Gomez (1984). Observations on growth and yield attributes of green gram was recorded at the time of harvest and the data was statistically analyzed following the analysis of variance for randomized block design as suggested by Panse and Sukhatme (1985). Soil samples were collected at harvest and separately homogenized and used for estimation of bacteria, fungi and actinomycetes by serial dilution plate count technique (Parmer and Schmidt, 1965).

Weed density and weed bio mass at harvest of greengram
 
Grasses (G)
 
Lowest density and dry weight of grasses was recorded with two hand weedings at 15 and 30 DAS (T₉), which was however, at par with atrazine 1.0 kg ha^-1 as PE fb one HW at 30 DAS (T₁), atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE (T₃) and atrazine 1.0 kg ha^-1 as PE fb tembotrione 120 g ha^-1 as PoE (T₂), whereas significantly highest density and biomass of grasses was registered with weedy check (T₁₀), during both the years of experimentation (Table 1 and 2).
 

 

 
Sedges (S)
 
Atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 67.5 g ha^-1 as PoE (T₄) registered lower sedge count and biomass, which was at par with atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 34 g + 2,4-D amine salt 290 g ha^-1 as PoE (T₈) and both of them were statistically lower compared to atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE (T₃), atrazine 1.0 kg ha^-1 as PE fb tembotrione 120 g ha^-1 as PoE (T₂), two hand weedings at 15 and 30 DAS (T₉) and atrazine 1.0 kg ha^-1 as PE fb one HW at 30 DAS (T₁), which in turn were comparable among themselves during both the years of study. The results indicated that recommended dose or half of the recommended dose of halosulfuron methyl was effective in controlling the sedges in maize followed by greengram sequence.
 
Broadleaved weeds (BLW)
 
Similar trend in broadleaved weed count and biomass was observed during the two years of study. Weedy check (T₁₀) recorded significantly highest broadleaved weed count and biomass, where as it was lowest with atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE (T₃), which was however, comparable with atrazine 1.0 kg ha^-1 as PE fb tembotrione 120 g ha^-1 as PoE (T₂), hand weeding twice at 15 and 30 DAS (T₉) and atrazine 1.0 kg ha^-1 as PE fb one HW at 30 DAS (T₁).
 
Total weed density
 
The total weed population and biomass in greengram due to residual effect of weed management practices imposed in preceding maize, was lowest with atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g  ha^-1 as PoE (T₃) (Table 1 and 2) during the first year of investigation and with hand weeding twice at 15 and 30 DAS (T₉) during second year of investigation and both in turn were comparable with atrazine 1.0 kg ha^-1 as PE fb one HW at 30 DAS (T₁) and atrazine 1.0 kg ha^-1 as PE fb tembotrione 120 g ha^-1 as PoE (T₂). Lower density and dry weight of total weeds might be due to higher weed control efficiency with these treatments in the preceding maize, that may lead to poor weed seed dispersal which in turn ensued lower weed count in succeeding greengram. The results were in conformity with the findings of Nazreen et al., (2018) and Verma et al., (2009).The density and dry weight of total weeds was significantly highest with weedy check (T₁₀), during both the years of study (Table 1 and 2). This might be due to higher density and dry weight of weeds in weedy check in maize that in turn favoured higher weed count and bio mass in succeeding greengram.
 
Germination percentage
 
Germination percentage of succeeding greengram crop was not significantly varied due to different weed management practices imposed in maize during both the years of study (Table 3). The results corroborate with the findings of Chand et al., (2014).
 

 
Growth, yield attributes and yield of succeeding greengram
 
Taller plants with higher stature and dry matter production of greengram were noticed with T₉ (hand weeding twice at 15 and 30 DAS), which was closely followed by atrazine 1.0 kg ha-1 as PE fb one HW at 30 DAS (T₁), atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE (T₃), atrazine 1.0 kg ha^-1 as PE fb tembotrione 120 g ha^-1 as PoE (T₂) and atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 67.5 g ha^-1 as PoE (T4),  in the order of descent, without any significant disparity among the treatments (Table 3). Higher plant height and dry matter production in succeeding greengram might be due to effective control of weeds in the above treatments imposed in maize that in turn might lead to lowest weed frequency and biomass of weeds in the succeeding greengram which may favoured greengram to utilize nutrients, moisture and light effectively to produce higher vegetative potential.
       
Higher number of pods plant^-1, number of seeds pod^-1, test weight,seed and haulm yield of succeeding greengram was reported with hand weeding twice at 15 and 30 DAS (T₉), which was however, at par with atrazine 1.0 kg ha^-1 as PE fb one HW at 30 DAS (T₁), atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE (T₃), atrazine 1.0 kg ha^-1 as PE fb tembotrione 120 g ha^-1 as PoE (T₂) and atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 67.5 g ha^-1 as PoE (T₄), in the order of descent, without any significant disparity among them due to weed management practices imposed in preceding maize. This might be attributed to minimum crop weed competition in greengram, which enhanced more synthesis and translocation of assimilates to developing pods and seeds in greengram (Table 3 and 4).
 

       
Weedy check (T₁₀), recorded the lowest growth parameters, yield attributes and yield of greengram compared to all other treatments. It might be ascribed due to higher density of weeds in the preceding maize, due to which more number of weeds were germinated per unit area in the succeeding greengram and offered severe competition for growth resources that might have lead to poor performance of greengram as noticed in the form of poor stature of the crop with lowest dry matter production, that in turn decreased number of pods plant^-1, number of seeds pod^-1, test weight and yield of greengram.
 
Enzyme activity and microbial population in soil of succeeding greengram
 
Enzyme activity viz., acid phosphatase, alkaline phosphatase, urease and dehydrogenase activity and microbial count i.e., total bacteria, fungi and actinomycetes population in the soil was recorded at the time of harvest of greeengram. Enzyme activity and microbial count was not statistically distinct at harvest of greengram, which indicated that weed control practices imposed in maize did not alter the enzyme activity and microbial count in the subsequent greengram, during both the instances of study as indicated in Table 5.
 

 
Economics of greengram
 
Gross returns (GR), net returns (NR) and benefit cost ratio (BCR) of greengram followed similar trend during both the years of study. Higher gross returns, net returns and benefit cost ratio of succeeding greengram was noticed with hand weeding twice at 15 and 30 DAS (T₉) and it was at par with atrazine 1.0 kg ha^-1 as PE fb one HW at 30 DAS (T₁), atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE (T₃), atrazine 1.0 kg ha^-1 as PE fb tembotrione 120 g ha^-1 as PoE (T₂) and  atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 67.5 g ha^-1 as PoE (T₄) (Table 4).This may be attributed to higher seed yield due to reduced crop weed competition.
       
The next best treatments with higher gross returns, net returns and benefit cost ratio were atrazine 1.0 kg ha^-1 as PE fb topramezone 15 g + 2,4-D amine salt 290 g ha^-1 as PoE (T₇), atrazine 1.0 kg ha^-1 as PE fb tembotrione 60 g + 2,4-D amine salt 290 g ha^-1 as PoE (T₆), atrazine 1.0 kg ha^-1 as PE fb 2,4-D amine salt 580 g ha^-1 as PoE (T₅) and atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 34 g + 2,4-D amine salt 290 g ha^-1 as PoE (T₈), in the order of descent without significant disparity among them. Lowest gross returns, net returns and benefit cost ratio of greengram was noticed with weedy check (T₁₀), during the two years of study and it might be attributed to low yields due to severe crop weed competition.

From the present study it can be concluded that higher seed yield, haulm yield, gross returns, net returns and benefit cost ratio of succeeding greengram were noticed with hand weeding twice at 15 and 30 DAS. The above treatment which was however, comparable with atrazine 1.0 kg ha^-1 as pre emergence fb one HW at 30 DAS topramezone 30 g ha^-1 or tembotrione 120 g ha^-1 or halosulfuron methyl 67.5 g ha^-1 as post emergence application in preceding maize.