Response of Weed Management Practices on Yield Loss, Soil Enzyme Activity and Microbial Populations in Maize (Zea mays L.)

Maize (Zea mays L.) is the most versatile and emerging food crop of global importance. It is popularly known as “Queen of cereals” because of its high genetic yield potential and its unmatchable suitability to diverse environmental conditions among the cereals. Maize is the third most important food grain crop in India after rice and wheat. Weeds resulted in the highest crop loss (33%), followed by pathogens (26%), insects (20%), storage pests (7%), rodents (6%) and others (8%) in India (Yaduraju and Mishra, 2018). Heavy infestation of weeds and shortage of labour for weeding in time are the two foremost constraints to enhance the productivity of maize. Conventional methods of weed control are slow, laborious and sometimes uneconomical. Usage of pre-emergence herbicides assumes greater importance in view of their effectiveness from the beginning of crop growth. Early post emergence or sequential use of pre fb post emergence herbicides may help in tackling the problem of weeds at later stages of crop growth (Devi and Venkateswarlu, 2017). Application of herbicides will affect various soil microbial processes and enzymatic activities in the soil, whose activity is very important for maintaining the soil fertility. Biological properties are critically important to the ecosystem functioning since they are involved in soil organic matter decomposition, nutrient cycling and degradation of pesticides, such as herbicides. Soil microbial biomass represents the active part of soil organic matter and is involved in several functions in soil, presenting a rapid turnover of soil C, N and P, while enzymes are a suitable indicator of the catabolic activity of soil microorganism (Sanjay and Divya, 2016). Keeping the above facts in view, an investigation was carried out to study the effectiveness of pre emergence, early post emergence and sequential application (single or in combination) of herbicides for broad spectrum weed control, increased yields and to detect the quantity of microbial population and enzyme activity in soil at harvest of maize.

The present field experiment was conducted during Rabi, 2017-18 and 2018-19 at S.V. Agricultural College, Tirupati campus of Acharya N.G. Ranga Agricultural University Andhra Pradesh, which 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 in the Southern Agro-Climatic Zone of Andhra Pradesh. The experiment was laid out in a randomized block design with three replications and ten weed management practices viz., atrazine 1.0 kg ha^-1 as pre emergence (PE) fb one HW at 30 DAS (T₁), atrazine 1.0 kg. ha^-1 as PE fb tembotrione 120 g ha^-1 as post emergence (PoE) (T₂), 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 halosulfuron methyl 67.5 g ha^-1 as PoE (T₄), atrazine 1.0 kg ha^-1 as PE  fb 2,4-D amine salt 580 g ha^-1 as PoE (T₅), 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 topramezone 15 g+2,4-D amine salt 290 g ha^-1 as PoE (T₇), 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), hand weeding twice at 15 and 30 DAS (T₉) and weedy check (T₁₀). A total rainfall of 43.3 mm was received in 2 rainy days as against the decennial average rainfall of 246.3 mm in 9.2 rainy days during Rabi, 2017-18 and in Rabi, 2018-19 a total rainfall of 128.2 mm was received in 8 rainy days as against the decennial average rainfall of 254.7 mm received in 10.5 rainy days. The soil of the experimental site was sandy clay loam in texture, neutral in soil reaction and moderately fertile being 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). Maize hybrid ‘DHM-117’ was sown at a spacing of 60 cm x 20 cm with a gross plot size of 5.4 m x 4. 6 m. Recommended dose of 240 kg N, 80 kg P and 80 kg K ha^-1 was supplied through urea, single super phosphate and muriate of potash to all the plots uniformly. Pre emergence herbicide was applied within 24 hours after sowing and early post-emergence herbicides were applied at 2-3 leaf stage of weeds in maize. Weed population was counted with the help of 0.5 x 0.5 m quadrant thrown randomly at two places in each plot and converted to population or density m^-2. While recording weed population the biomass was harvested from each quadrant. Microbial mass in the soil was normally expressed in colony forming units per gram of soil (CFU g^-1 of soil). The viable count for bacteria, fungi and actinomycetes was done on Nutrient agar (NA), Potato dextrose agar (PDA) and Actinomycetes isolate agar (AIA) media, respectively (Jones and Mollison).

The viable count of soil microbes was enumerated by following formula:
   

 

 
The enzyme activity was estimated in the experimental soil collected at 0-15 cm depth from different treatments at harvest of maize as described by Klein et al., (1971) and soil phosphatase activity was assayed by the method of Tabatabai and Bremner (1969). Data recorded on maize during the course of investigation was statistically analyzed following the analysis of variance for randomized block design as suggested by Panse and Sukhatme (1985).

Weed index was computed by using the following formula.                               
 

 

 
Where:           
X = Yield from two hand weedings treatment (kg ha^-1).   
Y = Yield from the treatment for which WI has to be worked out (kg ha^-1).

Enzyme activity in soil at harvest of maize as influenced by weed management practices
 
Acid phosphatase activity
 
Weed control practices imposed in maize have exerted significant influence on acid phosphatase activity at harvest of maize, during both the years of study as indicated in Table 1. In the pooled mean atrazine 1.0 kg ha^-1 as PE fb tembotrione 120 g ha^-1 as PoE recorded higher acid phosphatase activity in the soil at harvest of corn, which was however, statistically comparable with atrazine 1.0 kg ha^-1 as pre emergence (PE) fb 2,4-D amine salt 580 g ha^-1 as post emergence (PoE), atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 34 g + 2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb tembotrione 60 g+2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 67.5 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb topramezone  30 g ha^-1 as PoE,  atrazine 1.0 kg ha^-1 as PE fb topramezone 15 g+2,4-D amine salt 290 g ha^-1 as PoE  in the order of descent. Atrazine 1.0 kg ha^-1 as PE fb one hand weeding (HW) at 30 DAS was at par with HW twice at 15 and 30 DAS and both were  in turn at par with weedy check.


 
Alkaline phosphatase activity
 
Alkaline phosphatase activity at harvest of corn was lower with weedy check which was in statistical parity with atrazine 1.0 kg ha-1 as PE fb one HW at 30 DAS and HW twice at 15 and 30 DAS in the pooled mean (Table 1).

Atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE recorded higher alkaline phosphatase activity, which was in parity with atrazine 1.0 kg ha^-1 as PE fb topramezone 15 g+2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb 2,4-D amine salt 580 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as  PE fb tembotrione 120 g  ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 34 g+2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 67.5 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb tembotrione 60 g + 2,4-D amine salt 290 g ha^-1 as PoE and the above treatments were at par among themselves in the sequence of descent.
 
Urease activity
 
In the pooled mean urease activity (Table 1) was higher with atrazine 1.0 kg ha^-1 as  PE fb tembotrione 120 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 34 g+2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 67.5 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb 2,4-D amine salt 580 g ha^-1 as PoE,  atrazine 1.0 kg ha^-1 as PE fb topramezone 15 g+2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb topramezone  30 g ha^-1 as PoE and atrazine 1.0 kg ha^-1 as PE fb tembotrione 60 g+2,4-D amine salt 290 g ha^-1 as PoE and in the order of descent, Whereas lowest urease activity was recorded with HW twice at 15 and 30 DAS, which was however comparable with atrazine 1.0 kg ha^-1 as PE fb one HW at 30 DAS and weedy check. 
 
Dehydrogenase activity
 
Dehydrogenase activity was higher with atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 67.5 g ha^-1 as PoE, which was however comparable with atrazine 1.0 kg ha^-1 as PE fb 2,4-D amine salt 580 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb topramezone 15 g+2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb tembotrione 60 g+2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE,  atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 34 g+2,4-D amine salt 290 g ha^-1 as PoE and atrazine 1.0 kg ha^-1 as  PE fb tembotrione 120 g  ha^-1 as PoE, in the order of descent without statistical disparity among them in the pooled mean. Whereas lowest dehydrogenase activity was recorded with HW twice at 15 and 30 DAS, which was however comparable with weedy check and atrazine 1.0 kg ha-1 as PE fb one HW at 30 DAS. 

Pre emergence followed by recommended dose of post emergence application or tank mix application of half of the recommended doses of post emergence herbicides resulted in significantly higher enzyme activity i.e. soil phosphatase, urease and dehydrogenase activity compared to hand weeding twice, pre emergence application of atrazine 1.0 kg ha^-1 and weedy check. Harmful effect of these herbicides might have been reduced by microbial degradation at later stages of crop growth particularly at the time of harvest (Aruna et al., 2018).
 
Total microbial population in the soil
 
Total microbial population in the soil at harvest of maize as influenced by different weed management practices were depicted in Table 2.

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Bacterial population
 
Initial bacterial population in soil before sowing of maize was 21.2 and 20.4 (x 106 CFU g^-1 of soil) and initial fungi population in the soil before sowing of maize was 7.5 and 7.4 (x 104 CFU g^-1 of soil) during both the years of experimentation.

Bacterial population at harvest of maize was higher with atrazine 1.0 kg ha-1 as  PE fb tembotrione 120 g  ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb 2,4-D amine salt 580 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 34 g+2,4-D amine salt 290 g ha^-1 as PoE,  atrazine 1.0 kg ha^-1 as PE fb tembotrione 60 g+2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb topramezone 15 g+2,4-D amine salt 290 g ha^-1 as PoE and atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 67.5 g ha^-1 as PoE without significant disparity among them in the order of descent in the pooled mean.
 
Fungal  population
 
Initial fungi population in the soil before sowing of maize was 7.5 and 7.4 (x 104 CFU g^-1 of soil) during first and second year of experimentation respectively. Fungi population was higher with atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 34 g+2,4-D amine salt 290 g ha^-1 as PoE,  atrazine 1.0 kg ha-1 as PE fb 2,4-D amine salt 580 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb topramezone 15 g+2, 4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as  PE fb tembotrione 120 g  ha^-1 as PoE,  atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 67.5 g ha^-1 as PoE and atrazine 1.0 kg ha^-1 as PE fb tembotrione 60 g+2,4-D amine salt 290 g ha^-1 as PoE in the order of descent without significant disparity among them. Lower fungal count was recorded with atrazine 1.0 kg ha^-1 as PE fb one HW at 30 DAS, which was in parity with HW twice at 15 and 30 DAS and weedy check during both the years of investigation and in the pooled mean.
 
Actinomycetal population
 
Initial actinomycetes population in soil before sowing of maize was 25.6 and 25.8 (x 105 CFU g^-1 of soil) during both the years of experimentation. Atrazine 1.0 kg ha^-1 as PE fb 2,4-D amine salt 580 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb tembotrione 60 g+2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb topramezone 15 g+2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 34 g + 2,4-D amine salt 290 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as PE fb halosulfuron methyl 67.5 g ha^-1 as PoE, atrazine 1.0 kg ha^-1 as  PE fb tembotrione 120 g ha^-1 as PoE and atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE were comparable among themselves in the pooled analysis values. Actinomycetes population at harvest of maize was lower with atrazine 1.0 kg ha^-1 as PE fb one HW at 30 DAS during, 2018 and with weedy check during, 2019 and both were in parity with HW twice at 15 and 30 DAS during the two years of study and in the pooled mean.

Total microbial population was higher with application of pre emergence herbicides followed by recommended dose of post emergence herbicides or tank mix application of half of the recommended doses of post emergence herbicides (Simerjeet et al., 2014). This might be due to the fact that applied herbicides themselves might serve as source of carbon to microbes and  It could be further inferred that the microbial population started to regain after the weeds were also killed by the herbicides and got mixed in the soil during this period and these might have served to increase the nutrients which inturn increased microbial multiplication on increased supply of nutrients. Similar results of increased total microbial population at harvest were observed by Veeresh et al., (2014).
 
Maize yield loss, kernel and stover yield
 
Among the different herbicides tried highest kernel and stover yield of maize (Table 3) was registered with atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE, which was at par with atrazine 1.0 kg ha^-1 as PE fb tembotrione 120 g ha^-1 as PoE and atrazine 1.0 kg ha^-1 as PE fb one HW at 30 DAS, without significant disparity among them. Lower yield loss in the above might be due to effective control of weeds at all the stages of crop growth by sequential use of pre and post emergence herbicides. Similar results of lower yield loss with atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE was reported by Rao et al., (2016). Highest kernel and stover yield might be due to reduced competition between the crop and weeds for the existing resources throughout the crop growing period enabling the crop for maximum utilisation of nutrients, moisture, light and space, which enhanced the vegetative and reproductive potential of the crop that reflected in the form of higher kernel yield of maize. The results corroborate with the findings of Parameswari et al., (2017).

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The lowest kernel yield of maize was resulted with weedy check. This was mainly due to greater competition for the growth resources among the crop and weeds as evident by the lowest crop stature, yield attributes and finally kernel yield of maize (Bahirgul and Ramesh, 2019).

In conclusion, the present study has revealed that application of recommended dose of herbicides did not effect the soil microbial population and enzyme activity at the time of harvest. and so it can be inferred that application of recommended dose of herbicides to control weeds may not harm the environment. Highest kernel and stover yield of maize was registered with atrazine 1.0 kg ha^-1 as PE fb topramezone 30 g ha^-1 as PoE, which was at par with atrazine 1.0 kg ha^-1 as PE fb tembotrione 120 g ha^-1 as PoE and atrazine 1.0 kg ha^-1 as PE fb one HW at 30 DAS.

All authors declare that they have no conflict of interest.