Keywords: Residue burning, microbial consortia, yield parameters, yield

INTRODUCTION

Agriculture plays a crucial role in the Indian economy where 143 million hectares (M ha) of land is put under intensive agriculture producing approximately 285 million tonnes (Mt) of food grains. It has been assessed that ten major crops (rice, wheat, sorghum, pearl millet, barley, finger millet, sugar cane, potato tubers, pulses, and oilseeds) of India produce approximately 683 million tons (Mt) of crop residues (CR) both on-farm and off-farm ［1］. Out of the total CR produced approximately 140 Mt CR are subjected to open field burning. CR from rice accounted for 40% of the total residues burnt followed by wheat residue (22%) and sugarcane trash (20%) ［5.

Rice-wheat systems of Indo-Gangetic Plains (IGP) are the main contributor to India’s total cereal production, accounting for 23% and 40% of India’s total rice and wheat area, respectively ［7］. Henceforth, it is quite predictable that IGP is the key contributor to rice and wheat residues. Moreover, scarcity of labour, the high cost involved in incorporating/removing residues from fields and composting, lack of requisite machinery to incorporate crop residues in soil have compelled the farmers to adopt burning. Burning of paddy straw could cause an intact loss of about 79.38, 183.71 and 108.86 kg ha⁻¹ N, P, and K, respectively ［6, 8］. Hence, its uninterrupted removal and burning could lead to net losses of nutrients which eventually will cause greater nutrient input costs in the short run and a decline in soil health and productivity in the long run scenario. Here arises the significance of alternative as well as sustainable ways of crop residues management. The technique of ex-situ decomposition of crop residues or composting dates back to several decades, however, is still holds its importance in sustainable crop residue recycling. Nevertheless, the in situ or in-field decomposition of crop residue using microbial inoculums is rarely studied. However, the greater challenge is not only achieving the complete decomposition but also enhancing the rate of in situ decomposition to make the field available to the farmers for the next crop. Although there are few studies on the application of lignocellulolytic microbes for in situ residue decomposition ［2, 3］, still there is a need for further extensive studies to examine the efficacy of the microbial inoculants in abating the nuisance of crop residue burning. Henceforth, the present study was undertaken to evaluate the effect of paddy residue management practices on the growth and yield of zero tillage maize grown after rice.

MATERIAL AND METHODS

A field experiment was conducted in field no: C-12 of Agricultural College farm, Rajendranagar, Hyderabad which is geographically situated at 17⁰32’22’’N latitude and 78⁰41’11’’E longitude with an altitude of 550 m above the mean sea level. The experimental soil was neutral in reaction (7.8), low in organic carbon (0.38 %) and available nitrogen (145 kg ha^-1), and medium in available phosphorous (38 kg ha^-1) and available potassium (277 kg ha^-1). There were eight residue management methods viz.,R₁: Burning residue before sowing, R₂: Retention of residues, R₃: Removal of residues before sowing, R₄: Incorporation at 15 DAS, R₅: Incorporation at 15 DAS + SSP at equivalent to ‘P’ dose, R₆: Spraying consortia of decomposers @ 10% of residue weight + surface retention, R₇: Spraying consortia of decomposers @ 10% of residue weight + incorporation at 15 DAS, R₈: Spraying consortia of decomposers @ 10% of residue weight + incorporation at 15 DAS + SSP at equivalent to ‘P’ dose and three fertilizer doses viz., F₁: 75% RDF, F₂: 100% RDF and F₃: 125 % RDF. All these were tested in strip plot design, and replicated thrice. Deccan Hybrid Makka (DHM-117) was used for the study during the rabi seasons of the year 2020 and 2021, released from All India Coordinated Research Project on Maize, (Indian Institute for Maize Research), Hyderabad, Telangana State in 2009. Maize seeds were sown under zero tillage situation during rabi season in the same experimental site where kharif rice was grown in the previous season.The yield attributes like number of cobs plant^-1, length of the cob, girth of the cob, no of kernel rows cob^-1, number of kernels cob^-1, and test weight in maize were recorded at harvest. The tagged plants were used for recording yield attributes. From selected five plants, the cob length was measured from base to tip of the cob and computed as the average cob length in centimeters. The girth was measured at the point of maximum girth using a thread and measured with a scale. The mean girth of the cob was computed and expressed in cms. A number of kernel rows in each cob were counted manually. A grain sample was taken from each net plot, the sample was weighed and the seeds in the sample were counted. The 100-grain weight was computed and is expressed in grams.The harvested produce from each plot was tied in bundles separately, sun-dried and dry weight was recorded in kilograms with the help of electronic balance. The weight of cleaned grains obtained from each plot after shelling/threshing was recorded. The net plot grain and stover yield of five plants which were marked for recording post-harvest observations were added and the total yield was expressed in kg ha^-1.

RESULTS AND DISCUSSION

Number of Cobs Plant^-1: It is revealed from the data in Table 1 that the higher number of cobs per plant was significantly affected by the interaction of different residue management practices and fertility levels. Among the combinations, consortium + incorporation + SSP with 125 % RDF (R₈F₃) gave a maximum number of cobs per plant which was on par with consortium + incorporation + SSP with 100% RDF (R₈F₂) and consortium + incorporation + SSP with 75% RDF (R₈F₁) combinations. The reason for having a statistically higher number of cobs per plant with R₈ treatment might have been due to the concurrent availability of moisture and nutrients in synchrony with their need which resulted in better partitioning of photosynthates and increased the number of cobs plant^-1 during both the years of experiment than other treatments. In 2020-21, removal with 75% RDF (R₃F₁) had a lower number of cobs plant^-1 and was on par with in-situ burning (R₁F₁), retention (R₂F₁), retention + consortium (R6F₁), and incorporation (R4F₁), but it was significantly higher in 2021-22. Poor availability of nutrients and moisture as a result of the loss of organic matter caused by burning and removal may be the cause of variation in the number of cobs plant^-1 in relation to residue management practices ［4］.

Length of the Cob:  With the application of 125% RDF in conjunction with consortium + incorporation + SSP, much longer cobs were seen, and it was comparable to 100% RDF and 75% RDF (Table 2). Lower cob length was seen in removal with 75% RDF which was comparable to in-situ burning with 75% RDF,  retention with 75% RDF, and consortium + retention with 75% RDF. Similar findings were made earlier by Choudhary et al. (2016)［3］, who reported that wheat treated with several fungal isolates had longer spikes than the untreated control.

 Residue burning, microbial consortia, yield parameters, yield

The girth of the Cob: When compared to other residue management techniques, the incorporation of residues treated with consortium and SSP along with 125 % RDF considerably increased the cob girth of maize and was found to be on par with 100% RDF and 75% RDF as shown in Table 3. It could be because the microbial consortium plays a significant role in the degradation, produces favorable soil moisture, reduces soil temperature, and enhances the absorption and utilization of available nutrients, all of which contribute to an overall improvement in crop growth. This reflects the relationship between the source and the sink, which in turn increased the yield characteristics of maize in both years.

Number of Kernel Rows Cob^-1: During the two years of study, the data pertaining to the number of kernel rows cob^-1 of maize showed that it was unaffected by residue management practices and fertility levels as well as their interaction as shown in Table 4.

Number of Kernels Cob^-1: As shown in Table 5, consortium + incorporation + SSP with 125% RDF produced a higher number of kernels cob^-1 than R₈F₂ (consortium + incorporation + SSP with 100 percent RDF) and R₈F₁ (consortium + incorporation + SSP with 75 percent RDF). However, this result was comparable to R₈F₂ and R₈F₁. In 2020-21, R₃F₁ (removal with 75 percent RDF) was found to be on par with R₁F₁ (in-situ burning with 75 percent RDF), R₂F₁ (retention with 75 percent RDF), R₆F₁ (retention + consortium with 75 percent RDF), and R₄F₁ (incorporation with 75 percent RDF), while R₄F₁ (incorporation with 75 percent RDF) was found to be superior to R₃F₁, R₁F₁, R₂F₁ and R₆F₁ during second year of experiment i.e.,2021-22.

Test Weight: Non-significant effect of fertility levels and residue management interaction was recorded with the test weight in maize (Table 4).

Grain Yield:A critical look at the data indicates that the grain yield of maize was  influenced significantly due to the different residue management practices and fertility levels. Maize kernel yield was significantly higher with consortium + incorporation + SSP in combination with 125% RDF (R₈F₃) than with the other residue management practices examined. The kernel yield of maize mainly depends on the partitioning ability of photosynthates from source to sink i.e., developing cobs and kernels which leads to increased yield. All the yield-promoting characters were significantly higher with consortium + incorporation + SSP due to better partitioning of photosynthates to developing cobs. Consortium + incorporation with 125 % RDF (R₇F₃) was the next best treatment in terms of higher maize yield, and it distinguished itself significantly from the other treatments, namely, incorporation (R₄F₃) and incorporation + SSP(R₅F₃). The absence of consortium limited the availability of nutrients as well as the activity of microbes in sole incorporation plots, hence the decomposition rate was slow. So an additional dose of nutrients (125 % RDF) limited the immobilization and improved the yield in R₄ and R₅ plots. According to ［9］, the mere incorporation of residues into the soil has a negative impact on the available nutrients in the soil due to the immobilization of nutrients by the presence of residues with a wide C/N ratio, resulting in lower yields in rice and wheat. The grain yields under 125% RDF + removal, 125% RDF + in-situ burning and 125% RDF + retention, 125% RDF + retention + consortium were found to be statistically on par with each other, and 125% RDF + residue incorporation was also found at par during first year of study while it was significantly superior over R_3,R_1, R₂ and R₆ during second year i.e., rabi  2021-22.

Straw yield : It is apparent from the data that residue management practices and fertility levels had recorded a significant impact on straw yield. The highest straw yield was achieved when consortium, incorporation, and SSP (R₈) were used in conjunction with 125% RDF (F₃). During both rabi 2020-21 and 2021-22, the straw yields under 125% RDF + removal (R₃F₃), 125% RDF + in-situ burning (R₁F₃), 125% RDF + retention (R₂F₃), and 125% RDF + retention + consortium (R₆F₃) were found to be statistically equivalent to one another. When fertilizers are combined with residues and microbial consortium, the physical properties of the soil will be improved, micronutrients will be replenished, soil moisture will be retained and fertilizer efficiency will increase for high yield.

Conclusion: This experiment has shown that the incorporation of crop residues after the application of microbial consortia and SSP in conjunction with 125% RDF significantly increased yield and yield components of maize.