Impact of conservation agriculture production system on soil biological properties

Introduction

Conservation agriculture (CA) system consists of no or minimal tillage and permanent soil cover, either with a live crop or with crop stubbles and diversified crop rotation that include legumes (FAO, 2019) [8] . An overall CA farming system is meant to ensure the sustainability of agriculture through conserving and protecting soil, water, and biological resources as much as possible with minimal external inputs, and it is associated with many benefits such as greater soil aggregation and water storage, improved soil quality, decreased erosion and in some instances higher yield and net farm income. This has led to the identification of conservation agriculture as a valuable tool to ensure future food production and to buffer agricultural productivity (FAO, 2019) [8] . Applying conservation agriculture essentially means altering literally generations of traditional farming practices and implement use. As such, the movement towards conservation agriculturebased technologies normally is comprised of a sequence of step-wise changes in cropping system management to improve productivity and sustainability. Reduced tillage systems in the United States have been shown to reduce soil erosion, reduce nutrient losses from the field, sequester carbon as a result of increasing organic matter, and increase crop yields. The widespread adoption of CA resulted in significant development of farmer profitability which is achieved through increased agricultural productivity and reduced input costs. Soil tillage (soil surface management to alleviate soil related constraints to crop production) is a basic and an important input with short and long term effects on sustainability. It influences agriculture sustainability through its effects on soil properties, soil processes and crop growth. Appropriate tillage systems are soil and crop specific, and their adoption is governed by both bio-physical and socio-economic factors. In addition to increasing crop yields, tillage method facilitate soil and water conservation, improve root system development, maintain a favourable level of soil organic matter content and reduce soil degradation (Lal, 1991) [11] . The activity of dehydrogenase can be used as an excellent predictor of soil quality. As respiratory chain enzymes, dehydrogenases play an important role in the energy production of soil microbes (Boltan et al., 2004) [5] .

Phosphatase plays an important function in phosphorus cycle, including phospholipid breakdown. The addition of organic matter to the soil boosted the activity of the phosphatase enzyme (Singh et al., 2007) [16] . Urease enzyme took part in the hydrolysis of urea to carbon dioxide and ammonia in soil, and it is a key part of the nitrogen cycle. The maximum urease enzyme activity was observed when NPK was combined with manure application (Bhatt et al., 2016) [4] . Nidaye and Dkhar (2000) [13] reported soil enzyme activity has the potential to help in manage the ecosystems for long-term viability. Abbasi and Khizar (2012) [1] reported that application of urea resulted in a drop in MBC, whereas the use of farmyard manure as a soil amendment resulted in an increase in MBC. Crop residue and tillage affects the soil environment directly or indirectly, incorporation of crop residue into soil or retention on the surface through the adaptation of conservation agriculture practice has positive influence on physical, chemical and biological properties of soil. Hence, the present study was undertaken to assess the effect of different management practices on soil biological properties, the present investigation entitled "Effect of conservation production system on soil biological properties in rainfed condition" at AICRP on Dry Land Agriculture, UAS, GKVK.

Material and Methods

Experimental site and treatment details

The field experiment was carried out during Kharif-2020 at AICRP for Dry Land Agriculture, UAS, GKVK, Bengaluru-65. It is located in the Eastern Dry zone of Karnataka at 13º 05' N latitude and 77 0 34' E longitude with an altitude of 924 meters above Mean Sea Level (MSL). The total rainfall during 2020 at AICRP for Dryland Agriculture, GKVK, and Bengaluru was 1,182.2 mm with maximum rainfall during July (242.8 mm) and minimum during January and February (0.0 mm). The maximum and minimum temperature of 29.1 ºC and 18.2 ºC was observed during the cropping year. Relative humidity of 89.6 per cent was recorded during the cropping period. The soils of Gandhi Krishi Vignana Kendra (GKVK) belongs to Vijayapura series which is a dominant soil series of Bengaluru plateau. The soils of experimental site at AICRP on Dry Land Agriculture Project represents the typical lateritic area of Bengaluru plateau. These soils are classified as fine, kaolinitic, isohyperthermic, Typic Kandiustalf as per USDA classification. These soils are deep, yellowish red, lateritic, red sandy clay loam with good drainage and are derived from granite-gneiss under subtropical semi-arid climate.

Cropping history of the experimental plot

In the experimental plot Inter cropping of finger millet (Eleusine coracana (L.) Gaertn) + Pigeon pea (Cajanus cajan) was grown during Kharif 2019 and left fallow during rabi and summer.

B. Sub Plot Treatments

C1 Control (no cover crops) C2

Field bean (HA-4) leaving the residue after harvesting the green pods for vegetable C3

Horse gram in-situ and mulching

Soil sampling, processing and analysis

Soil samples from experimental area were collected from 0-15 cm, after the harvest of the crop. The collected soil samples were kept in refrigerator and analysed for various biological properties adopting standard procedure. The biological properties included the Soil microbial biomass carbon (SMBC) and nitrogen (SMBN) was estimated by fumigation-extraction method as proposed by Carter (1991) [6] in which Ninhydrinreactive N, as a measure of microbial biomass carbon released during soil fumigation by using ninhydrin reagent. The dehydrogenase activity in the soil was determined by the reduction of 2, 3, 5-triphenyl-tetrazolium chloride to 1, 3, 5triphenylformazan (TPF) given by Casida et al. (1964) [7] .

Statistical analysis

The observations recorded in these studies were analysed statistically for test of significance following the Fisher's method of analysis of variance (ANOVA) as outlined by Gomez and Gomez (1984) [9] . Whenever F-test was significant for comparison amongst the treatments means an appropriate value of critical differences (CD) was worked out. Otherwise against CD values, abbreviation NS (Non-Significant) was indicated. All the data were analysed and the results are presented and discussed at a probability level of 0.05 per cent and correlation and regression study was done as given by Gomez and Gomez (1984) [9] .

Results and Discussion

Impact of conservation agriculture production system on Soil biological properties

The results of the field experiment conducted to know the effect of conservation agriculture production system on soil biological properties viz. microbial biomass carbon, nitrogen and dehydrogenase enzyme activity are presented in Table 1.

Microbial Biomass Carbon (MBC)

The soil microbial biomass carbon reflects the soil ability to store and cycle nutrients (C, N, P and S) and has high turnover rate relative to the total soil organic matter. The rate of soil organic carbon input from plant biomass is generally considered the dominant factor controlling amount of soil microbial biomass carbon. Different tillage practices significantly influenced MBC with higher microbial biomass carbon (223.57 µg g -1 ) in zero tillage compared to conventional tillage (169.57 µg g -1 ). Among different cover crops significantly higher microbial biomass carbon (227.73 µg g -1 ), was observed in horse gram cover crop compared to control (152.30 µg g -1 ). Tillage practices and cover crops showed non-significant interaction, with higher value (262.30 µg g -1 ) in M 3 C 3 (Zero tillage + Horsegram cover crop).

The influence of tillage practice on SMB-C and N seems to be mainly confined to the surface layers, with a stronger stratification when tillage is reduced (Alvear et al., 2005 [2] , Salinas-Garcia et al., 2002) [15] . It is also reported that higher biomass carbon under zero tillage than the conventional tillage can be attributed to higher level of C substrates available for micro-organisms growth, better soil physical condition and higher water retention under zero tillage.

Microbial Biomass Nitrogen (MBN)

Microbial biomass nitrogen responds to changes in soil management often before effects are measured in terms of organic C and N. The SMB plays an important role in physical stabilization of aggregates. Different tillage practices significantly influenced MBN with higher microbial biomass nitrogen (26.03 µg g -1 ) in zero tillage compared to conventional tillage (19.74 µg g -1 ). Among different cover crops significantly higher microbial biomass nitrogen (26.51 µg g -1 ), was observed in horse gram cover crop compared to control (17.73 µg g -1 ). Tillage practices and cover crops showed significant interaction, with higher value (30.54 µg g -1 ) in M 3 C 3 (Zero tillage + Horsegram cover crop).

A study conducted on soybean-rapeseed crop rotation under CA for two years indicated that MBN content under CA treatments increased by 16.7 and 17.4 per cent for two and four years, respectively (Kumar et al., 2016) [10] . However, Mbuthia et al.

(2015) [12] reported an increase in MBN by 8.11 per cent under no tillage as compared to conventional tillage under long term study of 31 years. Salinas-Garcia et al. (2002) [15] reported that SMB-N was significantly affected by tillage, but primarily at the soil surface (0-5 cm) it was 25-50% greater with zero tillage and minimum tillage than with disk ploughing to 30 cm. The results are in line with Spedding et al. (2004) [17] who found that residue management had more influence than tillage system on microbial characteristics, and higher SMB-C and N levels were found in plots with residue retention than with residue removal.

Dehydrogenase activity (DHA)

The enzyme activity in soil is considered as an index of microbial activity, which is influenced by nature, age of crop and addition of fertilizers and manures. The presence of microorganisms in soil depends on chemical composition, moisture, pH, and structure. The dehydrogenase activity is proposed as the best indicator of microbiological redox system, which is considered as good and adequate parameter of microbial oxidative action in soil. Different tillage practices significantly influenced DHA with higher dehydrogenase activity (50.67 µg TPF g -1z soil 24 h -1 ) in zero tillage compared to conventional tillage (25.68 µg TPF g -1z soil 24 h -1 ). Among different cover crops significantly higher dehydrogenase activity (47.56 µg TPF g -1z soil 24 h -1 ), was observed in horse gram cover crop compared to control (32.76 µg TPF g -1z soil 24 h -1 ). Tillage practices and cover crops shown non-significant interaction, with higher value (54.72 µg TPF g -1z soil 24 h -1 ) in M 3 C 3 (Zero tillage + Horsegram cover crop). Bera et al. (2018) [3] evaluated the response of DHA to conservation agriculture practices under rice-wheat system in sandy loam soil of North Western India and reported that among wheat treatments, dehydrogenase was higher under ZTW+R than under ZTW-R and CTW-R at all growth stages of wheat. In the case of rice treatments (residual effects of rice establishment methods), the activity of all the soil enzymes were significantly higher after ZT-DSR compared with CT-DSR, DTR and the lowest after PTR. Parihar et al. (2016) [14] study effect of CA on maize based rotations and reported that dehydrogenase activity (DHA) was significantly affected by tillage and crop rotations and their interactions. They also reported that maximum soil DHA was recorded under ZT plots, which was significantly higher than CT plots. Further, the DHA in 0-30 cm soil layer was 43.5 and 30.6 per cent higher in ZT and PB treatments compared to CT, respectively.

Conclusion

Different tillage practices significantly influenced MBC, MBN and DHA in zero tillage compared to conventional tillage. Among different cover crops significantly higher microbial biomass carbon was observed in horse gram cover crop compared to control. Conservation agriculture practice has positive influence on biological properties of soil. Adoption of proper crop residue management practices leads to improved soil quality and increase the production with the minimum adverse effect on environment. Residue management have greater influence on carbon sequestration, microbial activities, mineralization rate which in turn increases the microbial community.

References

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