May , 2022, Volume : 3 Article : 7
Effect of Crop Residue Retention in Conservation Agriculture on Soil Quality
Author : Mohankumar K T, Abhishek Das, Hithashree D M and T G S Reddy,
ABSTRACT
At the current scenario, meeting the food security of ever growing population under shrinking cultivable land while sustaining agricultural systems is the major challenge. The adaptations of intensive conventional agriculture raise a serious risk to natural resources, soil and environmental quality and agricultural sustainable production. These lead to the conservation agriculture (CA) concept in the recent decades aiming at global level agriculture sustainability with improving crop yields and soil health. The CA in general and crop residue (CR) retention in particular improves the soil physical, chemical and biological parameters in turn resulting in better soil health/soil quality.
Keywords: Crop residue, conservation agriculture, soil quality and crop residue retention
In the current scenario of depleting natural resources, attaining sustainable agricultural production, productivity and food security for a growing population are the major challenges. On the other hand the conventional agricultural practices i.e., intensive tillage, mono-cropping and removal/ burning of crop residue which not only accelerate soil organic matter depletion, but also causes widespread multi-nutrient deficiencies, soil structural deterioration, soil erosion and environmental pollution (Montgomery, 2007), ultimately affecting the ecosystem functions. These lead to the concept of CA which aims at sustainable agriculture globally by improving soil health, crop yields and reducing environmental footprints (Parihar et al., 2016). The three principles of CA are minimum soil disturbance, permanent soil cover through crop residues or cover crops and crop rotations for achieving sustainable production (Bhan and Behara, 2014). Conservation agriculture avoids straw burning, improves soil organic carbon (SOC) content, enhances input use efficiency and has potential to reduce green-house gas emissions thus helps in mitigating adverse climatic impacts. Because of these the CA is gaining rapid importance worldwide by covering about 12.5% of the world arable land (180 M ha) and occupies about 1.5 M hectare area of the total cultivated area of India (Kassam et al., 2019). Crop residue defined as the part of the plant that is left in the field after harvest, varying greatly in properties and decomposition rates (Cherubin et al., 2018).
2. Crop residues generation in India
The Ministry of New and Renewable Energy (MNRE, 2009), Govt. of India has estimated about 500 Mt of crop residues generation every year. The contribution of different types of crop wastes to the total and surplus crop residues are given in fig 1 (Pathak et al., 2010) and they also estimated that 93 Mt of crop residues are burnt on-farm in the country which is otherwise can be used under CA. Most of the CR generated in India are are burnt leading to environmental pollution (Gupta and Dadlani, 2012).
3. Soil quality and its indicators
Soil quality is the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality and support human health and habitation (Doran and Parkin, 1994). The soil indicators are the soil properties which are sensitive to soil management practices and it is divided into physical, chemical and biological parameters.
4. Effect of crop residue on soil physical, chemical and biological parameters
4.1 Effect of crop residue on soil physical parameters
a. Soil aggregation and infiltration rate
Dhaliwal et al. (2020) and Modak et al. (2019) reported enhanced macro size water stable aggregates and mean weight diameter of aggregates under CR retained plots in rice-wheat and soybean-wheat CA, respectively. As the addition of CR increases the organic matter content of the soil and its decomposition releases secondary metabolites into the soil which helps in forming better aggregates by binding the soil particles together (Das et al., 2020; Dhaliwal et al., 2020).
b. Bulk density
Under zero tillage condition there will be less disturbance of soil which results in lesser total and macro porosity thereby it increases particle to particle contact and ultimately leading to higher strength of the soil layers. But when CR is retained, the decomposition of CR increases soil aggregation as explained earlier thus increasing the soil porosity which results in reduced BD and also the bulk density of crop residue itself is lower than that of the soil (Singh et al., 2016; Choudhary et al., 2018a;Dey et al., 2020).
c. Soil thermal regime (STR)
Optimum STR with lower fluctuations was observed under CR retention compared to crop residues removed treatments by altering the minimum and maximum temperatures during (Singh et al., 2016).
4.2 Effect of crop residue retention on soil chemical properties
a. Soil pH and EC
The soil pH in CR retained plots decreased effectively compared to CR removed plots because of production of low molecular weight organic acid during the decomposition process of the added organic matter (Sharma et al., 2018;Nandan et al., 2019). However CR retention not showed any significance difference in EC compared to CR removed plots (Nandan et al., 2019).
b. Soil organic carbon sequestration
Soil quality is largely governed by soil organic carbon (SOC), which is dynamic and responds effectively to changes in management. Long-term application of CR retention increased SOC and in turn it had positive effects on mean weight diameter and geometric mean diameter, which simultaneously decreased BD and increased IR of soil (Sing et al., 2018;Nandan et al., 2019). Crop residue retention with ZT is the better crop production strategy for increasing C-sequestration, improving and sustaining the soil quality and crop productivity (Sharma et al., 2019)
c. Soil nutrients
The crop residue releases plant nutrients upon degradation which depends on soil pH, soil moisture, C/N ratio etc. (Valadares et al., 2016). The availability of both macro and micro nutrient in the soil was more under CR retained compared to crop residue removed plots (Sharma et al., 2018;Nandan et al., 2019).
4.3 Effect of crop residue retention on soil biological properties
a. Soil microbial and enzymes activity
Soil microbial count increased under residue retained fields because of addition of fresh CR which acted as substrate for the microbial growth. (Choudhary et al., 2018b).The CR retention showed significantly higher microbial biomass carbon and basal soil respiration and also increased dehydrogenase, urease, phosphatase and β-glucosidase enzymes activity. This is due to more regular supply of organic matter which acts as substrate for soil microbial growth (Choudhary et al., 2018b; Dhaliwal et al., 2020).
5. Effect of crop residue retention on soil quality index
The retention of crop residue had positive effect on soil physical, chemical and biological properties therefore leading to the better soil quality index mainly through increased SOC stock (Choudhary et al., 2018a), which is the key indicator of soil quality. The SQI increased with CR retention and higher SQI was found under lentil retained treatments because of legume effect (Saha et al., 2018).
Conclusion
The CR retention under CA will increase the soil aggregation there by reducing the bulk density and penetration resistance, facilitating easy filtration of the soil water. The crop residue itself an organic matter will helps to sequester the carbon in the soil and also upon their decomposition will supply adequate amount of essential nutrients to the growing crop. Acting as food substrate for the microbial biomass in the soil, CR will increase their growth and activity leading to increased enzymatic activities which are involved in various biogeochemical processes. Finally by improving the physical, chemical and biological properties of the soil, the crop residue retention under CA will improves the soil quality and sustainability.
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