Crop residue management and soil health: A systems analysis

In developing countries, the key in promoting physical, chemical, and biological attributes of soil health in agricultural systems is mainly through the retention of crop residue in fields in view of scarcity of alternative source of organic amendments. The environmental and soil health benefits of crop residue management include reduced soil erosion, enhanced nutrient cycling, higher soil moisture retention, improved soil quality, and increased soil organic matter and carbon storage. The decreased soil temperature, nitrogen immobilization, and waterlogging are some of the limitations of crop residue retention on soil surface. The use of crop residues as feed for livestock can limit the amount of residue retained on the soil surface, but partial retention (more than 30 % soil cover) is recommended.

Core Ideas Farmers struggle to maintain and balance economic and environmental sustainability. Identification of knowledge gaps related to crop residue management. Discussion of crop residue manage expanded from the U.S. Midwest to a global perspective. Use of carbon flux tower data to validate simulation models. Crop residue harvesting impacts soil health, productivity, and greenhouse gas emissions. The amount of crop residues that can be sustainability removed is highly variable and is a function of many factors including the soil, climatic, and plant characteristics. For example, leaving an insufficient amount of crop residue on the soil surface can be detrimental for soil quality, result in loss of soil organic matter (SOM), and increase soil erosion, whereas leaving excessive amounts can impair soil‐seed contact, immobilize N, and/or keep soils cool and wet. This special issue evolved as an outcome of, “Crop Residues for Advanced Biofuels: Effects on Soil Carbon” workshop held in Sacramento, CA, in 2017. The goal of the special issue is to provide a forum for identifying knowledge gaps associated with crop residue management and to expand the discussion from a regional Midwestern U.S. to a global perspective. Several crop residue experiments as well as simulation modeling studies are included to examine effects of tillage, crop rotation, livestock grazing, and cover crops on greenhouse gas (GHG) emissions, crop yield, and soil or plant health. The special issue is divided into 4 sections that include (i) Estimating Crop Residue Removal and Modeling; (ii) Cultural Practice Impact on Soil Health; (iii) Residue Removal Impact on Soil and Plant Health; and (iv) Cultural Practice Impact on Carbon Storage and Greenhouse Gas Emissions.

Of late, intensive farming for higher food production is often associated with many negative implications for soil systems, such as decline of soil organic matter (SOM), increase in risks of soil erosion by wind and/or water, decline in soil biological diversity, increase in degradation of soil physical quality, lower nutrient-use efficiency, high risks of groundwater pollution, falling water tables, increasing salinization and waterlogging, in-field burning of crop residues, pollution of air and emission of greenhouse gases (GHG), leading to global warming, and decline in factor productivity. These negative implications necessitate an objective review of strategies to develop sustainable management practices, which could not only sustain soil health and ensure food security, but also enhance carbon sequestration, decrease GHG emissions, and offer clean and better ecosystem services. Conservation agriculture (CA), that includes reduced or no-till practices along with crop residue retention and mixed crop rotations, offers multiple benefits. Adoption of a system-based CA conserves water, improves and creates more efficient use of natural resources through the integrated management of available soil nutrients, water, and biological resources, and enhances use efficiency of external inputs. Due to apparent benefits of CA, it is increasingly being adopted and now covers about 180 million hectares (Mha) worldwide. However, in South Asia its spread is low (<5 Mha), mostly concentrated in the Indo-Gangetic Plains (IGP). In this region, one of the serious issues is “residue burning” with severe environmental impacts. A huge amount of crop residue left over after the combine harvest of rice has forced farmers to practice widespread residue burning (∼140 M tonnes) to cope with excessive stubble and also for timely planting/sowing of succeeding crops. In rice-wheat cropping systems, which cover more than 10 Mha in the IGP, CA practices are relatively more accepted by farmers. In these systems, any delay in sowing leads to yield penalty of 1–1.5% per day after the optimum sowing date of wheat. The strong adoption of CA practices in IGP is mainly to overcome delayed sowing due to the field preparation and control of weeds, timely planting, and also escape from terminal heat during the grain-filling stage. Major challenges to CA adoption in South Asia are small land holdings (<1 ha), low technological reach to farmers, nonavailability of suitable farm implements for small farm holders, and the staunch conventional farming mind-set. South Asia region consists of many countries of diverse agro-ecologies with contrasting farming systems and management. This region, recently known for rapid economic growth and increasing population, necessitates higher food production and also hot-spots for adoption of CA technologies. Therefore, in this review critically explores the possibility, extent of area, prospects, challenges, and benefits of CA in South Asia. HIGHLIGHTS Conservation agriculture (CA), consisting of reduced or no-tillage and crop residue retention, is a self–sustainable system which offers an alternative to crop residue burning. The CA approach improves soil health by increasing soil organic carbon (SOC) and aggregation and also conserves soil, water and energy than conventional farming systems. South Asian countries are suitable for adoption of CA practices but the area under CA remains low (<5 Mha) as compared to the global area (180 Mha). Adoption of CA in South Asia has skewed distribution, mainly in Indo-Gangetic Plains (IGP) in India, Pakistan, Nepal and Bangladesh in South Asia. Development of herbicide-resistant weed species and weed shift by continuous application of herbicides are the major challenges in adoption of CA. The traditional-farming mind-set, socio-economic conditions, small farm-holdings, weed and residue management, and non-availability of suitable machinery are key constraints to the low adoption of CA practices in South Asia.

Crop residues management has great effects on weeds in croplands. To understand the weed responses to crop residues management and weeds impact on crop yield, a field trial with three crop residues management strategies has been conducted in the North China Plain since 2008. Weed community composition and structure across the species, morphological types, life forms, and community levels were investigated during 2019–2020. The results show that the field with crop residues retention significantly decreased weed density than that in the field with no crop residues retention. Furthermore, total crop residues retention significantly decreased weed density than half crop residues retention. Compared with no crop residues retention, the weed aboveground dry matter in the field with total and half crop residues retention significantly decreased. Meanwhile, the maize grain yield significantly increased, resulting from weeds decreased with crop residues retention on the field. Negative correlations were found between maize grain yield and the density and aboveground dry matter of monocotyledonous weeds. These findings indicate that long term crop residues retention under conventional tillage might be an effective agronomic practice to retard weed growth. However, the mechanism of crop residues retention on weed control is still needed to research.

Rice-wheat cropping system (RWCS) is the most important system occupying around 26 M ha spread over the Indo Gangetic Plains in South Asia and China. Many long-term trials were led to assess the agronomic productivity and economic profitability of various combinations of conservation agricultural (CA) practices (zero tillage, residue management and crop establishment) in RWCS of Eastern Indo-Gangetic Plains (EIGP) of India. The purpose of this study was to investigate the best management practices involving different tillage-based crop establishment and residue retention techniques and their contribution to agricultural system sustainability through improvement in soil health by developing soil quality index (SQI). We have used SQI as an instrument based on physical [macro aggregate stability (MAS), available water capacity (AWC) and soil penetration resistance (SPR)], chemical [soil organic carbon (OC), available N, available P and available K] and biological [microbial biomass carbon (MBC), fluorescein diacetate (FDA) and dehydrogenase activity (DHA)] properties of soil, because these are very useful indicators of soil’s functions for agronomic productivity and soil fertility. Soil properties like MAS, OC, MBC, FDA and DHA were higher by 47, 18, 56, 48 and 53%, respectively, under ZTDSR-ZTW (T7: Zero-till direct seeded rice - Zero-till wheat) than RPTR-CTW (T1: Random puddled transplanted rice - Conventional till broadcasted wheat), at 0-10 cm. CA based treatment T7 also recorded lower SPR (126 N cm-1). SQI for different treatments were calculated by performing principal component analysis based on the total data set method. The higher system rice equivalent yield of 12.41 t ha-1 was observed at SQI value of 0.90 at 0-10 cm and 0.86 at 10-20 cm in T7. It can be concluded that crop residue retention on the surface with zero tillage is beneficial for the sustainability and productivity of the RWCS in EIGP of India.

Large amounts of surplus residues of different crops are available for in situ recycling for conservation agriculture (CA) in India. Recycling crop residues containing considerable quantities of nutrients can help save on the use of fertilizers. The importance of crop residue retention to the sustainability of crop production is widely acknowledged. Crop residue management practices and the quality and quantity of crop residues returned affect soil fertility through a series of chemical, physical, and biological changes in the soil. Retention of crop residues on the soil surface as in CA systems not only reduces runoff and soil erosion but also improves the soil physical characteristics (such as hydraulic properties and soil aggregation) and increases soil organic matter content, especially in the surface layer. Additionally, increases in soil microbial biomass and activity following crop residues addition improve the nutrient-supplying capacity of soil and reduce nutrient losses. Decomposition of crop residue is slower for surface retention compared with incorporation into the soil by conventional tillage, thereby making nutrients less prone to losses via leaching, volatilization, and denitrification. This chapter discusses the literature on the impact of surface retention of crop residues under CA on soil quality parameters (physical, chemical, and biological) and crop yields under important cropping systems of India.

The effects of planting cereal or leguminous crops in rotation with irrigated cotton (Gossypium hirsutum L.) on the properties of cracking clay (swelling) soils in the Macquarie and Namoi Valleys of New South Wales, Australia were evaluated during the summer of 1992–3. The observations were made on commercial farmers' fields. The soil properties evaluated were the particle size distribution, the dispersion index, the plastic limit, the percentage of coarse (particle diameter 212–2000 μm) and fine (particle diameter 53‐212 μm) particulate soil organic matter, soil respiration rate, soil reactivity, soil aggregate density, pH, nitrate‐N and exchangeable Ca, Mg, K and Na. In general, the planting of rotation crops decreased the dispersion index, plastic limit and soil aggregate density, and increased the amount of coarse particulate organic matter. Planting rotation crops also resulted in significantly higher clay and lower silt contents in the Macquarie Valley, and significantly higher soil respiration in the Namoi Valley. Soil pH, nitrate‐N and exchangeable cation concentrations were not significantly affected by planting rotation crops in the Macquarie Valley, whereas exchangeable Na was increased in the Namoi Valley. The retention of crop residues in situ, compared with burning crop residues, decreased the dispersion index, plastic limit and aggregate density, and increased the amount of coarse particulate soil organic matter at all measured depths of the Macquarie Valley. The retention of crop residues in the Namoi Valley decreased the plastic limit and dispersion index only in the 0–50 mm depth range, whereas burning crop residues increased exchangeable K at all depths. In general, planting rotation crops and the retention of crop residues had greater beneficial effects on the soil physical properties in the Macquarie Valley than in the Namoi Valley, and in the topsoil compared with the subsoil. These differences are attributed to a shorter rotation interval in the Namoi Valley, smaller amounts of coarse particulate soil organic matter in the subsoil, and differing soil types in the two valleys. In the Namoi Valley the coarse organic matter produced by leguminous crops appeared to be more effective in promoting structural stability than that from non‐leguminous crops, although no such difference was observed in the Macquarie Valley.

High Yielding Varieties (HYV) along with chemical fertilizer, pesticides and irrigation had introduced in Bangladesh in the name of “Green Revolution” to feed the huge population of the country. This results degradation in soil health and reduce productivity in the long run. In this context, conservation agriculture (CA) is becoming increasingly important in overcoming the problems of declining agricultural productivity. This paper investigates the benefits and impacts of CA practiced by the farmers in Bangladesh. The study covered a range of soils and cropping systems for the evaluation of CA in Rajshahi; Mymensingh; Rajbari, and Thakurgaon districts. Data and information were gathered through focus group discussion (FGD), household survey, and case studies. A total of 458 households were interviewed considering the level of adoption of CA from different cropping systems. The results show that most of the farmers under Mymensingh and Thakurgaon districts don’t have any knowledge in sowing/transplanting by machineries whereas farmers in Rajbari and Rajshahi districts have comparatively better knowledge on this. Overall 76.45% respondents know the benefits of using organic matter in soil. For tillage operation, draft power use is higher than other machineries in all cropping seasons. The retention of crop residues was found higher in Boro rice compared to Aman and Aus rice and other crops. A few farm households had a little knowledge on how to improve soil health through retention of crop residues. Only 39.30% respondents practiced crop rotations, and 30% respondents practiced mixed cropping, and most of them experienced increased production. The major constraints of adoption of CA mentioned by the respondents are low production, more weeds, low animal feed, lower cooking fuel and bothering job. Providing adequate knowledge and training of CA should be provided to the farmers for sustainable agricultural productivity.

Organic matter content increases in soil with no-tilled permanent raised beds (PBs) compared with soil with conventionally tilled beds (CBs), and this might affect greenhouse gas (GHG) emissions. Greenhouse gas (CO2, N2O, and CH4) emissions were measured from PBs, from which crop residue was either removed or retained and from CBs where crop residue was retained. The CO2 emission was not affected by tillage, but CH4 and N2O emissions were lower in PBs when residue was retained than in CBs. Removing crop residue from PBs reduced CO2 emissions compared with when it was retained, but it had no effect on N2O and CH4 emissions. The global warming potential (GWP) of GHG emissions was higher in CBs (801 kg CO2/ha/year) than in PBs (517 kg CO2/ha/year) with crop-residue retention, but more C was sequestered in the 0–60 cm soil layer in PBs (83.4 Mg C/ha) than in CBs (79.2 Mg C/ha). Crop-residue removal in PBs had little effect on the GWP of GHG compared with PBs with crop residue retained, but less C was sequestered in the latter (63.1 Mg C/ha). Net GWP (considering soil C sequestration, GHG emissions, fuel used, glyphosate application, fertilizer and seed production) was lower in CBs with crop-residue retention (1062 kg CO2/ha/year) than in PBs with crop-residue removal (6,120 kg CO2/ha/year), but it was larger than in PBs with crop-residue retention (−681 kg CO2/ha/year). We found that reduced tillage when beds were made permanent and crop-residue retention greatly reduced net GWP compared with when beds were tilled and remade each year.We found that retention of crop residue in PBs increased the emission of CO2 compared with where it was removed, but tillage did not affect fluxes of CO2. Emission of CH4 and N2O was larger from CBs than from PBs, but crop-residue management in PBs had no significant effect on fluxes of CH4 and N2O. Concentrations of mineral N were larger in CBs than in PBs, whereas the removal of crop residue from PBs increased mineral N concentration. Soil temperature was higher in CBs than in PBs and in PBs with crop residue retained compared with where it was removed. Soil water was better preserved in PBs than in CBs and in PBs where residue was retained than where it was removed. The higher water content in the PB compared with the CB will favor plant growth during dry spells. However, retaining crop residues in PBs will require sufficient application of inorganic N, as mineral N in soil is lower in PBs than in CBs or PBs with crop residue removed. Limited N availability in PBs with crop residue retained might reduce yields as poor farmers in the central highlands of Mexico apply little or no N fertilizer. Reduced tillage on PBs and crop-residue retention strongly reduced the net GWP of the system compared with the case when beds were remade each year. PBs with residue retention reduced net GWP by 50% compared with CBs with residue retention, but the removal of residues from the PBs more than doubled it.

Present trends, sustainable strategies and energy potentials of crop residue management in India: A review

Soil is a very important factor of the plant growth and crop yield. But now a days, very small area of the soil can actually be fertile for agriculture, and if we manage improperly it can be depleted. So the big problem, how we manage and increase the fertility of soil. It has been reported that soil organic carbon and soil matter is the most important indicator of soil quality and soil health. It is also beneficial for agricultural sustainability. In this review, we summarized how crop residue management affects soil organic carbon (SOC), soil organic matter (SOM), soil aggregation, effect of residue burning and crop productivity in different cropping system. Proper use of crop residue can increase or maintain the physical and chemical properties of SOM and improve the quality of soil. Manure or crop residue alone may not be adequate to maintain SOC levels. Knowledge and assessment of changes (positive or negative) in SOC and SOM with time is still needed to evaluate the impact of different management practices.

Diversity in crop residue management across an intensification gradient in southern Africa: System dynamics and crop productivity

Social and income trade-offs of conservation agriculture practices on crop residue use in Mexico’s central highlands

Organic carbon and total nitrogen stocks in a Vertisol following 40 years of no-tillage, crop residue retention and nitrogen fertilisation

Tillage intensity, crop residue retention and nitrogen application can significantly impact the soil properties and crop productivity. We studied the effect of tillage (deep tillage [DT] vs. shallow tillage [ST]) in main plots and residue management viz. conventional tillage without residue (CT-R), conventional tillage with residue (CT+R), minimum tillage without residue (MT-R) and minimum tillage with residue (MT+R) in sub plots and fertilizer-N at 75, 100 and 125% N (viz. N75, N100 and N125) in sub-sub plots. Field treatments were established in maize-wheat (Zea mays-Triticum aestivum) cropping system during 2016-2019 at two different locations in north-western India and were arranged in split-split plot design. The soil penetration resistance was significantly lower under deep tillage (3.4 to 3.7%) as compared to shallow tillage. CT+R recorded lowest penetration resistance as compared to other tillage and residue combinations but other soil properties like OC, available NPK, soil aggregation, infiltration rate did not differ significantly. The addition of crop residue both under minimum and conventional tillage significantly increased the soil microorganism count and dehydrogenase enzyme activity at both locations. CT-R recorded lowest microorganism count and dehydrogenase enzyme activity. The available soil nitrogen, microorganism count and dehydrogenase enzyme activity significantly increased with increasing nitrogen doses at both locations and were highest under 125% N level as compared to 75% and 100% levels. In both crops, the grain yield was not significantly affected by tillage and crop residue combinations while the different levels of nitrogen fertilizer significantly affected the grain yield. From soil health and sustainability point of view, CT+R treatment with 100% recommended dose of nitrogen in maize-wheat crop rotation seemed beneficial.