Determine metrics and set targets for soil quality on agriculture residue and energy crop pathways

Energy from agricultural residues and consequences for land requirements for food production

Crop rotation and residue management effects under no till on the soil quality of a Haplic Cambisol in Alice, Eastern Cape, South Africa

Agricultural residues have near-term potential as a feedstock for bioenergy production, but their removal must be managed carefully to maintain soil health and productivity. Recent studies have shown that subfield scale variability in soil properties (e.g., slope, texture, and organic matter content) that affect grain yield significantly affect the amount of residue that can be sustainably removed from different areas within a single field. This modeling study examines the concept of variable-rate residue removal equipment that would be capable of on-the-fly residue removal rate adjustments ranging from 0 to 80%. Thirteen residue removal rates (0% and 25-80% in 5% increments) were simulated using a subfield scale integrated modeling framework that evaluates residue removal sustainability considering wind erosion, water erosion, and soil carbon constraints. Three Iowa fields with diverse soil, slope, and grain yield characteristics were examined and showed sustainable, variable-rate agricultural residue removal that averaged 2.35, 7.69, and 5.62 Mg ha, respectively. In contrast, the projected sustainable removal rates using rake and bale removal for the entire field averaged 0.0, 6.40, and 5.06 Mg ha, respectively. The modeling procedure also projected that variable-rate residue harvest would result in 100% of the land area in all three fields being managed in a sustainable manner, whereas Field 1 could not be sustainably managed using rake and bale removal, and only 83 and 62% of the land area in Fields 2 and 3 would be managed sustainably using a rake and bale operation for the entire field. In addition, it was found that residue removal adjustments of 40 to 65% are sufficient to collect 90% of the sustainably available agricultural residue.

This paper evaluates life cycle greenhouse gas (GHG) emissions from the use of different biomass feedstock categories (agriculture residues, dedicated energy crops, forestry, industry, parks and gardens, wastes) independently on biomass-only (biomass as a standalone fuel) and cofiring (biomass used in combination with coal) electricity generation systems. The statistical evaluation of the life cycle GHG emissions (expressed in grams of carbon dioxide equivalent per kilowatt hour, gCO2e/kWh) for biomass electricity generation systems was based on the review of 19 life cycle assessment studies (representing 66 biomass cases). The mean life cycle GHG emissions resulting from the use of agriculture residues (N = 4), dedicated energy crops (N = 19), forestry (N = 6), industry (N = 4), and wastes (N = 2) in biomass-only electricity generation systems are 291.25 gCO2e/kWh, 208.41 gCO2e/kWh, 43 gCO2e/kWh, 45.93 gCO2e/kWh, and 1731.36 gCO2e/kWh, respectively. The mean life cycle GHG emissions for cofiring electricity generation systems using agriculture residues (N = 10), dedicated energy crops (N = 9), forestry (N = 9), industry (N = 2), and parks and gardens (N = 1) are 1039.92 gCO2e/kWh, 1001.38 gCO2e/kWh, 961.45 gCO2e/kWh, 926.1 gCO2e/kWh, and 1065.92 gCO2e/kWh, respectively. Forestry and industry (avoiding the impacts of biomass production and emissions from waste management) contribute the least amount of GHGs, irrespective of the biomass electricity generation system.

This study developed a computational strategy that utilizes data inputs from multiple spatial scales to investigate how variability within individual fields can impact sustainable residue removal for bioenergy production. Sustainable use of agricultural residues for bioenergy production requires consideration of the important role that residues play in limiting soil erosion and maintaining soil C, health, and productivity. Increased availability of subfield‐scale data sets such as grain yield data, high‐fidelity digital elevation models, and soil characteristic data provides an opportunity to investigate the impacts of subfield‐scale variability on sustainable agricultural residue removal. Using three representative fields in Iowa, this study contrasted the results of current NRCS conservation management planning analysis with subfield‐scale analysis for rake‐and‐bale removal of agricultural residue. The results of the comparison show that the field‐average assumptions used in NRCS conservation management planning may lead to unsustainable residue removal decisions for significant portions of some fields. This highlights the need for additional research on subfield‐scale sustainable agricultural residue removal including the development of real‐time variable removal technologies for agricultural residue.

Agricultural residues are the largest potential near term source of biomass for bioenergy production. Sustainable use of agricultural residues for bioenergy production requires consideration of the important role that residues play in maintaining soil health and productivity. Innovation equipment designs for residue harvesting systems can help economically collect agricultural residues while mitigating sustainability concerns. A key challenge in developing these equipment designs is establishing sustainable reside removal rates at the sub-field scale. Several previous analysis studies have developed methodologies and tools to estimate sustainable agricultural residue removal by considering environmental constraints including soil loss from wind and water erosion and soil organic carbon at field scale or larger but have not considered variation at the sub-field scale. This paper introduces a computational strategy to integrate data and models from multiple spatial scales to investigate how variability of soil, grade, and yield within an individual cornfield can impact sustainable residue removal for bioenergy production. This strategy includes the current modeling tools (i.e., RUSLE2, WEPS, and SCI), the existing data sources (i.e., SSURGO soils, CLIGEN, WINDGEN, and NRCS managements), and the available high fidelity spatial information (i.e., LiDAR slope and crop yield monitor output). Rather than using average or representative values for crop yields, soil characteristics, and slope for a field, county, or larger area, the modeling inputs are based on the same spatial scale as the precision farming data available. There are three challenges for developing an integrated model for sub-field variability of sustainable agricultural residue removal—the computational challenge of iteratively computing with 400 or more spatial points per hectare, the inclusion of geoprocessing tools, and the integration of data from different spatial scales. Using a representative field in Iowa, this paper demonstrates the computational algorithms used and establishes key design parameters for an innovative residue removal equipment design concept.

Changes in agricultural management strategies have received much attention in recent years with a view to increasing or maintaining the amount of carbon (C) sequestered as soil organic C (SOC). In many parts of the world, minimum or no‐till management has been promoted as a means of improving soil quality, reducing losses of erosion and potentially increasing SOC stocks. However, no‐till systems can become problematic and potentially disease‐prone, especially due to high crop residue loadings. Consequently, residue removal either by harvesting or burning off may be employed to reduce these pressures. Here, we examined the effect of crop residue removal on C storage in soil that had been under no‐till management for 20 yr. We predicted improved physical properties (i.e. lower bulk density) and greater microbial activity under the residue retention soils due to greater readily available C and nutrients derived from crop residues. In contrast, we predicted relative reductions in SOC in the no residue soils due to a lack of available residue‐derived C for microbial use. Residue removal caused a relative C loss from the soil, which was related to C input, amount of nutrient availability and microbial activity. We demonstrate the importance of maintaining crop residue cover in no‐till cropping systems for soil function and highlight the potentially deleterious effects of changing management strategy to increased residue harvesting or removal by burning.

Dedicated energy crops and crop residues will meet herbaceous feedstock demands for the new bioeconomy in the Central and Eastern USA. Perennial warm-season grasses and corn stover are well-suited to the eastern half of the USA and provide opportunities for expanding agricultural operations in the region. A suite of warm-season grasses and associated management practices have been developed by researchers from the Agricultural Research Service of the US Department of Agriculture (USDA) and collaborators associated with USDA Regional Biomass Research Centers. Second generation biofuel feedstocks provide an opportunity to increase the production of transportation fuels from recently fixed plant carbon rather than from fossil fuels. Although there is no “one-size-fits-all” bioenergy feedstock, crop residues like corn (Zea maysL.) stover are the most readily available bioenergy feedstocks. However, on marginally productive cropland, perennial grasses provide a feedstock supply while enhancing ecosystem services. Twenty-five years of research has demonstrated that perennial grasses like switchgrass (Panicum virgatumL.) are profitable and environmentally sustainable on marginally productive cropland in the western Corn Belt and Southeastern USA.

Climate, water and agriculture in the tropics: I. J. Jackson, Longman, London, 1977, xii + 248 pp., £3.75

Tillage intensive cropping practices have deteriorated soil physical quality and decreased soil organic carbon (SOC) levels in rice–growing areas of South Asia. Consequently, crop productivity has declined over the years demonstrating the need for sustainable alternatives. Given that, a field experiment was conducted for six years to assess the impact of four tillage based crop establishment treatments [puddled transplant rice followed by conventional tillage in wheat/maize (CTTPR–CT), non–puddled transplant rice followed by zero–tillage in wheat/maize (NPTPR–ZT), zero–till transplant rice followed by zero–tillage in wheat/maize (ZTTPR–ZT), zero–tillage direct seeded rice followed by zero–tillage in wheat/maize (ZTDSR–ZT)], two residue management treatments [residue removal, residue retention (~33%)], and two cropping systems [rice–wheat, rice–maize] on soil aggregation, carbon pools, nutrient availability, and crop productivity. After six years of rotation, in top 0.2 m soil depth, zero–till crop establishment treatments (ZTTPR–ZT and ZTDSR–ZT) had higher (p < 0.05) total organic carbon (TOC) over conventional tillage treatment (CTTPR–CT). Zero–till crop establishment treatments increased very–labile C faction (Cfrac1) by 21% followed by labile fraction (Cfrac2) (16%), non–labile fraction (Cfrac4) (13%) and less–labile fraction (Cfrac3) (7%). Notably, higher passive C–pool in conservation tillage practices over CTTPR–CT suggests that conservation tillage could stabilize the recalcitrant form of carbon that persists longer in the soil. Meantime, zero–till crop establishment treatments had higher (p < 0.05) water stable macro–aggregates, macro–aggregates: micro–aggregates ratio and aggregate carbon content over CTTPR–CT. The treatment NPTPR–ZT significantly increased soil quality parameters over CTTPR–CT. However, the effect was not as prominent as that of ZTTPR–ZT and ZTDSR–ZT. Retention of crop residue increased (p < 0.05) TOC (12%) and soil available nutrients mainly available–P (16%), followed by available–K (12%), DTPA–extractable Zn (11%), and available–S (6%) over residue removal treatment. The constructive changes in soil properties following conservation tillage and crop residue retention led to increased crop productivity over conventional CTTPR–CT. Therefore, conservation tillage (particularly ZTTPR–ZT and ZTDSR–ZT) and crop residue retention could be recommended in tropical rice–based cropping systems for improving soil quality and production sustainability.

In the investigation, the effect of variable crop residues and inorganic fertilizers on soil organic carbon (SOC) dynamics and its management indices was assessed in upland rice–lentil system. Treatments comprised of 4 levels of residue incorporation [residue removal, only rice residue (R), only lentil residue (L) and both rice + lentil (RL) residue] and 3 levels of fertilizer rate in lentil crop (0, 50, 100 % of RDF) fitted in split-plot design. After 7 years of continuous cropping, residue incorporation significantly (P ≤ 0.05) increased the very labile (Cfrac1), labile (Cfrac2) and less labile (Cfrac3) fractions of the total organic carbon (TOC) over residue removal, and the quantitative increase in C-fractions with residue incorporation followed the order Cfrac2 > Cfrac3 > Cfrac1 > Cfrac4. However, the enrichment in different C-fractions and TOC was almost similar to the incorporation of either rice (R) or lentil (L) residue. Likewise, incorporation of both crop residues (RL) marginally increased in TOC and its fractions over single crop residue (R or L), but failed to bring significant changes, which indicates lower C-stabilization rate of additional crop residues. Substantial depletion in all the C-fractions was observed with zero fertilization in rabi season lentil crop and greatly restricted the buildup of Cfrac1. The quality indicators like lability index and carbon management index were improved with residue incorporation and effect restricted to surface depth (0–0.20 m) only. Thus, the findings suggest incorporation of minimum one crop residue, and optimal recommended fertilization in rabi crop would be helpful in economically managing the SOC in rice–lentil rotation of subtropical India.

Core Ideas Cover crop generally had no effect on water infiltration, water retention, and available water after 5 and 6 yr. Corn residue removal reduced water infiltration, water retention, and available water after 5 and 6 yr. Cover crop partially mitigated the negative impacts of corn residue removal on soil hydraulic properties. Reductions in soil micropores and soil C concentration due to corn residue removal partly explained the reduction in plant‐available water. Large‐scale crop residue removal may negatively affect soil water dynamics. Integrating cover crop (CC) with crop residue management can be a strategy to offset potential adverse effects of residue removal. We studied: (i) the impact of corn (Zea mays L.) residue removal (56%) with and without the use of winter rye (Secale cereale L.) CC on soil hydraulic properties, (ii) whether CC would ameliorate residue removal effects on hydraulic properties, and (iii) relationships of hydraulic properties with soil organic C (SOC) and other properties under irrigated no‐till continuous corn on a silt loam in south central Nebraska after 5 and 6 yr of management. Cover crops did not affect soil hydraulic properties. However, residue removal reduced cumulative water infiltration by about 45% in one year. Across years, residue removal reduced plant available water (PAW) by 32% and mean weight diameter of water‐stable aggregates (MWD) by 23% for the upper 5‐cm soil depth. Under no CC, residue removal reduced SOC concentration by 25% in the 0‐ to 5‐cm and by 11% in the 5‐ to 10‐cm depths. Under residue removal, CC increased SOC concentration by 18% in the 0‐ to 5‐cm and by 8% in the 5 to 10‐cm depths. Cover crop did not completely offset the residue removal‐induced decrease in SOC concentration in the upper 5‐cm depth. Plant available water decreased as SOC concentration and MWD decreased. After 6 yr, corn residue removal adversely affected soil hydraulic properties and SOC concentration, but CC was unable to fully offset such adverse impacts.

Soil quality restoration and crop productivity maximization are the global challenge to feed the galloping population. The task is much more daunting in a risk-prone, fragile, and low productive hilly region due to the depletion of supporting and regulating ecosystem services. A five-year long-term (2012–2017) field experiment was conducted to stabilize the yield and soil quality through legume green manuring and crop residue recycling in intensified cropping systems in the Eastern Himalayan region of India. Four treatments involving three green manures [green gram (Vigna radiata); cowpea (Vigna unguiculata);Sesbania(Sesbania aculeata) along with control (no-green manure)], three cropping systems [groundnut (Arachis hypogaea)—pea (Pisum sativum); maize (Zea mays)—pea, and maize + groundnut–pea] and two levels of residue management practices [residue removal and residue retention] were evaluated in three times replicated split–split plot design. Among the green manure options,Sesbaniaexerted a significant positive impact on the soil organic carbon (SOC) stock, available micro- (Fe, Mn, Zn, and Cu), and macronutrients (N, P and K) in surface (0–0.15 m) and subsurface (0.15–0.45 m) soils. The improvement in soil enzymatic activities (acid phosphatase, alkaline phosphatase, dehydrogenase, beta-glucosidase, and aryl sulfatase activity) (p&amp;lt; 0.05) inSesbania-treated soil was +28.1% to +38.9% in surface and +18.3% to +27.3% in subsurface soils over non-green manure.Sesbania-treated soils also exhibited higher soil quality index (SQI) and stratification ratio (SR) of available soil nutrients and enzymes over non-green manured soils. Among the cropping systems, groundnut intercropped with maize followed by peas (MGP) within situresidue retention increased (p&amp;lt; 0.05) the available soil macro- and micronutrients, SOC stock, soil enzymes, SR, and SQI in comparison to other cropping systems.Sesbaniagreen manuring and residue retention improved the yield sustainability by +19% and +11% in the MGP system over non-green manuring and residue removal, respectively. Therefore,Sesbaniagreen manuring in the MGP cropping system along with residue retention is recommended for stabilizing the soil quality through enhancing supporting and regulating ecosystem services and maintaining long-term productivity in the fragile Eastern Himalayan ecosystem of India.

Crop residues are a potential source of renewable feedstocks for cellulosic ethanol production because of their high cellulose content and easy availability. Indiscriminate removal as biofuel may, however, have adverse impacts on soil, environment, and crop production. This article reviews available information on the impacts of crop residue removal on soil properties, crop yields, and soil erosion across a wide range of soils and ecosystems. It explicitly synthesizes data on the independent impacts of crop residue removal on soil and environment rather than on the interrelated tillage-crop-residue management impacts. Published literature shows that residue removal adversely impacts near-surface soil physical, chemical, and biological properties. Unmulched soils are prone to particle detachment, surface sealing, crusting, and compaction. Residue removal reduces input of organic binding agents essential to formation and stability of aggregates. It also closes open-ended biochannels by raindrop impacts and reduces water infiltration, saturated/unsaturated hydraulic conductivity, and air permeability, and thereby increases runoff/soil erosion and transport of non-point source pollutants (e.g., sediment and chemicals). Residue removal accelerates evaporation, increases diurnal fluctuations in soil temperature, and reduces input of organic matter needed to improve the soils' ability to retain water. It reduces macro- (e.g., K, P, N, Ca, and Mg) and micronutrient (e.g., Fe, Mn, B, Zn, and S) pools in the soil by removing nutrient-rich residue materials and by inducing losses of soil organic matter (SOM)-enriched sediments in runoff. Residue removal drastically reduces earthworm population and microbial carbon (C) and nitrogen (N) biomass. It adversely affects agronomic production by altering the dynamics of soil water and temperature regimes. The short-term ( < 10 yr) data show nevertheless that residue removal may not always degrade soil physical properties and decrease crop yields in the short term depending on the soil type, topography, and fluctuations in annual weather conditions. Sloping and erosion-prone soils are more rapidly and adversely affected by residue removal than those on flat terrains with heavy texture and poorly drained conditions. Sloping terrains are not only highly susceptible to water and wind erosion but also to tillage erosion. In these soils, therefore, a fraction of the total crop residue produced may be available for biofuel production and other expanded uses. Standard guidelines on when, where, and how much residues to remove need to be, however, established. Modeling rates of residue removal are presently based on the needs of soil cover to control erosion without consideration to maintaining SOM and nutrient pools, enhancing soil physical, chemical, and biological quality, and sustaining crop production. Threshold levels of residue removal must be assessed for principal soil types based on the needs to maintain or enhance soil productivity and improve environmental quality. For those soils in which some residues are removed, best management practices (e.g., cover crops, diverse crop rotations, and manure application) must be adopted to minimize adverse impacts of residue removal. Because indiscriminate harvesting of crop residues for biofuel may deteriorate soil properties, reduce crop yields, and degrade the environment, there exists an urgent research need for developing alternative sustainable renewable energy feedstocks (e.g., warm season grasses and short-rotation woody crops).

Sustainable agricultural residue removal for bioenergy: A spatially comprehensive US national assessment