Residue Return Research Articles

Post-harvest residue management effects on recalcitrant carbon pools and plant biomarkers within the soil heavy fraction in Pinus radiata plantations

Forest soils contain about 30% of terrestrial carbon (C) and so knowledge of the influence of forest management on stability of soil C pools is important for understanding the global C cycle. Here we present the changes of soil C pools in the 0–5 cm layer in two second-rotation Pinus radiata (D.Don) plantations which were subjected to three contrasting harvest residue management treatments in New Zealand. These treatments included whole-tree harvest plus forest floor removal (defined as forest floor removal hereafter), whole-tree, and stem-only harvest. Soil samples were collected 5, 10 and 15 years after tree planting at Kinleith Forest (on sandy loam soils) and 4, 12 and 20 years after tree planting at Woodhill Forest (on sandy soils). These soils were then physically divided into light (labile) and heavy (stable) pools based on density fractionation (1.70 g cm−3). At Woodhill, soil C mass in the heavy fraction was significantly greater in the whole-tree and stem-only harvest plots than the forest floor removal plots in all sampling years. At Kinleith, the soil C mass in the heavy fraction was also greater in the stem-only harvest plots than the forest floor removal plots at year 15. The larger stable soil C pools with increased residue return was supported by analyses of the chemical composition and plant biomarkers in the soil organic matter (SOM) heavy fractions using NMR and GC/MS. At Woodhill, alkyl C, cutin-, suberin- and lignin-derived C contents in the SOM heavy fraction were significantly greater in the whole-tree and stem-only harvest plots than in the forest floor removal plots in all sampling years. At Kinleith, alkyl C (year 15), cutin-derived C (year 5 and 15) and lignin-derived C (Year 5 and 10) contents in the SOM heavy fraction were significantly greater in stem-only harvest plots than in plots where the forest floor was removed. The analyses of plant C biomarkers and soil δ13C in the light and heavy fractions of SOM indicate that the increased stable soil C in the heavy fraction with increased residue return might be derived from a greater input of recalcitrant C in the residue substrate.

Activity and Composition of Ammonia-Oxidizing Bacteria in an Aquic Brown Soil as Influenced by Land Use and Fertilization

The effects of long-term (19 years) different land use and fertilization on activity and composition of ammonia-oxidizing bacteria (AOB) in an aquic brown soil were investigated in a field experiment in Liaoning Province, China. The 19-year experiment conducted from 1990 to 2008 involved seven treatments designed: cropping rotation of soybean-corn-corn with no fertilizer (control, CK), recycled manure (RM), fertilizer nitrogen (N), phosphorous (P) and potassium (K) (NPK), NPK+RM, and no-crop bare land, mowed fallow, and non-mowed fallow. The results showed that the potential nitrification rates of the RM, NPK+RM, mowed fallow, and non-mowed fallow treatments were significantly higher ( P < 0.05) than those of the CK and NPK treatments, indicating that the long-term applications of recycled manure and return of plant residues both significantly increased the activity of AOB. Although the application of NPK did not enhance soil potential nitrification because of decreased pH, available K had an important effect on potential nitrification. Denaturing gradient gel electrophoresis (DGGE) fingerprint profiles showed that no-crop treatments had an increase in the diversity of the AOB community compared to the CK, RM, and NPK treatments, implying that agricultural practices, especially tillage, had an adverse effect on the soil AOB community. The NPK+RM treatment had the most diverse DGGE patterns possibly because of the increased available P in this treatment. A phylogenetic analysis showed that most of the DGGE bands derived belonged to Nitrosospira cluster 3, not Nitrosospira cluster 2. These demonstrated that different land use and fertilization significantly influenced the activity and composition of the AOB community by altering the soil properties, mainly including pH, total C, available K, and available P.

Grain yield and crop N offtake in response to residual fertilizer N in long-term field experiments

Organic inputs [e.g. animal manure (AM) and plant residues] contribute directly to the soil organic N pool, whereas mineral N fertilizer contributes indirectly by increasing the return of the crop residues and by microbial immobilization. To evaluate the residual effect of N treatments established in four long-term (> 35 yr) field experiments, we measured the response of barley (grain yield and N offtake at crop maturity) to six rates (0, 30, 60, 90, 120 and 150 kg N/ha) of mineral fertilizer N (N new ) applied in subplots replacing the customary long-term plot treatments of fertilizer inputs (N prev ). Rates of Np rev above 50-100 kg N/ha had no consistent effect on the soil N content, but this was up to 20% greater than that in unfertilized treatments. Long-term unfertilized plots should not be used as control to test the residual value of N in modern agriculture with large production potentials. Although the effect of mineral N prev on grain yield and N offtake could be substituted by N new within a range of previous inputs, the value of Np rev was not eliminated irrespective of N new rate. Provided a sufficient supply of plant nutrients other than N, the use-efficiency of N new did not change significantly with previous mineral N fertilizer rate. The residual effect of mineral N fertilizer was negligible compared with the residual effect of N from AM and catch crop residues.

Dryland residue and soil organic matter as influenced by tillage, crop rotation, and cultural practice

Novel management practices are needed to increase dryland soil organic matter and crop yields that have been declining due to long-term conventional tillage with spring wheat (Triticum aestivum L.)-fallow system in the northern Great Plains, USA. The effects of tillage, crop rotation, and cultural practice were evaluated on dryland crop biomass (stems + leaves) yield, surface residue, and soil organic C (SOC) and total N (STN) at the 0–20 cm depth in a Williams loam (fine-loamy, mixed, superactive, frigid, Typic Argiustolls) from 2004 to 2007 in eastern Montana, USA. Treatments were two tillage practices [no-tillage (NT) and conventional tillage (CT)], four crop rotations [continuous spring wheat (CW), spring wheat-pea (Pisum sativum L.) (W-P), spring wheat-barley (Hordeum vulgaris L.) hay-pea (W-B-P), and spring wheat-barley hay-corn (Zea mays L.)-pea (W-B-C-P)], and two cultural practices [regular (conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height) and ecological (variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height)]. Crop biomass and N content were 4 to 44% greater in W-B-C-P than in CW in 2004 and 2005 and greater in ecological than in regular cultural practice in CT. Soil surface residue amount and C and N contents were greater in NT than in CT, greater in CW, W-P, and W-B-C-P than in W-B-P, and greater in 2006 and 2007 than in 2004 and 2005. The SOC and STN concentrations at 0–5 cm were 4 to 6% greater in CW than in W-P or W-B-P in NT and CT from 2005 and 2007. In 2007, SOC content at 10–20 cm was greater in W-P and W-B-P than in W-B-C-P in CT but STN was greater in W-B-P and W-B-C-P than in CW in NT. From 2004 to 2007, SOC and STN concentrations varied at 0–5 cm but increased at 5–20 cm. Diversified crop rotation and delayed planting with higher seed rates and banded N fertilization increased the amount of crop biomass returned to the soil and surface residue C and N. Although no-tillage increased surface residue C and N, continuous nonlegume cropping increased soil C and N levels at the surface layer compared with other crop rotations. Continued return of crop residue from 2004 to 2007 may increase soil C and N levels but long-term studies are needed to better evaluate the effect of management practices on soil C and N levels under dryland cropping systems in the northern Great Plains.

Life-Cycle Implications of Using Crop Residues for Various Energy Demands in China

Crop residues are a critical component of the sustainable energy and natural resource strategy within a country. In this study, we use hybrid life-cycle environmental and economic analyses to evaluate and compare the atmospheric chemical, climatic, ecological, and economic issues associated with a set of energy conversion technologies that use crop residues for various energy demands in China. Our analysis combines conventional process-based life cycle assessment with economic input-output life cycle assessment. The results show that the return of crop residues to the fields, silo/amination and anaerobic digestion (household scale) offer the greatest ecological benefits, with net greenhouse gas reduction costs of US$3.1/tC, US$11.5/tC, and US$14.9/tC, respectively. However, if a positive net income for market-oriented operations is the overriding criterion for technology selection, the cofiring of crop residues with coal and crop residue gasification for power generation offer greater economic scope and technical feasibility, with net incomes of US$4.4/Mg and US$4.9/Mg, respectively. We identify that poor economies of scale and the absence of key technologies mean that enterprises that use pure combustion for power generation (US$212/tC), gasification for heat generation (US$366/tC) and large-scale anaerobic digestion for power generation (US$169/tC) or heat generation (US$206/tC) are all prone to operational deficits. In the near term, the Chinese government should also be cautious about any large-scale investment in bioethanol derived from crop residues because, with a carbon price of as high as US$748/tC, bioethanol is the most expensive of all energy conversion technologies in China.

Long-Term Effects of Tillage and Manure Applications on Soil Phosphorus Fractions

Application of manure on the basis of crop nitrogen (N) need increases the level of soil phosphorus (P), which is concern for deterioration of surface water quality. Soil samples were collected from a long-term field study to investigate the impact of crop N need–based manure application on soil P fractions and P adsorption and release kinetics. The field experiment was initiated in 1990. The soil was moderately well-drained Kennebec (fine silty, mixed, mesic Cumulic Hapludolls). No-tillage (NT) and conventional-tillage (CT) treatments were established in main plots, and subplots had five N treatments, including a control, and annual application of 84 or 168 kg N ha−1 applied as ammonium nitrate (NH4NO3) or beef (Bos taurus) manure. Manure at the high N application rate had significantly greater Bray 1 P under NT than under CT at 0- to 5-cm soil depth. Nitrogen fertilizer treatments were not significantly different than the control for Bray 1 P. Continuous application of manure at the high N rate significantly increased all Hedley P fractions; however, the major increase was observed in high bioavailable P pools [iron oxide (FeO) P and sodium bicarbonate (NaHCO3) Pi] and hydrochloric acid (HCl) P fractions. Soil organic P (Po) pools, including both labile (NaHCO3-Po) and resistant [sodium hydroxide (NaOH) Po], were increased by application of N from any source, suggesting biomass production and return of residue to soil surface was the responsible factor. Continuous application of manure based on N need also significantly increased FeO-P, NaHCO3-Pi, and HCl-P fractions at lower soil depths (5–15 and 15–30 cm). Results from the P-adsorption study suggest that ability of soil to adsorb additional P was decreased by manure application and that EPC0 was increased. Maximum desorbable P was observed for manure treatments under NT, although the release constant k (h−1) was significantly less than with fertilizer N treatments.

Effects of fungal residues return on soil enzymatic activities and fertility dynamics in a paddy soil under a rice-wheat rotation in Chengdu Plain

In the Peoples Republic of China, more than 4 Mt of fungal residues needs to be treated yearly. To investigate the effect of Agaricus bisporus residues return on soil fertility, this study compared the effects of five treatments on soil nutrients, soil enzymatic activities, N use efficiency and crop yields in a paddy soil under a rice-wheat rotation. Five treatments were designed including application of chemical fertilizer only (CF), a combined application of 30% fungal residues and 70% chemical fertilizer with the ratio of total N in the fungal residues to that in CF being 0.3:1 (30%FR), a combined application of 70% fungal residues and 30% chemical fertilizer with the ratio of total N in the fungal residues to that in CF being 0.7:1 (70%FR), a full dose of fungal residues return only with the ratio of total N in fungal residues to that in CF being 1:1 (100%FR), and a full return of fungal residues only with the ratio of total N in fungal residues to that in CF being 1.5:1 (150%FR). We found that the content of soil nutrients and soil enzymatic activities in the same treatment were higher at VGS (vegetative growth stage) than at RGS (reproductive growth stage) in rice and wheat seasons. 100%FR and 150%FR treatments had higher level of soil organic matter, available N, P, K, invertase, urease, neutral-phosphatase, catalase, N use efficiency and crop yields than CF treatment. These results indicated that A. bisporus residues return could positively affect soil nutrients, soil enzymatic activities, N use efficiency and crop yields as organic manure in a paddy soil. The information obtained will be helpful to more rational utilization of fungal residues.

Simulating Soil Organic Carbon Dynamics with Residue Removal Using the CQESTR Model

Concerns about CO2 emissions and fossil fuel supplies have enhanced interest in using crop residues for biofuel production; however, maintaining soil organic C (SOC) through residue return is vital for maintaining soil productivity. Our objectives were to simulate long‐term SOC dynamics using CQESTR and to examine the effect of residue harvest on SOC stocks under disking (DT) and conservation tillage (CS). A long‐term study in the mid‐Coastal Plain region of South Carolina was used to simulate four residue harvest rates (0, 50, 66, and 90%) during two harvest periods. The yearly variation of SOC was predicted well (r2 = 0.84, P &lt; 0.0001). Without residue removal, average increases of 0.10 and 0.39 g SOC kg−1 yr−1 were predicted under DT and CS, respectively, consistent with observed increases of 0.12 and 0.44 g SOC kg−1 yr−1 After 23 yr, simulated SOC stock gain was more than threefold greater under CS than DT (9.0 vs. 2.4 g SOC kg−1). The model predicted 1.86 and 4.47 g SOC kg−1 losses in the top 5 cm of soil under DT and CS, respectively, during 23 yr of 66% residue harvest compared with no residue harvest. The predicted SOC stocks under CS were ∼5 g SOC kg−1 greater than under DT, however, even with 90% residue harvest. The quantities of crop residue that can be sustainably harvested were directly influenced by the initial SOC concentration and tillage practices. While CS can somewhat mitigate the loss of soil C, residue harvest from loamy sand soils may have an adverse impact on SOC stocks.

Tillage and Residue Removal Effects on Soil Carbon and Nitrogen Storage in the North China Plain

Little information is available about their influences of conservation tillage on the distribution and storage of soil organic C (SOC) and total N in soil profiles in the North China Plain. We investigated the changes in SOC and total N as related to the shift from conventional to conservation tillage using a long‐term field experiment with a winter wheat (Triticum aestivum L.)–corn (Zea mays L.) double cropping system. The experiment included four tillage treatments for winter wheat: moldboard plow without corn residue return (MP−R), moldboard plow with corn residue return (MP+R), rotary tillage (RT), and no‐till (NT). Compared with the MP−R treatment, returning crop residue to the soil (MP+R, RT, and NT) increased SOC and total N in the 0‐ to 30‐cm soil layer, but no distinct changes in SOC and total N concentration were observed among the four treatments at soil depths &gt;30 cm. Compared with the MP+R treatment, the RT and NT treatments increased SOC and total N concentration significantly in the 0‐ to 10‐cm layer but decreased SOC and total N concentration in the 10‐ to 20‐cm layers. As a consequence, soil profile SOC and total N storage did not vary among the MP+R, RT, and NT treatments. Thus under the experimental conditions, conservation tillage (RT and NT) increased SOC and total N contents in the upper soil layers, but did not increase SOC and total N storage over conventional tillage (MP+R) in the soil profile.

New agricultural practices in the Loess Plateau of China do not reduce colonisation by arbuscular mycorrhizal or root invading fungi and do not carry a yield penalty

Agricultural practices aimed to reduce soil erosion and improve crop yield have been suggested to influence the activity of arbuscular mycorrhizal (AM) and root pathogenic fungi. We conducted a two-year field survey to investigate the effect of recently introduced agricultural practices on crop yield, AM colonisation and percentage isolation of root-invading fungi on the heavily eroded Loess Plateau of China. A rotation of maize (Zea mays L.), winter wheat (Triticum aestivum L.) and soybean (Glycine max L.) replaced monoculture of winter wheat. No-tillage (NT), and return of previous crop residues to the field in tilled (CTR) and non-tilled (NTR) systems replaced conventional tillage (CT). Yield, biomass and phosphorus content of the crops showed similar trends. Residue application increased yields of maize and soybean independent of tillage treatment in 2004, but only under CT in 2005. CT slightly increased maize yield. Neither residue application nor tillage treatment affected yield of wheat. None of the treatments influenced total percent isolation of root-invading fungi from wheat roots. The increase of some individual pathogenic fungi in NT did not translate into reduction of yield by disease. Importantly, the recommended practices did not have a penalty on yield while maintaining high levels of AM colonisation.

Specific transport and storage solutions for residues return programmes

AbstractThe treatment of used nuclear fuel, performed at AREVA's La Hague plant, allows recovering uranium 95% and plutonium 1% for recycling, the remaining 4% being considered as ultimate waste that can be sorted into two categories: high level activity waste (HLW) which is vitrified, and long-lived intermediate level waste (ILW) composed of structural elements of used nuclear fuel which is compacted. Whether vitrified or compacted, the waste is conditioned in the same universal and multipurpose container, named the Universal Canister. The resulting residue is named CSD-V for vitrified waste and CSD-C for compacted waste; they both remain property of the utilities and must be returned to countries of origin. In order to transport Universal Canisters in the best technical and economical conditions, TN International designs two kinds of cask solutions for its customers, either for transport only or for dual purpose, storage and transport, depending on the facility. Since the mid-1990s, TN International has...

Spatial variability of soil organic C and total N in a small catchment of the Loess Plateau, China

Data from the Donggou small catchment, located in a typical wind-water erosion crisscross zone on the Loess Plateau of China, illustrate the spatial variability of soil organic carbon (SOC) and total nitrogen (STN) for the 0–0.10 m, 0.10–0.20 m and 0.20–0.40 m soil depths. Statistical analysis revealed that SOC and STN presented moderate spatial variability in the small catchment, and varied with land use. The SOC and STN contents and variations were also influenced by the five land use patterns in a complex manner. Geostatistical analysis showed that Gaussian models were the best fitting descriptors for these SOC and STN data set. The nugget-to-sill ratio ranged from 39.4–56.3% for SOC semivariograms, and 42.6–59.0% for STN semivariograms, indicating moderate spatial dependence at the three soil depths. Regression analysis indicated that land uses, topographic variables, and soil texture accounted for approximately 57.3% of the SOC variability and 70.1% of the STN variability for the 0–0.10 m soil layer. All regression models were reasonable enough to predict SOC and STN in similar loess areas. It was proposed that creating a mosaic pattern to increase spatial variation of areas by land use arrangement would be an effective management strategy to trap soil nutrients to stay in the ecosystem. Our data also suggested that more C input such as manure addition and crop residues return, and alternative cultivation practices such as application of contour cultivation and building terraces for soil erosion control would improve SOC and nutrients on the hilly areas similar to the Loess Plateau of China.

Effects of reduced tillage, crop residue management and manure application practices on crop yields and soil carbon sequestration on an Andisol in northern Japan

Soil carbon sequestration in agricultural lands has been deemed a sustainable option to mitigate rising atmospheric CO2 levels. In this context, the effects of different tillage and C input management (residue management and manure application) practices on crop yields, residue C and annual changes in total soil organic C (SOC) (0–30 cm depth) were investigated over one cycle of a 4-year crop rotation (2003–2006) on a cropped Andisol in northern Japan. For tillage practices, the effects of reduced tillage (no deep plowing, a single shallow harrowing for seedbed preparation [RT]) and conventional deep moldboard plow tillage (CT) were compared. The combination of RT, residue return and manure application (20 Mg ha−1 in each year) increased spring wheat and potato yields significantly; however, soybean and sugar beet yields were not influenced by tillage practices. For all crops studied, manure application enhanced the production of above-ground residue C. Thus, manure application served not only as a direct input of C to the soil, but the greater crop biomass production engendered enhanced subsequent C inputs to the soil from residues. The SOC contents in both the 0–5 cm and 5–10 cm layers of the soil profile were greater under RT than under CT treatments because the crop residue and manure were densely incorporated into the shallow soil layers. Comparatively, neither tillage nor C input management practices had significant effects on annual changes in SOC content in either the 10–20 cm or 20–30 cm layers of the soil profile. When soil C sequestration rates, as represented by annual changes in total SOC (0–30 cm), were assessed on a total soil mass basis, an anova showed that tillage practices had no significant effect on total C sequestration, but C input management practices had significant positive effects (P ≤ 0.05). These results indicate that continuous C input to the soil through crop residue return and manure application is a crucial practice for enhancing crop yields and soil C sequestration in the Andisol region of northern Japan.

Effectiveness and Efficacy of Conservation Options after Potato Harvest

Soil erosion and phosphorus (P) runoff can be severe in potato production systems in the Northeast USA, which are characterized by intensive tillage, minimal ground cover, low crop residue return, and steep slopes. We used rainfall simulators in the greenhouse and field to assess sediment and P movement associated with two conservation practices: straw mulching and application of polyacrylamide (PAM). In the greenhouse, a Nokomis sandy loam soil (fine-loamy, mixed, frigid Typic Haplorthods) was packed into 0.2 by 1.0 m boxes and subjected to four rainfall events at an intensity of 70 mm h(-1). Runoff amount, sediment concentration, and inorganic and sediment-bound P were measured for 30 min after initiation of runoff. Linear increases in straw mulch biomass (up to equivalent of 3000 kg ha(-1)) resulted in exponential decreases in sediment and P loss. Mulch applied at rates as low as 600 kg ha(-1) provided nearly 50% ground cover and reduced sediment movement and sediment-bound P concentration and loss by >50%. Higher application rates reduced sediment loss by up to 95% but contributed dissolved reactive P (DRP) to runoff water. Field observations using simulated rainfall on mulch-covered and bare soil were consistent with greenhouse results. Linear increases in PAM application rate (to 20 kg ha(-1)) also reduced sediment loss. The efficacy of this practice decreases slightly with successive rainfall events but still had significant benefit through four simulated rainfalls on soil packed into boxes. This was not the case in the field where the effect of PAM was limited to the first two rainfall events. In general, runoff volume was not strongly influenced by any of these practices, and most of the P loss was comprised of sediment-bound P. Both conservation practices are effective at reducing soil and nutrient loss in intensive potato systems.

White lupine as a beneficial crop in Southern Europe: I. Potential for N mineralization in lupine amended soil and yield and N 2 fixation by white lupine

Two experiments were carried out at Pegões (central Portugal) to determine the potential N mineralization in a pulse amended disturbed and undisturbed soil incubated at several temperatures, and to evaluate for 2 years the yield and N 2 fixation capacity of sweet lupine ( Lupinus albus L. cv. Estoril) inoculated with a mixture of rhizobia strains or nodulated by indigenous soil bacteria and submitted to conventional tillage or no-till practices. A completely randomized block design for soil mobilization with three replicates was used for the laboratory study, and completely randomized blocks for inoculation and tillage treatments with four replicates were used for the lupine yield and N 2 fixation experiment. Residue N immobilization occurred immediately after mature residue return to the soil independent of temperature, and was greater at 7 °C especially in the disturbed topsoil. Greater immobilization was also observed by doubling the amount of mature residue incorporated in the soil. This was expected since soil microorganisms would be in direct contact with the fresh organic matter and would be provided with more organic carbon under these circumstances. Nitrogen mineralization proceeded after 5 days of amendment. Potential N mineralization was higher at 25 °C than at 18 or 7 °C, for both conventional and no-till practices. At 25 °C, 42% of buried residue- 15N was released over 210 days, at a smaller rate than 18 °C (49%) over 81 days. Lupine yield and N 2 fixation capacity were similar in plots that were not inoculated and those receiving the mixture of three rhizobia strains. White lupine had an efficient symbiosis with indigenous soil rhizobia at pod-filling (>99%, >100 kg N ha −1 year −1) which was not affected by tillage. At this stage, plant residue including visible roots and nodules accounted for a soil N input of +96 kg ha −1 year −1 (91% of crop N), showing the large soil N benefit by the crop at this stage. The lupine residue at pod-filling stage can be used as a green manure under the conditions of organic farming systems. The apparent N “harvest” index of the pulse at pod-filling was only 9% though at maturity phase it should result in a higher value and the legume will show a lower fertilizer N value.

Effects of Wheat Residue Application and Site-Specific Nitrogen Management on Growth and Development in Direct-Seeding Rice

The objective of this study was to investigate the growth and development of rice ( Oryza sativa L.) under the treatments of wheat ( Triticum aestivum L.) residue incorporation (RI) and nitrogen (N) fertilizer application. A mid-season japonica rice cultivar Yangjing 9538 was directly sown in field. Either in RI treatment or in the treatment with no residue return to field (R0), 3 nitrogen (N) fertilizer application levels were carried out, i.e., no N application, farmers' fertilizer practice (FFP), and site-specific N management (SSNM). The SSNM was based on chlorophyll meter readings in field. Compared with FFP, SSNM reduced N application by 30.0–31.3% and increased grain yield by 7.61% on an average. The average grain yield was 2.65% higher in the RI treatment than in the R0 treatment. Compared with the R0 or FFP treatment, the RI or SSNM treatment decreased stem and tiller numbers, leaf area index, and biomass accumulation at early growing period, but the differences were not significant after heading stage. RI was favorable for increasing the content of organic acid in leaves and enlarging the variations of temperature and relative humidity between day and night. The RI and SSNM treatments had positive effects on the percentage of productive tillers, photosynthetic rate of flag leaf, root activity, and ATPase activity during grain-filling stage.

Carbon, nitrogen and phosphorus mineralization potential of semiarid Sahelian soils amended with native shrub residues

Two native shrubs ( Piliostigma reticulatum and Guiera senegalensis) commonly coexist with crops in fields throughout the Sahel but aboveground residue is annually coppiced and burned. An alternative, with potential to improve soil quality, would be non-thermal return of residues to soils but information is needed on the potential of residues’ to provide nutrients before such systems can be adopted. The objective of this research was to characterize carbon (C), net nitrogen (N) and phosphorus (P) mineralization of shrub residues during decomposition in soil beneath or outside shrub canopies. Two lab incubation (30 °C for 118 days) studies (1 for each shrub species/soil type system) had a 2 by 4 factorial design with two soil sources (beneath or outside the shrub canopy) and four residue soil amendments (leaf, leaf + stem, beef manure, or control of soil only). Soils amended with P. reticulatum or G. senegalensis leaf residues immobilized N during the first 62 and 76 days, respectively, but later had net release of inorganic N. The addition of stems to leaf amendments for both shrub species resulted in net N immobilization throughout the incubation. Manure had positive but shrub residues negative release of inorganic P. However, if the leached P released at time zero is included in the summation, all amendments released more P than the control. Cumulative net release of C, N or P over the incubation was higher in soil originating from beneath than outside the shrub canopy except for release of P from soil associated with G. senegalensis. Residue chemistry was related to nutrient release, particularly high lignin content of stems, which corresponded to N immobilization. Our results suggest that none of the shrub residues when added to soil would potentially provide short-term plant available N and that additional fertilizer would be required for optimal crop yield.

Soil organic matter dynamics and losses in manured maize-based forage systems

Soil organic matter (SOM) produces positive effects on multiple soil properties. Increasing its level also provides an opportunity to reduce atmospheric concentration of carbon dioxide (CO 2). Recycling animal manure and returning crop residue are among the main practices to enhance organic carbon (C) stock in arable croplands. This study analysed data of soil organic carbon (SOC) stocks from a medium-term field trial (established in 1992) through a Hénin–Dupuis-based equation to determine the proportion of different organic materials retained in the soil as SOM. The treatments included in the experiment simulated different typical management techniques and implied the application to the soil of various organic materials, i.e. cattle slurry, cattle farmyard manure, maize straw, root, maize and ley stubble. Soil organic carbon and total nitrogen (N) (Kjeldhal N) were measured in the 0–30 cm layer during spring 1999 and spring 2003. The relationship between SOC and N stocks measured in 1999 and 2003 and the annual additions of C and N was described by the Hénin–Dupuis-based equation, assuming the presence of two C and N pools (stable and fresh). Our results showed that the application of farmyard manure, slurry and maize straw induced higher C and N content compared to the application of urea without return of crop residue. The different levels of urea application did not produce any significant difference in C and N soil content. We found that approximately 2% of SOC is lost to the atmosphere annually. Furthermore, the amount of C and N retained in the soil each year varied by organic materials: 46% C and 44% N with farmyard manure, 26% C and 11% N with slurry, 28% C and 10% N with root and 6% C with maize straw and ley stubble. These results were used to inform an estimate of C lost or removed to/from atmosphere following manure application and crop residue return for the compilation of greenhouse gas inventories. We found that the most C conservative management is the production and spreading of farmyard manure and that increasing amounts of mineral N fertilizer did not affect the C sequestration extent.

Effect of crop‐residue management on the production and agronomic nitrogen efficiency in a rice–wheat cropping system

AbstractThe rice–wheat cropping system (RWCS), producing about 5–10 Mg ha–1 y–1 of grain, is the backbone of food‐crop production in South‐East Asia. However, this system shows signs of fatigue as indicated by declining yields, negative nitrogen (N) balances, and reduced responses to applied fertilizer at some research centers. The return of rice and wheat residues can recycle up to 20%–30% of the N absorbed by the crops. However, their wide C : N ratio can temporarily immobilize native and applied N. To overcome this immobilization, wheat‐straw application was supplemented with the incorporation of Sesbania green manure and mungbean residues, and their effects on productivity, agronomic N efficiency, and system's apparent N balances were studied. Combining the application of wheat straw with Sesbania green manure or mungbean residues increased cereal grain yield and agronomic N efficiency and improved the generally negative apparent N balances. The combined use of wheat straw and mungbean produced an additional 0.5–0.6 t ha–1 protein‐rich grain and thus appears to be the most promising residue‐management option for rice–wheat cropping systems in South Asia, provided that the transition cropping season between wheat harvest and rice transplanting is long enough.

Biogenic greenhouse gas emissions linked to the life cycles of biodiesel derived from European rapeseed and Brazilian soybeans

Biogenic emissions of carbonaceous greenhouse gases and N 2O turn out to be important determinants of life cycle emissions of greenhouse gases linked to the life cycle of biodiesel from European rapeseed and Brazilian soybeans. For biodiesel from European rapeseed and for biodiesel from Brazilian soybeans grown for up to 25 years with no tillage on arable soil for which tropical rainforest or Cerrado (savannah) have been cleared, the life cycle emissions of greenhouse gases are estimated to be worse than for conventional diesel. Improving agricultural practices should be an important focus for cleaner production of biodiesel. These may include increasing soil carbon stocks by, e.g., conservation tillage and return of harvest residues and improving N-efficiency by precision agriculture and/or improved irrigation practices.