Residue Management Strategies Research Articles

Carbon dioxide flux and soil carbon stock as affected by crop residue management and soil texture in semi‐arid maize croplands in Tanzania

AbstractCrop residue management strategies must be adapted for improving carbon (C) balance and soil C stock in agroecosystems in sub‐Saharan Africa with consideration of the crop residue availability and site‐specific soil characteristics. We conducted field experiments to determine the effects of crop residue application method (incorporation/mulching) and quality (maize/cowpea) and N fertilizer application on the soil respiration rate and soil C stock in the surface soil layer (0–15 cm) in maize croplands with contrasting soil textures (clay/sandy) over 2 years from 2012 to 2014 in Tanzania. At the clay site, the incorporation of maize residues showed a 38% increase in CO2 flux compared to mulching, whereas, at the sandy site, mulching showed a 16% increase compared to the incorporation. At the sandy site, mulching practice retained soil moisture content and apparently enhanced the decomposition of the original soil organic C in the surface layer. It is, therefore, suggested that mulching practice may accelerate a long‐term depletion of soil C stock at the sandy site. The cowpea residue incorporation led to rapid decomposition because of its high biodegradability at both sites. The N fertilizer application stimulated the decomposition of labile soil organic matter. The soil C stock in the surface layer did not significantly change after the 2‐year experiment, irrespective of crop residue treatment and soil type. In conclusion, adequate crop residue management in terms of suppressing CO2 flux during a cropping season depends on soil type, but the long‐term effect on soil C stock is unclear.

Residue and Potassium Management Strategies to Improve Crop Productivity, Potassium Mobilization, and Assimilation under Zero-Till Maize–Wheat Cropping System

Understanding of the potassium (K) nutrient cycle and its microbial transformation of unavailable forms of soil K to plant-available K is crucial in any agroecosystem for strategic nutrient management through inorganic fertilizer, crop residue (CR), and microbial applications. Therefore, the present investigation was undertaken to study the effect of crop residue and K management practices on crop productivity, K mobilization from native soil K-pool, and crop assimilation of K under a zero-till maize–wheat cropping system. The experiment consisted of four residue levels (0, 2, 4, and 6 Mg ha−1) and five K levels (0, 50%, 100%, 150% RDK [recommended dose of K] and 50% RDK + potassium solubilizing bacteria, KSB). Results showed that CR retention at 6.0 Mg ha−1 significantly improved grain yield (of maize by 10.17%; wheat by 9.87%), dry matter accumulation, K uptake and redistribution in native soil K pools (water soluble K (WSK), exchangeable K (EK) and non-exchangeable K (NEK)) at 30 and 60 days after sowing and at harvest as compared to no CR. Among the K management, 50% RDK+KSB reported significantly higher grain yield (of maize by 26.22%; wheat by 24.70%), dry matter accumulation, K uptake, and native K pools (WSK, EK, and NEK) at different growth stages compared to no K. Total K did not differ significantly due to residue and K management. The highest actual change of K reported with 6.0 Mg ha−1 CR (51 kg ha−1) and 50% RDK+KSB (59 kg ha−1) over control. Significant (p ≤ 0.01) positive correlation was found among grain yield, dry matter accumulation, K uptake, the actual change in K and different native K pools. It can be concluded that retention of 6 Mg ha−1 CR and supply of 50% K through inorganic fertilizer along with seed inoculation of KSB biofertilizers, improved crop growth, productivity by enhancing K assimilation as a consequence of the release of non-exchangeable K and through the application of CR and K treatments under a zero tillage maize–wheat system.

Improving soil properties and grains yield of winter wheat and summer corn under residue management strategies

AbstractIn this study, a 6‐year field experiment was conducted to explore the effects of different amounts of corn stover returned to the field on soil properties and grain yield of double‐cropped of winter wheat and summer maize. A randomized block design with three replications was employed including three treatments: based on all stalks of winter wheat returned to the field, (1) all summer maize stalks were mechanically pulverized and returned to the field (SR); (2) a half of summer maize stalks were mechanically pulverized and returned to the field (1/2 SR); and (3) all summer maize stalks were fully removed (control; CK). Compared with CK, the yield of summer maize and winter wheat were increased in both SR and 1/2SR. The total soil porosity, water‐stable aggregate content, and organic matter content were significantly higher in both SR and 1/2SR treatments than those in CK. The total P and available K were increased in both SR and 1/2SR, compared with those in CK. However, differences in soil properties and grain yield were not significant between SR and 1/2SR. These results indicated that corn stover returned to the field could significantly improve soil properties and yield. It can maintain soil sustainability and provide a high‐quality soil environment through treatment of 1/2SR, and the efficient use of straw can be achieved by using the remaining half of the straw for biomass energy. Overall, our data provided a basis for the use of stover resources to keep a sustainable soil production capacity.

Energy and carbon footprints of wheat establishment following different rice residue management strategies vis-à-vis conventional tillage coupled with rice residue burning in north-western India

Energy and carbon (C) footprints have close nexus in agriculture. Agri-inputs are energy intensive and lead to significant C equivalent (CE) emissions. We studied energy and C footprints during wheat establishment following different rice residue management (RRM) strategies: residue retention with Happy Seeder (HS); removal after bailing + zero till drill (ZT); incorporation with rotavator tillage + drill (RT) and mould board plough tillage + drill (MBP) vis-à-vis burning + conventional tillage + drill (CT)to identify options for balancing energy, C footprints and C sequestration. Total energy input (EI) with residue retention was significantly (p < 0.05) lower by 1540.9–3884.5 MJ ha−1 (5.9–13.8%) than residue removal/burning. Although, energy output (EO) was significantly lower with residue retention/removal, yet energy productivity (EP) did not differ significantly. Total CE emissions were highest in CT and lowest in ZT. Fertilizer-N was the major hotspot of energy (37.5–45.2% of EI) and C footprints (53.6–87.9% of total CE emissions). As compared to CT, residue retention offers reduction in C and energy footprints ∼14.1 and 12.9%, respectively. Results reveal that rice residue burning is not a viable option as it leaves high C footprints and lowers the amount of C added to soil organic C pool and C sustainability.

Effects of residue management strategies on greenhouse gases and yield under double cropping of winter wheat and summer maize

The North China Plain (NCP) is typically cropped using a winter wheat–summer maize double cropping system, which has huge potential for straw production. The region also experiences atmospheric pollution caused by straw burning, which has become an important contributor to global warming. The goals of this experiment were to resolve the conflict between soil fertility and greenhouse gas emission when using straw return to the field and to identify the best balance between environmental protection and agricultural production. A randomized block design with three replicates was used. The design included three treatments based on the return of all winter wheat stalks to the field: (1) all summer maize stalks were pulverized mechanically and returned to the field (SR); (2) half of the summer maize stalks were pulverized mechanically and returned to the field (1/2 SR); and (3) all summer maize stalks were fully removed (control: CK). This long-term test was performed for 6 years. Straw returned to the field significantly increased greenhouse gas emissions. The cumulative CO2 emissions were higher by 32% under SR and by 17% under 1/2 SR compared with CK. The cumulative N2O emissions were higher by 28% under SR and 15% under 1/2 SR compared with CK. The greenhouse gas efflux increased with increased amounts of straw returned to the field. Compared with SR, 1/2 SR significantly reduced greenhouse gas emissions, while still ensuring sustainable soil fertility. Additionally, our research showed that the upper part of the corn stalk is better for generating biomass energy than the lower part. This study provides a theoretical basis for using the upper stalk for bioenergy and the lower stalk for direct return to the field for fertilization.

Application of Multivariate Analysis Techniques for Selecting Soil Physical Quality Indicators: A Case Study in Long‐Term Field Experiments in Apulia (Southern Italy)

Core Ideas Soil physical quality (SPQ) on two long‐term experiments was evaluated. Relationships among five SPQ indicators (BD, PMAC, AC, PAWC and RFC) were evaluated. Two multivariate analysis techniques (PCA, SDA) were applied to select key indicators. PCA and SDA generally identified RFC as a key soil physical indicator. An optimal AC range was suggested to assess the air capacity of agricultural soils Long‐term field experiments and multivariate analysis techniques represent research tools that may improve our knowledge on soil physical quality (SPQ) assessment. These techniques allow us to measure relatively stable soil conditions and to improve soil quality judgment, thereby reducing uncertainties. A monitoring of SPQ under long‐term experiments, aimed at comparing crop residue management strategies (burning vs. incorporation of straw, FE1) and soil management (minimum tillage vs. no tillage, FE2), was established during the crop growing season of durum wheat. The relationships between five SPQ indicators (bulk density [BD], macroporosity [PMAC], air capacity [AC], plant available water capacity [PAWC], and relative field capacity [RFC]) were evaluated, and two techniques of multivariate analysis (principal component analysis and stepwise discriminant analysis) were applied to select key indicators for SPQ assessment. According to the used indicators, an SPQ from optimal to intermediate (i.e., not definitely poor) was detected in 65% of the observations in FE1 and in 54% in FE2. The main results showed a significant negative relationship between RFC and AC, and multivariate analysis identified RFC as a key SPQ indicator, mainly in FE2. Plant available water capacity and BD showed the highest discriminating capability in the FE1 dataset. The highest scores of RFC assessment were highlighted for burning and minimum tillage treatments (+1 and +2). An optimal AC range, derived from optimal RFC limits, was obtained and was suggested to better assess the AC of agricultural soils (0.10 ≤ AC ≤ 0.26 cm3 cm–3).

Decomposition of maize stover varies with maize type and stover management strategies: A microcosm study on a Black soil (Mollisol) in northeast China

Crop residue decomposition has an important impact on soil organic carbon (SOC) sequestration and CO2 emission. Residue quality and management strategies are two important factors regulating decomposition process and SOC mineralization and greenhouse gas emission. In this study, a microcosm experiment in field condition was conducted on a silty loam (a Black soil) in Northeast China to investigate stover decomposition and soil CO2 emission characteristics as influenced by different crop cultivars and stover field incorporation methods. Stover from two popular maize cultivars Xianyu335 (XY) and Liangyu99 (LY) were applied in two modes (soil surface application vs soil incorporation) at a rate of 11 t ha−1, and CO2 efflux was monitored during the decomposition duration of 144 days. The structural transformation of carbon functional groups in maize stover were evaluated using solid state 13C-CPMAS NMR and elemental analysis techniques. Results showed that up to 71.7%∼86.9% (weight basis) of C and N in soil-incorporated stover was decomposed during the study period, which was significantly greater than the losses (32.8%∼55.3%) of C or N from the surface-applied stover for both maize cultivars; decomposition rates of main C functional groups were significantly higher in soil incorporation (71.1%∼88.8%) than in surface application (20.9%∼60.2%) systems. The concentrations of SOC, total N, available N, and microbial biomass C and N in soil were also higher with stover incorporation than surface application. Stover incorporation resulted in a notably lower CO2 emission rate and accumulative CO2 efflux (53.9–55.4 mol m−2) during the stover decomposition compared with surface application (57.4–67.0 mol m−2). Between the two maize cultivars, the LY stover showed a higher decomposition rate and greater capacity for SOC sequestration when incorporated into soil. The LY stover induced higher (16.8%) CO2 emission than XY when applied on soil surface, but no significant difference was found between the two cultivars when incorporated into soil. The results suggested that cultivar selection and stover management strategies have great potential in reducing soil CO2 emission while improving soil biochemical properties. Incorporating the LY stover into soil rather than surface mulching could enhance SOC sequestration and reduce CO2 emission.

Impact of crop residue management on crop production and soil chemistry after seven years of crop rotation in temperate climate, loamy soils.

Society is increasingly demanding a more sustainable management of agro-ecosystems in a context of climate change and an ever growing global population. The fate of crop residues is one of the important management aspects under debate, since it represents an unneglectable quantity of organic matter which can be kept in or removed from the agro-ecosystem. The topic of residue management is not new, but the need for global conclusion on the impact of crop residue management on the agro-ecosystem linked to local pedo-climatic conditions has become apparent with an increasing amount of studies showing a diversity of conclusions. This study specifically focusses on temperate climate and loamy soil using a seven-year data set. Between 2008 and 2016, we compared four contrasting residue management strategies differing in the amount of crop residues returned to the soil (incorporation vs. exportation of residues) and in the type of tillage (reduced tillage (10 cm depth) vs. conventional tillage (ploughing at 25 cm depth)) in a field experiment. We assessed the impact of the crop residue management on crop production (three crops—winter wheat, faba bean and maize—cultivated over six cropping seasons), soil organic carbon content, nitrate (n}{}{mathrm{NO}}_{3}^{-}), phosphorus (P) and potassium (K) soil content and uptake by the crops. The main differences came primarily from the tillage practice and less from the restitution or removal of residues. All years and crops combined, conventional tillage resulted in a yield advantage of 3.4% as compared to reduced tillage, which can be partly explained by a lower germination rate observed under reduced tillage, especially during drier years. On average, only small differences were observed for total organic carbon (TOC) content of the soil, but reduced tillage resulted in a very clear stratification of TOC and also of P and K content as compared to conventional tillage. We observed no effect of residue management on the n}{}{mathrm{NO}}_{3}^{-} content, since the effect of fertilization dominated the effect of residue management. To confirm the results and enhance early tendencies, we believe that the experiment should be followed up in the future to observe whether more consistent changes in the whole agro-ecosystem functioning are present on the long term when managing residues with contrasted strategies.

No-till durum wheat yield success probability in semi arid climate: A methodological framework

The aim of this study is to develop a framework for the evaluation of no-till (NT) yield success probability as a decision tool for farmers or decision makers. The effect of soil management on durum wheat yield has been tested on many long-term field experiments. Results of these researches were collected in a unique dataset to evaluate the success of NT management in comparison to conventional tillage (CT) as influenced by the aridity index, crop residue management and cropping system. A total of 519 observations of long-term experiments (>3years) regarding durum wheat in a number of areas with semi arid climate were included in the present study. The relative ratio of yield under NT and CT was correlated to the aridity index (Ai) for different cropping systems and residue management strategies. No-till performed better with lower values of the Ai. When NT and CT yields were the same, the Ai value was defined as the Ai threshold, and this value resulted as being strongly dependent upon crop management.The developed framework, in any given site, allows us (i) to know the threshold for different managements tecniques, (ii) to estimate the probability of success in adopting NT and CT soil management techniques; (iii) to predict the best management with reference to Ai variation.

Implications of Cereal Rye/Crimson Clover Management for Conventional and Organic Cotton Producers

Core Ideas Cereal rye/crimson clover cover crop mixtures can be used for weed suppression and soil moisture conservation in cotton production.Cover crop management at cotton planting can influence cotton emergence, weed suppression, and soil moisture dynamics.Cotton emergence declined when cotton was planted directly into standing cover crop and without row cleaners engaged, but this reduction did not affect cotton lint yield.Soil temperature was reduced and soil moisture was increased by the presence of a cover crop mulch regardless of cover crop residue management strategy at cotton planting.Cover crop residue management did not affect cotton lint yield when herbicides were used, indicating that conventional producers have flexibility in terminating cover crops and residue management at cotton planting. Cover crop residue management can affect performance of the subsequent crop. This experiment was conducted in five environments in North Carolina from 2014 to 2016 to determine the effect of a cereal rye (Secale cereale)/crimson clover (Trifolium incarnatum) mulch on cotton (Gossypium hirsutum L.) emergence, soil temperature, soil moisture, weed suppression, and cotton yield under a conventional and organic weed control context. The cereal rye and crimson clover mixture was planted in mid‐October and terminated 1 wk prior to cotton planting using a roller‐crimper or herbicide application. Cover crop residue management included fertilized, rolled cover crop with row cleaners engaged at planting (Roll+F+RC), rolled cover crop with row cleaners engaged at planting (Roll+RC), rolled cover crop (Roll), standing cover crop with row cleaners engaged at planting (Stand+RC), and no cover crop (BARE). Weed treatments included with and without herbicides. Cover crop dry biomass ranged from 3820 to 6610 kg ha−1 across environments. Fertilizing the cover crop enhanced cover crop dry biomass production by 250 to 1860 kg ha−1. Cotton emergence declined when cotton was planted directly into standing cover crop and without row cleaners engaged. Soil temperature was reduced and soil moisture was increased by the presence of a cover crop. Cover crop residue management did not affect late‐season weed biomass at four of the five environments. Cover crop residue management did not affect cotton lint yield when herbicides were used, indicating that conventional producers have flexibility in terminating cover crops and residue management at cotton planting.

Response of Maize Root Growth to Residue Management Strategies

Core Ideas Efficient use of crop residues can improve circular economy in agro‐ecosystems.Amount of stover to the field explained the variation in root length density and root dry weight density in double cropping of winter wheat and summer maize.Returning stover increased the yield of summer maize.Root characteristics and the yield of summer maize improved by returning stover. A 5‐yr experiment was conducted to explore the effects of returning various amounts of stover to the field on root characteristics and yield in a wheat (Triticum aestivum L.) and maize (Zea mays L.) double‐cropping system. The experiment was designed as a randomized block design with three replications for three treatments: based on all stalks of winter wheat returned to the field (i) all summer maize stalks were mechanically pulverized and returned to the field (SR); (ii) half of the summer maize stalks were mechanically pulverized and returned to the field (1/2 SR); and (iii) all summer maize stalks were fully removed (CK). Results indicated that, in the SR treatment, root fresh weight (RFW) and root dry weight (RDW) were 19.4 and 18.5% higher, respectively, compared with the CK treatment. Root length density (RLD), root surface area density (RSAD) were 13.7 and 29.4% higher in the SR treatment, compared with the CK treatment. The yield of summer maize was 15.1 and 17.1% higher in the SR and 1/2 SR treatments, respectively, compared with the CK treatment. Furthermore, RLD, RSAD, root dry weight density (RDWD), and root length in the 1/2 SR treatment were significantly higher than those in the SR treatment. These results indicated that moderate amounts of straw returned to the field had the greatest effect on root growth and development of maize. This work provides a theoretical basis for optimizing crop yield and the use of straw resources.

Assessment of N2O emissions from a fertilised vegetable cropping soil under different plant residue management strategies using 15N tracing techniques

Combined application of plant residues and N fertilisers strongly affect soil mineral N dynamics and N2O emissions depending on the quality of the plant residues, their application methods and other management strategies. We investigated the effect of combined application of two vegetable plant residues (cauliflower and sweet corn) and 15N fertiliser on N dynamics and N2O emission in a glasshouse pot study. The experiment was conducted under two residue management practices (soil incorporation vs surface mulching) over 98days with growing basil (Ocimum basilicum) plants. We also assessed the efficacy of applying the nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP) to the plant residues, for reducing N loss and mitigating N2O emissions. Application of plant residues, both on the soil surface or into soil, resulted in net N mineralisation and increased cumulative N2O emission compared with the application of N fertiliser alone. Soil surface mulching of sweet corn decreased total and residue-induced cumulative N2O emission compared with the incorporation method, while it showed opposite effect on N2O emissions from cauliflower residue. The application of DMPP with sweet corn residue reduced total, residue- and fertiliser-induced N2O emissions; however its application with cauliflower residue did not show any mitigating effect on the N2O emissions. The residue application methods and the use of DMPP did not significantly affect 15N recovery by the basil plants. In contrast, soil incorporation of these residues doubled the microbial immobilisation of applied 15N into soil organic matter. Linear regression analysis of N2O emission during the experimental period indicated that in the treatments without DMPP application, soil NO3−-N concentration was the most important factor in controlling the magnitude of N2O emissions, while the application of DMPP changed the dominant regulating factor from NO3−-N to NH4+-N concentration.

Corn Residue Management Strategies to Improve Soybean Yield in Northern Climates

Many soybean [Glycine max (Merr.)] growers in northern climates are reverting back to some tillage based on perceptions that increasing corn residues interfere with no‐till (NT) soybean performance. Field trials were established in southern Ontario, Canada, to investigate the impact of corn residues on soybean among seven tillage strategies (NT, stalk chop, vertical tillage (VT) twice in the fall, fall and spring VT, fall disc plus spring cultivate, fall disc plus fall cultivate, and fall plowed plus spring cultivate), three corn residue removal treatments (none, intermediate, and nearly complete), and two planters (row‐unit and drill). Overall, soybean yields were not different between NT and plowed systems, despite delayed development, and cooler/wetter seedbeds where corn residue was not removed. Shallow tillage after corn harvest did not increase yields from NT alone. Removal of corn residue did not increase soybean yields when averaged across tillage systems. However, NT yield was lowered by 0.36 Mg ha−1 when corn stalks were chopped in the fall, but only in the drill‐planted treatments. This result was significant since many farmers have purchased corn combine heads that chop stalks in an attempt to manage residue. Soybean planted with a row‐unit planter yielded 0.13 Mg ha−1 higher compared to a drill when averaged across tillage‐residue treatments; differences between planters were higher when contending with high amounts of corn residue or an uneven soil surface at planting. Our results show that shallow tillage and/or physically removing corn residue did not improve soybean yield compared to NT alone.

Balancing energy, conservation, and soil health requirements for plant biomass

The global importance of plant biomass for mitigating water and wind erosion, sustaining soil organic carbon (SOC), and providing animal feed and bedding is well recognized, but those needs are no longer the only factors influencing crop residue management decisions. As fossil energy sources diminish, the need for cellulosic derived liquid fuels is going to increase. Supplying bio-based fuels while simultaneously meeting food, feed, and fiber demands of more than nine billion people will require tremendous grain and biomass yield increases, as well as innovative crop residue management strategies for efficient agricultural operations. Our goal is to examine the challenges farmers, conservationists, and land managers face as they strive to manage crop residues without degrading soil health. Harvesting a portion of our nation's crop residues, such as corn ( Zea mays L.) stover, to simultaneously provide liquid fuels and enhance agricultural operations will occur, provided it is done in a manner that sustains critical ecosystem and soil health services within the landscape. Harvest rates must be site-specific at subfield scales (Bonner et al. 2014a, 2014b) to ensure a sufficient amount of plant biomass remains at every harvest location to protect the soil surface from wind and water erosion and to sustain…

Review of Alternative Management Options of Vegetable Crop Residues to Reduce Nitrate Leaching in Intensive Vegetable Rotations

Vegetable crop residues take a particular position relative to arable crops due to often large amounts of biomass with a N content up to 200 kg N ha−1 left behind on the field. An important amount of vegetable crops are harvested during late autumn and despite decreasing soil temperatures during autumn, high rates of N mineralization and nitrification still occur. Vegetable crop residues may lead to considerable N losses through leaching during winter and pose a threat to meeting water quality objectives. However, at the same time vegetable crop residues are a vital link in closing the nutrient and organic matter cycle of soils. Appropriate and sustainable management is needed to harness the full potential of vegetable crop residues. Two fundamentally different crop residue management strategies to reduce N losses during winter in intensive vegetable rotations are reviewed, namely (i) on-field management options and modifications to crop rotations and (ii) removal of crop residues, followed by a useful and profitable application.

Effects of harvest residue management on soil carbon and nitrogen processes in a Chinese fir plantation

Plantation management can affect ecosystem soil carbon (C) and nitrogen (N) cycles. However, how different harvest residue management strategies impact soil C and N processes over the long term is largely unclear. In this study, we examined effects of harvest residue management on soil C and N concentrations, labile soil C and N pools and soil CO2 efflux (Rs) at different stages after Chinese fir (Cunninghamia lanceolata) was replanted in subtropical China. The residue management treatments were slash and burning, whole-tree harvesting, stem-only harvesting and stem only harvesting with double residue retention. Our results showed that the harvest residue management treatments did not differ significantly in their effect on soil C and N, mineral N (NH4+-N plus NO3−-N), dissolved organic C or total dissolved N concentrations, except for soil N concentrations in surface soil (0–10cm) at year 3 and soil total dissolved N concentrations at year 12, which were significantly lower where the slash was burnt than in the double residue retention treatment. Similarly, Rs did not differ significantly among the four residue management strategies at year 15. Topsoil temperature and topsoil moisture were also unaffected by harvest residue management treatment. Soil temperature was found to be the most important factor controlling the temporal pattern of Rs, accounting for 65.8% of seasonal variation of Rs. There was no significant difference in temperature sensitivity of Rs (Q10) or annual Rs among the four treatments. These results indicated that harvest residue management may not significantly cause long-term effects on soil C cycling and N availability in subtropical Chinese fir plantations.

Management of crop residues affects the transfer of phosphorus to plant and soil pools: Results from a dual-labelling experiment

Release of nutrients, including phosphorus (P), from crop residues remaining post-harvest is an important potential source of nutrients for subsequent crops. A glasshouse experiment examined the effect of size (ground <2 mm and large 50 mm) and placement (fully incorporated and no-till) of field-collected pea residue on subsequent P uptake by wheat and that found in soil hexanol-released P and resin-extractable P. The experiment used a dual-labelling approach (33P and 32P) to measure the contribution of soil, fertiliser and residue P to the growing plants, hexanol-released and resin-extractable soil P fractions. Soil and plant samples were taken 60 and 80 days after application of residues to soil. Residue treatment had no effect on plant dry matter, but the application of large residue pieces increased plant P uptake whether incorporated or surface-placed. The percentage of P contained in wheat derived from the residue ranged from 9 to 44% across the four residue treatments. The remaining P was derived from fertiliser (19–24%) and soil (33–76%) pools. On average, >60% of the added residue P was detected in plant, microbial and resin P pools when incorporated in soil compared to ∼25% for the two surface-placed residue treatments. When considering residue management strategies based on the potential for influencing P supply to crops, incorporating residues will increase the rate of release and decomposition and therefore the potential for plant roots (if present) to access this P. The results also show that even though residue P takes longer to break down when retained on the soil surface (e.g. under no-till management), this system was still able to provide small but agronomically significant amounts (0.6–0.7 kg P ha−1) of P to subsequent crops.

Effects of Biochar Derived from Maize Stover and Rice Straw on the Early Growth of their Seedlings

Crop residues such as maize and rice are important sources of nutrients and their restitution to the soil is an important residue management strategy for maintaining or improving soil and crop productivity. However, most maize and rice farmers in Sierra Leone burn crop residues during land preparation thereby depriving the soil of this vital resource. An alternative approach is the recycling of crop residues through biochar production. This study was therefore carried out to assess the effects of (i) maize stover biochar on the early growth of maize and (ii) rice straw biochar on the early growth of rice. In this study, biochar (0g, 12.5g, 25.0g, 37.5g and 50.0g) was mixed with 3kg of soil (fine sandy loam) and placed in perforated black polythene bags. Maize or rice seeds (3 per pot) were planted to 2cm depth and later thinned to one plant per pot. All pots were placed in the open under direct sunlight and rainfall. No supplemental irrigation was done since there was sufficient rainfall to supply the required moisture. The experiment was laid in completely randomized design with five treatments and three replications. After four weeks, the experiment was terminated. Mean plant height, stem girth, fresh- and dry-shoot weights of both maize and rice plants generally increased significantly (p<0.05) relative to the control at biochar applications ≥8.3g/kg soil. The results showed that growing maize and rice on soils treated with biochar derived from their residues (maize stover and rice straw respectively) has the potential to improve crop production. Confirmatory field trials and costs/benefits analysis of converting rice and maize residues to biochar will serve as a good guide for policy makers and end-users (farmers) for increased productivity of maize and rice in Sierra Leone.

Organic Fertilization, Green Manure, and Vetch Mulch to Improve Organic Zucchini Yield and Quality

A 2-year field experiment was carried out in a Mediterranean environment to study the effects of vetch (Vicia sativa L.) residue management strategies incorporating green manure (GM) using a roller-crimper (RC) and different organic fertilizers (municipal solid waste compost, anaerobic digestate, and a commercial organic fertilizer) on organic zucchini (Cucurbita pepo L.) yield and quality. Zucchini yield was influenced positively by the vetch residue management strategy, although the response was significantly different between years. The vetch cover crop increased marketable zucchini yield in the first year by 46.6% compared with the fallow (FA) treatment, indicating that this fertility-building crop could reduce off-farm nitrogen (N) fertilizer input for subsequent crops. Averaging over 2 years of the experiment, marketable zucchini yield increased by 15.2% and 38% with the RC mulch and GM plow-down, respectively, compared with the FA treatment, although differences were significant in the first year only. The application of organic fertilizers in vetch management plots increased marketable zucchini yield by 21.8% in the first year compared with the unfertilized control. This result is particularly relevant, because organic fertilizers were applied at ≈50% of the normal application rate for zucchini after taking into account biological N fixation attributable to the vetch. The concentrations of soil mineral N at harvest were 19, 27, and 28 mg·kg−1 for the RC, FA, and GM treatments, respectively. These mineral N concentrations indicated that a portion of applied organic fertilizer N, and N attributable to vetch (GM and RC), remained in the soil at harvest, suggesting the potential for leaching, which should be taken into account in the overall fertilization program. These research findings suggest that effective vetch cover crop management and the application of organic fertilizers can improve yield and quality of organically managed zucchini.

Harvest residue management effects on tree growth and ecosystem carbon in a Chinese fir plantation in subtropical China

This study aimed to determine the influence of different harvest residue management strategies on tree growth, soil carbon (C) concentrations, soil nitrogen (N) availability and ecosystem C stocks 15 years after replanting second rotation Chinese fir (Cunninghamia lanceolata), an important plantation species in subtropical China. Such information is needed for designing improved management strategies for reforestation programmes in subtropical environments aimed at mitigating CO2 emissions. Four harvest residue management treatments including slash burning, whole tree, stem-only and double residue retention were applied to sixteen 20 m × 30 m plots in a randomized complete block design with four replicates. Tree growth was measured annually and soil properties were measured at 3 year intervals over a 15 year period after re-planting. Cumulative diameter growth at age 15 years was significantly smaller in the slash burning than the whole tree and double residue harvest treatments. Hot water extractable N concentrations increased with the increased organic residue retention levels and significant differences were observed between double residue and slash burning treatments. Harvest residue management had no significant effect on the soil C concentrations to 40 cm depth. ANOVA showed that harvest residue management had no significant effect on total biomass carbon at age 15, but the plantation ecosystem (soil C at 0–40 cm depth plus forest biomass C) had significantly lower C mass in the slash burning treatment compared with whole tree, stem only harvest and double residue harvest treatments. These observations suggest that organic residue retention during the harvesting could improve the growth and ecosystem C stocks of Chinese fir in second rotation forest plantations in subtropical China and highlight the importance of viewing the ecosystem as a whole when evaluating the impact of harvest residue management on C stocks.