Above-ground Residues Research Articles

Evaluation of the RothC model as a prognostic tool for the prediction of SOC trends in response to management practices on arable land

RothC is an established model for predicting soil organic carbon (SOC) changes in response to environmental conditions and management. The model lacks algorithms for carbon input estimation and a differentiated consideration of carbon input sequestration from organic amendments commonly used in agriculture. Moreover, it does not consider the higher stability of below-ground crop residues in relation to above-ground crop residues.RothC was combined with two empirical approaches for quantifying carbon inputs from above- and below-ground crop residues and tested on 439 SOC data series from 36 arable long-term field experiments in Central and Northern Europe. Effects of carbon input quality on model fit were quantified with linear mixed models based on the analytical solution of RothC. Model parameters that describe the stability of incoming carbon were calibrated using a multi-site approach and Bayesian calibration. A second calibration study combined the determination of partitioning of incoming carbon into pools with different turnover rates and model responses to temperature and soil water content. With this calibration we showed that the contribution of above-ground residues to SOC is lower than when estimated with default RothC paramerization. We also show that the relative contribution from roots to SOC is higher than that from above-ground residues. Moreover, the degradability of organic amendments was highly variable between amendment categories and increased for all model configurations in the following order: farmyard manure < farmyard compost < sawdust < sewage sludge < peat. The proposed RothC partition coefficients for above-ground residues, roots and several commonly used organic amendments as estimated for this large data set should be useful for other studies in temperate climates. We also show that the analytical solution of RothC is closely related to the much simpler empirical humus balancing approaches used by farm advisory services. This provides opportunities to build bridges between the more process-oriented SOC models used in research and the well established instruments used by the farming community to assess the effects of agricultural management practices on SOC changes.

Dry matter partitioning and residue N content for 11 major field crops in Canada adjusted for rooting depth and yield

To improve the estimates of C and N inputs to soil, we developed new estimates of partitioning between the harvested portion, aboveground residue, and belowground residue for 11 major crops based on depth-adjusted root/shoot ratios and grain yield-adjusted harvest indices. We updated the mean N concentration of each partition.

Root and detritus of transgenic Bt crop did not change nematode abundance and community composition but enhanced trophic connections

Transgenic Bacillus thuringensis (Bt) crops are widely deployed to control lepidopterous pests with minimal impact on non-target soil invertebrates. However, most of the results were obtained from field works, the great environmental variation may conceal the small spatial-temporal scaled changes in microhabitats, such as those created near the roots (rhizosphere) or around decomposing residues (detritusphere), which are expected to impact free-living soil organisms more than the bulk soils. The objective of this study was to assess the impact of root and straw residues of transgenic crops on soil, by comparing nematode communities in the rhizosphere (soil microsites only affected by living root), the detritusphere (soil microsites affected by crop aboveground residues) and the rhizosphere-detritusphere interface (soil microsites intensively co-affected by root and residues) of Bt rice and its non-Bt near isoline. Bt rice did not affect nematode abundance and community composition, however, it enhanced the network connections within nematode communities, in both the rhizosphere and detritusphere, indicating the frequency of co-occurring species increased due to the moderate stress of crystal (Cry) as a labile resource of protein or as a moderate pressure of toxic compounds. Furthermore, 60–80% of the correlation between Cry protein (Cry1Ab/Cry1Ac) and nematode genera were positive in the rhizosphere and detritusphere of Bt rice, suggesting that higher Cry protein concentration was associated with the intensive co-occurrence among nematode populations. This finding offers new insights into how the biotic interactions of non-target soil community response to both live and dead parts of transgenic crop, highlighting the moderate stress of Cry protein might affect the community structure and consequent functioning of soil ecosystem based on the elaborately developed knowledge of biotic interactions via ecological network analysis.

Dual-labelling (15N and 33P) provides insights into stoichiometry and release of nitrogen and phosphorus from in situ mature lupin and canola below-ground residues

Belowground (BG) residues may contribute significant amounts of N and P via nutrient cycling to following crops, particularly in low fertiliser input systems or where all the above-ground residues are removed. Reports of simultaneous measures of nitrogen (N) and phosphorus (P) release from mature crop residues, especially from intact root systems in situ, are rare. A single stem-feed of 15N followed by 33P was used to (i) estimate total amounts of N and P accumulated in situ BG by mature canola and lupin plants including the stoichiometry of N and P in recovered and non-recovered components of these BG residues, and ii) simultaneously trace and quantify the relative release of that N and P. One set of pots were destructively sampled at lupin and canola maturity to quantify total accumulation of BG P and BG N, including estimated N and P in unrecovered roots plus root-derived materials (RD N and RD P). Shoots were removed from a second set of pots into which wheat was sown after a 3 weeks fallow. Release of P and N from the decomposing in situ 33P/15N labelled lupin and canola BG residues was assessed as uptake in 5 weeks old wheat. Canola root had higher P and lower N concentrations than lupin. Canola total BG P was greater than lupin with a higher proportion as estimated RD P. Estimated RD N was similar in both species but lupin had more N in roots and so higher total BG N. C:P ratio of lupin roots was 708:1 and 188:1 for canola. Root C:N ratio was 39:1 for canola and 24:1 for lupin. N:P ratio for lupin roots was wider (29:1) than canola (5:1), but N:P ratio of RD fractions was similar (6:1 canola; 7:1 lupin). Proportion of BG P released and taken up by wheat was 21% after canola and 19% after lupin, and since total amount of BG P was much greater for canola the quantity of P released was double that after lupin. Proportion of lupin BG N (37%) released was similar to that for canola BG N (33%) although a larger amount of N was released from lupin given the larger BG N pool. The proportion of P and N released from in situ BG residues of mature canola and lupin and taken up by wheat in this short term study was broadly inversely related to C:P, C:N and N:P ratio of recovered roots but results suggest a likely influence also of N:P ratio of the unrecovered BG residues. Quantities of N and P released were a function of the estimated total amount of plant N and P accumulated in situ BG.

Amount and incorporation of plant residue inputs modify residue stabilisation dynamics in soil organic matter fractions

Carbon sequestration in agricultural soils has been promoted as a means to reduce atmospheric concentrations of greenhouse gases (GHG) whilst improving soil productivity. Although there is broad agreement on practices that increase carbon (C) stocks, uncertainty remains on how agricultural management affects the stability of these gains. The fate of above-ground residue into soil organic matter (SOM) was tracked using isotopically labelled (13C and 15N) residue over 12 months in a pasture soil in sub-tropical Australia. Agricultural residue management was simulated by (1) altering the rate of residue input and (2) incorporating residue with topsoil or leaving on soil surface. Increased input and incorporation of residue increased residue-derived SOM content, with the majority of residue-derived SOM accumulating as particulate organic matter (POM) (65%) with more modest gains in mineral-associated fractions. Rapid accumulation of residue-derived SOM in the mineral-associated fractions in the initial stages of decomposition, coinciding with a high loss of labile residue components, indicate an important role for soluble OM inputs in providing an immediate and long-term sink for C and N. However, this must be considered alongside high rates of accumulation in the more readily mineralised POM fraction, particularly when a soil is approaching saturation, which is likely to lead to greater mineralisation of SOM.

Zinc biofortification of wheat through preceding crop residue incorporation into the soil

Abstract We conducted a two-year field experiment to investigate the potential benefit of preceding crop residue incorporation into the soil as a strategy to enhance the density of bioavailable grain zinc (Zn) in a subsequent wheat ( Triticum aestivum L.) crop. Sunflower ( Heilianthus annuus L. cv. Allstar), sorghum ( Sorghum bicolor L. cv. Speed Feed), clover ( Trifolium pratense L.) and safflower ( Carthamus tinctorius L. cv. Koseh-e-Isfahan) were grown as preceding crop (precrop) on a Zn-deficient calcareous soil in central Iran, followed by a culture of two wheat cultivars i.e., Kavir and Back Cross Rushan. The harvested aboveground plant matter was air-dried, crushed into pieces of 0.5–2 cm size, mixed, and after taking a sample for analysis, incorporated manually into the upper 15 cm of the soil of one half of the same plot from which it had been harvested, while the other half received no residues. The aboveground residues of precrops were incorporated into soil or removed. A treatment with no preceding crop (fallow) and no residue incorporation, but with the same management otherwise, was implemented as control treatment. For both wheat cultivars studied, higher grain yield was obtained after clover (between 14 and 25.6%) and sunflower (between 11.3 and 19.5%) than that after safflower, sorghum and the fallow. All precrop treatments significantly increased the accumulation of grain Zn and N and decreased the phytic-acid-to-Zn (PA:Zn) molar ratio (by 5–41% in Kavir and by 11–48% in Back Cross), most effectively the clover treatment. The treatment effects on grain Zn were closely correlated with soil pH and dissolved soil organic carbon (DOC). The results show that the cultivation of appropriate precrops, especially legumes, can be an effective strategy to biofortify wheat grains with Zn without compromising yields.

Contribution of above‐ and belowground bioenergy crop residues to soil carbon

AbstractGHG mitigation by bioenergy crops depends on crop type, management practices, and the input of residue carbon (C) to the soil. Perennial grasses may increase soil C compared to annual crops because of more extensive root systems, but it is less clear how much soil C is derived from above‐ vs. belowground inputs. The objective of this study was to synthesize the existing knowledge regarding soil C inputs from above‐ and belowground crop residues in regions cultivated with sugarcane, corn, and miscanthus, and to predict the impact of residue removal and tillage on soil C stocks. The literature review showed that aboveground inputs to soil C (to 1‐m depth) ranged from 70% to 81% for sugarcane and corn vs. 40% for miscanthus. Modeled aboveground C inputs (to 30 cm depth) ranged from 54% to 82% for sugarcane, but were 67% for miscanthus. Because 50% of observed miscanthus belowground biomass is below 30 cm depth, it may be necessary to increase the depth of modeled soil C dynamics to reconcile modeled belowground C inputs with measured. Modeled removal of aboveground corn residue (25–100%) resulted in C stock reduction in areas of corn–corn–soybean rotation under conventional tillage, while no‐till management lessoned this impact. In sugarcane, soil C stocks were reduced when total aboveground residue was removed at one site, while partial removal of sugarcane residue did not reduce soil C stocks in either area. This study suggests that aboveground crop residues were the main C‐residue source to the soil in the current bioethanol sector (corn and sugarcane) and the indiscriminate removal of crop residues to produce cellulosic biofuels can reduce soil C stocks and reduce the environmental benefits of bioenergy. Moreover, a switch to feedstocks such as miscanthus with more allocation to belowground C could increase soil C stocks at a much faster rate.

English

Sustaining the productive capacity of soils has raised interest in the maintenance of soil organic matter through management practices and use of crop residues. While the impact of management practices has been studied, little is done to understand how the charateristics of the residue itself impact the decomposition at the soil surface. This study relates the chemical composition and the surface area of the aboveground residue to the decomposition rates for three cultivars each of three crops: cotton, peanut and sorghum. The rates were determined by mass loss. Change in the residue specific surface area to mass loss was also measured. Findings show that after 14 days, the aboveground residue for the three crops were from the most rapid loss to the slowest: cotton (43%) > peanut (32%) > sorghum (24%). Changes in the specific surface area-to-mass ratio were from the slowest to the most rapid loss: cotton (1.60×10-4) > peanut (1.50×10-4> sorghum (1.20×10-4). Since varietal differences within crops have led to variation in decomposition rates, cultivars with slower decaying residues might be recommended for C sequestration and for erodible lands in semi-arid zones of the Sahel. Likewise, crop residues with faster decomposition rates can be recommended for soil fertility improvement. Key words: Decomposition rate, crop type, crop residue, chemical composition, specific surface area-to-mass ratio.

Organic Carbon Convergence in Diverse Soils toward Steady State: A 21‐Year Field Bioassay

Core Ideas We report long‐term SOM change in different soils transplanted to one plot. Mainly, initial SOM concentrations highly influence change over time. Sand and land management history influence SOM change. High C soils lose C and low C soils gain C; thus, soils converge to new equilibrium. Light‐fraction OM converges at a faster rate than C and N. The response of soil organic matter (SOM) to an abrupt change in environment and management was studied in a long‐term field bioassay. Thirty‐six soils, with a wide range of SOM reflecting large differences in management, climate, and ecological histories, were selected and transported to a common site at Lethbridge, Alberta, Canada. The experiment included control and N‐fertilized treatment plots. The plots were seeded annually to spring wheat and managed under no‐till rain‐fed conditions, with annual removal of aboveground residues. The soils were sampled every 7 yr and analyzed for organic C (OC), total N (TN), and light fraction C (LF‐C) and N (LF‐N). Most of the soils lost OC and TN over 21 yr, and the amount of loss was highly related to the original contents (9–74 g C kg−1, 1.4–6.4 g N kg−1). Similarly, LF‐C and LF‐N, indices of labile OM, declined in most soils, but the rate of loss was faster than for OC. In a few soils, SOM slowly increased from initially low levels. The soils seem to be progressing toward a steady state, although complete convergence of OC and TN may not occur for a century or longer based on an exponential model. Labile OM may converge within a few decades, so that these soils, conceivably, will still have widely different OC and TN but similar labile SOM, with possible implications for soil health. Our findings demonstrate the value of long‐term field bioassays for improved understanding of SOM dynamics in response to management and climate change.

An evaluation of C and N on fresh and aged crop residue from mixed long-term no-till cropping systems

ABSTRACTConservation crop residue management increases soil organic carbon (SOC) storage, nutrient cycling and availability and improves soil quality. This study was conducted to evaluate the amount of residue biomass, residue carbon to nitrogen (C:N) ratio, residue carbon (C) and nitrogen (N), and residue N fertilizer deficit (supplemental N fertilizer requirement) from crop residue decomposition in long-term no-till production. Aboveground aged and fresh residues were collected in spring 2011 and fall 2012, respectively. Results showed slightly greater residue dry matter weight in aged residue than fresh residue. C:N ratios were wider in fresh residue than the aged residue. Both aged and fresh residue also showed wider C:N ratio in the corn (Zea mays L.)-soybean (Glycine max L.) rotation (66.6 and 64.4, respectively) and narrower C:N ratio in the spring wheat (Triticum aestivum L.)-winter wheat (Triticum aestivum L.)-alfalfa (Medicago sativa L.)-alfalfa-corn (Zea mays L.)-soybean (Glycine max L.) (45.6 and 35.7, respectively). Individual fresh crop residues showed narrower C:N ratios for legume and cover crops than non-legume crops. Analysis of potential supplemental N fertilizer requirements showed greater potential N requirement for the fresh residue than the aged residue.

The influence of above-ground residue input and incorporation on GHG fluxes and stable SOM formation in a sandy soil

Carbon sequestration in agricultural soils has been promoted as a means to reduce atmospheric concentrations of greenhouse gases (GHG) whilst improving soil productivity. Although there is broad agreement on practices that increase carbon (C) stocks, there is a lack of understanding on the stability of these gains and how changes in soil organic carbon (SOC) pools can influence GHG fluxes. We tracked the fate of above-ground residues into functionally different SOC pools and GHG fluxes using isotopically labelled residues (13C and 15N) over 12 months in a pasture soil in sub-tropical Australia. Agricultural residue management was simulated by: (1) altering the rate of residue input and, (2) mixing residue with topsoil. GHG fluxes were significantly greater at high residue input levels due to the priming of existing SOC and elevated N2O losses, fuelled by a greater availability of labile substrate. There was evidence of an asymptotic relationship between C input and residue-derived C accumulation in stable soil C pools at higher input levels, indicating that the soil was reaching its protective capacity. Mixing of residues contributed to a 40% increase in GHG fluxes in comparison to surface applied treatment, most notably from residue-derived C and N. This can be attributed to (i) the physical disruption of soil, particularly that of aggregates, which changed the microenvironment stimulating microbial activity, and (ii) greater residue-soil contact. Greater residue-soil contact through mixing also contributed to a 2 fold increase in the residue-derived C recovered in the mineral soil with the majority (56%) in the active C pool. Over a 12 month period, C sequestration was outweighed by GHG fluxes at high rates of input and when residues were mixed with the topsoil. C sequestration policies and associated management approaches must be assessed holistically under a range of conditions and in the long-term to ensure that detrimental practices are not promoted.

Carbon budget in a Mediterranean peach orchard under different management practices

The soil organic carbon (SOC) content of many Mediterranean soils is low (∼1%) and this hinders both economic and ecologic progress. The climate in much of the Mediterranean region (low annual precipitation, cool wet winters, hot dry summers), combined with traditional agricultural practices has a major impact on the carbon (C) cycle. To increase our knowledge of C fluxes in Mediterranean agro-ecosystems, this paper examines the effects on the soil and biome C budgets of a peach (Prunus persica L. Batsch) orchard, seven years after adopting sustainable management practices (Smng). The result is compared with the continued use of locally conventional management practices (Cmng). Sustainable management involved zero-tillage, weed mowing, retention of above-ground residues and the import of organic amendments, while Cmng involved tillage, removal of pruning residues and the application of mineral fertilisers. The annual net ecosystem production (NEP) was determined through field measurements of soil respiration (Li-6400, LI-COR, USA) and above- and below-ground biomass sampling. The mean annual NEP was close to 320 and 475gCm−2yr−1 in the Cmng and Smng plots, respectively. As managed ecosystems, anthropogenic C imports/exports and related changes of soil C pool were then accounted for through the net ecosystem C balance (NECB). The NECB approximated 90gCm−2yr−1 for Cmng and 730gCm−2yr−1 for Smng. This result highlights the critical role of appropriate management of the variable components on sustaining ecosystem resilience, including the management of pruning residues, the import of organic materials, and the maintenance of a cover crop. Over a 7-year study period, C stock (SOC and litter) increased at a mean rate of ∼145gCm−2yr−1 in the Smng plot while it increased at only ∼7.5gCm−2yr−1 in the Cmng plot. Whole-tree standing biomass was measured by tree excavation revealing that the C sequestered over the 14-year lifetime of the orchard was close to 25tCha−1. This study provides information on C stock variation (soil+biome) and on annual net atmospheric C removal (NEP) in a cultivated peach orchard under Mediterranean climate conditions.

Water erosion in surface soil conditions: runoff velocity, concentration and D50 index of sediments in runoff

Water erosion and contamination of water resources are influenced by concentration and diameter of sediments in runoff. This study aimed to quantify runoff velocity and concentration and the D50 index of sediments in runoff under different soil surface managements, in the following treatments: i) cropped systems: no-tilled soil covered by ryegrass (Lolium multiflorum Lam.) residue, with high soil cover and minimal roughness (HCR); no tilled soil covered by vetch (Vicia sativa L.) residue, with high soil cover and minimal roughness (HCV); chiseled soil after ryegrass crop removing the above-ground residues and keeping only the root system, with high roughness (HRR); chiseled soil after vetch crop removing the above-ground residues and keeping only the root system, with high roughness (HRV); ii) bare and chiseled soil, with high roughness (BHR). The research was conducted on a Humic Dystrupept under simulated rainfall. The design was completely randomized and each treatment was replicated twice. Eight rainfall events of controlled intensity (65 mm h−1) were applied to each treatment for 90 minutes. The D50 index, runoff velocity and sediment concentration were influenced by crop and soil management. Runoff velocity was more intensely reduced by cover crop residues than by surface roughness. Regardless of surface condition, the D50 index and concentration of sediment in runoff were lower under ryegrass than vetch crop. Runoff velocity and the D50 index were exponentially and inversely correlated with soil cover by residues and with surface roughness, while the D50 index was positively and exponentially correlated with runoff velocity.

Preceding crops and nitrogen fertilization influence soil nitrogen cycling in no-till canola and wheat cropping systems

Crop rotation and nitrogen (N) fertilization can influence soil N cycling, however, less is known about their interactive effects under varying soil and climatic conditions. We examined the interactive effects of preceding crops and N fertilizer rates on soil N cycling in canola (Brassica napus L.) and spring wheat (Triticum aestivum L.) cropping systems in no-till soils in the Canadian prairies. Field pea (Pisum sativum L.), lentil (Lens culinaris Medik), faba bean (Vicia faba L.; faba bean-seed), canola and wheat grown for grain, and faba bean green manure (faba bean-GRM) were the preceding crops and were direct-seeded at 7 and 6 locations in 2009 and 2010, respectively. Canola and wheat were seeded in 2010 and 2011 (2012 for wheat at one site), respectively with N fertilizer applied at 0, 30, 60, 90 and 120kgNha−1. Above-ground residue N returned was greatest for faba bean-GRM and lowest for canola and wheat. On average across sites, apparent in-crop N mineralization (ANM) under canola was greater following faba bean-GRM than all other preceding crops, except field pea, while under wheat, ANM was greater following all the legumes than following canola and wheat. Crop N uptake increased with N fertilizer rate, but the response was generally lower following faba bean-GRM and lentil. The N budget showed that 40–65% of crop N uptake (35–100% at highest ANM site) was possibly derived from ANM, more so following legumes, as compared to 35–60% from N fertilizer. The surplus and unaccounted N were particularly pronounced when canola and wheat were preceded by legumes rather than by canola or wheat. Our findings indicate that legumes can enhance soil N supply in no-till soils, and also highlight the importance of adjusting N fertilizer rates based on preceding crops to minimize the potential for N losses.

Whole-tree, stem-only, and stump harvesting impacts on site nutrient capital of a Norway spruce-dominated peatland forest

About 15 million hectares of peat soils have been drained for forestry in temperate and boreal zones. Increasing interest in wood biomass as a source of bioenergy has led to more intensive harvests also in peatland forests. These harvestings remove branches, needles, and stump/root systems that would earlier have remained on-site. However, in drained peatland forests, some key growth-limiting nutrients, such as potassium (K) and boron (B), are largely stored in the living tree biomass, while the stores in peat in tree rooting layer are small. A concern has thus been raised that bioenergy harvesting may induce nutrient insufficiency and decrease second rotation forest productivity. We studied the effect of whole-tree and stump harvesting on site nitrogen (N), phosphorus (P), K, and B capitals in final harvesting of a well-productive, Norway spruce-dominated peatland forest. Harvesting of stumps and above-ground harvest residues resulted in minor depletion of site N and P stores, but significant depletion of K and B. Maximizing harvest residue biomass recovery, but minimizing nutrient depletion, our results indicated that stump harvesting is a more feasible option than harvesting of above-ground residues. If above-ground harvest residues are to be harvested for bioenergy, K and B depletion may be decreased by letting the branches dry out somewhat and the needles fall down before branch harvesting. Combining our results with data on waterborne K losses suggested that K depletion may become a serious problem in second rotation forests on drained peatlands, even if harvest residues and stumps were left completely non-harvested.

Long‐Term Durum Wheat‐Based Cropping Systems Result in the Rapid Saturation of Soil Carbon in the Mediterranean Semi‐arid Environment

AbstractClimate, soil physical–chemical characteristics, land management, and carbon (C) input from crop residues greatly affect soil organic carbon (SOC) sequestration. According to the concept of SOC saturation, the ability of SOC to increase with C input decreases as SOC increases and approaches a SOC saturation level. In a 12‐year experiment, six semi‐arid cropping systems characterized by different rates of C input to soil were compared for ability to sequester SOC, SOC saturation level, and the time necessary to reach the SOC saturation level. SOC stocks, soil aggregate sizes, and C inputs were measured in durum wheat monocropping with (Ws) and without (W) return of aboveground residue to the soil and in the following cropping systems without return of aboveground residue to soil: durum wheat/fallow (Wfall), durum wheat/berseem clover, durum wheat/barley/faba bean, and durum wheat/Hedysarum coronarium. The C sequestration rate and SOC content were lowest in Wfall plots but did not differ among the other cropping systems. The C sequestration rate ranged from 0.47 Mg C ha−1 y−1 in Ws plots to 0.66 Mg C ha−1 y−1 in W plots but was negative (−0.06 Mg C ha−1 y−1) in Wfall plots. Increases in SOC were related to C input up to a SOC saturation value; over this value, further C inputs did not lead to SOC increase. Across all cropping systems, the C saturation value for the experimental soil was 57.7 Mg ha−1, which was reached with a cumulative C input of 15 Mg ha−1. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Decomposition, contribution and soil organic matter balances of crop residues and vermicompost in maize-based cropping systems in southwest Mexico

Soil fertility depletion is one of the main concerns of the farmers in the Costa Chica, Mexico. The current crop management exacerbates nutrient cycling unbalances and threatens the sustainability of the common maize production systems. It is necessary to supply the soil with organic sources. Field experiments were established in farmers’ fields to estimate the decomposition rate and N release of organic materials: aboveground and belowground plant residues, and vermicompost. Decomposition was monitored using the litterbag method, and decomposition patterns were fitted by means of a dynamic mono-component mineralization model. To calculate the effects of crop residues retention and vermicompost on OM balance, five scenarios were evaluated with farm DESIGN model. The decomposition rate was greater during the first 4 months. After that period the remaining dry matter proportion of aboveground residues varied between 45 and 67%. In case of root residues, the dry weight loss ranged between 20 and 47% after the first month. For both types of residues, N released within the first month was 37%, on average. At the end of the sampling period 9 months, the remaining dry matter proportion of aboveground and belowground residues ranged from 30 to 55%, whereas more than 80% of their total N was released. After 6.5 months only 35% of the vermicompost mass was decomposed, but about 65% of its N was mineralized. Besides, around 70% of the vermicompost N was released during the first 30 days. In fields with vermicompost maize was responsible for 70% of total N uptake, on average. The N balance was 93% higher than maize fields without vermicompost. In scenario with 30% of crop residue retention along with vermicompost, OM balance was 86% higher than under current management. Vermicompost can be regarded as an attractive amendment for both crop N supply and soil organic matter build-up.

Nitrogen yield and nitrogen fixation of winter faba beans

Introducing autumn-sown legumes into Central European farming systems could be beneficial for addressing two challenges for European agriculture, i.e., the substantial deficit of protein sources for livestock and expected changes in agroclimatic conditions. Therefore, a two-year field experiment was conucted under Pannonian climate conditions in eastern Austria to assess nitrogen (N) yield and N fixation of several winter faba bean varieties from different European countries as compared to a spring faba bean. Winter wheat was used as a reference crop for estimating atmospheric N fixation. Winter faba beans were susceptible to frost damage especially in the harder of the two winters. Winter faba bean varieties could not achieve a higher grain yield and a higher grain N yield than the spring faba bean but had a higher grain N concentration (except for one variety). Grain yield and grain N yield of faba beans were severely impaired by drought in one year (with a mean of varieties of 8.3 g N m−2, winter wheat: 6.4 g N m−2); in the other year, grain N yield of faba beans considerably surpassed that of winter wheat (with a mean of varieties of 21.5 g N m−2, winter wheat: 8.8 g N m−2). After harvest, faba beans left higher nitrate residues in the soil, especially in the subsoil, and higher amounts of N in above-ground residues compared to winter wheat. Faba beans showed high N fixation under optimum conditions (with a mean of varieties of 21.9 g N m−2) whereas drought considerably impaired N fixation (with a mean of varieties of 6.3 g N m−2; with no differences between autumn- and spring-sown faba beans). In conclusion, growing winter faba bean varieties in eastern Austria did not result in higher grain yield, grain N yield, and N fixation compared to growing a spring faba bean.

Climate-smart crop production in semi-arid areas through increased knowledge of varieties, environment and management factors

In large regions of sub-Saharan Africa, semi-arid conditions are likely to increase with climate change, yet these regions are becoming more important to feed production zones due to increasing population pressure. A production system in the semi-arid south eastern Zimbabwe was studied to assess different possible growth conditions of food crop in relation to seasonal differences, spatial rainfall distribution, use of organic nutrients and different position in the landscape. The growth and yield of four crops (maize, sorghum, millet and groundnut) were assessed with or without manure during two seasons (2008/2009 and 2009/2010) in different landscape positions. Daily rainfall, soil and manure nutrient levels, seed germination, crop establishment, grain yield and above-ground residue biomass were measured. Most important determining factors of crop yield were landscape position and the different within season rainfall distribution of the two seasons. Manure increased yield of sorghum grown in upland and maize grown in lower lowlands. Millet was affected by Quelea quelea birds, the reason why it is unpopular in south eastern Zimbabwe. Best-fit strategies can double total yield from 1.67 to 3.29 t/ha from the average 5.1 ha that farmers usually crop in south east Zimbabwe. Farmers in semi-arid areas can reduce risk of total crop failure by making a clever use of both the low lying and the upland areas depending on crops of their interest.

Labile carbon pools and biological activity in volcanic soils of the Canary Islands .

It is important to assess the mineralisation of soil organic carbon (SOC) to predict the short-term response of biosphere carbon reservoirs to changing environmental conditions. We investigated the labile (easily-mineralisable) SOC in volcanic soils, where the bioavailability of SOC is typically affected by physico-chemical stabilisation mechanisms that are characteristic of these soils. Ten soils were selected that represent the most typical soil types (mainly Andosols) and natural habitats (xerophytic scrubland, laurel forest and pine forest) in the Canary Islands, a volcanic archipelago. Over two years we measured several physico-chemical SOC fractions with different degrees of bioavailability: water-soluble carbon in fresh soil samples (WSC) and in the saturated extract (WSC&lt;sub&gt;se&lt;/sub&gt;), hot water-extractable carbon (HWC), potassium sulphate-extractable carbon (PSC), microbial biomass carbon (MBC), particulate organic carbon (POC), humic substances carbon (HSC), and total organic carbon (TOC), and performed CO&lt;sub&gt;2&lt;/sub&gt; emission incubation assays. We related these measurements to the potential C inputs of plant litter and roots and to the activity of certain hydrolytic enzymes (CM-cellulase, β-D-glucosidase, and dehydrogenase) that are involved in carbon turnover. In vitro carbon mineralisation measurements from short assays (ten days) were fitted with simple first-order kinetics to investigate SOC. This procedure was simple and allowed us to obtain estimates both for potentially mineralisable SOC and for the heterogeneity of the substrates that were consumed during incubation. The investigated volcanic soils had large labile SOC concentrations in which simple carbohydrates predominated and that were mainly derived from roots and aboveground non-woody residues. Among the analysed physico-chemical SOC fractions, HWC (3.1 g kg&lt;sup&gt;-1&lt;/sup&gt; on average at 0-30 cm depth in Andosols) was the most correlated with C&lt;sub&gt;0&lt;/sub&gt; (1.2 g kg&lt;sup&gt;-1&lt;/sup&gt;) and therefore best represents potentially mineralisable SOC. PSC (0.77 g kg&lt;sup&gt;-1&lt;/sup&gt;), which represents an SOC pool of low bioavailability, was protected by its adsorption to allophane in silandic Andosols.