Anaerobic Soil Disinfestation (ASD) Combined with Soil Solarization as a Methyl Bromide Alternative: Vegetable Crop Performance and Soil Nutrient Dynamics

Background and Aims

Soil treatment by anaerobic soil disinfestation (ASD) combined with soil solarization can effectively control soilborne plant pathogens and plant-parasitic nematodes in specialty crop production systems. At the same time, research is limited on the impact of soil treatment by ASD?+?solarization on soil fertility, crop performance and plant nutrition. Our objectives were to evaluate the response of 1) soil nutrients and 2) vegetable crop performance to ASD?+?solarization with differing levels of irrigation, molasses amendment, and partially-composted poultry litter amendment (CPL) compared to an untreated control and a methyl bromide (MeBr)?+?chloropicrin-fumigated control.

Methods

A 2-year field study was established in 2008 at the USDA-ARS U.S. Horticultural Research Lab in Fort Pierce, Florida, USA to determine the effectiveness of ASD as an alternative to MeBr fumigation for a bell pepper (Capsicum annum L.)-eggplant (Solanum melongena L.) double crop system. A complete factorial combination of treatments in a split-split plot was established to evaluate three levels of initial irrigation [10, 5, or 0 cm], two levels of CPL (amended or unamended), and two levels of molasses (amended or unamended) in combination with solarization. Untreated and MeBr controls were established for comparison to ASD treatments.

Conclusions

Results suggest that ASD treatment using molasses as the carbon source paired with solarization can be an effective strategy to maintain crop yields in the absence of soil fumigants. For both bell pepper and eggplant crops, ASD treatments with molasses as the carbon source had equivalent or greater marketable yields than the MeBr control. The application of organic amendments in ASD treatment (molasses or molasses?+?CPL) caused differences in soil nutrients and plant nutrition compared to the MeBr control that must be effectively managed in order to implement ASD on a commercial scale as a MeBr replacement.     

Rapeseed rotation, compost and biocontrol amendments reduce soilborne diseases and increase tuber yield in organic and conventional potato production systems

Aims

Integrating multiple soil and disease management practices may improve crop productivity and disease control, but potential interactions and limitations need to be determined.

Methods

Three different potential disease-suppressive management practices, including a Brassica napus (rapeseed) green manure rotation crop, conifer-based compost amendment, and three biological control organisms (Trichoderma virens, Bacillus subtilis, and Rhizoctonia solani hypovirulent isolate Rhs1A1) were evaluated alone and in combination at sites with both organic and conventional management histories for their effects on soilborne diseases and tuber yield.

Results

Rapeseed rotation reduced all observed soilborne diseases (stem canker, black scurf, common scab, and silver scurf) by 10 to 52 % in at least one year at both sites. Compost amendment had variable effects on tuber diseases, but consistently increased yield (by 9 to 15 %) at both sites. Biocontrol effects on disease varied, though Rhs1A1 decreased black scurf at the conventional site and T. virens reduced multiple diseases at the organic site in at least one year. Combining rapeseed rotation with compost amendment both reduced disease and increased yield, whereas biocontrol additions produced only marginal additive effects.

Conclusions

Use of these treatments alone, and in combination, can be effective at reducing disease and increasing yield under both conventional and organic production practices.     

Contribution of winter cover crop amendments on global warming potential in rice paddy soil during cultivation

Background and aims

Winter cover crop cultivation during the fallow season has been strongly recommended in mono-rice paddy soil to improve soil quality, but its impact in increasing the greenhouse gases (GHGs) emissions during rice cultivation when applied as green manure has not been extensively studied. In order to recommend a preferable cover crop which can increase soil productivity and suppress GHG emission impact in paddy soil, the effect of winter cover crop addition on rice yield and total global warming potential (GWP) was studied during rice cultivation.

Methods

Two cover crops (Chinese milk vetch, Astragalus sinicus L., hereafter vetch, and rye, Secale cerealis) having different carbon/nitrogen (C/N) ratios were cultivated during the rice fallow season. The fresh above-ground biomasses of vetch [25 Mg fresh weight (FW) ha^?1, moisture content (MC) 86.9 %, C/N ratio 14.8] and rye (29 Mg rye FW ha^?1, MC 78.0 %, C/N ratio 64.3) were incorporated as green manure 1 week before rice transplanting (NPK + vetch, and NPK + rye). The NPK treatment was installed for comparison as the control. During the rice cultivation, methane (CH₄) and nitrous oxide (N₂O) gases were collected simultaneously once a week using the closed-chamber method, and carbon dioxide (CO₂) flux was estimated using the soil C balance analysis. Total GWP impact was calculated as CO₂ equivalents by multiplying the seasonal CH₄, CO₂, and N₂O fluxes by 25, 1, and 298, respectively.

Results

Methane mainly covered 79–81 % of the total GWP, followed by CO₂ (14–17 %), but the N₂O contribution was very small (2–5 %) regardless of the treatment. Seasonal CH₄ fluxes significantly increased to 61 and 122 % by vetch and rye additions, respectively, compared to that of the NPK treatment. Similarly, the estimated seasonal CO₂ fluxes increased at about 197 and 266 % in the vetch and rye treatments, respectively, compared with the NPK control plots. Based on these results, the total GWP increased to 163 and 221 % with vetch and rye applications, respectively, over the control treatment. Rice productivity was significantly increased with the application of green manure due to nutrient supply; however, vetch was more effective. Total GWP per grain yield was similar with the vetch (low C/N ratio) and NPK treatments, but significantly increased with the rye (high C/N ratio) application, mainly due to its higher CH₄ emission characteristic and lower rice productivity increase.

Conclusions

A low C/N ratio cover crop, such as vetch, may be a more desirable green manure to reduce total GWP per grain yield and to improve rice productivity.     

Seven-Year Impact of Cover Crops on Soil Health When Corn Residue Is Removed

Removing plant residue from soil has been shown to have an adverse effect on soil health; however, the addition of cover crops may help mitigate these impacts. This study was conducted to assess the effect of incorporating cover crops on soil health with varying removal rates of corn (Zea mays L.) residues. Corn was grown in rotation with soybean (Glycine max) in a randomized, split-block design with three different corn residue removal levels (37, 55, and 98% of total above-ground C) as whole plot treatments and the presence or absence of cover crops as the split plot treatment. Soil samples were collected from both crop phases following 7 years of cover crop treatment and subjected to a suite of soil health measurements. In the soybean phase immediately following corn residue removal, there were significant (P?=?0.025) increases in the erodible fraction (EF) of soil aggregates and reductions in the stable, larger aggregate fractions. Cover crops mitigated these changes in aggregate distributions in the highest residue removal treatment. Residue removal resulted in a significant decrease in fPOM (P?=?0.03) while the addition of cover crops increased fPOM levels during the soybean phase (P?=?0.002). Residue removal significantly (P?=?0.017) decreased soil microbial enzyme activities while cover crops restored activities in the highest residue removal treatment (P?=?0.037). We also found higher fungal:bacterial ratios with cover cropping compared to no cover crops. We conclude that cover cropping continued over multiple years can partially mitigate negative effects of crop residue removal on soil health thus limiting soil erosion and maintaining nutrient cycling activities in the vulnerable period following residue removal.     

Nitrogen release from incorporated 15N-labelled Chinese milk vetch (Astragalus sinicus L.) residue and its dynamics in a double rice cropping system

Background and aims

Chinese milk vetch (Astragalus sinicus L. CMV), a leguminous cover crop, has been shown to provide N benefits to rice crops, but little is known about the pathway of incorporated CMV and its N dynamics. In this study, effects of CMV under different application treatments (incorporated alone, applied in conjunction with urea fertilizer and applied with ryegrass (Lolium multiflorum Lam.)) on N dynamics, rice yields and N uptake were investigated and compared with those of chemical fertilizer (CF) and no fertilizer (NF) in a double rice cropping system.

Methods

Nitrogen release from incorporated CMV residue was quantified by using a bag method. Nitrogen dynamics of CMV were evaluated by using ¹⁵N-labelled fresh CMV tops and compared with those of CF (¹⁵N-labelled urea).

Results

CMV residue decomposition pattern and its N release pattern followed a single exponential decay model, with 87.8–89.5 % of the applied CMV decomposed and 95.1–96.1 % of the original N released in the double rice season (177 days after fertilizer application). CMV treatments had higher rice N uptake efficiency than CF (39.2–51.3 % vs. 29.9 %) at the sum of early and late rice seasons. Rice yield, N accumulation and mineral fertilizer efficiency in CMV treated treatments were higher than those in CF. After two consecutive rice seasons the amounts of residual N remained in the soil were higher in the CMV treated fields than in CF (29.4–33.2 % vs. 14.1 %).

Conclusions

CMV can be considered an efficient N source alternative to chemical fertilizer in double rice cropping systems.     

Biochar application to a fertile sandy clay loam in boreal conditions: effects on soil properties and yield formation of wheat, turnip rape and faba bean

Background and aims

We studied the effect of different biochar (BC) application rates on soil properties, crop growth dynamics and yield on a fertile sandy clay loam in boreal conditions.

Methods

In a three-year field experiment conducted in Finland, the field was divided into three sub-experiments with a split-plot experimental design, one for each crop: wheat (Triticum aestivum), turnip rape (Brassica rapa), and faba bean (Vicia faba). The main plot factor was BC rate (0, 5 and 10 t DM ha^?1) and the sub-plot factor was the N-P-K fertiliser rate. Soil physico-chemical properties as well as plant development, yield components and quality were investigated.

Results

BC addition did not significantly affect the soil chemical composition other than the increased C and initially increased K contents. Increased soil moisture content was associated with BC application, especially at the end of the growing seasons. BC decreased the N content of turnip rape and wheat biomass in 2010, thus possibly indicating an initial N immobilisation. In dry years, the seed number per plant was significantly higher in faba bean and turnip rape when grown with BC, possibly due to compensation for decreased plant density and relieved water deficit. However, the grain yields and N uptake with BC addition were not significantly different from the control in any year.

Conclusions

Even though BC application to a fertile sandy clay loam in a boreal climate might have relieved transient water deficit and thereby supported yield formation of crops, it did not improve the yield or N uptake.     

Influence of cover crops and tillage systems on nematode populations in a maize-cover crop intercrop

Cropping systems affect the distribution/diversity of soil microorganisms, including soilborne pathogens. In order to examine the effect of the cropping systems on soil nematodes, maize (Zea mays) was intercropped with different cover crops [Glycine max (GM), Macrotyloma uniflorum (MU), Centrosema pascuorum (CP), Cucurbita maxima (CM) and a control experiment with no cover crop (NC)] under different tillage systems [no till, reduced tillage and conventional tillage] to evaluate the effect of the various treatments on nematode population. The treatments were arranged in a split-plot design with three replications each. Tillage was the main treatment while cover crops were applied to subtreatment. In all, nematodes belonging to twenty-two (22) plant parasitic nematode genera were identified. While most of the genera were identified on all the treatments, the interaction of tillage systems and cover crops had significant effect on the population of Xiphinema and Trichodorus only, showing the nullifying effect of some tillage practices on the other nematodes which were significant under crops as only treatments inter alia. This information could be used in nematode management when integrated management systems are being considered for such intercrop mixtures.     

Estimating belowground nitrogen inputs of pea and canola and their contribution to soil inorganic N pools using 15N labeling

Background and aims

Crop species grown in a diversified crop rotation can influence soil N dynamics to varying degrees due to differences in the quantity and quality of the residues returned to the soil. The aim of this study was to quantify the contribution of N rhizodeposition by canola (Brassica napus L.) and pea (Pisum sativum L.) to the crop residue N balance and soil inorganic N pool.

Methods

Canola and pea were grown in a soil-sand mixture and were subject to cotton-wick ¹⁵N labeling in a greenhouse experiment. Nitrogen-15 recovered in the soil and roots were used to estimate N rhizodeposition.

Results

Belowground N, including root N and N rhizodeposits, comprised 70 % and 61 % of total crop residue N for canola and pea, respectively. Canola released the greatest amount of total root-derived N to the soil, which was related to greater root biomass production by canola. However, root-derived N in the soil inorganic N pool was greater under pea (13 %) than canola (4 %).

Conclusions

Our results show a significant belowground N contribution to total crop residue from pea and canola. Further investigation is required to determine whether input of the more labile N rhizodeposits of pea improves soil N supply to succeeding crops or increases the potential for N loss from the soil system relative to canola.     

Soil fertility and its significance to crop productivity and sustainability in typical agroecosystem: a summary of long-term fertilizer experiments in China

Aims and background

Soil fertility quality index is a useful indicator that helps to improve sustainable land use management and achieve economical yield in agriculture production. The objectives of this study were to evaluate the changes of soil fertility quality between the 1980s and 2000s in different cropping systems and its significance to crop productivity and sustainability.

Methods

We collected all published data on crop yields and soil parameters from 58 long-term experiments in three typical double-cropping systems in China, including maize-wheat (M-W), rice-rice (R-R) and rice-wheat (R-W) cropping systems, and selected seven fertilizer treatments in each experiment, including inorganic fertilizer [nitrogen and phosphorus fertilizer (NP), nitrogen and potassium fertilizer (NK), phosphorus and potassium fertilizer (PK) and balanced mineral fertilizer (NPK)], combined NPK with farmyard manure (NPKM) or crop straw (NPKS), and no fertilizer application (served as control). For comparison, an integrated fertility quality index (IFQI) was used to estimate the variations in soil fertility in different cropping systems. Moreover, the mean production variability index (PVI, %) in each cropping system was calculated to evaluate the stability of crop production.

Results

Over cropping systems, the averaged relative yields of PK, NK and NP ranged from 38.0 to 97.4 %, while the mean yields can be increased by 2.4–5.1 % in NPKM, compared to NPK. The mean yields were similar between NPK and NPKS for maize and wheat crops, but the yield was increased by 4.3–10.0 % in NPKS. Among the different treatments, the highest variability of cereal productivity was obtained in NK, PK or Control, while the lowest value was mostly recorded in NPKM or NPKS in these three cropping systems. Relative to the control, the IFQIs in fertilization treatments were increased by 9.4–150.0 %, 6.2–41.5 % and 1.3–17.5 % in M-W, R-W and R-R systems, respectively (except for PK treatment in R-R system). However, changes of IFQI in topsoil differed among fertilizer treatments, and greater increases existed in the treatments receiving organic residues (NPKM and NPKS).

Conclusions

The increase in crop yield is exponentially correlated with the increased IFQI over treatments in three cropping systems. Over the treatments and systems, production variability among years is shown to be negatively, linearly related to IFQI (P?<?0.001). Therefore, the high grain yield and low production variability can be simultaneously achieved by increasing soil fertility in all three cropping systems.     

Influence of agricultural practices and seasons on the abundance and community structure of culturable pseudomonads in soils under no-till management in Argentina

Background and aims

Members of the genus Pseudomonas are common inhabitants of rhizospheres and soils, and it is known that soil types and crop species influence their population density and structure. 20?×?10⁶ ha are cultivated under no-tillage in Argentina and there is a need to find new biologically-based soil quality indexes to distinguish between sustainable and non-sustainable agricultural practices. Pseudomonads abundance and community structure were analyzed in no-till soils with different agricultural practices, in productive fields along 400 km of Argentinean Pampas.

Methods

We sampled soils and root systems from agricultural plots in which sustainable or non-sustainable agricultural practices have been applied. Samples were collected in summer and winter during 2010 and 2011. Culturable fluorescent and total pseudomonads were enumerated by plating on Gould’s selective medium S1. Colonies from these plates served as DNA source to carry out PCR-RFLP community structure analysis of the pseudomonads-specific marker genes oprF and gacA.

Results

Abundance of total and fluorescent culturable pseudomonads in bulk soils was influenced by seasonal changes and agricultural practices. Rhizospheric counts from the same crop were affected by agricultural treatments. Also, crop species influenced pseudomonads density in the rhizosphere. Combined PCR-RFLP profile of both genes showed a seasonal grouping of samples.

Conclusions

Sustainable soil management seems to promote pseudomonads development in soils, favoring root colonization of crops from those plots. Crop species influence total pseudomonads load of rhizospheres and its community structure. Total or relative pseudomonads load could function as soil quality indicator of good agricultural practices.     

Effects of take-all (Gaeumannomyces graminis var. tritici) on crop N uptake and residual mineral N in soil at harvest of winter wheat

Background and aims

Take-all, caused by the fungus Gaeumannomyces graminis var. tritici, is the most damaging root disease of wheat. A severe attack often leads to premature ripening and death of the plant resulting in a reduction in grain yield and effects on grain quality (Gutteridge et al. in Pest Manag Sci 59:215–224, 2003). Premature death of the plant could also lead to inefficient use of applied nitrogen (Macdonald et al. in J Agric Sci 129(2):125–154, 1997). The aim of this study was to determine crop N uptake and the amount of residual mineral N in the soil after harvest where different severities of take-all had occurred.

Methods

Plant and soil samples were taken at anthesis and final harvest from areas showing good and poor growth (later confirmed to be caused by take-all disease) in three winter wheat crops grown on the same soil type on Rothamsted Farm in SE England in 1995, 2007 and 2008 (harvest sampling only). All crops received fertiliser N in spring at recomended rates (190–200?kg?N ha^?1). On each ocassion crops were assessed for severity of take-all infection (TAR) and crop N uptakes and soil nitrate plus ammonium (SMN) was determined. Grain yields were also measured.

Results

Grain yields (at 85% dry matter) of crops with moderate infection (good crops) ranged from 4.3 to 13.0?t ha^?1, compared with only 0.9–4.5?t ha^?1 for those with severe infection (poor crops). There were significant (P?<?0.05) negative relationships between crop N uptake and TAR at anthesis and final harvest. At harvest, good crops contained 129–245?kg?N ha^?1 in grain, straw and stubble, of which 85–200?kg?N ha^?1 was in the grain. In contrast, poor crops contained only 46–121?kg?N ha^?1, of which only 22–87?kg?N ha^?1 was in the grain. Positive relationships between SMN and TAR were found at anthesis and final harvest. The SMN in the 0–50?cm layer following harvest of poor crops was significantly (P?<?0.05) greater than that under good crops, and most (73–93%) was present as nitrate.

Conclusions

Localised patches of severe take-all infection decreased the efficiency with which hexaploid wheat plants recovered soil and fertiliser derived N, and increased the subsequent risk of nitrate leaching. The risk of gaseous N losses to the atmosphere from these areas may also have been enhanced.     

The effect of rate and Cd concentration of repeated phosphate fertilizer applications on seed Cd concentration varies with crop type and environment

Background and aims

Limited information is available on how cadmium (Cd) applied in phosphate fertilizer interacts with soil and environmental conditions over time to affect crop Cd concentrations.

Methods

Field studies from 2002 to 2009 at seven locations evaluated the cumulative effects of P fertilizer rate and Cd concentration on seed Cd concentration of durum wheat (Triticum turgidum L.) and flax (Linum usitatissiumum L.).

Results

Soil characteristics and environment affected Cd availability. Durum wheat grain Cd increased with P fertilizer rate but effect on flaxseed Cd concentration was smaller. Cadmium concentration in fertilizer had a greater effect on flaxseed than durum wheat Cd concentration. Seed Cd concentration of both crops was greatest with the highest rate P fertilizer containing the highest Cd concentration. There was not a strong cumulative effect of fertilization over the 8 years of the study, indicating attenuation of Cd availability over time.

Conclusions

Cadmium in phosphate fertilizer increases Cd available for crop uptake, but crop Cd concentration is also affected by soil characteristics and annual environmental conditions. Type of crop produced and soil and environmental characteristics that affect phytoavailability must be taken into account when assessing the Cd risk from P fertilization.     

Growth response of crops to soil microbial communities from conventional monocropping and tree-based intercropping systems

Background and aims

Recent studies have shown that tree-based intercropping (TBI) systems support a more diverse soil microbial community compared to conventional agricultural systems. However, it is unclear whether differences in soil microbial diversity between these two agricultural systems have a functional effect on crop growth.

Methods

In this study, we used a series of greenhouse experiments to test whether crops respond differently to the total soil microbial community (Experiment 1) and to arbuscular mycorrhizal (AM) fungal communities alone (Experiment 2) from conventionally monocropped (CM) and TBI systems.

Results

The crops had a similar growth response to the total soil microbial communities from both cropping systems. However, when compared to sterilized controls, barley (Hordeum vulgare) and canola (Brassica napus) exhibited a negative growth response to the total soil microbial communities, while soybean (Glycine max) was unaffected. During the AM fungal establishment phase of the second experiment, ‘nurse’ plants had a strong positive growth response to AM fungal inoculation, and significantly higher biomass when inoculated with AM fungi from the CM system compared to the TBI system. Soybean was the only crop species to exhibit a significant positive growth response to AM fungal inoculation. Similar to the total soil microbial communities, AM fungi from the two cropping systems did not differ in their effect on crop growth.

Conclusion

Overall, AM fungi from both cropping systems had a positive effect on the growth of plants that formed a functional symbiosis. However, the results from these experiments suggest that negative effects of non-AM fungal microbes are stronger than the beneficial effects of AM fungi from these cropping systems.     

Potassium release characteristics, potassium balance, and fingermillet (Eleusine coracana G.) yield sustainability in a 27- year long experiment on an Alfisol in the semi-arid tropical India

Aims

In Alfisols, potassium (K) deficiency limits productivity, as these soils are poor in K-bearing minerals such as mica. As nutrient management practices greatly influence K nutrition of crops especially in the longer term, we evaluated the effects of 27 (1978–2004) years of cropping fingermillet (Eleusine coracana G.) under different manure and mineral fertilizer treatments on K release, balance and yield sustainability on K deficient Alfisols in the semi-arid tropical region of southern India.

Methods

Fingermillet (variety: PR-202) was grown each year under rainfed conditions with 5 different nutrient management treatments: control (no amendment), 10 Mg ha^?1 farm yard manure (FYM), 10 Mg ha^?1 FYM +50 % NPK, 10 Mg ha^?1 FYM +100 % NPK and 100 % NPK. Potassium release characteristics in the soil profile were determined using 1 N boiling HNO₃ (strong extracting solution), 0.01 M HCl (medium extracting solution) and 0.01 M CaCl₂ (mild extracting solution).

Results

Continuous cropping of Alfisols for 27 years resulted in a decrease in K supplying capacity due to soil K depletion through crop K uptake. In soils without K addition, inherent soil supply could not meet the K requirement of fingermillet; thus, a negative K balance following 27 years of cropping affected K nutrition of the crop in all the treatments. As a result, the highest sustainable yield index (SYI) was observed using an integrated nutrient supply (combined application of nutrients from organic and inorganic sources), and the lowest index was obtained without K additions.

Conclusion

For balanced nutrient management in cereal production systems, K nutrition needs urgent attention in the K deficient Alfisol region of southern India. Addition of any amount of organic manures available at field level offers an alternative strategy for maintaining soil K fertility to improve and sustain crop productivity.     

Influence of organic residues and soil incorporation on temporal measures of microbial biomass and plant available nitrogen

Aims

Despite our current understanding of plant nitrogen (N) uptake and soil N dynamics in arable systems, the supply and demand of N are infrequently matched as a result of variable seasonal and soil conditions. Consequently, inefficiencies in N utilisation often lead to constrained production and can contribute to potential environmental impacts. The aim of this study was to examine the influence of plant residue quality (C/N ratio) and extent of residue incorporation into soil on temporal changes in soil mineral N and the associated plant N uptake by wheat in the semi-arid agricultural production zone of Western Australia.

Methods

Oat (Avena sativa); lupin (Lupinus angustifolius) and field pea (Pisum sativum) were incorporated into a Red-Brown Earth using varying degrees of mechanical disturbance (0 to 100% residue incorporated). Soil samples for inorganic N (NO ₃ ^? and NH ₄ ⁺ ) profiles (0?C50?cm), microbial biomass-C (0?C50?cm) and plant N uptake were taken throughout the growing season of the subsequent wheat (Triticum aestivum) crop. Grain yield and yield components were determined at harvest.

Results

Despite observed treatment effects for plant residue type and soil disturbance, fluctuations in inorganic N were more readily influenced by seasonal variability associated with wet-dry cycles. Treatment effects resulting from residue management and extent of soil disturbance were also more readily distinguished in the NO ₃ ^? pool. The release of N from crop residues significantly increased (p?=?0.05) with greater soil-residue contact which related to the method of incorporation; the greater the extent of soil disturbance, the greater the net supply of inorganic N. Differences in microbial biomass-C were primarily associated with the type of plant residue incorporated, with higher microbial biomass generally associated with legume crops. No effect of residue incorporation method was noted for microbial biomass suggesting little effect of soil disturbance on the microbial population in this soil.

Conclusions

Despite differences in the magnitude of N release, neither crop type nor incorporation method significantly altered the timing or pattern of N release. As such asynchrony of N supply was not improved through residue or soil management, or through increased microbial biomass in this semi-arid environment. N fluxes were primarily controlled by abiotic factors (e.g. climate), which in this study dominated over imposed agricultural management practices associated with residue management.     

The effects of a permanently elevated water table in an acid sulphate soil on reed canary grass for combustion

Aims and background

Acid sulphate (AS) soils require careful management to prevent the environmental hazards that result from the oxidation of sulphide-bearing deep soil layers and the consequent acidification of soil and waters. Management with a high water table precludes many food crops, so their suitability for perennial energy cropping was investigated in a 3-year study using reed canary grass (Phalaris arundinacea L., RCG).

Methods

Monolithic lysimeters made of undisturbed AS soil and equipped with ground-water level control and measurement instruments were planted with 1- year-old RCG turfs taken from a non-AS field. Two water tables were imposed, high (HWT, 20 cm below soil surface) and low (LWT, 70 cm below soil surface, considered normal for agriculturally managed AS soils) for a 3 year period. Growth and physiological characters of RCG were determined and its ash content and the elemental composition of its dry biomass (Ca, Cl, K, Mg, and S) were analysed.

Results

The level of the water table had significant effects on crop growth and quality. Shoots were 25 to 29 % taller, consequently yielding more dry matter in HWT than in LWT lysimeters. Concentrations of K, Mg and S that can affect the combustion process were higher in biomass harvested from LWT lysimeters than from the HWT plants. At the end of the experiment, the spatial distribution of roots within the soil profile differed between treatments. Roots penetrated to the bottom of LWT lysimeters with total root dry mass nearly twice that in HWT.

Conclusions

RCG intended for burning grows and performs well in acid sulphate soils managed with a raised water table. This management option minimizes the risk of acid flows from oxidized soils, and allows farmers to harvest a non-food crop from soils that would have to be drained to provide a food or feed crop.     

Conventional tillage versus cover crops in relation to carbon fixation in Mediterranean olive cultivation

Background and Aims

For croplands, controversy persists concerning the adequacy of the soil use and the management of environmental problems such as soil erosion and fertility in a context of climate change. In this study, we used the RothC model to evaluate the capacity of carbon fixation by the soil in a Mediterranean olive grove for two different scenarios: the land-use change from native vegetation (NV) to conventional tillage (T) in the olive grove, and for the change in soil management from conventional tillage to cover crop (CC).

Methods

In three experimental olive groves in Andalusia (S Spain) two soil-management systems were sampled: T and CC. Areas of NV adjacent to the grove were also sampled as indicative of the initial state of the soil without olive trees. We measured the aboveground biomass production of the cover and the clay content, bulk density, and soil organic carbon (SOC) for 0–5, 5–15 and 15–30 cm depth.

Results

The removal of NV to implement T resulted in a significantly loss of SOC that depended mainly on the relief of the terrain. However, the use of CC increased the SOC because of greater inputs (above-and belowground plant inputs) to the soil. The final concentration at each location was related to the carbon inputs and the clay content. The CC resulted in carbon storage during the first year of 4.02?±?1.65 Mg C ha^?1, and a total carbon fixation by the soil of 5.91?±?2.06 Mg C ha^?1.

Conclusion

The use of cover crops in Mediterranean olive groves proved to be a suitable strategy to increase the carbon storage into the soil and then to decrease the CO₂ concentration in the atmosphere.     

Biochar from Miscanthus: a potential silicon fertilizer

Background and aims

Silicon (Si) is largely recognized to improve plant growth subjected to various biotic and abiotic stresses. As plants accumulate Si in the form of readily-soluble phytolith, we examine the possibility of using phytolith-rich biochar as a bio-available Si source for increasing the agronomical productivity of Si high-accumulator plants while augmenting soil fertility and C sequestration.

Methods

By adding three different biochars (Miscanthus x giganteus straws, coffee husks and woody material) at two different concentrations (1 % and 3 %; w/w) to soil samples, we investigated the effects on the soil respiration, the chemical characteristics and the kinetic release of bio-available Si (CaCl₂-extractable Si).

Results

Here we show that the biochar from Miscanthus straws was the most attractive amendment. Its incorporation at a 3 % rate improved the soil fertility parameters (pH and available cations) and combined the highest mean residence time of carbon (C) in soil (MRT?=?50 years) with the highest rate of release of bio-available Si. We attribute this result to the presence of phytoliths in this biochar, as revealed by SEM-EDS analysis.

Conclusions

Not only did the biochar from Miscanthus enhance both soil C sequestration and fertility, but the results of this study suggest that it can also be considered as a potential source of bio-available Si. Although our conclusions should be substantiated in the field, we suggest that Miscanthus biochar could be used as a potential source of bio-available silicon for the culture of such crop as Si-accumulator plants growing, for instance, in highly weathered tropical soils with low content in carbon, nutrients and bio-available Si.     

The effect of catch crop species on selenium availability for succeeding crops

Background and Aims

Selenium (Se) is an essential nutrient for humans and animals. In order to ensure an optimal concentration of Se in crops, Se fertilisers are applied. Catch crops may be an alternative way to increase Se concentrations in vegetables.

Methods

Three experiments in Denmark between 2007–10 investigated the ability of catch crops (Italian ryegrass, fodder radish and hairy vetch) under different fertiliser regimes to reduce soil Se content in the autumn and to increase its availability in spring to the succeeding crop.

Results and Conclusions

The catch crops (Italian ryegrass and fodder radish) increased water-extractable Se content in the 0.25–0.75?m soil layer in only one of the experiments. Selenium uptake by the catch crops varied between 65 and 3263?mg?ha^?1, depending on species, year and fertilisation treatment; this corresponded to 0.1–3.0% of the water-extractable soil Se content. The influence of catch crops on Se concentrations and uptake in onions and cabbage was low. There was a decrease in Se uptake and recovery of applied Se by onions following catch crops, which might indicate Se immobilisation during catch crop decomposition.     

Short-term effects of soil solarization in suppressing Calonectria microsclerotia

Background and aims

Calonectria species have been reported as devastating pathogens mostly on horticultural and forest crops worldwide. Since these pathogens represent a serious threat for the nursery production, the aim of this study was to investigate on the short-term potential of soil solarization for eradicating Calonectria microsclerotia.

Methods

Twenty Calonectria isolates collected in Italy from different hosts and locations were identified by using DNA sequencing of β-tubulin. The effect of thermal regimes and innovative solarizing films on the soil survival of Calonectria microsclerotia was evaluated through time at different sampling periods in growth chamber and greenhouse experiments.

Results

Eleven and nine isolates were identified as Calonectria pauciramosa and Calonectria polizzii, respectively. No viable Calonectria inoculum was recovered after 12 days from all solarized plots inside ethylene-tetrafluoroethylene (ETFE) greenhouse and at 15-cm depth from solarized plots inside ethylene-vinyl-acetate (EVA) greenhouse. Under EVA cover, solarization killed C. pauciramosa microsclerotia within 9 and 17 d at 15- and 30-cm depths in soil, respectively, whereas no viable inoculum was retrieved within 6 and 12 days from solarized plots inside ETFE greenhouse.

Conclusions

This paper demonstrates that short-term soil solarization is effective for Calonectria microsclerotia suppression in nurseries, and shows that ETFE film as well as other innovative materials could improve this technique.