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.     

Effect of biochar amendment on maize yield and greenhouse gas emissions from a soil organic carbon poor calcareous loamy soil from Central China Plain

Aims

A field experiment was conducted to investigate the effect of biochar on maize yield and greenhouse gases (GHGs) in a calcareous loamy soil poor in organic carbon from Henan, central great plain, China.

Methods

Biochar was applied at rates of 0, 20 and 40?t?ha^?1 with or without N fertilization. With N fertilization, urea was applied at 300?kg?N ha^?1, of which 60% was applied as basal fertilizer and 40% as supplementary fertilizer during crop growth. Soil emissions of CO₂, CH₄ and N₂O were monitored using closed chambers at 7?days intervals throughout the whole maize growing season (WMGS).

Results

Biochar amendments significantly increased maize production but decreased GHGs. Maize yield was increased by 15.8% and 7.3% without N fertilization, and by 8.8% and 12.1% with N fertilization under biochar amendment at 20?t?ha^?1 and 40?t?ha^?1, respectively. Total N₂O emission was decreased by 10.7% and by 41.8% under biochar amendment at 20?t?ha^?1 and 40?t?ha^?1 compared to no biochar amendment with N fertilization. The high rate of biochar (40?t?ha^?1) increased the total CO₂ emission by 12% without N fertilization. Overall, biochar amendments of 20?t?ha^?1 and 40?t?ha^?1 decreased the total global warming potential (GWP) of CH₄ and N₂O by 9.8% and by 41.5% without N fertilization, and by 23.8% and 47.6% with N fertilization, respectively. Biochar amendments also decreased soil bulk density and increased soil total N contents but had no effect on soil mineral N.

Conclusions

These results suggest that application of biochar to calcareous and infertile dry croplands poor in soil organic carbon will enhance crop productivity and reduce GHGs emissions.     

Carbon footprint of canola and mustard is a function of the rate of N fertilizer

Purpose  

Best agricultural practices can be adopted to increase crop productivity and lower carbon footprint of grain products. The aims of this study were to provide a quantitative estimate of the carbon footprint of selected oilseed crops grown on the semiarid northern Great Plains and to determine the effects of N fertilization and environments on the carbon footprint.     

Background nitrous oxide emissions in agricultural and natural lands: a meta-analysis

Aim

This study aimed at better characterising background nitrous oxide (N₂O) emissions (BNE) in agricultural and natural lands.

Methods

We compiled and analysed field-measured data for annual background N₂O emission in agricultural (BNEA) and natural (BNEN) lands from 600 and 307 independent experimental studies, respectively.

Results

There were no significant differences between BNEA (median: 0.70 & mean: 1.52 kg N₂O???N ha^?1 yr^?1) and BNEN (median:0.31 & mean:1.75 kg N₂O???N ha^?1 yr^?1) (P?>?0.05). A simultaneous comparison across all BNEA and BNEN indicated that BNEs from riparian, vegetable crop fields and intentional fallow areas were significantly higher than from boreal forests (P?<?0.05). Correlation and regression analyses supported the underlying associations of soil organic carbon (C), nitrogen (N), pH, bulk density (BD),and/or air temperature (AT) with BNEs to a varying degree as a function of land-use or ecosystem type (Ps?<?0.05).

Conclusions

Although overall BNEN tended to be lower than BNEA on median basis, results in general suggest that land-use shifts between natural and managed production systems would not result in consistent changes in BNE.     

Role of maize stover incorporation on nitrogen oxide emissions in a non-irrigated Mediterranean barley field

Aims

Agricultural soils in semiarid Mediterranean areas are characterized by low organic matter contents and low fertility levels. Application of crop residues and/or manures as amendments is a cost-effective and sustainable alternative to overcome this problem. However, these management practices may induce important changes in the nitrogen oxide emissions from these agroecosystems, with additional impacts on carbon dioxide emissions. In this context, a field experiment was carried out with a barley (Hordeum vulgare L.) crop under Mediterranean conditions to evaluate the effect of combining maize (Zea mays L.) residues and N fertilizer inputs (organic and/or mineral) on these emissions.

Methods

Crop yield and N uptake, soil mineral N concentrations, dissolved organic carbon (DOC), denitrification capacity, N₂O, NO and CO₂ fluxes were measured during the growing season.

Results

The incorporation of maize stover increased N₂O emissions during the experimental period by c. 105 %. Conversely, NO emissions were significantly reduced in the plots amended with crop residues. The partial substitution of urea by pig slurry reduced net N₂O emissions by 46 and 39 %, with and without the incorporation of crop residues respectively. Net emissions of NO were reduced 38 and 17 % for the same treatments. Molar DOC:NO ₃ ^? ratio was found to be a robust predictor of N₂O and NO fluxes.

Conclusions

The main effect of the interaction between crop residue and N fertilizer application occurred in the medium term (4–6 month after application), enhancing N₂O emissions and decreasing NO emissions as consequence of residue incorporation. The substitution of urea by pig slurry can be considered a good management strategy since N₂O and NO emissions were reduced by the use of the organic residue.     

Annual emissions of nitrous oxide and nitric oxide from rice-wheat rotation and vegetable fields: a case study in the Tai-Lake region, China

Background and aims

Knowledge on nitrous oxide (N₂O) and nitric oxide (NO) emissions from typical cropping systems in the Tai-Lake region is important for estimating regional inventory and proposing effective N₂O and NO mitigation options. This study aimed at a) characterizing the seasonal and annual emissions of both gases from the major cropping systems, and b) determining their direct emission factors (EF_ds) as the key parameters for inventory compilation.

Methods

Measurements of N₂O and NO emissions were conducted year-round in the Tai-Lake region using a static opaque chamber method. The measurements involved a typical rice-wheat rotation ecosystem and a vegetable field. The two types of croplands were subjected to both a fertilized treatment and a control treatment without nitrogen addition. In the rice-wheat ecosystem, N₂O emissions were measured throughout an entire year-round rotation spanning from June 2003 to June 2004, whereas NO emissions were measured only during the non-rice period. In the vegetable field, both N₂O and NO emissions were measured from November 2003 to November 2004.

Results

During the investigation period, the average cumulative N₂O and NO emissions under the fertilized conditions amounted to 3.80 and 0.80 (during the non-rice period for NO) kg?N?ha^?1, respectively, in the rice-wheat field, and 20.81 and 47.13?kg?N ha^?1, respectively, in the vegetable field. The average total N₂O and NO emissions under the control conditions were 1.39 and 0.29 (during the non-rice period for NO) kg?N?ha^?1, respectively, in the rice?wheat rotation, and 2.98 and 0.80?kg?N ha^?1, respectively, in the vegetable field. The direct emission factor (EF_d, which is defined as the loss rate of applied nitrogen via N₂O or NO emissions in the current season or year) of N₂O was annually determined to be 0.56?% in the rice-wheat field, while the seasonal EF_d of NO was 0.34?% during the non-rice period of the rotation cycle. In the vegetable field, the seasonal EF_ds of N₂O and NO varied from 0.15?% to 14.50?% and 0.80?% to 28.21?%, respectively, among different crop seasons; and the annual EF_ds were 1.38?% and 3.59?%, respectively.

Conclusions

This study suggests that conventional vegetable fields associated with intensive synthetic nitrogen application, as well as addition of manure slurry, may substantially contribute to the regional N₂O and NO emissions though they account for a relatively small portion of the farmlands in the Tai-Lake region. However, further studies to be conducted at multiple field sites with conventional vegetable and rice-based fields are needed to test this conclusion.     

Direct nitrous oxide emissions from oilseed rape cropping – a meta‐analysis

Oilseed rape is one of the leading feedstocks for biofuel production in Europe. The climate change mitigation effect of rape methyl ester (RME) is particularly challenged by the greenhouse gas (GHG) emissions during crop production, mainly as nitrous oxide (N₂O) from soils. Oilseed rape requires high nitrogen fertilization and crop residues are rich in nitrogen, both potentially causing enhanced N₂O emissions. However, GHG emissions of oilseed rape production are often estimated using emission factors that account for crop‐type specifics only with respect to crop residues. This meta‐analysis therefore aimed to assess annual N₂O emissions from winter oilseed rape, to compare them to those of cereals and to explore the underlying reasons for differences. For the identification of the most important factors, linear mixed effects models were fitted with 43 N₂O emission data points deriving from 12 different field sites. N₂O emissions increased exponentially with N‐fertilization rates, but interyear and site‐specific variability were high and climate variables or soil parameters did not improve the prediction model. Annual N₂O emissions from winter oilseed rape were 22% higher than those from winter cereals fertilized at the same rate. At a common fertilization rate of 200 kg N ha^?1 yr^?1, the mean fraction of fertilizer N that was lost as N₂O‐N was 1.27% for oilseed rape compared to 1.04% for cereals. The risk of high yield‐scaled N₂O emissions increased after a critical N surplus of about 80 kg N ha^?1 yr^?1. The difference in N₂O emissions between oilseed rape and cereal cultivation was especially high after harvest due to the high N contents in oilseed rape's crop residues. However, annual N₂O emissions of winter oilseed rape were still lower than predicted by the Stehfest and Bouwman model. Hence, the assignment of oilseed rape to the crop‐type classes of cereals or other crops should be reconsidered.     

Quantification of ammonia exchange between agricultural cropland and the atmosphere: Measurements over two complete growth cycles of oilseed rape,wheat, barley and pea

The exchange of ammonia between the atmosphere and the canopy of barley, wheat, oilseed rape and pea crops was studied over two growing seasons by use of a modified aerodynamic gradient technique in which passive horizontal flux samplers were applied with a wind profile in gradient configuration. The crop foliage was a net source of NH₃ to the atmosphere, with NH₃ emissions on a seasonal basis between 1 and 5 kg NH₃–N ha^–1. The amount of NH₃ lost constituted between 1 and 4% of the applied nitrogen and between 1 and 4% of the actual amount of nitrogen present in the mature shoots. The volatile NH₃ losses depended on seasonal variations in climatic conditions affecting the growth and nitrogen economy of the crops and increased under conditions with excessive N absorption by roots and a high N concentration in the foliage. The accumulated NH₃ loss was positively correlated with the above-ground crop N content at anthesis, but not with that at final maturity. There were no indications that NH₃ emissions were larger under conditions unfavourable for nitrogen remobilization from vegetative plant parts (low N harvest index). Nevertheless, a distinct peak in NH₃ emission occurred during senescence. It is concluded that crops in many areas will represent a significant input of ammonia to the atmosphere and that NH₃ losses may become large enough to significantly affect crop N budgets.     

Nitrous oxide emissions and nitrate leaching from a rain-fed wheat-maize rotation in the Sichuan Basin, China

Aims

A 3-year field experiment (October 2004–October 2007) was conducted to quantify N₂O fluxes and determine the regulating factors from rain-fed, N fertilized wheat-maize rotation in the Sichuan Basin, China.

Methods

Static chamber-GC techniques were used to measure soil N₂O fluxes in three treatments (three replicates per treatment): CK (no fertilizer); N150 (300 kg N fertilizer ha^?1 yr^?1 or 150 kg N?ha^?1 per crop); N250 (500 kg N fertilizer ha^?1 yr^?1 kg or 250 kg N?ha^?1 per crop). Nitrate (NO ₃ ^? ) leaching losses were measured at nearby sites using free-drained lysimeters.

Results

The annual N₂O fluxes from the N fertilized treatments were in the range of 1.9 to 6.7 kg N?ha^?1 yr^?1 corresponding to an N₂O emission factor ranging from 0.12 % to 1.06 % (mean value: 0.61 %). The relationship between monthly soil N₂O fluxes and NO ₃ ^- leaching losses can be described by a significant exponential decaying function.

Conclusions

The N₂O emission factor obtained in our study was somewhat lower than the current IPCC default emission factor (1 %). Nitrate leaching, through removal of topsoil NO ₃ ^? , is an underrated regulating factor of soil N₂O fluxes from cropland, especially in the regions where high NO ₃ ^- leaching losses occur.     

Successive straw biochar application as a strategy to sequester carbon and improve fertility: A pot experiment with two rice/wheat rotations in paddy soil

Aims

A pot study spanning four consecutive crop seasons was conducted to compare the effects of successive rice straw biochar/rice straw amendments on C sequestration and soil fertility in rice/wheat rotated paddy soil.

Methods

We adopted 4.5 t ha^?1, 9.0 t ha^?1 biochar and 3.75 t ha^?1 straw for each crop season with an identical dose of NPK fertilizers.

Results

We found no major losses of biochar-C over the 2-year experimental period. Obvious reductions in CH₄ emission were observed from rice seasons under the biochar application, despite the fact that the biochar brought more C into the soil than the straw. N₂O emissions with biochar were similar to the controls without additives over the 2-year experimental period. Biochar application had positive effects on crop growth, along with positive effects on nutrient (N, P, K, Ca and Mg) uptake by crop plants and the availability of soil P, K, Ca and Mg. High levels of biochar application over the course of the crop rotation suppressed NH₃ volatilization in the rice season, but stimulated it in the wheat season.

Conclusions

Converting straw to biochar followed by successive application to soil is viable for soil C sequestration, CH₄ mitigation, improvements of soil and crop productivity. Biochar soil amendment influences NH₃ volatilization differently in the flooded rice and upland wheat seasons, respectively.     

Greenhouse Gas Emissions, Nitrate Leaching, and Biomass Yields from Production of Miscanthus × giganteus in Illinois, USA

Understanding the effects of nitrogen (N) fertilization on Miscanthus × giganteus greenhouse gas emissions, nitrate leaching, and biomass production is an important consideration when using this grass as a biomass feedstock. The objective of this study was to determine the effect of three N fertilization rates (0, 60, and 120?kg?N?ha^?1 using urea as the N source) on nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions, nitrogen leaching, and the biomass yields and N content of M. × giganteus planted in July 2008, and evaluated from 2009 through early 2011 in Urbana, Illinois, USA. While there was no biomass yield response to N fertilization rates in 2009 and 2010, the amount of N in the harvested biomass in 2010 was significantly greater at the 60 and 120?kg?N?ha^?1?N rates. There was no significant CO₂ emission response to N rates in 2009 or 2010. Similarly, N fertilization did not increase cumulative N₂O emissions in 2009, but cumulative N₂O emissions did increase in 2010 with N fertilization. During 2009, nitrate (NO ₃ ^? ) leaching at the 50-cm soil depth was not related to fertilization rate, but there was a significant increase in NO ₃ ^? leaching between the 0 and 120?kg?N?ha^?1 treatments in 2010 (8.9 and 28.9?kg?NO₃?CN?ha^?1?year^?1, respectively). Overall, N fertilization of M. × giganteus led to N₂O releases, increased fluxes of inorganic N (primarily NO ₃ ^? ) through the soil profile; and increased harvested N without a significant increase in biomass production.     

Root interactions between intercropped legumes and non-legumes—a competition study of red clover and red beet at different nitrogen levels

Aims

To investigate root competition in a legume/non-legume mixture, and how root growth of the legume is affected by the competition at increasing nitrogen (N) supply.

Methods

Red beet (Beta vulgaris L.) and red clover (Trifolium pratense L.) were grown in transparent rhizotron tubes either in mixture or as sole crop at N supplies of 0, 75 or 150 kg ha^-1. The root growth was evaluated by the root intensity on the rhizotron surface, root depth and plant uptake of ¹⁵N injected into the soil at the deeper part of the red clover root system.

Results

Competition with red beet decreased clover root intensity in deeper soil layers compared to clover grown as sole crop. The difference between clover in sole crop and in mixture was not evident at the highest N supply because the root growth of clover in sole crop appeared to be lowered at high N level. Increased N supply increased the dominance of red beet, but generally did not alter the root growth and distribution of the two species grown in mixture.

Conclusions

Clover root growth and rooting depth were inhibited by competition with red beet but the effect was not enhanced by increased N supply; hence the increased dominance of red beet at higher N level was likely due to its increased growth and competitiveness for other soil resources.     

Nitrous oxide emissions during the non-rice growing seasons of two subtropical rice-based rotation systems in southwest China

Background and aims

High nitrous oxide (N₂O) emissions may occur during the non-rice growing season of Chinese rice-upland crop rotation systems. However, our understanding of N₂O emission during this season is poor due to a scarcity of available field N₂O measurements.

Methods

Using the static manual chamber-GC technique, seasonal N₂O emissions during the non-rice growing season were simultaneously measured at two adjacent rice-wheat and rice-rapeseed fields in southwest China for three consecutive annual rotation cycles (May 2005 to May 2008).

Results

Compared to the control, N fertilizer applications significantly enhanced soil N₂O emissions from both wheat and rapeseed systems. Seasonal cumulative N₂O fluxes from wheat systems were on average 2.6 kg N ha^?1 for the recommended practice (RP [150 kg N ha^?1]) and 5.0 kg N ha^?1 for the conventional practice (CP [250 kg N ha^?1]). Lower N₂O emissions were observed from the adjacent rapeseed systems. Average cumulative seasonal N₂O fluxes from rapeseed were 1.5 and 2.2 kg N ha^?1 for the RP and CP treatments, respectively. The first 3 weeks after N fertilization were the “hot moment” of N₂O emissions for both the wheat and rapeseed systems. The lowest yield-scaled N₂O fluxes for wheat were obtained at the RP treatment (mean: 0.81 kg N Mg^?1) while for rapeseed the CP treatment produced the lowest yield-scaled fluxes (mean: 0.79 kg N Mg^?1). On average, the direct N₂O emission factors (EF_d) for the wheat system (1.76 %) were over two times higher than for the rapeseed system (0.73 %).

Conclusions

Intercropping of rapeseed tends to result in lower N₂O emissions than wheat for rice-upland crop rotation systems of southwest China, indicating that either the N fertilization or the cropping system need to be considered not only for improving the estimate of regional and/or national N₂O fluxes but also for proposing the climate-smart agricultural management practice to reduce N₂O emissions from agricultural soils.     

Hyperaccumulation of thallium is population-specific and uncorrelated with caesium accumulation in the thallium hyperaccumulator, Biscutella laevigata

Purpose

This study investigated the residual contribution of legume and fertilizer nitrogen (N) to a subsequent crop under the effect of elevated carbon dioxide concentration ([CO₂]).

Methods

Field pea (Pisum sativum L.) was labeled in situ with ¹⁵N (by absorption of a ¹⁵N-labeled urea solution through cut tendrils) under ambient and elevated (700 μmol mol^–1) [CO₂] in controlled environment glasshouse chambers. Barley (Hordeum vulgare L.) and its soil were also labeled under the same conditions by addition of ¹⁵N-enriched urea to the soil. Wheat (Triticum aestivum L.) was subsequently grown to physiological maturity on the soil containing either ¹⁵N-labeled field pea residues (including ¹⁵N-labeled rhizodeposits) or ¹⁵N-labeled barley plus fertilizer ¹⁵N residues.

Results

Elevated [CO₂] increased the total biomass of field pea (21 %) and N-fertilized barley (23 %), but did not significantly affect the biomass of unfertilized barley. Elevated [CO₂] increased the C:N ratio of residues of field pea (18 %) and N-fertilized barley (19 %), but had no significant effect on that of unfertilized barley. Elevated [CO₂] increased total biomass (11 %) and grain yield (40 %) of subsequent wheat crop regardless of rotation type in the first phase. Irrespective of [CO₂], the grain yield and total N uptake by wheat following field pea were 24 % and 11 %, respectively, higher than those of the wheat following N-fertilized barley. The residual N contribution from field pea to wheat was 20 % under ambient [CO₂], but dropped to 11 % under elevated [CO₂], while that from fertilizer did not differ significantly between ambient [CO₂] (4 %) and elevated [CO₂] (5 %).

Conclusions

The relative value of legume derived N to subsequent cereals may be reduced under elevated [CO₂]. However, compared to N fertilizer application, legume incorporation will be more beneficial to grain yield and N supply to subsequent cereals under future (elevated [CO₂]) climates.     

Crop residue incorporation negates the positive effect of elevated atmospheric carbon dioxide concentration on wheat productivity and fertilizer nitrogen recovery

Background and purpose

Rapid increases in atmospheric carbon dioxide concentration ([CO₂]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO₂] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO₂] on the growth, grain yield and the recovery of ¹⁵N-labeled fertilizer by wheat (Triticum aestivum L. cv. Yitpi) under controlled environmental conditions.

Methods

Residue for ambient and elevated [CO₂] treatments, obtained from wheat grown previously under ambient and elevated [CO₂], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage ¹⁵N-labeled granular urea (10.22 atom%) was applied at 50 kg?N ha^?1 and the wheat grown to maturity.

Results

When residue was not incorporated into the soil, elevated [CO₂] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO₂] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO₂] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO₂] decreased fertilizer N recovery.

Conclusions

A higher fertilizer application rate will be required under future elevated [CO₂] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO₂] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment.     

Impact of biochar application on nitrogen nutrition of rice, greenhouse-gas emissions and soil organic carbon dynamics in two paddy soils of China

Aims

Two field microcosm experiments and ¹⁵N labeling techniques were used to investigate the effects of biochar addition on rice N nutrition and GHG emissions in an Inceptisol and an Ultisol.

Methods

Biochar N bioavailability and effect of biochar on fertilizer nitrogen-use efficiency (NUE) were studied by ¹⁵N-enriched wheat biochar (7.8803 atom% ¹⁵N) and fertilizer urea (5.0026 atom% ¹⁵N) (Experiment I). Corn biochar and corn stalks were applied at 12 Mg?ha^?1 to study their effects on GHG emissions (Experiment II).

Results

Biochar had no significant impact on rice production and less than 2 % of the biochar N was available to plants in the first season. Biochar addition increased soil C and N contents and decreased urea NUE. Seasonal cumulative CH₄ emissions with biochar were similar to the controls, but significantly lower than the local practice of straw amendment. N₂O emissions with biochar were similar to the control in the acidic Ultisol, but significantly higher in the slightly alkaline Inceptisol. Carbon-balance calculations found no major losses of biochar-C.

Conclusion

Low bio-availability of biochar N did not make a significantly impact on rice production or N nutrition during the first year. Replacement of straw amendments with biochar could decrease CH₄ emissions and increase SOC stocks.     

Life cycle assessment of the supply and use of bioenergy: impact of regional factors on biogas production

Purpose

This article evaluates the parameters that influence the results of a life cycle assessment (LCA) of biogas production from maize and the conversion of biogas into electricity. The environmental impacts of biogas vary according to regional farming procedures and, therefore, the soil, climate conditions, crop yield, and cultivation management. This study focuses on these regional parameters and the existing infrastructure, including the number of installed biogas plants and their share of used heat.

Materials and methods

To assess the regional impact, the LCAs of maize cultivation, on the one hand, and the production and use of biogas, on the other, were performed for three different areas. These areas were the administrative districts of Celle, Hildesheim, and Goettingen; all located in the south of Lower Saxony, Germany. The areas differed in geographic location conditions, crop yield, and the number of installed biogas plants. The necessary data for modeling the cultivation of maize were derived from the specific regional and local parameters of each area. The most important parameters were the soil characteristics and the climate conditions for cultivating maize. The share of used heat from combined heat and power unit (CHP) was another relevant factor for biogas production and use.

Results

Our results demonstrate significant differences among the investigated areas. The smallest environmental impact of all the considered categories occurs in Goettingen and the largest in Celle. The net greenhouse gas emissions vary from 0.179?kg CO₂ eq./kWh_el in Celle to 0.058?kg CO₂ eq./kWh_el in Goettingen. This result is due to the maize cultivation system and the different credits for using heat from the CHP. Variances in energy crop cultivation result from different nitrogen and irrigation demands. In addition, despite higher applications of nitrogen fertilizer and irrigation, the maize yield is lower in Celle. The impact category of total fossil energy shows similar results to that of the greenhouse gas (GHG) emissions. The results range from ?0.274 to 0.175 kWh/kWh_el. The results of acidification and eutrophication vary from 1.62 in Goettingen to 1.94?g SO₂ eq./kWh_el in Celle and respectively 0.330 to 0.397?g PO ₄ ^3? eq./kWh_el. These differences are primarily caused by maize cultivation, especially irrigation.

Conclusions and perspectives

Cultivating maize and using waste heat from the CHP were identified as the most influential parameters for the GHG emissions and total fossil energy demand. Regarding acidification and eutrophication, the most relevant factors are the application of digester output and the emissions from the CHP. Our results show the need to consider regional parameters in the LCA of bioenergies, particularly biogas production and use, especially if the LCA studies are used for generalized evaluations such as statements on the climate protection potential of biogas.     

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.     

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.     

Evidence from field nitrogen balance and 15N natural abundance data for the contribution of biological N2 fixation to Brazilian sugarcane varieties

Aims

In Brazil N fertilization of sugarcane (Saccharum spp.) is low compared to most other countries. ¹⁵N-aided studies and the occurrence of many N₂-fixing bacteria associated with cane plants suggest significant contributions from biological N₂ fixation (BNF). The objective of this study was to evaluate BNF contributions to nine cane varieties under field conditions using N balance and ¹⁵N natural abundance techniques.

Methods

The field experiment was planted near Rio de Janeiro in 1989, replanted in 1999 and harvested 13 times until 2004. Soil total N was evaluated at planting and again in 2004. Samples of cane leaves and weeds for the evaluation of ¹⁵N natural abundance were taken in 2000, 2003 and 2004.

Results

N accumulation of the commercial cane varieties and a variety of Saccharum spontaneum were persistently high and N balances (60 to 107?kg?N ha^?1?yr^?1) significantly (p?<?0.05) positive. The δ¹⁵N of leaf samples were lower than any of the weed reference plants and data obtained from a greenhouse study indicated that this was not due to the cane plants tapping into soil of lower ¹⁵N abundance at greater depth.

Conclusion

The results indicate that the Brazilian varieties of sugarcane were able to obtain at least 40?kg?N ha^?1?yr^?1 from BNF.