Effects of white clover (Trifolium repens L.) on plant and soil nitrogen and soil organic matter in mixtures with perennial ryegrass (Lolium perenne L.)

To increase our insight into the above- and belowground N flows in grass and grass-clover swards relations between crop and soil parameters were studied in a cutting trial with perennial ryegrass (Lolium perenne) monocultures and ryegrass–white clover (Trifolium repens) mixtures. The effects of clover cultivar on herbage yield, the amount of clover-derived nitrogen, apparent N transfer to companion grass, dynamics of N and organic matter in the soil were estimated.The grass monocultures had very low DM yields (<2.1 t ha^-1) and a low N concentration in the harvested herbage. During 1992–1995 the annual herbage DM yield in the mixtures ranged from 7.0 to 14.3 t ha^-1, the white clover DM yield from 2.4 to 11.2 t ha^-1 and the mean annual clover content in the herbage DM harvested from 34 to 78%. Mixtures with the large-leaved clover cv. Alice yielded significantly more herbage and clover DM and had a higher clover content than mixtures with small/medium-leaved cvs. Gwenda and Retor. Grass cultivar did not consistently affect yield, botanical composition or soil characteristics.The apparent N₂ fixation was very high, ranging from 150 to 545 kg N ha^-1 in the different mixtures. For each tonne of clover DM in the harvested herbage 49 to 63 kg N was harvested, while the apparent N transfer from clover to grass varied between 55 and 113 kg N ha^-1 year^-1.The net N mineralization rate was lower under monocultures than under mixtures. The C mineralization and the amounts of C and N in active soil organic matter fractions were similar for monocultures and mixtures, but the C:N ratio of the active soil organic matter fractions were higher under grass than under mixtures. This explains the lower N mineralization under grass.     

Effect of Potassium and Nitrogen Fertilizer on Switchgrass Productivity and Nutrient Removal Rates under Two Harvest Systems on a Low Potassium Soil

Biomass demand for energy will lead to utilization of marginal, low fertility soil. Application of fertilizer to such soil may increase switchgrass (Panicum virgatum L.) biomass production. In this three-way factorial field experiment, biomass yield response to potassium (K) fertilizer (0 and 68 kg?K?ha^?1) on nitrogen (N)-sufficient and N-deficient switchgrass (0 and 135 kg?N?ha^?1) was evaluated under two harvest systems. Harvest system included harvesting once per year after frost (December) and twice per year in summer (July) at boot stage and subsequent regrowth after frost. Under the one-cut system, there was no response to N or K only (13.4 Mg?ha^?1) compared to no fertilizer (12.4 Mg?ha^?1). Switchgrass receiving both N and K (14.6 Mg?ha^?1) produced 18 % greater dry matter (DM) yield compared to no fertilizer check. Under the two-cut harvest system, N only (16.0 Mg?ha^?1) or K only (14.1 Mg?ha^?1) fertilizer produced similar DM to no fertilizer (15.1 Mg?ha^?1). Switchgrass receiving both N and K in the two-cut system (19.2 Mg?ha^?1) produced the greatest (P?<?0.05) DM yield, which was 32 % greater than switchgrass receiving both N and K in the one-cut system. Nutrient removal (biomass?×?nutrient concentration) was greatest in plots receiving both N and K, and the two-cut system had greater nutrient removal than the one-cut system. Based on these results, harvesting only once during winter months reduces nutrient removal in harvested biomass and requires less inorganic fertilizer for sustained yields from year to year compared to two-cut system.     

Long-Term Miscanthus Yields Influenced by Location,Genotype, Row Distance,Fertilization and Harvest Season

Long-term yield studies in perennial crops like miscanthus are important to determine mean annual energy yield and the farmer’s economy. In two Danish field trials, annual yield of two miscanthus genotypes was followed over a 20-year period. The trials were established in 1993 on loamy sand in Foulum and on coarse sand in Jyndevad. Effects of genotype, row distance and fertilization were investigated. In both trials, yield development over time was characterized by an increase during the first years, optimum yields after 7–8 years and a decrease to a lower level which remained relatively constant from year 11 to 20. Spring harvest reduced the yield by 34–42 % compared to autumn harvest. In Foulum annual fertilization with 75 kg ha^?1 N increased the yield of the genotype Goliath (Miscanthus sinensis) by 26 %. Additional N fertilization only increased the yield of Goliath little, and the genotype Giganteus (Miscanthus?×?giganteus) did not respond to fertilization at all. The highest mean yield in Foulum for the period 1997–2012 was obtained with the shortest row distance (～18,000 rather than ～12,000 plants ha^?1) and harvested in late autumn, namely 13.1 and 12.0 Mg ha^?1 DM annually for Giganteus and Goliath, respectively. In Jyndevad, where only Goliath was studied, the highest yield during 1995–2001 was obtained by short row distance, autumn harvest and annual fertilization with 75 kg ha^?1 N, with yield increasing up to 116 % in response to fertilization. A mean yield of 14.4 Mg ha^?1 DM was achieved over the period 1995–2012.     

Effect of different manuring and defoliation patterns on broad-leaved dock (Rumex obtusifolius) in grassland

The effects of cutting frequency and cutting height on broad‐leaved dock (Rumex obtusifolius) in Lolium perenne‐based agricultural grassland at two levels of fertiliser input were investigated at North Wyke, Devon, UK. Two micro‐plot field experiments, containing immature dock plants at uniform densities, with a factorial design, were used to compare: (a) ‘organic’ and ‘low‐input’ fertilisation, i.e. cattle slurry only vs slurry plus mineral fertiliser (NPK at 100‐0‐64 kg ha^?1 yr^?1), (b) cutting heights of 5–6 cm vs 10–12 cm, and (c) four harvesting frequencies representative of different grassland management practices (regular 4‐weekly cutting, a ‘hay‐stage’ cutting, and two treatments with ‘silage‐stage’ cutting). Expt 1 was established in 1995 with 13 dock plants m^?2 (from excised dock‐root sections) and Expt 2 established in 1996 with 25 plants m^?2 (as seed‐grown plug plants). Treatments were assessed over the 2 subsequent years to determine treatment effects on total herbage dry matter (DM) yield and dock DM yield, and on in‐situ measures of dock ramets. In both experiments, total DM yield was increased by 1.0–2.01 ha^?1 yr^?1 for treatments receiving NK fertiliser; the proportion of dock was also higher than from slurry‐only treatments. In Expt 1, the dock ramet density, mean dock ramet height, mean leaf length and numbers of dock leaves per m² were also greater on NK fertilised treatments in autumn of yr 1. Height of cut had no consistent effect on dock yield, but dock ramet density and leaf density in autumn were greater on the 5–6 cm than the 10–12 cm cutting treatment, Expt 2 only. In yr 2 of both experiments cutting at 4‐weekly intervals resulted in less dock in the herbage than hay‐stage cutting and, particularly in Expt 1, there were associated differences in leaf density and ramet height in autumn; silage‐stage treatments were intermediate. Results are discussed in relation to requirements for management options where there is a need to avoid or reduce herbicides.     

Agricultural Management of Switchgrass for Fuel Quality and Thermal Energy Yield on Highly Erodible Land in the Driftless Area of Southwest Wisconsin

Converting row crop production to a perennial grass crop on highly erodible land has numerous benefits. Switchgrass, grown as a biofuel crop, can provide soil conservation benefits as a perennial crop and also provide economic value to the grower. However, little information exists regarding switchgrass management and production on these lands. The objectives of this study were to determine the effect of two management practices, nitrogen (N) fertilizer rate (0, 56, 112, 168, and 224 kg ha^?1) and harvest timing (mid-fall, late-fall, and spring), on: (1) dry matter (DM) yield, (2) switchgrass quality components (moisture, ash, and chloride (Cl^?) concentrations), and (3) combustion energy content and yield. The study was conducted in 2009 and 2010 on highly erodible lands in the Driftless Area of southwest Wisconsin. Results showed a positive response of switchgrass DM to N fertilizer, with no yield gain above 112 kg ha^?1 of N, although application of N increased Cl^? concentrations. Harvest timing also affected switchgrass yield, with decreases in yield observed with progressively later harvest timings; this yield decrease was slightly greater compared with previous studies. Progressively later harvest timings led to a decrease in moisture, ash concentration, and Cl^? concentration in both years. Energy content of switchgrass was not significantly affected by management. Energy yields, similar to DM yields, were maximized with 112 kg ha^?1 of N with a mid-fall harvest. The similarities between this study and other research indicate there is a universal response of switchgrass to N in the northern USA and yields determined in this study indicate that highly erodible lands in the Driftless Area can be used to produce switchgrass at regionally expected yields.     

Integrated effects of organic,inorganic and biological amendments on methane emission,soil quality and rice productivity in irrigated paddy ecosystem of Bangladesh: field study of two consecutive rice growing seasons

Aims

Effects of different soil amendments were investigated on methane (CH₄) emission, soil quality parameters and rice productivity in irrigated paddy field of Bangladesh.

Methods

The experiment was laid out in a randomized complete block design with five treatments and three replications. The experimental treatments were urea (220 kg ha^?1) + rice straw compost (2 t ha^?1) as a control, urea (170 kg ha^?1) + rice straw compost (2 t ha^?1) + silicate fertilizer, urea (170 kg ha^?1) + sesbania biomass (2 t ha^?1 ) + silicate fertilizer, urea (170 kg ha^?1) + azolla biomass (2 t ha^?1) + cyanobacterial mixture 15 kg ha^?1 silicate fertilizer, urea (170 kg ha^?1) + cattle manure compost (2 t ha^?1) + silicate fertilizer.

Results

The average of two growing seasons CH₄ flux 132 kg ha^?1 was recorded from the conventional urea (220 kg ha^?1) with rice straw compost incorporated field plot followed by 126.7 (4 % reduction), 130.7 (1.5 % reduction), 116 (12 % reduction) and 126 (5 % reduction) kg CH₄ flux ha^?1 respectively, with rice straw compost, sesbania biomass, azolla anabaena and cattle manure compost in combination urea and silicate fertilizer applied plots. Rice grain yield was increased by 15 % and 10 % over the control (4.95 Mg ha^?1) with silicate plus composted cattle manure and silicate plus azolla anabaena, respectively. Soil quality parameters such as soil organic carbon, total nitrogen, microbial biomass carbon, soil redox status and cations exchange capacity were improved with the added organic materials and azolla biofertilizer amendments with silicate slag and optimum urea application (170 kg ha^?1) in paddy field.

Conclusion

Integrated application of silicate fertilizer, well composted organic manures and azolla biofertilizer could be an effective strategy to minimize the use of conventional urea fertilizer, reducing CH₄ emissions, improving soil quality parameters and increasing rice productivity in subtropical countries like Bangladesh.     

Yield and Nitrogen Removal of Bioenergy Grasses as Influenced by Nitrogen Rate and Harvest Management in the Coastal Plain Region of North Carolina

The agronomic performances of giant miscanthus (Miscanthus x giganteus) and switchgrass (Panicum virgatum L.) grown as bioenergy grasses are still unclear in North Carolina, due to a relatively short period of introduction. The objectives of the study were to compare the biomass yield and annual N removal of perennial bioenergy grasses and the commonly grown coastal bermudagrass [Cynodon dactylon (L.) Pers.], and to determine the optimum N rates and harvest practices for switchgrass and miscanthus. A 4-year field trial of the grasses under five annual harvest frequencies (May/Oct, June/Oct, July/Oct, Aug/Oct, and October only) and five annual N rates (0, 67,134, 202, and 268 kg N ha^?1) was established at a research farm in Eastern North Carolina in 2011. Across harvest treatments and N rates, greatest biomass was achieved in the second growth year for both miscanthus (19.0 Mg ha^?1) and switchgrass (15.9 Mg ha^?1). Grasses demonstrated no N response until the second or the third year after crop establishment. Miscanthus reached a yield plateau with a N rate of 134 kg ha^?1 since achieving plant maturity in 2013, whereas switchgrass demonstrated an increasing fertilizer N response from 134 kg N ha^?1 in the third growth year (2014) to 268 kg N ha^?1 in the fourth growth year (2015). The two-cut harvest system is not recommended for bioenergy biomass production in this region because it does not improve biomass yield and increased N removal leads to additional costs.     

Management of Warm- and Cool-Season Grasses for Biomass on Marginal Lands: I. Yield and Soil Fertility Status

Switchgrass (Panicum virgatum L.), tall fescue [Lolium arundinaceum (Schreb.)], and reed canarygrass (Phalaris arundinacea L.) are known for high biomass productivity and for various traits that make these species more suitable for marginal environmental growing conditions. The goal of this study was to evaluate the impact of organic vs. inorganic fertilizer application on grass biomass production and soil nutrient status. Switchgrass, tall fescue, and reed canarygrass were established on a sandy soil and a clay soil at the Cornell University Willsboro Research Farm in Willsboro, NY. The experiment was a split-split plot randomized block design with six replicates. Sites were whole plots, grass species were subplots, and fertility treatments were sub-subplots. The six treatments were (1) 168 kg ha^?1 of N fertilizer for cool-season grasses, 84 kg ha^?1 for switchgrass; (2) 56 kg ha^?1 of 0-46-0 P fertilizer plus N (#1); (3) 112 kg ha^?1 of 0-0-60 K fertilizer plus N (#1); (4) 89.6 Mg dairy manure ha^?1; (5) 44.8 Mg dairy manure compost ha^?1; and (6) no fertilizer applied (control plots). Switchgrass with a single harvest per season yielded on average 13.0 Mg ha^?1, while tall fescue and reed canarygrass averaged 8.4 and 7.7 Mg ha^?1, respectively, under two-cut systems. Switchgrass with no fertilization produced 84% of maximum yield of fertilized treatments. Application of a similar amount of organic N with fresh and composted dairy manure resulted in greater yields for fresh dairy manure. Organic fertilizers strongly impacted the P and K status of soils. Switchgrass is capable of high yields in marginal environments and can provide a land base for environmentally acceptable application of animal manure, although from a yield standpoint it is not very responsive to fertilizer applications.     

Nitrate supply affects root growth differentially in two rice cultivars differing in nitrogen use efficiency

Peatland soils contain large amounts of nitrogen (N) in the soil and mineralization can contribute substantially to the annual mineral N supply of grasslands. We investigated the contribution of N mineralization from peat with respect to the total annual N uptake on grasslands with anthropogenic A horizons and submerged tile drains. The study included i) a pot experiment to determine potential N mineralization from the topsoil and the subsoil, ii) a 1-year field experiment to study herbage yields and N uptake under fertilized and non-fertilized conditions and iii) a 3-year field study where herbage yield and N uptake from the top 30 cm and the entire soil profile were monitored. The 3-year field study yielded an average N uptake of 342 kg?ha^?1 under non-fertilized conditions but the contribution of subsoil peat N mineralization to the total N uptake was found to be negligible. Our calculations demonstrate that peat N mineralization contributed only 10% to 30% to the total N-uptake, mainly coming from the top 30 cm. Most of the N uptake under unfertilized conditions appears to be largely the result of mineralization from long-term inputs of dung, ditch sludge, farmyard manure, cow slurry and non-harvested herbage.     

Biomass Yield and Nutrient Uptake of Energy Sorghum in Response to Nitrogen Fertilizer Rate on Marginal Land in a Semi-Arid Region

Energy sorghum tolerates adverse climatic and edaphic conditions and has great potential as biofuel feedstock in marginal land. This study investigates the potential energy sorghum biomass production and uptake of nitrogen (N), phosphorus (P), and potassium (K) on a sandy loam marginal land in a semi-arid region, in order to define optimum N fertilizer rate to produce the highest biomass yield with minimal nutrient elimination. Five N rate treatments (0, 60, 120, 180, and 240 kg ha^?1) and two sorghum varieties (sweet type Guotian-8 (GT-8) and biomass type Guoneng-11 (GN-11)) were used. Yield increment was observed as N level increased, but the standout treatment appeared to be N rate of 60 kg ha^?1 which significantly increased biomass yield vs. controls by 68.8% in 2014 and 64.1% in 2015. Biomass yield exhibited non-significant differences between N rate treatments from 60 to 240 kg ha^?1, although the highest biomass yield (9.2–11.9 t ha^?1) was observed in the 120 kg N ha^?1 treatment. Nutrient analysis showed that N, P, and K accumulation in aboveground plants increased with N rate increase, ranging between 32.2 and 119.1, 7.9 and 19.2, and 22.1 and 94.0 kg ha^?1, respectively, for the highest N rate of 240 kg ha^?1. Substantial amounts of N were extracted from the soil in control and 60 kg N ha^?1 treatments, despite the low fertility and organic matter content of the soil. Moreover, nitrogen (N) use efficiency (NUE) was maximized at lower N rates. A decline in physiological N use efficiency (PNUE) resulted in decreased agronomic N use efficiency (ANUE) at higher N rates. Hence, it is concluded that N fertilizer rate between 60 and 120 kg ha^?1 would be the optimal N requirement to facilitate sustainable production of energy sorghum on a sandy wasteland.     

N2O and CH4 Emissions,and NO3 − Leaching on a Crop-Yield Basis from a Subtropical Rain-fed Wheat–Maize Rotation in Response to Different Types of Nitrogen Fertilizer

Guaranteeing high crop yields while reducing environmental impacts of nitrogen fertilizer use due to associated losses of N₂O emissions and nitrate (NO₃ ^?) leaching is a key challenge in the context of sustainable intensification of crop production. However, few field data sets are available that explore the effect of different forms of N management on yields as well as on N losses in the form of N₂O or NO₃ ^?. Here we report on a large-scale field lysimeter (8 × 4 m²) experiment, which was designed to determine soil CH₄ and N₂O emissions, NO₃ ^? leaching losses and crop yields from a subtropical rain-fed wheat–maize rotation in the Sichuan Basin, one of the most intensively used agricultural regions in China. One control and three different fertilizer treatments with the same total rate of N application (280 kg N ha^?1 y^?1) were included: NF: control (no fertilizer); NPK: synthetic N fertilizer; OMNPK: synthetic N fertilizer plus pig manure; RSDNPK: synthetic N fertilizer plus crop residues. As compared to the standard NPK treatment, annual NO₃ ^? leaching losses for OMNPK and RSDNPK treatments were decreased by 36 and 22%, respectively (P < 0.05). Similarly, crop yield-scaled NO₃ ^? leaching for NPK treatment was higher than those for either OMNPK or RSDNPK treatments (P < 0.05). Direct N₂O emissions for RSDNPK treatment were decreased as compared with NPK and OMNPK treatments (P < 0.05). Furthermore, the yield-scaled GWP (global warming potential) was lower for the treatments where either pig manure or crop residues were incorporated as compared to the standard NPK treatment (P < 0.05). Our study indicates that it is possible to reduce the negative environmental impact of NO₃ ^? leaching and N₂O emissions without compromising crop productivity. Yield-scaled NO₃ ^? leaching, similar to the yield-scaled GWP, represents another valuable-integrated metric to address the dual goals of reducing nitrogen pollution and maintaining crop grain yield for a given agricultural system.     

The Impact of Using Alternative Forages on the Nutrient Value within Slurry and Its Implications for Forage Productivity in Agricultural Systems

Alternative forages can be used to provide valuable home-grown feed for ruminant livestock. Utilising these different forages could affect the manure value and the implications of incorporating these forages into farming systems, needs to be better understood. An experiment tested the hypothesis that applying slurries from ruminants, fed ensiled red clover (Trifolium pratense), lucerne (Medicago sativa) or kale (Brassica oleracea) would improve the yield of hybrid ryegrass (Lolium hybridicum), compared with applying slurries from ruminants fed ensiled hybrid ryegrass, or applying inorganic N alone. Slurries from sheep offered one of four silages were applied to ryegrass plots (at 35 t ha⁻¹) with 100 kg N ha⁻¹ inorganic fertiliser; dry matter (DM) yield was compared to plots only receiving ammonium nitrate at rates of 0, 100 and 250 kg N ha⁻¹ year⁻¹. The DM yield of plots treated with 250 kg N, lucerne or red clover slurry was significantly higher than other treatments (P<0.001). The estimated relative fertiliser N equivalence (FNE) (fertiliser-N needed to produce same yield as slurry N), was greatest for lucerne (114 kg) >red clover (81 kg) >kale (44 kg) >ryegrass (26 kg ha⁻¹ yr⁻¹). These FNE values represent relative efficiencies of 22% (ryegrass), 52% (kale), 47% (red clover) and 60% for lucerne slurry, with the ryegrass slurry efficiency being lowest (P = 0.005). Soil magnesium levels in plots treated with legume slurry were higher than other treatments (P<0.001). Overall, slurries from ruminants fed alternative ensiled forages increased soil nutrient status, forage productivity and better N efficiency than slurries from ruminants fed ryegrass silage. The efficiency of fertiliser use is one of the major factors influencing the sustainability of farming systems, these findings highlight the cascade in benefits from feeding ruminants alternative forages, and the need to ensure their value is effectively captured to reduce environmental risks.     

Switchgrass Biofuel Production on Reclaimed Surface Mines: II. Feedstock Quality and Theoretical Ethanol Production

Switchgrass (Panicum virgatum L.), a warm-season perennial grass, is an important bioenergy crop candidate because it produces high biomass yields on marginal lands and on reclaimed surface mined sites. In companion studies, dry matter (DM) yields for Cave-in-Rock, Shawnee, and Carthage cultivars varied from 4.2 to 13.0 Mg ha^?1averaged over 6 years at the reclaimed Hampshire site, and fertilization increased yields of Cave-in-Rock at Black Castle and Coal Mac sites from 0.3 to 2 Mg ha^?1 during the first 3 years. The objective of these experiments was to compare the impacts of cultivar and soil amendments on biomass quality and theoretical ethanol production of switchgrass grown on surface mines with differing soil characteristics. Biomass quality was determined for fiber, ash, lignin, digestibility, and carbohydrate contents via near-infrared reflectance spectroscopy, and carbohydrates were used to calculate theoretical ethanol yield (TEY; L Mg^?1) and multiplied by biomass yield to calculate theoretical ethanol production (TEP; L ha^?1). Cultivars at the Hampshire site did not differ in TEY and ranged from 426 to 457 L Mg^?1. Theoretical ethanol production from Cave-in-Rock at Hampshire was 7350 L ha^?1, which was higher than other cultivars because of its greater biomass production. This TEP was higher than in other studies which predicted 4000 to 5000 L ha^?1. At the Black Castle and Coal Mac sites, fertilizer applications slightly affected biomass quality of switchgrass and TEY, but provided greater TEP as a function of increased yield. Similar to other findings, total switchgrass biomass production has more impact than compositional differences on TEP, so maximizing biomass production is critical for maximizing potential biofuel production. With appropriate soil substrates, fertilization, planning, and management, large areas of reclaimed surface mines can be converted to switchgrass stands to produce high biomass quality and yields to support a bioethanol industry.     

The effect of rabbit (Oryctolagus cuniculus) grazing damage on the growth, botanical composition and yield of a ryegrass re-seed

A perennial ryegrass sward was established in the autumn of 1989 in an enclosed 0.3 ha site and was exposed to captive wild rabbit (Oryctolagus cuniculus) grazing. Rabbit numbers were varied from 16 rabbits ha^-1 in winter to 55 rabbits ha^-1 corresponding to natural fluctuations in the field. The original sward was grown for three seasons (1989/1990 to 1990/1991) and a range of grazing regimes imposed. In 1989/1990 four grazing regimes were arranged in a replicated split block design in the experimental area. These were ungrazed, winter grazed, spring grazed and totally grazed. In the second year of the experiment all plots were exposed to grazing with the exception of the originally protected plots. This was to examine the effects of longer-term grazing damage on a ryegrass sward. In the final year half of all treatments were protected to study recovery of a sward which had been damaged previously. The remainder of the plots were exposed to grazing. Three cuts were harvested in each year and the productivity assessed in terms of yield and botanical composition. There was a significant reduction in ryegrass proportion in grazed swards following the first winter of grazing, while clover, other grasses and weeds were enhanced. The promotion of clover content in grazed swards was a feature throughout the 3 yr of the study. In the second year, protection of grazed swards led to a restoration of yields, although the botanical composition remained altered. The exposure of previously ungrazed plots in the final year of the experiment showed that these swards were particularly attractive to rabbits and they suffered the greatest yield losses relative to the protected plots at the first cut in 1991. In this year dry weather conditions were experienced following the first cut and demonstrated that yield losses are exacerbated when rabbit grazing is compounded with adverse growing conditions. The results overall indicate that protection of ryegrass swards at the establishment phase is important, but that a degree of recovery is possible by providing protection at a later stage, although the ryegrass component is still impaired in swards which suffer early damage.     

Screening Perennial Warm-Season Bioenergy Crops as an Alternative for Phytoremediation of Excess Soil P

A recent alternative strategy to reduce environmental problems associated with P transport from agricultural soils is the use of bioenergy crops to remediate excess soil P. In addition to the positive impacts associated with P mitigation, harvested biomass used as a renewable energy source can also offset the cost associated with plant-based P remediation strategies. The objective of this study was to identify potential crop species that can be used for remediation of soil P and as a cellulosic feedstock for production of renewable energy in South Florida. Fifteen crop entries were investigated for their potential to remove P from a P-enriched soil. Dry matter (DM) yield varied among crop species with greatest yield observed for elephantgrass (Pennisetum purpureum Schum.) and sugarcane (Saccharum spp.) (43 and 39 Mg?ha^?1 year^?1, respectively). Similarly, greater P removal rates were observed for elephantgrass (up to 126 kg?P?ha^?1 year^?1 in 2008) followed by sugarcane (62 kg?P?ha^?1 year^?1 in 2008). Although there was no effect (P?=?0.45) of crop species on P reduction in the soil, soil P concentrations decreased linearly during the 3-year study. Because of its relatively greater DM yield and P removal rates, elephantgrass was shown to be a good candidate for remediation of excess soil P in South Florida Spodosols.     

Effects of Nitrogen fertilisation and regrowth period on fatty acid concentrations in perennial ryegrass (Lolium perenne L.)

Information on lipids in forages is scarce, and effects of nitrogen (N) application level and regrowth period on the fatty acid (FA) concentration and composition of perennial ryegrass (Lolium perenne L.) were studied. N was applied at 0, 45 and 100 kg ha^?1, and swards were cut after various regrowth periods, resulting in six treatments designed as randomised blocks with three replicates. The stages of development ranged from vegetative to elongating swards, with herbage yield levels from 1.9 to 4.2 t dry matter (DM) ha^?1. Concentrations of individual FA were determined by gas chromatography, and canopy characteristics and herbage quality were assessed. The treatments resulted in canopies with contrasting DM yields and protein concentrations. Five FAs, representing 98% of total FAs, were studied in detail. On an average, the concentration of these major FAs in fresh grass was 15.1 g kg^?1 DM, and 69% of the major FAs consisted of C18:3. Regrowth period affected (P < 0.05) the total FA concentration, and significantly (P < 0.01) lower concentrations of C18:3 and C16:1 were found after a longer period of regrowth. N application resulted in higher (P < 0.001) concentrations of all FAs. The FA composition was not affected by N application, but a longer regrowth period significantly (P < 0.001) decreased the proportion of C18:3 and increased those of C18:2 and C16:0. A strong, positive overall linear relation was found between the concentrations of total FAs and C18:3 with the crude protein concentration in the herbage. These studies demonstrate opportunities to affect the FA concentration and composition of FA in herbage through management strategies, which could affect milk FA composition.     

Annual nitrous oxide emissions from open-air and greenhouse vegetable cropping systems in China

Aims

A field experiment was conducted to quantify annual nitrous oxide (N₂O) fluxes from control and fertilized plots under open-air and greenhouse vegetable cropping systems in southeast China. We compiled the reported global field annual N₂O flux measurements to estimate the emission factor of N fertilizer for N₂O and its background emissions from vegetable fields.

Methods

Fluxes of N₂O were measured using static chamber-GC techniques over the 2010–2011 annual cycle with multiple cropping seasons.

Results

The mean annual N₂O fluxes from the controls were 46.1?±?2.3 μg N₂O-N m^?2 hr^?1 and 68.3?±?4.1 μg N₂O-N m^?2 hr^?1 in the open-air and greenhouse vegetable systems, respectively. For the plots receiving 900 kg?N?ha^?1, annual N₂O emissions averaged 90.6?±?8.9 μg N₂O-N m^?2 hr^?1 and 106.4?±?6.6 μg N₂O-N?m^?2 hr^?1 in the open-air and greenhouse vegetable systems, respectively. By pooling published field N₂O flux measurements taken over or close to a full year, the N₂O emission factor for N fertilizer averaged 0.63?±?0.09 %, with a background emission of 2.67?±?0.80 kg N₂O-N ha^?1 in Chinese vegetable fields. Annual N₂O emissions from Chinese vegetable systems were estimated to be 84.7 Gg N₂O-N yr^?1, consisting of 72.5 Gg N₂O-N yr^?1 and 12.2 Gg N₂O-N yr^?1 in the open-air and greenhouse vegetable systems, respectively.

Conclusions

While N₂O emissions from the greenhouse vegetable cropping system tended to be slightly higher compared to the open-air system in our experiment, the synthesis of literature data suggests that N₂O emissions would be greater at low N-rates but smaller at high N-rates in greenhouse systems than in open-air vegetable cropping systems. The estimates of this study suggest that vegetable cropping systems covering 11.4 % in national total cropping area, contributed 21–25 % to the total N₂O emission from Chinese croplands.     

Soil mineralizable nitrogen and soil nitrogen supply under two-year potato rotations

Two-year potato rotations were evaluated for their effects on soil mineralizable N and soil N supply. Pre-plant soil samples (0–15 cm) collected from the potato year after seven rotation cycles were used to estimate soil mineralizable N using a 24 week aerobic incubation. Potentially mineralizable N (N ₀ ) ranged from 102 to 149 kg N ha^?1, and was greater after pea/white clover and oats/Italian ryegrass than after oats by an average of 35 and 22%, respectively. Labile, intermediate and stable mineralizable N pools were increased after pea/white clover compared with oats, whereas only the stable mineralizable N pool was increased after oats/Italian ryegrass. Potato plant N uptake with no fertilizer applied was greater in potato-pea/white clover compared with the three other rotations (126 vs. average of 67 kg N ha^?1). Choice of rotation crop in potato production influences both the quantity and quality of soil mineralizable N.     

Short-term simulated nitrogen deposition increases carbon sequestration in a Pleioblastus amarus plantation

In order to understand the influence of nitrogen (N) deposition on the key processes relevant to the carbon (C) balance in a bamboo plantation, a two-year field experiment involving the simulated deposition of N in a Pleioblastus amarus plantation was conducted in the rainy region of SW China. Four levels of N treatments: control (no N added), low-N (50 kg N ha^?1 year^?1), medium-N (150 kg N ha^?1 year^?1), and high-N (300 kg N ha^?1 year^?1) were set in the present study. The results showed that soil respiration followed a clear seasonal pattern, with the maximum rates in mid-summer and the minimum in late winter. The annual cumulative soil respiration was 585?±?43 g CO₂-C m^?2 year^?1 in the control plots. Simulated N deposition significantly increased the mean annual soil respiration rate, fine root biomass, soil microbial biomass C (MBC), and N concentration in fine roots and fresh leaf litter. Soil respirations exhibited a positive exponential relationship with soil temperature, and a linear relationship with MBC. The net primary production (NPP) ranged from 10.95 to 15.01 Mg C ha^?1 year^?1 and was higher than the annual soil respiration (5.85 to 7.62 Mg C ha^?1 year^?1) in all treatments. Simulated N deposition increased the net ecosystem production (NEP), and there was a significant difference between the control and high N treatment NEP, whereas, the difference of NEP among control, low-N, and medium-N was not significant. Results suggest that N controlled the primary production in this bamboo plantation ecosystem. Simulated N deposition increased the C sequestration of the P. amarus plantation ecosystem through increasing the plant C pool, though CO₂ emission through soil respiration was also enhanced.     

Soil carbon dioxide and methane fluxes as affected by tillage and N fertilization in dryland conditions

Background and aims

The effects of tillage and N fertilization on CO₂ and CH₄ emissions are a cause for concern worldwide. This paper quantifies these effects in a Mediterranean dryland area.

Methods

CO₂ and CH₄ fluxes were measured in two field experiments. A long-term experiment compared two types of tillage (NT, no-tillage, and CT, conventional intensive tillage) and three N fertilization rates (0, 60 and 120 kg N ha^?1). A short-term experiment compared NT and CT, three N fertilization doses (0, 75 and 150 kg N ha^?1) and two types of fertilizer (mineral N and organic N with pig slurry). Aboveground and root biomass C inputs, soil organic carbon stocks and grain yield were also quantified.

Results

The NT treatment showed a greater mean CO₂ flux than the CT treatment in both experiments. In the long-term experiment CH₄ oxidation was greater under NT, whereas in the short-term experiment it was greater under CT. The fertilization treatments also affected CO₂ emissions in the short-term experiment, with the greatest fluxes when 75 and 150 kg organic N ha^?1 was applied. Overall, the amount of CO₂ emitted ranged between 0.47 and 6.0 kg CO₂?equivalent kg grain^?1. NT lowered yield-scaled emissions in both experiments, but these treatment effects were largely driven by an increase in grain yield.

Conclusions

In dryland Mediterranean agroecosystems the combination of NT and medium rates of either mineral or organic N fertilization can be an appropriate strategy for optimizing CO₂ and CH₄ emissions and grain yield.