Fertilization of SRC Willow,II: Leaching and Element Balances

Short rotation coppice (SRC) willow is an emerging cropping system in focus for production of biomass for energy. To increase production, the willow is commonly fertilized, but studies have shown differing effects of fertilization on biomass production, ranging from almost no response to considerable positive effects. Focus has also been on replacing mineral fertilizer with organic waste products, such as manure and sludge. However, the effect on biomass production and environmental impact of various dosage and types of fertilizer is not well described. Therefore we studied the environmental impacts of different doses of mineral fertilizer, manure and sewage sludge in a commercially grown SRC willow stand. We examined macro nutrient and heavy metal leaching rates and calculated element balances to evaluate the environmental impact. Growth responses were reported in a former paper (Sevel et al. “Fertilization of SRC Willow, I: Biomass Production Response” Bioenergy Research, 2013). Nitrogen leaching was generally low, between 1 and 7 kg N ha^?1 year^?1 when doses of up to 120 kg N ha^?1 year^?1 were applied. Higher doses of 240 and 360 kg N ha^?1 as single applications caused leaching of 66 and 99 kg N ha^?1 year^?1, respectively, indicating N saturation of the system. Previous intensive farming including high doses of fertilizer may be responsible for a high soil N status and the high N leaching rates. However, moderate fertilization input could not compensate P and K exports with the biomass harvest. No elevated leaching of heavy metals was observed for any fertilization treatments and more cadmium than applied with the fertilizer was removed with the biomass from the system.     

Fertilization of Willow Coppice Over Three Consecutive 2-Year Rotations—Effects on Biomass Production,Soil Nutrients and Water

Short rotation coppice (SRC) willow is a promising bioenergy feedstock. Fertilization is an integrated part of the production system, but knowledge about the effects in consecutive rotations is scarce. The objective of this study was to identify an appropriate fertilization regime for achieving high yields, reducing risks of nutrient leaching and maintaining the soil nutrient stocks in SRC willow on a former arable land. Ten different fertilization treatments were applied, with different application frequencies, fertilizer types and doses over three consecutive 2-year rotations. The biomass production was determined at harvest, soil solution samples were collected monthly, water fluxes were modelled using CoupModel and nutrient budgets were calculated. The unfertilized control had a mean biomass production of 8.3, 8.3 and 9.5 odt ha^?1 year^?1, respectively, in the three rotations. This indicated that nutrients were adequately available to maintain production for at least 6 years without fertilization. When adding 60 kg N ha^?1 year^?1, biomass production tended to be higher than the control, by 33% (p = 0.055), and the treatment where 360 kg N ha^?1 rotation^?1 was added, by 31% (p = 0.08). Treatments with one-time addition of 240 and 360 kg N ha^?1 rotation^?1 had significantly higher nitrogen leaching than all other treatments. Organic fertilizers did not increase biomass production nor N leaching significantly compared to the control, but nutrient budgets indicated a nutrient build-up in the soil. We concluded that application of 60 kg N ha^?1 year^?1 is recommendable, for achieving high biomass yields, low nitrogen leaching and maintenance of the soil nutrient stock.     

Impact of Nitrogen Fertilization to Short-Rotation Willow Coppice Plantations Grown in Sweden on Yield and Economy

A fertilization trial was carried out in established short-rotation willow coppice (SRWC) plantations of two bred varieties of willow (Salix spp.; "Tora" and "Jorr") at five sites in central Sweden between 2008 and 2010. Mineral nitrogen was applied at four different rates: No fertilization (Control), 160 kg nitrogen ha^?1 as a single dose after harvest (Economy), 60–100–60 kg nitrogen ha^?1 in year 1–2–3 (Normal), and 160 kg nitrogen ha^?1 year^?1 in years 1–3 (Intensive), using a randomized block design with four replicates. The yield response (biomass increase per kg fertilizer nitrogen) was 65, 67 and 46 kg kg^?1 in the Economy, Normal and Intensive treatments, respectively. The results from the fertilization trial were used for economic calculations of different fertilization strategies given varying costs for fertilization and marginal value of the increased yield (price received for wood chips minus the costs for harvest and transportation of wood chips to a district heating plant). Comparative calculations were made based on data from a previous fertilization trial during the first cutting cycle of old, non-bred varieties. The calculations showed positive net present values of fertilizing bred willow varieties given a realistic fertilization response and a price for wood chips close to the market price for forestry-based wood chips in Sweden.     

Establishment and Early Growth of Willow at Different Levels of Weed Competition and Nitrogen Fertilization

To evaluate the effects of weed competition and nitrogen fertilization on the early growth performance of willow, cuttings of the clone Tora (Salix schwerinii x S. viminalis) were planted in buckets together with model weeds (spring barley or white mustard) sown 15, 26, and 30 days after willow planting. The buckets were fertilized with 30 or 90 kg N ha^?1. Willow with weeds sown after 15 days produced less biomass and smaller leaf area and had a lower maximum shoot height compared to willow planted without weeds and willow with weeds sown after 26 or 30 days. Fertilization with 90 kg N ha^?1 gave higher willow biomass production in willow with weeds sown after 26 or 30 days. Type of model weed had no effect on willow performance. Weed biomass and maximum shoot height were higher in weeds planted without willows compared to the willow-weed mixtures. A high nitrogen level gave more weed biomass when planted without willows and in the willow-weed mixture with weeds sown after 15 days. We conclude that for the given high density of willow, competition from weeds emerging soon after willow planting had strong effect on early production. Furthermore, if there is a risk of weed infestation, fertilization should be delayed.     

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.     

Field Evaluation of Willow Under Short Rotation Coppice for Phytomanagement of Metal-Polluted Agricultural Soils

Short rotation coppice (SRC) of willow and poplar might be a promising phytoremediation option since it uses fast growing, high biomass producing tree species with often a sufficient metal uptake. This study evaluates growth, metal uptake and extraction potentials of eight willow clones (Belders, Belgisch Rood, Christina, Inger, Jorr, Loden, Tora and Zwarte Driebast) on a metal-contaminated agricultural soil, with total cadmium (Cd) and zinc (Zn) concentrations of 6.5 ± 0.8 and 377 ± 69 mg kg^?1 soil, respectively. Although, during the first cycle, on average generally low productivity levels (3.7 ton DM (dry matter) ha^?1 y^?1) were obtained on this sandy soil, certain clones exhibited quite acceptable productivity levels (e.g. Zwarte Driebast 12.5 ton DM ha^?1 y^?1). Even at low biomass productivity levels, SRC of willow showed promising removal potentials of 72 g Cd and 2.0 kg Zn ha^?1 y^?1, which is much higher than e.g. energy maize or rapeseed grown on the same soil. Cd and Zn removal can be increased by 40% if leaves are harvested as well. Nevertheless, nowadays the wood price remains the most critical factor in order to implement SRC as an acceptable, economically feasible alternative crop on metal-contaminated agricultural soils.     

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.     

Biomass Yield and Nutrient Responses of Switchgrass to Phosphorus Application

Increasing desire for renewable energy sources has increased research on biomass energy crops in marginal areas with low potential for food and fiber crop production. In this study, experiments were established on low phosphorus (P) soils in southern Oklahoma, USA to determine switchgrass biomass yield, nutrient concentrations, and nutrient removal responses to P and nitrogen (N) fertilizer application. Four P rates (0, 15, 30, and 45?kg?P?ha^?1) and two N fertilizer rates (0 and 135?kg?N?ha^?1) were evaluated at two locations (Ardmore and Waurika) for 3?years. While P fertilization had no effect on yield at Ardmore, application of 45?kg?P?ha^?1 increased yield at Waurika by 17% from 10.5 to 12.3?Mg?ha^?1. Across P fertilizer rates, N fertilizer application increased yields every year at both locations. In Ardmore, non-N-fertilized switchgrass produced 3.9, 6.7, and 8.8?Mg?ha^?1, and N-fertilized produced 6.6, 15.7, and 16.6?Mg?ha^?1 in 2008, 2009, and 2010, respectively. At Waurika, corresponding yields were 7.9, 8.4, and 12.2?Mg?ha^?1 and 10.0, 12.1, and 15.9?Mg?ha^?1. Applying 45?kg?P?ha^?1 increased biomass N, and P concentration and N, P, potassium, and magnesium removal at both locations. Increased removal of nutrients with N fertilization was due to both increased biomass and biomass nutrient concentrations. In soils of generally low fertility and low plant available P, application of P fertilizer at 45?kg?P?ha^?1 was beneficial for increasing biomass yields. Addition of N fertilizer improves stand establishment and biomass production on low P sites.     

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.     

Impact of long-term additions of chemical fertilizers and farm yard manure on carbon and nitrogen sequestration under rice-cowpea cropping system in semi-arid tropics

Restoration of soil organic carbon (SOC) in arable lands represents potential sink for atmospheric CO₂. The strategies for restoration of SOC include the appropriate land use management, cropping sequence, fertilizer and organic manures application. To achieve this goal, the dynamics of SOC and nitrogen (N) in soils needs to be better understood for which the long-term experiments are an important tool. A study was thus conducted to determine SOC and nitrogen dynamics in a long-term experiment in relation to inorganic, integrated and organic fertilizer application in rice-cowpea system on a sandy loam soil (Typic Rhodualf). The fertilizer treatments during rice included (i) 100% N (@ 100 kg N ha^?1), (ii) 100% NP (100 kg N and 50 kg P₂O₅ ha^?1), (iii) 100% NPK (100 kg N, 50 kg P₂O₅ and 50 kg K₂O ha^?1) as inorganic fertilizers, (iv) 50% NPK + 50% farm yard manure (FYM) (@ 5 t ha^?1) and (v) FYM alone @ 10 t ha^?1 compared with (vi) control treatment i.e. without any fertilization. The N alone or N and P did not have any significant effect on soil carbon and nitrogen. The light fraction carbon was 53% higher in NPK + FYM plots and 56% higher in FYM plots than in control plots, in comparison to 30% increase with inorganic fertilizers alone. The microbial biomass carbon and water-soluble carbon were relatively higher both in FYM or NPK + FYM plots. The clay fraction had highest concentration of C and N followed by silt, fine sand and coarse sand fractions in both surface (0–15 cm) and subsurface soil layers (15–30 cm). The C:N ratio was lowest in the clay fraction and increased with increase in particle size. The C and N enrichment ratio was highest for the clay fraction followed by silt and both the sand fractions. Relative decrease in enrichment ratio of clay in treatments receiving NPK and or FYM indicates comparatively greater accumulation of C and N in soil fractions other than clay.     

Poultry Manure as an Organic Fertilizer with or without Biochar Amendment: Influence on Growth and Heavy Metal Accumulation in Lettuce and Spinach and Soil Nutrients

This pot-based study investigated the influence of poultry manure and 1:1 mixture of poultry manure + biochar (produced from farmyard manure [FYM] or wood), on the biomass production and concentration of heavy metals in leaves of lettuce and spinach. The concentration of mineral nitrogen (N) and soluble inorganic phosphorus (P) of soils cultivated with these vegetables was also investigated. The application of poultry manure or FYM biochar in soil as 10% (equivalent to 60 t ha^–1 , an estimated 1726.8 kg ha^–1 N in poultry manure and 1353.9 kg ha^–1 N in FYM) and 15% amendment (equivalent to 90 t ha^–1 , an estimated 2590.2 kg ha^–1 N in poultry manure and 2030.8 kg ha^–1 N in FYM) significantly decreased biomass production of lettuce as compared to control (no fertilizer added) treatment. However, mixture of poultry manure with wood-derived biochar at both application rates (i.e., 10% and 15%) and with FYM biochar at lower application rate (i.e., 10%) caused 2–3-fold increase in aboveground plant biomass and 2–14-fold increase in root biomass (p < 0.05). Furthermore, as compared to control treatment, a significant ~2–3-fold increase in aboveground plant biomass was also observed in response to mixture of poultry manure with wood-derived and FYM derived biochars at 10% amendment rates. As compared to control treatment, concentration of mineral N and soluble inorganic P were higher in soils of all other treatments. In spinach, amendment of poultry manure or its co-amendment with biochar of FYM significantly increased aboveground plant biomass at 7% (equivalent to 42 t ha^–1 ) as compared to 3% and 5% amendment rates (equivalent to 18 and 30 t ha^–1 respectively). The concentration of soil mineral N and soil soluble mineral P was not different between treatments. In lettuce, wood-derived biochar did not reduce concentration of heavy metals (i.e., manganese (Mn), copper (Cu), iron, (Fe), cadmium (Cd), lead (Pb), nickel (Ni) and cobalt (Co) than FYM-derived biochar while in spinach, as compared to poultry manure, co-amendment of poultry manure with wood-derived biochar reduced concentration of heavy metals, indicating differential responses of crops to organic amendments.     

Effect of Nitrogen Fertilization and Residual Nitrogen on Biomass Yield of Switchgrass

Switchgrass, Panicum virgatum L., grown for biomass has been extensively researched where the annual precipitation >760 mm and the climate varies from humid to moist-subhumid. Research is needed for areas that receive <700 mm of precipitation, where the climate varies from dry-subhumid to semiarid. The objectives were to determine (1) the effect of nitrogen fertilization on biomass production, (2) the effect of residual nitrogen on biomass production, (3) the nitrogen yield from harvested biomass, and (4) the concentration of soil organic carbon (SOC) from switchgrass plots. Plots were fertilized annually with nitrogen at the rates of 0, 40, 80, and 120 kg ha^?1 from 2008 to 2011 and unfertilized from 2012 to 2015. The biomass yield varied with N rate × production year interactions (P < 0.05), and biomass yield as a function of N rate was either linear or curvilinear depending upon production year. When fertilized, the biomass yield averaged 4.4, 9.4, 11.6, and 13.2 ± 0.4 Mg ha^?1 for the 0, 40, 80, and 120 kg ha^?1 N rates, respectively. Residual nitrogen sustained high biomass yields for 1 year after fertilization ceased. The nitrogen harvested in biomass varied with N rate × production year interactions (P < 0.05), and the harvested nitrogen yield as a function of N rate was linear each year. Fertilization increased the concentration of SOC an average of 1.0 ± 0.2 mg g^?1 of soil. The data suggest that producers could occasionally skip a year of nitrogen fertilization without detrimentally impacting the production of switchgrass biomass.     

Perennial Grass Bioenergy Cropping on Wet Marginal Land: Impacts on Soil Properties,Soil Organic Carbon,and Biomass During Initial Establishment

The control of soil moisture, vegetation type, and prior land use on soil health parameters of perennial grass cropping systems on marginal lands is not well known. A fallow wetness-prone marginal site in New York (USA) was converted to perennial grass bioenergy feedstock production. Quadruplicate treatments were fallow control, reed canarygrass (Phalaris arundinaceae L. Bellevue) with nitrogen (N) fertilizer (75 kg N ha^?1), switchgrass (Panicum virgatum L. Shawnee), and switchgrass with N fertilizer (75 kg N ha^?1). Based on periodic soil water measurements, permanent sampling locations were assigned to various wetness groups. Surface (0–15 cm) soil organic carbon (SOC), active carbon, wet aggregate stability, pH, total nitrogen (TN), root biomass, and harvested aboveground biomass were measured annually (2011–2014). Multi-year decreases in SOC, wet aggregate stability, and pH followed plowing in 2011. For all years, wettest soils had the greatest SOC and active carbon, while driest soils had the greatest wet aggregate stability and lowest pH. In 2014, wettest soils had significantly (p?<?0.0001) greater SOC and TN than drier soils, and fallow soils had 14 to 20% greater SOC than soils of reed canarygrass + N, switchgrass, and switchgrass + N. Crop type and N fertilization did not result in significant differences in SOC, active carbon, or wet aggregate stability. Cumulative 3-year aboveground biomass yields of driest switchgrass + N soils (18.8 Mg ha^?1) were 121% greater than the three wettest switchgrass (no N) treatments. Overall, soil moisture status must be accounted for when assessing soil dynamics during feedstock establishment.     

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.     

Environmental Effects over the First 2½ Rotation Periods of a Fertilised Poplar Short Rotation Coppice

A short rotation coppice (SRC) with poplar was established in a randomised fertilisation experiment on sandy loam soil in Potsdam (Northeast Germany). The main objective of this study was to assess if negative environmental effects as nitrogen leaching and greenhouse gas emissions are enhanced by mineral nitrogen (N) fertiliser applied to poplar at rates of 0, 50 and 75 kg N ha^?1 year^?1 and how these effects are influenced by tree age with increasing number of rotation periods and cycles of organic matter decomposition and tree growth after each harvesting event. Between 2008 and 2012, the leaching of nitrate (NO₃ ^?) was monitored with self-integrating accumulators over 6-month periods and the emissions of the greenhouse gases (GHG) nitrous oxide (N₂O) and carbon dioxide (CO₂) were determined in closed gas chambers. During the first 4 years of the poplar SRC, most nitrogen was lost through NO₃ ^? leaching from the main root zone; however, there was no significant relationship to the rate of N fertilisation. On average, 5.8 kg N ha^?1 year^?1 (13.0 kg CO_2equ) was leached from the root zone. Nitrogen leaching rates decreased in the course of the 4-year study parallel to an increase of the fine root biomass and the degree of mycorrhization. In contrast to N leaching, the loss of nitrogen by N₂O emissions from the soil was very low with an average of 0.61 kg N ha^?1 year^?1 (182 kg CO_2equ) and were also not affected by N fertilisation over the whole study period. Real CO₂ emissions from the poplar soil were two orders of magnitude higher ranging between 15,122 and 19,091 kg CO₂ ha^?1 year^?1 and followed the rotation period with enhanced emission rates in the years of harvest. As key-factors for NO₃ ^? leaching and N₂O emissions, the time after planting and after harvest and the rotation period have been identified by a mixed effects model.     

Nitrogen fertilization increases diversity and productivity of prairie communities used for bioenergy

Using prairie biomass as a renewable source of energy may constitute an important opportunity to improve the environmental sustainability of managed land. To date, assessments of the feasibility of using prairies for bioenergy production have focused on marginal areas with low yield potential. Growing prairies on more fertile soil or with moderate levels of fertilization may be an effective means of increasing yields, but increased fertility often reduces plant community diversity. At a fertile site in central Iowa with high production potential, we tested the hypothesis that nitrogen fertilization would increase aboveground biomass production but would decrease diversity of prairies sown and managed for bioenergy production. Over a 3 year period (years 2–4 after seeding), we measured aboveground biomass after plant senescence and species and functional‐group diversity in June and August for multispecies mixtures of prairie plants that received no fertilizer or 84 kg N ha^?1 year^?1. We found that nitrogen fertilization increased aboveground biomass production, but with or without fertilization, the prairies produced a substantial amount of biomass: averaging (±SE) 12.2 ± 1.3 and 9.1 ± 1.0 Mg ha^?1 in fertilized and unfertilized prairies, respectively. Unfertilized prairies had higher species diversity in June, whereas fertilized prairies had higher species diversity in August at the end of the study period. Functional‐group diversity was almost always higher in fertilized prairies. Composition of unfertilized prairies was characterized by native C₄ grasses and legumes, whereas fertilized prairies were characterized by native C₃ grasses and forbs. Although most research has found that nitrogen fertilization reduces prairie diversity, our results indicate that early‐spring nitrogen fertilization, when used with a postsenescence annual harvest, may increase prairie diversity. Managing prairies for bioenergy production, including the judicious use of fertilization, may be an effective means of increasing the amount of saleable products from managed lands while potentially increasing plant diversity.     

26年长期施肥对土壤微生物量碳、氮及土壤呼吸的影响

研究长期小麦连作施肥条件下土壤微生物量碳、氮,土壤呼吸的变化及其与土壤养分的相关性。以陕西长武长期定位试验为平台,应用氯仿熏蒸-K2SO4提取法、碱液吸收法和化学分析法分析了长达26a不同施肥处理农田土壤微生物量碳、微生物量氮和土壤呼吸之间的差异及其调控土壤肥力的作用。长期施肥及种植作物,均能提高土壤微生物量碳、氮含量,尤其是施用有机肥,土壤微生物量碳、氮含量高于单施无机肥的处理,土壤呼吸量也提高15.91%—75.73%,而施用无机肥对于土壤呼吸无促进作用。土壤微生物生物量碳氮、土壤呼吸与土壤有机质、全氮呈极显著相关。长期有机无机肥配施可以提高土壤微生物量碳氮、土壤呼吸,氮磷肥与厩肥配施对提高土壤肥力效果最好。微生物量碳氮及土壤呼吸可以反映土壤质量的变化,作为评价土壤肥力的生物学指标。     

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.     

Impacts of fertilizer practices on environmental risk of nitrate in semiarid farmlands in the Loess Plateau of China

The lack of understanding of nitrate dynamics in soil profiles of semiarid regions hampers the assessment of the environmental risks associated with nitrate. A long-term field experiment established in the Loess Plateau of Northwest China in 1984 was used to investigate the seasonal dynamics of water and nitrate contents in the soil profile (0–300 cm) under bare fallow and continuous winter wheat (Triticum aestivum L.) with various fertilizer treatments. For treatments without mineral N input (i.e., no fertilizer, farmyard manure alone, and with P fertilizer), the amount of nitrate accumulated in the soil profile (52–120 kg N ha^?1, the average for June, August, February and April) was significantly lower than that (292 kg N ha^?1) accumulated in the bare fallow treatment. A large amount of nitrate (1,065 kg N ha^?1) was found accumulated in the soil profile with the treatment applied with mineral N at a rate of 120 kg N ha^?1 year^?1 for 17 years (1984–2001) and this nitrate moved downward during the wet season (from August to February). Clearly, the amount of nitrate accumulated in the soil profiles, and its tendency of downward movement, appears to potentially be an environmental risk as it may reach groundwater. Fertilization as mineral N fertilizers coupled with FYM or P resulted in 50–70% less nitrate accumulation in the soil profiles than that using mineral N fertilizer alone, and therefore the environmental risk was reduced. It is proposed that a “break point” of nitrate distribution existed in the soil profiles, providing an indication of soil depth to which nitrate can transfer.     

Establishment of reed canary grass with perennial legumes or barley and different fertilization treatments: effects on yield,botanical composition and nitrogen fixation

In two field experiments in northern Sweden, we investigated if intercropping reed canary grass (RCG; Phalaris arundinacea L.) with nitrogen‐fixing perennial legumes could reduce N‐fertilizer requirements and also if RCG ash or sewage sludge could be used as a supplement for mineral P and K. We compared biomass production, N uptake and N‐fixation of RCG in monoculture and mixtures of RCG with alsike clover (Trifolium hybridum L.), red clover (Trifolium pratense L.), goat's rue (Galega orientalis Lam.) and kura clover (Trifolium ambiguum M. Bieb.). In one experiment, RCG was also undersown in barley (Hordeum vulgare L.). Three fertilization treatments were applied: 100 kg N ha^?1, 50 kg N ha^?1 and 50 kg N ha^?1 + RCG ash/sewage sludge. We used a delayed harvest method: cutting the biomass in late autumn, leaving it on the field during the winter and harvesting in spring. The legume biomass of the mixtures at the inland experimental site was small and did not affect RCG growth negatively. At the coastal site, competition from higher amount of clover biomass affected RCG growth and spring yield negatively. N‐fixation in red clover and alsike clover mixtures in the first production year approximately covered half of recommended N‐fertilization rate. Goat's rue and kura clover did not establish well at the costal site, but at the inland site goat's rue formed a small but vital undergrowth. RCG undersown in barley gave lower yield, both in autumn and spring, than the other treatments. The high N treatment gave a higher spring yield at the inland site than the low N treatments, but there were no differences due to fertilization treatments at the coastal site. For spring harvest, there were no yield benefits of RCG/legume intercropping compared with RCG monoculture. However, intercropping might be more beneficial in a two‐harvest system.