Effects of species richness and functional groups on chemical constituents relevant for methane yields from anaerobic digestion: results from a grassland diversity experiment

Changes in livestock production systems have led to land‐use changes and abandonment, especially of semi‐natural grassland in agriculturally less favoured regions. The generation of energy from biomass of extensive, high‐diversity grasslands can be an alternative to their abandonment, and anaerobic digestion is one possible method for converting grassland biomass into energy. However, little is known about the effects of species richness (SR) and functional groups on chemical constituents relevant for anaerobic digestion and the resulting energy potential. In this study, changes in the herbage chemical constituents that are relevant for forage quality were studied along a well‐defined diversity gradient (one to sixty species) and across different combinations of functional groups (legumes, small herbs, tall herbs and grasses). Substrate‐specific methane yield (CH_4 sub) was estimated through the concentrations of forage‐quality parameters such as crude fibre (CF), crude protein (CP), crude lipid, nitrogen‐free extract and their documented digestibility values, as well as the respective methane yields. Results show that with increasing SR, the CF increased and CP decreased, even though these effects could not be fully disentangled from the presence of grasses. These trends led to a negative effect of SR on CH_4 sub, while the area‐specific methane yield (CH_4 area = CH_4 sub × biomass yield) increased due to a strong increase in biomass with increasing SR. The CH_4 sub was increased when legumes were present, and it declined with the presence of grasses. Generally, CH_4 sub and CH_4 area varied between functional‐group monocultures and all functional‐group mixtures.     

Colluvisols under cultivation in Schleswig-Holstein. 2. Carbon distribution and soil organic matter composition

Soils under intensive cultivation have altered due to water erosion. This study was conducted to determine whether soil organic matter (SOM) composition of the colluvial source (Ap horizons) differs from the colluvial sink (M horizons). The SOM of a sandy Catena with erodic Cambisols and colluvic soils (Colluvisols) in Schleswig-Holstein, Northwest Germany, was investigated. A wet chemical analysis was combined with CPMAS ¹³C-NMR spectroscopy. In one case a significant correlation between the SOM composition of the Ap horizon of the erodic Cambisol and the M horizon of the Colluvisol was high (r² = 0.904^-), whereas the correlation for the other set was much weaker (r² = 0.640*). Two possible paths of pedogenesis are discussed. About 70% of the SOM of the colluvial source is decomposed during translocation or after deposition. A selective preservation or new formation of humins in the M material is probable. These humins contain, obviously, large amounts of polysaccharides, which were not detected by the wet chemical analysis. Further investigations of colluvic and erodic soils are necessary in order to specify the SOM quality and its possible modification due to soil translocation and accumulation.     

NH3 Volatilization,N2O Emission and Microbial Biomass Turnover from 15N-Labeled Manure Under Laboratory Conditions

On irrigated agricultural soils from semi-arid and arid regions, ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission can be a considerable source of N losses. This study was designed to test the capture of ¹⁵N loss as NH₃ and N₂O from previous and recent manure application using a sandy, calcareous soil from Oman amended one or two times with ¹⁵N labeled manure to elucidate microbial turnover processes under laboratory conditions. The system allowed to detect ¹⁵N enrichments in evolved N₂O-N and NH₃-N of up to 17% and 9%, respectively, and total N, K₂SO₄ extractable N and microbial N pools from previous and recent ¹⁵N labeled manure applications of up to 7%, 8%, and 15%. One time manured soil had higher cumulative N₂O-N emissions (141 µg kg^?1) than repeatedly manured soil with 43 µg kg^?1 of which only 22% derived from recent manure application indicating a priming effect.     

Performance and environmental effects of forage production on sandy soils. II. Impact of defoliation system and nitrogen input on nitrate leaching losses

A field experiment was conducted over a 4‐year period to determine NO₃ leaching losses from grassland on a freely draining sandy soil. The experiment consisted of all combinations of five defoliation systems; cutting‐only (CO), rotational grazing (GO), mixed systems with one (MSI) or two silage cuts (MSII) plus subsequent rotational grazing, and simulated grazing (SG), four mineral nitrogen (N) application rates (0, 100, 200, and 300 kg N ha^?1 year^?1), and two slurry levels (0 and 20 m³ slurry ha^?1 year^?1). Due to the high N return by grazing animals, leaching losses in the rotational grazing systems generally were associated with NO₃‐N concentrations which exceeded the EU limit for drinking water. NO₃ leaching losses in a rotational grazing system could be reduced by lowering the N fertilizer intensity and the inclusion of one or two silage cuts in spring. However, even in the unfertilized mixed systems, N fixation by white clover exceeded the amounts of N removed via animal products, which resulted in NO₃‐N concentrations well above the EU limit for drinking water. In terms of leaching losses, the cutting‐only system was the most advantageous treatment. NO₃ leaching losses on grassland could be predicted by the amount of soil mineral N at the end of the growing season and by the N surplus calculated from N balances at the field scale. From the results obtained a revised nitrogen fertilization policy and a reduced grazing intensity by integrating silage cuts are suggested.     

Performance and environmental effects of forage production on sandy soils. III. Energy efficiency in forage production from grassland and maize for silage

Based on experimental data gathered in a research project on nitrogen fluxes in intensive dairy farming in Northern Germany, an analysis of fossil energy input and energy efficiency in forage production from permanent grassland and maize for silage was conducted. Field experiments comprised different defoliation systems and different rates of mineral N fertilizer and slurry application. Each change from grazing to cutting in grassland systems reduced the energy efficiency. Energy efficiency consistently decreased with increasing rates of mineral N application. In the production of maize for silage, maximum energy efficiency was obtained with an application of 50 kg N ha^?1 from slurry only. Net energy yields of maize for silage were much higher than that of grassland when compared at the same level of fossil energy and nitrogen fertilizer input. Considering both nitrate‐leaching losses and a necessary minimum quantity of grass herbage in a well‐balanced ration, it is suggested that a high proportion of maize for silage in combination with N‐unfertilized grass/clover swards used in a mixed cutting/grazing system represents a good trade‐off between the leaching of nitrates and energy efficiency.     

Performance and environmental effects of forage production on sandy soils. V. Impact of grass understorey, slurry application and mineral N fertilizer on nitrate leaching under maize for silage

A field experiment with maize for silage was conducted to assess the effects of mineral nitrogen (N) fertilizer application rates (0, 50, 100, 150 kg ha^?1), slurry application rates (0, 20, 40 m³ ha^?1) and the use of an understorey with perennial ryegrass on nitrate (NO₃)‐leaching losses. Leachate was collected using ceramic suction cups. Soil mineral N (SMN) was determined to a depth of 90 cm at the end of the growing season. Higher levels of N supply with mineral fertilizer or slurry resulted in higher leaching losses. The grass understorey significantly reduced the losses. The amount of N lost to the groundwater was positively related to SMN at the end of the growing season, with leaching losses representing less than 0·45 of SMN on average. Leaching losses were positively related to the N surplus, which was calculated from the difference between N input (N from fertilizer, slurry and atmospheric deposition) and N output (N removed with maize herbage mass and bound in the understorey biomass in spring). In view of the large variation in weather conditions between the experimental years, it is suggested that for the sandy soils in this experiment N‐leaching losses under maize can be estimated satisfactorily from SMN and the calculated N surplus.     

Utilization of semi-natural grassland through integrated generation of solid fuel and biogas from biomass. I. Effects of hydrothermal conditioning and mechanical dehydration on mass flows of organic and mineral plant compounds, and nutrient balances

The use of semi-natural grasslands for the production of renewable energy through conventional conversion techniques faces major limitations because of chemical and physical properties of the biomass. A new conversion procedure was developed which separates the biomass, as silage, into a liquid phase for biogas production and into a solid fraction to be used as fuel. Separation (mechanical dehydration) is carried out with a screw press after mashing with water (hydrothermal conditioning). The effect of hydrothermal conditioning at different temperatures (5, 60 and 80°C) and mechanical dehydration on mass flows of plant compounds into the press fluid was investigated for five grassland pastures typical of mountain areas of Germany. Results show that 0·18 of the crude fibre was transferred into the fluid, whereas more digestible organic compounds, such as crude protein and nitrogen-free extract, showed mass flows of 0·40 and 0·31 respectively. While 0·52–0·89 of potassium (K), magnesium (Mg) and chloride (Cl), which are detrimental for the combustion of the press cake, were transferred into the press fluid, more than 0·50 of calcium, which has positive combustion properties, remained in the press cake. Significantly ( P  <   0·05) higher mass flows were detected at conditioning temperatures of 60°C (K and Mg) and 80°C (crude fibre and nitrogen-free extract) compared with the 5°C treatment. Because of the separation of solids and liquids, high proportions of P (0·61–0·74) and K (0·64–0·85) but only 0·32–0·45 of nitrogen exported from the grassland would be recycled with an application of the digestates from the anaerobic digestion of the press liquid.     

Nitrogen turnover in a repeatedly manured arid subtropical soil: Incubation studies with 15N isotopes

Under the hot and moist conditions of irrigated agriculture in the arid subtropics, turnover of organic matter is high, which can lead to considerable carbon (C) and nitrogen (N) losses. Therefore, sustainable use of these soils requires regular manure application at high rates. To investigate the contribution of consecutive manure applications to an arid sandy soil to various soil N pools, goat manure was isotopically labeled by feeding ¹⁵N‐enriched Rhodes grass hay and applied to the soil during a two‐year field experiment. In the first year, soils received ¹⁵N‐labeled manure to distinguish between soil‐derived and manure‐derived N. In the second year, these plots were split for the application of either ¹⁵N‐labeled or unlabeled manure to discriminate N derived from previous (first year) and recent (second year) manure application. Soil samples (of control and ¹⁵N‐manured soil) were collected at the end of the first and the second year, and incubated in two laboratory experiments with labeled or unlabeled manure. At the beginning of Experiment 1, 7% of total N, 11% of K₂SO₄ extractable N, and 16% of microbial biomass N were derived from previously field‐applied manure. While the application of manure during incubation increased microbial biomass N by 225% and 410% in the control soil and the previously field‐manured soil, respectively, N₂O emissions were more affected on the control soil, releasing considerable amounts of the soil N‐pool (80% of total emissions). In Experiment 2, 4% of total N, 7% of K₂SO₄ extractable N, and 7% of microbial biomass N derived from previously applied manure, and 4%, 8%, and 3% from recently applied manure, respectively. Microbial biomass N and N₂O‐N derived from manure declined with time after manure application, whereas in Experiment 1 this tendency was only observed for microbial biomass N.     

Performance and environmental effects of forage production on sandy soils. IV. Impact of slurry application, mineral N fertilizer and grass understorey on yield and nitrogen surplus of maize for silage

A field experiment was conducted from 1998 to 2001 to measure the performance and environmental effects of a maize crop (Zea mais L.) in a continuous production system with and without a grass understorey (Lolium perenne L.), with varied N inputs. The experiment was located on a sandy soil in northern Germany and comprised all combinations of slurry application rate (0, 20, 40 m³ ha^?1) and mineral N fertilizer (0, 50, 100, 150 kg N ha^?1). Understorey treatments included maize with and without perennial ryegrass. Net energy (NEL) yield of maize increased with mineral N application rate but reached a plateau at high rates. Increase in yield of dry matter because of mineral N fertilizer was lower with increased slurry application rate. Neither slurry and mineral N application nor a grass understorey affected NEL concentration of maize, whereas crude protein (CP) concentration increased with increase in application of slurry and mineral N fertilizer. Nitrogen supply by slurry or mineral fertilizer had no effect on the amount of N in the grass understorey after the harvest of maize. The average amount of N bound annually in the understorey was 60 kg N ha^?1. The reduced biomass of the understorey because of enhanced maize competition was compensated for by an increased CP concentration in the grass. The grass understorey affected the NEL yield of maize negatively only at very low levels of N input but increased the N surplus at all levels.