Quantifying dung carbon incorporation by earthworms in pasture soils

The effect of different earthworm functional groups on the incorporation of maize (C4 plant) dung into a soil (C3 organic matter background) sown with ryegrass (C3 plant) was explored by using differences in the carbon (C) isotope ratios (¹²C and ¹³C) between plant and soil samples in a field mesocosm study. The abundance of earthworms increased with dung inputs, reaching over 4000 earthworms per m², presumably because of the increased food resources used. The amount of dung C incorporated into the soil profile in the presence of earthworms was dependent on the amount of organic matter deposited on the soil surface (925–4620 g C m^?2) and reached rates of 1200 g C m^?2 annually in the treatment receiving repeat dung applications. Dung incorporation was largely concentrated in the surface 0–75 mm, although small amounts of dung‐derived C were observed to a depth of 300 mm. This was especially so in the presence of anecic earthworms, equating to an extra 70 g C m^?2 annually for the 150–300 mm depth increment. It is important to note, in calculating C incorporation rates from earthworms, that only 10–20% of the soil surface in grazed pastures is covered by dung. After 444 days, less than 32% of the applied dung was detected within the upper 300 mm of the soil profile. This study emphasized the need for all three earthworm functional groups to be present within the soil in order to maximize the amount of surface dung that could be incorporated into soil organic matter.     

Wetland conversion to beef cattle pasture changes in soil properties

Background and Objective  Largely influenced by the passage of the Swamp Land Act of 1849, many wetlands have been lost in the coastal plain region of southeastern United States primarily as a result of drainage to convert land for agriculture. While further wetland conversion or loss is universally acknowledged, the process continues with little public recognition of the causes or consequences. This study examined changes in soil carbon, pH, and Mehlich extractable nutrients in soils following conversion of wetland to beef cattle pasture. Methods  To better understand the chemical response of soils during wetland conversion to beef cattle pasture, soil samples were collected from the converted beef cattle pastures and from the adjoining reference wetland. Soil samples were collected from eleven sites in the beef cattle pasture, and from four in the adjoining reference wetland. Data that were collected from the reference wetland sites were used as the reference/baseline data to detect potential changes in soil properties associated with the conversion of wetlands to beef cattle pastures from 1940 to 2002. Results and Discussion  Compared with the adjoining reference wetland, the beef cattle pasture soils in 2002, 62 years after being drained, exhibited: (1) a decrease in organic carbon, TOC (-172.3 g kg^-1), nitrogen, TN (-10.1 g kg^-1), water soluble phosphorus, WSP (-5.1mg kg^-1), and potassium, K (-0.7 mg kg^-1); (2) an increase in soil pH (+1.8 pH unit), calcium, Ca (+88.4 mg kg^-1), magnesium, Mg (+7.5 mg kgc), manganese, Mn (+0.3 mg kg^-1), and iron, Fe (+6.9 mg kg^-1); and (3) no significant changes in sodium (Na), zinc (Zn), copper (Cu), and aluminum (Al). In 2002, the amount of TOC and the concentration of soil organic matter (OM) in pasture fields were significantly lower than the concentration in the reference wetland with average values of 7.8 ± 8 g kg^-1 and 36 ± 26 g kg^-1 and 180.1 ± 188 g kg^-1 and 257 ± 168 g kg^-1, respectively. It appeared that conversion of wetlands was proceeding toward a soil condition/composition like that of mineral soils. Conclusion and Outlook  Overall, conversion of wetland had significant effects on soil carbon, pH, nitrogen, phosphorus, and extractable nutrients. Results of our study have shown a decrease in TOC, TN, WSP, and K and an increase in soil pH, Ca, Mg, Mn, and Fe. These results are important in establishing useful baseline information on soil properties in pasture and adjoining reference wetland prior to restoring and converting pasture back to its original wetland conditions as a major part of the restoration effort being underway.     

A survey of clover and Lotus rhizobia in Northern Ireland pasture soils

192 sites covering the main soil types in Northern Ireland were analysed for numbers and effectiveness of clover and Lotus rhizobia, and chemical properties. Peat sites were generally highly acid (pH <5.5) and mineral sites near neutral (pH 5.5–7.8). Clover rhizobia were generally absent from peat sites and present in mineral sites as large populations (> 10⁶ g^?1 dry soil). 79% of isolates were effective on T. repens var. Grasslands Huia. Lotus rhizobia were generally absent from peat sites, less often present than clover rhizobia in mineral sites, and as smaller populations. They were mainly effective on L. pedunculatus var. G4705 and were all of the slow-growing type belonging to the genus Bradyrhizobium. Numbers of clover rhizobia were significantly correlated with soil pH, exchangeable Ca, base saturation and Al saturation, but effectiveness of clover rhizobia and numbers of Lotus rhizobia were not correlated with any soil chemical property.     

Nitrous oxide fluxes and denitrification sensitivity to temperature in Irish pasture soils

Nitrous oxide (N₂O) emissions from grazed pastures constitute approximately 28% of total global anthropogenic N₂O emissions. The aims of this study were to investigate the effect of inorganic N fertilizer application on fluxes of N₂O, quantify the emission factors (EFs) for a sandy loam soil which is typical of large areas in Ireland and to investigate denitrification sensitivity to temperature. Nitrous oxide flux measurements from a cut and grazed pasture field for 1 year and denitrification laboratory incubation were carried out. The soil pH was 7.3 and had a mean organic C and N content at 0–20 cm of 44.1 and 4.4 g/kg dry weight, respectively. The highest observed peaks of N₂O fluxes of 67 and 38.7 g N₂O‐N per hectare per day were associated with times of application of inorganic N fertilizer. Annual fluxes of N₂O from control and fertilized treatments were 1 and 2.4 kg N₂O‐N per hectare, respectively. Approximately 63% of the annual flux was associated with N fertilizer application. Multiple regression analysis revealed that soil nitrate and the interaction between soil nitrate and soil water content were the main factors controlling N₂O flux from the soil. The derived EF of 0.83% was approximately 66% of the IPCC default EF value of 1.25% as used by the Irish EPA to estimate greenhouse gases (GHGs) in Ireland. The IPCC‐revised EF value is 0.9%. A highly significant exponential regression (r² = 0.98) was found between denitrification and incubation temperature. The calculated Q₁₀ ranged from 4.4 to 6.2 for a temperature range of 10–25 °C and the activation energy was 47 kJ/mol. Our results show that denitrification is very sensitive to increasing temperature, suggesting that future global warming could lead to a significant increase in soil denitrification and consequently N₂O fluxes from soils.     

The ability of the DGT soil phosphorus test to predict pasture response in Australian pasture soils – a preliminary assessment

Diffusive gradients in thin‐films (DGT) technology provides an alternative assessment of available phosphorus (P) for a range of crops, suggesting a preliminary examination of the performance of the new DGT‐P test, compared to existing bicarbonate extractable Olsen and Colwell P tests, for pastures is justified. This study utilized historic data from the Australian National Reactive Phosphate Rock (NRPR) study (1992–1994) that included 25 experimental sites representing a wide range of soil types and climates used for pasture production. Stored (~19 yr) soil samples were analysed for DGT‐P, Olsen P and a single point P buffering index (PBI) and re‐analysed for Colwell P. Results showed the traditional bicarbonate extractable Colwell (r² = 0.45, P < 0.001) and Olsen P (r² = 0.27, P < 0.001) methods predicted relative pasture P response more accurately, compared to the novel DGT‐P test (r² = 0.09, P = 0.03) when all 3 yr of data were examined. We hypothesize that the harsher bicarbonate extraction used for the Olsen and Colwell methods more accurately reflects the ability of perennial pasture roots to access less labile forms of P, in contrast to the DGT‐P test, which does not change the soil pH or dilute the soil and appears unable to fully account for a plants ability to solubilize P. Further studies are needed to compare the capacity of DGT‐P to measure P availability in perennial pasture systems and to better understand the soil chemical differences between pasture and cropping systems.     

The use of magnetic susceptibility to measure long-term soil redistribution

Several studies have documented the severity of recent soil erosion on the Canadian prairies where cultivation started about a century ago. Little quantitative information is available on erosion before 1960. This study attempts to quantify post- and pre-1960 soil erosion in a small cultivated basin near Saskatoon, Saskatchewan, Canada, by measuring ¹³⁷Cs and magnetic susceptibility (χ) distribution with depth. Soil cores were collected along six transects (three across closed depressions and three across the drainage channel) in the cultivated field, and one transect across an uncultivated depression. The cores were sliced into 3-cm layers and the soil analyzed for ¹³⁷Cs, χ, and organic and inorganic C. High variability in χ with depth in eroding areas (as indicated by ¹³⁷Cs) made it impossible to use χ to quantify past soil losses in these locations. However, these eroding upper and middle slope positions have a much higher χ than lower slope areas where soil deposition occurs and where the variability in χ with depth could be used to estimate soil deposition. Estimating soil deposition from the χ vs. depth profiles was more successful in the closed depressions than in the drainage channel, where the χ profiles may reflect the variable source areas of the materials rather than the pedological conditions. The data indicated that soil deposition since 1960 has been about 30 to 50% of that prior to 1960. This suggests that soil deposition rates, and by implication, soil erosion rates, have been relatively steady since cultivation of these soils started, although there are clear indications that the spatial pattern of deposition has varied.     

A gas-flow soil core method to measure field denitrification rates

A method was developed for rapid measurement of soil denitrification under conditions where natural soil structure and aeration status is maintained. Air was continuously recirculated by means of a membrane pump through a soil core and a sample loop of a gas chromatograph equipped with an electron capture detector. Addition of acetylene to the recirculating air permitted measurement of denitrification in the soil core. Because of the rapid distribution of C₂H₂ and removal of N₂O provided by the gas flow, denitrification rates could usually be determined in less than 2 h. By means of external 6-way and 8-way valves, four soil cores could be simultaneously analyzed on one gas Chromatograph equipped with dual detectors. Soil cores could also be stored at 4°C for later analysis without affecting the denitrification rate. The detection limit for denitrification rate measurements was 0.5 ngN g^?1 soil day^?1 or approximately 2.6 g N ha^?1 day^?1. Coefficients of variation for repeated measurements on the same soil core were usually less than 15%, but coefficients of variation for repacked or natural cores of the same soil were much higher (70–90%) Disruption of the natural soil structure by sieving increased the denitrification rate in an aggregated clay loam soil, but decreased the rate in a non-aggregated sandy soil. These results illustrate the importance of maintaining natural soil structure during denitrification measurements. The effect of pumping gas through soil was evaluated by comparing denitrification rates in soil cores where C₂H₂ was allowed to distribute into the soil by passive diffusion with rates obtained by pumping. Lower denitrification rates were observed in the static incubation presumably due to limited diffusion of C₂H₂ into or N₂O out of the denitrifying sites in the soil. This diffusion limitation could be overcome in the static incubations if C₂H₂ was initially distributed through the soil by pumping. This gas flow method is well suited to the study of soil denitrification rates under nearly natural conditions because the indigenous substrates and anaerobic microsites are preserved, the rapidity in which denitrification rates can be measured, and the high sensitivity and relatively low analytical variability of the method.     

Short-term effects of ammonium nitrogen in upland pasture soil affected or not affected by cattle

The short-term effects of excessive NH₄⁺-N on selected characteristics of soil unaffected (low annual N inputs) and affected (high annual N inputs) by cattle were investigated under laboratory conditions. The major hypothesis tested was that above a theoretical upper limit of NH₄⁺ concentration, an excess of NH₄⁺-N does not further increase NO₃⁻ formation rate in the soil, but only supports accumulation of NO₂⁻-N and gaseous losses of N as N₂O. Soils were amended with 10 to 500 μg NH₄⁺-N g⁻¹ soil. In both soils, addition of NH₄⁺-N increased production of NO₃⁻-N until some limit. This limit was higher in cattle-affected soil than in unaffected soil. Production of N₂O increased in the whole range of amendments in both soils. At the highest level of NH₄⁺-N addition, NO₂⁻-N accumulated in cattle-affected soil while NO₃⁻-N production decreased in cattle-unaffected soil. Despite being statistically significant, observed effects of high NH₄⁺-N addition were relatively weak. Uptake of mineral N, stimulated by glucose amendment, decreased the mineral N content in both soils, but it also greatly increased production of N₂O.     

Assessment of the influence of phosphate fertilizers on the microbial activity of pasture soils

The objective of the present work was to examine the effects of phosphate fertilizers on the microbial activity of pasture soils. Various microbial characteristics were measured using soils from an existing long-term phosphate fertilizer field trial and a short-term incubation experiment. The measurements included basal respiration, substrate induced respiration, inhibition of substrate-induced respiration by streptomycin sulphate (fungal activity) and actidione (bacterial activity) and microbial biomass C. The long-term field trials was initiated during 1985 to examine the effectiveness of different sources of phosphate fertilizers (single superphosphate, North Carolina phosphate rock, partially acidulated North Carolina phosphate rock, and diammonium phosphate) on pasture yield. The incubation experiment was conducted for 8 weeks using the same soil and the sources of phosphate fertilizers used in the field trial. In the incubation experiment the fertilizer addition caused an initial decrease in basal and substrate-induced respiration but had no effect on total microbial biomass. The initial decline in basal and substrate-induced respiration with the fertilizer addition was restored within 8 weeks after incubation. In the field experiment the fertilizer addtion had no significant effect on basal respiration but increased substrate-induced respiration and microbial biomass C. The short-term and the long-term effects of phosphate fertilizer addition on the microbial characteristies of the soils are discussed in relation to its effects on pH, salt concentration, and the nutrient status of the soils.     

A simple laboratory infiltration method for measuring the tendency of soils to crust

Abstract. Rainfall simulation experiments give an indication of the tendency of soils to crust or seal but are time-consuming and require several kilograms of soil per sample. We developed a laboratory infiltration method that is less time-consuming than rainfall simulation and uses less than 40 g of soil. The method involves the leaching of an agitated 1:5 soil/water suspension through a packed soil column, which simulates the crusting process. The preparation of a dispersed soil suspension is a key feature of the method as it simulates disturbance of a soil surface by rain. This laboratory infiltration method was performed on sandy, granite-derived soils from annually burnt as well as unburnt plots in the Kruger National Park, South Africa and gave results which correlated strongly with results from rainfall simulation experiments on the same soils. We suggest that this new method may be useful for assessing the effect of different land management practices on the tendency of soils to crust.     

Potential contribution of lysed bacterial cells to phosphorus solubilisation in two rewetted Australian pasture soils

Soil drying renders considerable amounts of phosphorus soluble upon rewetting, which may be partly derived from lysed microbial cells. Using direct bacterial cell counting in water and tetra-sodium pyrophosphate extracts of two Australian pasture soils, we found that almost all extractable cells were lysed following the rewetting of dry soils. The amounts of phosphorus in the lysed cells corresponded closely to the increases in water-extractable phosphorus following soil drying, suggesting that bacterial cell lysis is a major source of the released phosphorus.     

A simple method for the estimation of potential primary pasture productivity over Mozambique

Pasture production not only depends on precipitation amount and distribution patterns, but also on soil type and evaporative demand. The simulation model of Rose et al., developed using improved pastures, is one that accounts for these factors and also takes into account the effect of fertilizer levels on production. From this a simplified model is proposed for Mozambique using as inputs annual precipitation, annual potential evapotranspiration and soil moisture storage capacity. The model is applicable only under negligible soil slope and no bush or tree cover, but can be adapted to varying phosphate fertilizer levels. Estimates from this proposed model show close agreement with experimental data from cleared natural pastures in Zimbabwe and with improved pastures of Townsville stylo in Australia under high phosphate fertilizer levels.     

基于热成像技术的牛舍围护结构传热阻测试方法

针对传统的接触式传热阻测试方法对测试场合要求高、操作复杂、操作时间相对较长等难以应用于环境较为恶劣的畜禽舍问题,该文引入热成像技术,开展了黑龙江地区2种不同类型牛舍的围护结构热特性参数现场测试,获得了基于热成像法和传统接触式测试法下牛舍墙体、屋面、门窗的特征温度值。在此基础上,计算了牛舍围护结构材料的传热阻,并与相应建筑材料的传热阻理论计算值进行了对比分析。结果表明,对于墙体、屋面等围护结构,2种方法所获得的传热阻测试值与理论计算值的偏差小于15%;对于围护结构窗体和门,2种方法所获得的传热阻测试值与理论计算值的偏差在20%~30%之间;虽然热成像法和接触式测试法现场实测值与理论计算值之间都存在偏差,但因现场测试能综合材料老化、脱落、受潮和施工质量等实际情况,相对而言实测值的可信度更高;但综合考虑2种方法,热成像法的操作简单、便捷,可以很好地用于畜禽舍围护结构的热工性能评价。     

Comparison of two different methods to measure nitric oxide turnover in soils

 The NO turnover in soils was measured in two different experimental set-ups, a flow-through system, which is very time-consuming and needs rather sophisticated equipment, and a closed system using serum bottles. We compared the NO turnover parameters (NO consumption rate constant, NO production rate, NO compensation concentration) that were measured with both systems in different soils, under different conditions and in the presence of 10 Pa acetylene to inhibit nitrification. The values of the NO turnover parameters that were measured with the two systems under oxic conditions were usually comparable. The addition of acetylene did not affect the NO consumption rate constants of the soils with the exception of soil G1. However, the NO production rates and the NO compensation concentrations decreased significantly in the presence of acetylene, indicating that nitrification was the main source of NO in these soils. Only one soil (Bol) showed no nitrifying activity. Increasing soil moisture content resulted in decreasing NO consumption rate constants and NO production rates. Even at a high soil moisture content of 80% water holding capacity, nitrification was the main source of NO. The values of the NO turnover parameters that were measured with the two systems were not comparable under anoxic conditions. The NO consumption rate constants and the NO production rates were much lower in the closed than in the flow-through system, indicating that the NO consumption activity became saturated by the high NO concentrations accumulating in the closed system. Under oxic conditions, however, closed serum bottles were a cheap, easy and reliable tool with which to determine NO turnover parameters and to distinguish between nitrification and denitrification as sources of NO. Received: 21 April 1998     

A new method to determine the carbon content of water-soluble organic compounds in soils

The possibility to use the oxidation rate of different waters by dichromate as measured by photometry for the determination of the organic carbon content in water extracts from the organic horizons of soddy-podzolic soils (in the Republic of Komi) was confirmed. The advantages of the method proposed are discussed.     

Fungal and bacterial growth following the application of slurry and anaerobic digestate of livestock manure to temperate pasture soils

How land-application of digestate sourced from anaerobic digestion (AD) of animal waste influences the functioning of a mixed pasture agroecosystem is not well characterised, particularly with regard to the response of the actively growing microbial community. We studied the impact of the liquid AD digestate on the decomposer community in two different soils, seeded with two different common grassland crops; a mixture of either grass or grass/clover in a greenhouse experiment. We studied bacterial (leucine incorporation into bacteria) and fungal (acetate incorporation into ergosterol) growth responses to AD cattle slurry digestate, undigested cattle slurry, mineral fertiliser (NPK and N) added at a rate equivalent to 150?kg?N?ha^?1, and a no-fertiliser control treatment. Differences in fungal and bacterial growth were evident between the soil and sward types. However, the fertilisers consistently stimulated a higher bacterial growth than the no-fertiliser control, and liquid digestate resulted in a level of bacterial growth higher or equal to that of mineral fertiliser, whilst undigested slurry resulted in lower bacterial growth. These fertiliser effects on bacterial growth mirrored the effects on plant growth. In contrast, the fungal community responded only marginally to fertiliser treatments. We conclude that the application of digestate stimulates the bacterial decomposer community in a similar way to that of mineral fertilisers. Our results suggest that mineral fertiliser can be exchanged for liquid digestate with limited impact on the actively growing soil microbial community that, in turn, regulate important soil processes including nutrient cycling in agricultural soils.     

Starter fertilizer and the method and rate of potassium fertilizer effects on cotton grown on soils with and without winter grazing by cattle

Abstract

A three‐year field study was conducted on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudult) in North Alabama. The objective of the study was to evaluate the effects of winter grazing by cattle on the potassium (K) and starter fertilizer needs of cotton (Gossypium hirsutum L.) the following season. Grazed and non‐grazed treatments were established by planting a wheat (Triticum aestivum L.) cover crop in the fall and allowing cattle to graze half of the treatment area for 35 to 65 days in late winter‐early spring. After grazing, the grazed and non‐grazed wheat was killed and cotton was planted using a strip‐tillage system. Test areas had medium to high soil test ratings for K. Fertility treatments consisted of three rates of K (0, 37, and 74 kg K ha^‐1), three methods of K application (surface broadcast; in‐row, band application at a depth of 30.5 cm; and surface banding using a spacing of 50.8 cm) and two rates of starter fertilizer (no starter and 168 kg#lbha^‐l of a liquid 15–15–0). Seed cotton yields were affected by grazing of the winter cover crop prior to planting, but not by the method of K fertilizer application. During the two years that a yield reduction was observed, winter grazing reduced seed cotton yields by an average of 14%. Cotton responded to K rate only under the ungrazed system. During the first and second year of the test, an application of 37 kg K ha^‐1 increased seed cotton yields by an average of 351 kg#lbha^‐1. Starter fertilizer consistently gave slightly higher yields with a significant response occurring in two out of the three years.