Addition of a clay subsoil to a sandy topsoil changes the response of microbial activity to drying and rewetting after residue addition – a model experiment

The effect of drying and rewetting (DRW) on C mineralization has been studied extensively but mostly in absence of freshly added residues. But in agricultural soils large amounts of residues can be present after harvest; therefore, the impact of DRW in soil after residue addition is of interest. Further, sandy soils may be ameliorated by adding clay‐rich subsoil which could change the response of microbes to DRW. The aim of this study was to investigate the effect of DRW on microbial activity and growth in soils that were modified by mixing clay subsoil into sandy top soil and wheat residues were added. We conducted an incubation experiment by mixing finely ground wheat residue (20 g kg^–1) into top loamy sand soil with clay‐rich subsoil at 0, 5, 10, 20, 30, and 40% (w/w). At each clay addition rate, two moisture treatments were imposed: constantly moist control (CM) at 75% WHC or dry and rewet. Soil respiration was measured continuously, and microbial biomass C (MBC) was determined on day 5 (before drying), when the soil was dried, after 5 d dry, and 5 d after rewetting. In the constantly moist treatment, increasing addition rate of clay subsoil decreased cumulative respiration per g soil, but had no effect on cumulative respiration per g total organic C (TOC), indicating that the lower respiration with clay subsoil was due to the low TOC content of the sand‐clay mixes. Clay subsoil addition did not affect the MBC concentration per g TOC but reduced the concentration of K₂SO₄ extractable C per g TOC. In the DRW treatment, cumulative respiration per g TOC during the dry phase increased with increasing clay subsoil addition rate. Rewetting of dry soil caused a flush of respiration in all soils but cumulative respiration at the end of the experiment remained lower than in the constantly moist soils. Respiration rates after rewetting were higher than at the corresponding days in constantly moist soils only at clay subsoil addition rates of 20 to 40%. We conclude that in presence of residues, addition of clay subsoil to a sandy top soil improves microbial activity during the dry phase and upon rewetting but has little effect on microbial biomass.     

深翻结合心土与不同改土物料混合改良白浆土的效果

该研究通过设置心土混拌配施改土物料区和浅翻深松区进行小区对比试验,调查心土混拌配施不同改土物料对白浆土心土理化性质的改良效果,进而进一步拓宽白浆土心土改良途径。试验共设置浅翻深松区(CK);心土混合区(SML);秸秆+心土混合区(S+SML);秸秆+心土混合区+磷肥(S+SML+P),秸秆+心土混合区+石灰(S+SML+L);秸秆+心土混合区+石灰+磷肥(S+SML+L+P)6个处理。研究结果表明:1)与浅翻深松(CK)相比,深翻结合心土与不同改土物料混合能够改善心土层土壤物理性质,20~40 cm土层土壤含水率提高幅度为2.11~6.11个百分点;硬度降低40%~50%,且没有出现峰值;提高土壤通透性,改善土壤三相比值,固相降低幅度为8.5~9.97个百分点,液相增加幅度为2.82~5.41个百分点,气相增加幅度为3.89~6.65个百分点,容重下降幅度为10.13%~17.09%。2)提高心土层养分含量,碱解氮提高82.75%~121.63%,有效磷提高190.91%~681.82%,特别是添加磷肥处理变化明显,是对照处理6.5~6.8倍,速效钾提高20.7%~40.74%。有机质提高157.14%~185.71%。缓解土壤酸性,加石灰处理p H值提高0.45~0.47个单位。提高土壤全量养分,全氮提高45.76%~52.54%,全磷提高108.14%~144.19%,全钾提高8.10%~26.34%。3)连续两年提高作物产量。与对照区相比,第1年大豆增产13.42%~24.46%,第2年玉米增产13.43%~19.17%,一次改土后效时间长,增产效果显著。研究结果认为,心土混合配施秸秆、石灰和磷肥是白浆土区比较理想的心土改良技术,可为白浆土及其同类低产土壤改良及作物增产提供技术支撑。     

Differentiating sources of CO2 from organic soil under bioenergy crop cultivation: A field-based approach using 14C

We tested here a plant-soil system to separate recent, plant-derived and native, soil-derived carbon in soil respiration. The approach uses a perennial crop cultivated on an organic soil where upper soil layers have been removed as a result of peat extraction. There, the ¹⁴C signal from native organic matter is highly depleted compared to that in vegetation established at the site after peat extraction ceased. Radiocarbon was analyzed in carbon dioxide respired from soil over one growing season, and a two-pool isotope mixing model was applied to calculate the relative contribution of old vs. new carbon sources. The analysis showed that the approach is reliable for source partitioning with isotopes. After six years of cultivation, old peat decomposition contributed less to total soil respiration than respiration of recent plant material (30% vs. 70% on average, respectively), but the relative proportions were highly variable over the growing season. The approach offers a new possibility to follow the fate of old, native soil organic matter in highly organic soils.     

Differentiating sources of CO2 from organic soil under bioenergy crop cultivation: A field-based approach using C

We tested here a plant-soil system to separate recent, plant-derived and native, soil-derived carbon in soil respiration. The approach uses a perennial crop cultivated on an organic soil where upper soil layers have been removed as a result of peat extraction. There, the ¹⁴C signal from native organic matter is highly depleted compared to that in vegetation established at the site after peat extraction ceased. Radiocarbon was analyzed in carbon dioxide respired from soil over one growing season, and a two-pool isotope mixing model was applied to calculate the relative contribution of old vs. new carbon sources. The analysis showed that the approach is reliable for source partitioning with isotopes. After six years of cultivation, old peat decomposition contributed less to total soil respiration than respiration of recent plant material (30% vs. 70% on average, respectively), but the relative proportions were highly variable over the growing season. The approach offers a new possibility to follow the fate of old, native soil organic matter in highly organic soils.     

Persistence of soil compaction due to high axle load traffic. II. Long-term effects on the properties of fine-textured and organic soils

The long-term effects of high axle load traffic on soil structure were investigated in three field experiments. Two of the experiments were located on fine-textured mineral soils (Vertic Cambisol). The clay soil had 48 g clay (particle size less than 2 μm) per 100 g in the topsoil and 65 g per 100 g in the subsoil, and the loam soil had clay contents of 30 g and 42 g per 100 g in the topsoil and subsoil, respectively. One experiment was located on an organic soil (Mollic Gleysol) consisting of well-decomposed sedge peat mixed with clay from 0.2 to 0.4–0.5 m depth, and underlain by gythia (organic soil with high clay content). In the autumn of 1981, one pass and four repeated passes with a heavy tractor-trailer combination compacted the soils to 0.4–0.5 m depth. The trailer tandem axle load was 19 Mg on the clay and 16 Mg on the other soils.

For 9 years after the experimental traffic, the main crops grown were spring cereals. During this time, the maximum axle load applied during field operations was 5 Mg and the maximum tyre inflation pressure was 150 kPa. The clay and loam froze to 0.5 m depth for 6 and 2 years, respectively. During several growing seasons all three soils dried and cracked. In the ninth year after the loading, soil penetrometer resistance, saturated hydraulic conductivity (K_sat), macroporosity and number and area of cylindrical biopores were measured and the visual structure of the soils examined.

Compaction in the plough layer was alleviated by ploughing and natural processes, whereas in the subsoil the effects of the compaction were still measurable, in all experiments, in the ninth year after the high axle load traffic. In the clay soil in the 0.3–0.5 m layer and in the organic soil in the 0.28–0.4 m layer, the penetrometer resistance was 22–26% greater and the soil structure more massive in the plots compacted with four passes than in the control plots. In the 0.4–0.55 m layer in all soils, the loading with four passes decreased K_sat by 60–98% and macroporosity (diameter greater than 300 μm) by 37–70%. In the fine-textured mineral subsoils, cylindrical biopores were found in all treatments. The trend of the results was, however, for biopores to be fewer in compacted than in control plots.     

秸秆心土混合犁改良白浆土效果

为将表层秸秆施入心土,改善贫瘠的心土层创造有利条件,该文设计了将白浆土"上翻20 cm,下混30~40 cm,同时将有机物料施入心土层"的秸秆心土混合犁。该研究通过设置秸秆心土混合区和浅翻深松区田间对比试验,调查机械作业后土壤理化性质,指示作物农艺性状以及产量指标等,明确秸秆心土混合的改土增产机理,进一步拓宽白浆土改良途径,为机械改土技术的广泛应用提供技术支撑。研究结果表明:与浅翻深松相比,秸秆心土混合改善心土层土壤物理性质,20~40 cm土层土壤含水率提高2.69~4.90个百分点;硬度降低44.45%左右,且没有出现峰值;改善土壤通透性,固相降低幅度为4.51~2.14个百分点,液相增加幅度为1.17~4.13个百分点,气相增加幅度为0.38~0.98个百分点,容重下降幅度为0.16~0.11 g/cm~3;提高心土层养分含量,碱解氮提高17.33%,有效磷提高116.39%,速效钾提高37.86%,有机质提高36.66%,同时提高心土层全量养分含量,缓解土壤酸性。连续2 a调查大豆产量,秸秆心土混合区比对照区增产15.77%~16.33%,一次改土后效时间长,增产效果显著。该研究结果可为白浆土及其同类低产土壤改良及作物高产提供技术支撑。     

The Potential for Waste‐Derived Materials to Form Soil Covers for the Restoration of Mine Tailings in Ireland

Revegetation of mine tailings sites can require significant amounts of topsoil, the sourcing of which can be costly and have detrimental impacts. To address this problem at an Irish mine tailings site, engineered soils were created by mixing varying rates of glacial till with stockpiled peat and compost. Soil status was assessed using a range of soil parameters and vegetation growth characteristics and compared with locally sourced topsoil. Hordeum vulgare (Barley) germination and growth trials were assessed on engineered soils: compost with glacial till, peat with glacial till, compost/ peat with glacial till and topsoil. A range of soil quality parameters were examined including: nutrient status, dehydrogenase activity, metals availability and physical characteristics (bulk/particle density and porosity). Results demonstrate that compost derived soils yielded superior plant biomass and nutrient content, whilst peat derived treatments exhibited nutrient deficiency. Whilst the engineered soils offer potential as an alternative to sourcing topsoil for covering mine tailings, the phosphorus and metal content of composts should be assessed prior to inclusion. Copyright © 2015 John Wiley & Sons, Ltd.     

Gas Diffusion Coefficient of Undisturbed Peat Soils

Determination of the gas diffusion coefficient D _s of peat soils is essential to understand the mechanisms of soil gas transport in peatlands, which have been one of major potential sources of gaseous carbons. In the present study, we aimed at determining the D _s of peat soils for various values of the air-filled porosity a and we tested the validity of the Three-Porosity Model (Moldrup et al. 2004) and the Millington-Quirk model (1961) for predicting the relative gas diffusivity, the ratio of D _s to D ₀, the gas diffusion coefficient in free air. Undisturbed peat soil cores were sampled from aerobic layers in the Bibai mire, Hokkaido, Japan. The MQ model reproduced the measured D _s/ D ₀ curves better than the TPM. The TPM, a predictive model for undisturbed mineral soils, overestimated the D _s/ D ₀ values for peat soils, implying that in the peat soils the pore pathways were more tortuous than those in the mineral soils. Since the changes in the D _s/ D ₀ ratios with the a values of a well-decomposed black peat soil tended to be more remarkable than those of other high-moor peat soils, the existence of a positive feedback mechanism was assumed, such that peat soil decomposition itself would increase the soil gas diffusivity and promote soil respiration.     

Leaching of Solutes from an Intensively Managed Peat Soil to Surface Water

In many peat land areas in The Netherlands target concentrations for nitrogen (N) and phosphorus (P) in surface water are exceeded. A considerable, but poorly quantified, fraction, of the N and P loading of surface water in these areas originate from the subsoil. Waterboards, responsible for the water management, are currently exploring options to improve surface water quality, whilst sustaining agricultural production. Therefore, insight into dynamics of nutrient pools in peat soils is required. The aim of this study was to measure concentration profiles (0–12 m) of the soil solution in an intensively managed grassland on peat soil and to explore the effects of a rise in surface water level on N and P loading of surface water, using budgeting approaches and two dimensional simulation modeling. The concentration profiles of N, P and Cl reflect by the presence of nutrient-rich anaerobic peat and a nearly impermeable marine clay in the subsoil. Concentrations of N, P and Cl tended to increase with depth till about 6 m and then decreased. In the top soil, inputs of N and P via fertilizers and animal manure were only partly retrieved in the soil solution, suggestion that biogeochemical processes, uptake and lateral transport processes had a dominant influence on dissolved N and P. Exploring scenario simulations showed that major drainage fluxes passed through the peat layer that transported nutrients to adjacent surface water. Raising surface water levels with 20 cm suppresses this kind of nutrient loading of surface water by more than 30%, but nutrient rich peat layers will remain persistent as a potential source of nutrients in surface water in many peat polders in the western part of The Netherlands.     

Functioning of microbial complexes in aerated layers of a highmoor peat bog

Monitoring was carried out using the luminescent-microscopic method of the abundance parameters of different groups of microorganisms in a monolith and in the mixed layers of a highmoor peat bog (oligotrophic residual-eutrophic peat soil) in a year-long model experiment. The increase of the aeration as a result of mixing of the layers enhanced the activity of the soil fungi. This was attested to by the following changes: the increase of the fungal mycelium length by 6 times and of the fungal biomass by 4 times and the double decrease of the fraction of spores in the fungal complex. The response of the fungal complex to mixing was different in the different layers of the peat bog. The maximal effect was observed in the T1 layer and the minimal one in the T2 layer. The emission of CO₂ in the mixed samples was 1.5–2 times higher than that from the undisturbed peat samples. In contrast with the fungi, the bacteria and actinomycetes were not affected by the aeration of the highmoor layers.     

Persistence of soil compaction due to high axle load traffic. I. Short-term effects on the properties of clay and organic soils

Short-term effects of high axle load traffic on soil total porosity and pore size distribution were examined in field experiments on a clay (Vertic Cambisol) and an organic soil (Mollic Gleysol) for 3 years after the heavy loading. The clay soil had 48 g clay (particle size less than 2 μm) per 100 g in the topsoil and 65 g per 100 g in the subsoil. The organic soil consisted of well-decomposed sedge peat mixed with clay below 0.2 m depth down to 0.4–0.5 m and was underlain by gythia (organic soil with high clay content). The experimental traffic was applied with a tractor-trailer combination in autumn 1981. The trailer tandem axle load was 19 Mg on the clay and 16 Mg on the organic soil. There were three treatments: one pass with the heavy axle vehicle, with wheel tracks completely covering the plot area, four repeated passes in the same direction, and a control treatment without experimental traffic. During loading, the clay was nearly at field capacity below 0.1 m depth. The organic soil was wetter than field capacity.

One and four passes with the high axle load compacted both soils to a depth of 0.4–0.5 m. On the clay soil the total porosity was reduced by the heavy loading nearly as much as macroporosity (diameter over 30 μm) to 0.5 m depth. On the organic soil, macroporosity was reduced and microporosity (under 30 μm) increased in the 0.2–0.5 m layer by the heavy loading. Total porosity did not reveal the effects of compaction on the organic soil. The compaction of the clay below 0.1 m persisted for 3 years following the treatment despite annual ploughing to a depth of 0.2 m, cropping and deep cracking and freezing. Likewise, in the subsoil (below 0.2 m) of the organic soil, differences in pore size distribution persisted for a period of at least 3 years after the heavy loading.     

Influence of subsoil amelioration with lime,phosphorus and potassium on the yield of soybeans and barley

Abstract

The effects of mixing lime and large quantities of phosphorus and potassium fertilizers with the subsoil were studied on 16 Maryland subsoils. These subsoils were covered with 10. cm of a fertile surface soil so the subsoils’ effect would be the major variable. Soybeans were grown on these soils in the greenhouse. These subsoils received 65.2 and 83.0 ug/g of phosphorus and potassium respectively. Two treated subsoils were also studied in the field. Simulated subsoiling in the field was accomplished by digging to a depth of 50.8 cm. Lime, 148 or 440 Kg P/ha, and 186 or 558 Kg K/ha were mixed with each 15 cm depth of subsoil. Soybeans and/or barley were planted on the field plots.

In general, the subsoils studied in the greenhouse indicated that the combined amendments of lime, phosphorus and potassium to the subsoils increased root production in the subsoil, nitrogen content in the soybean shoots, and yield.

First year field results on the Othello (Typic Ochraquult) soil indicated that soybean yields on treated subsoil plots were not significantly different from soil receiving the same surface applications of fertilizer. However the second year after treatment, the yields of double cropped soybeans and barley were increased by 706 Kg/ha (10.5 bu/acre) and 710 Kg/ha (14.4 bu/acre) respectively when compared to similar quantities of phosphorus and potassium applied to the surface soil of nonsubsoiled plots.

On the Monaouth (Typic Hapludult) soil, the first year yields of subsoil plots treated with lime, phosphorus, and potassium also failed to improve yields compared to surface application of the fertilizer. Lime, 440 Kg P/ha, and 558 Kg K/ha applied to the subsoil did significantly improve yields of full season soybeans over the untreated soil by 720 Kg/ha (10.7 bu/acre).     

An assessment of subsoil organic carbon stocks in England and Wales

It is estimated that half the soil carbon globally is in the subsoil, but data are scarce. We updated estimates of subsoil organic carbon (OC) in England and Wales made by Bradley et al. (2005) using soil and land‐use databases and compared the results with other published data. We estimated that the soils of England and Wales contained 1633, 1143 and 506 Tg of OC at 0–30, 30–100 and 100–150 cm depths, respectively. Thus, half of the soil OC was found below 30 cm depth. Peat soils accounted for the largest proportion, containing 44% of all the OC below 30 cm despite their small areal extent, followed by brown soils, surface‐water gley soils, ground‐water gley soils and podzolic soils. Peat soils had more than 25% of their profile OC per unit area in the 100–150 cm depth, whereas most other soils had <8% at this depth. The differences between soil types were consistent with differences in soil formation processes. Differences in depth distributions between land uses were small, but subsoil OC stocks in cultivated soils were generally smaller than in soils under grassland or other land uses. Data on subsoil OC stocks in the literature were scarce, but what there was broadly agreed with the findings of the above database exercise. There was little evidence by which to assess how subsoil OC stocks were changing over time.     

Nutritional Environment of Tropical Peat Soils in Sarawak,Malaysia Based on Soil Solution Composition

It has been considered that natural peat soils and swamp forest ecosystems in the tropics are quite oligotrophic. This concept seems to be related to the low mineral contents in the soil solid phase of the peat soils. However, some nutritional elements such as K, Mg, Ca, and/or P may be abundant in the soil solution phase and could easily migrate in peat soils. In order to analyze the nutritional environment of peat soils, chemical composition of the soil solid phase and soil solution was compared.

This study was carried out in Naman Forest Reserve, Sibu and in/around Sg. Talau Peat Research Station, Mukah, Sarawak, Malaysia. In both areas, each of the three study sites with a different depth of underlying mineral layer was selected for sampling of soil and soil solution. All the soils studied except for one shallow peat profile were classified into Oligotrophic peat based on Fleischer’s criteria. The soil solution collected monthly showed the following characteristics in its composition.

1. Concentrations of Al, Si, and Fe were higher in the soil solution from the shallow peat than in that from the deep peat, reflecting the effect of underlying mineral layers on the soil solution composition.

2. Concentrations of Na, Mg, and Cl in the soil solution and Na and Mg contents in the soil solid phase reflected the distance from the sea. In the Naman series, accumulation of K and Ca in the soil solution was larger in the surface layer in the deep peat than in the shallow peat, though such clear trend was not observed for the K content in the soil solid phase.

3. The concentrations of N and P were fairly high in the soil solution in all the profiles except for P in the profile near the center of the peat dome. Dissolved P consisted mostly of ortho-phosphate, whereas a larger part of N was in the organic form.

4. At the Sago plantation farm on deep peat, depletion of K and P was observed during the rainy season. Such instability in the concentrations in the soil solution was attributed to forest clear-cutting and subsequent disturbance of nutrient cycling.

In general, the concentrations of N, P, K, and Ca in the soil solution were not low even in the Oligotrophic peat. However, in taking account of the fact that the peat soils showed low mineral contents in the available forms and that the bulk density was also quite low, the potential capacity to supply K, Ca, and/ or P was not necessarily high in spite of the apparent high intensity observed for the soil solution composition. Therefore, from the viewpoint of nutrient dynamics, the potential for the use of reclaimed peat land was considered to be rather limited especially under low input management.     

Effect of Three Different Qualities of Biochar on Selected Soil Properties

An incubation study was conducted to determine how biochar interacts with a nitrogen fertilizer and how it reacts in the soil as well as to measure the effect of different biochars on soil chemical properties. Two Iowa soils, Nicollet surface soil (fine-loamy, mixed, superactive, mesic Aquic Hapludoll) and Storden subsoil (fine-loamy, mixed, superactive, mesic Eutrudept), were mixed with three different qualities of biochar and a nitrogen fertilizer (urea). The biochar was created from corn stover that was pyrolized with three different amounts of atmospheric air: 0% (biochar 1), 10% (biochar 2), and 25% (biochar 3). Soil tests for pH, total nitrogen (N), extractable phosphorus (P), extractable potassium (K), ammonium N, nitrate N, organic matter, and total carbon (C) were performed. The different biochars significantly affected the total N, total organic C, and pH in both soils at all rates of urea applied. The conditions during pyrolysis influenced how the biochar/fertilizer reacted with the soil.     

Fifty years after deep-ploughing: Effects on yield,roots, nutrient stocks and soil structure

Deep-ploughing far beyond the common depth of 30 cm was used more than 50 years ago in Northern Germany with the aim to break root-restricting layers and thereby improve access to subsoil water and nutrient resources. We hypothesized that effects of this earlier intervention on soil properties and yields prevailed after 50 years. Hence, we sampled two sandy soils and one silty soil (Cambisols and a Luvisol) of which half of the field had been deep-ploughed 50 years ago (soils then re-classified as Treposols). The adjacent other half was not deep-ploughed and thus served as the control. At all the three sites, both deep-ploughed and control parts were then conventionally managed over the last 50 years. We assessed yields during the dry year 2019 and additionally in 2020, and rooting intensity at the year of sampling (2019), as well as changes in soil structure, carbon and nutrient stocks in that year. We found that deep-ploughing improved yields in the dry spell of 2019 at the sandy sites, which was supported by a more general pattern of higher NDVI indices in deep-ploughed parts for the period from 2016 to 2021 across varying weather conditions. Subsoil stocks of soil organic carbon and total plant-available phosphorus were enhanced by 21%–199% in the different sites. Root biomass in the subsoil was reduced due to deep-ploughing at the silty site and was increased or unaffected at the sandy sites. Overall, the effects of deep-ploughing were site-specific, with reduced bulk density in the buried topsoil stripes in the subsoil of the sandy sites, but with elevated subsoil density in the silty site. Hence, even 50 years after deep-ploughing, changes in soil properties are still detectable, although effect size differed among sites.     

碳酸氢根与水肥同层对玉米幼苗生长和吸收养分的影响

把水分(NaHCO3溶液或纯水)供应于底施了铵态或硝态N肥的土层内,以研究HCO3-及水肥供应方式对石灰性土壤上玉米生长及养分吸收的影响。结果表明,在限制灌水量的条件下,在土壤上层供应HCO3-显著抑制根系生长,但在下层供应对生长无明显影响;当施用不同形态N素时,HCO3-对N素吸收并无明显影响;此外,供应HCO3-溶液能明显提高灌水土层的土壤pH。总体来看,在供试条件下,HCO3-对玉米幼苗生长量、根系分布及养分吸收量的影响均较为有限,而后三者主要受施肥灌水层次的影响,即:在土壤上层施肥灌水,幼苗生长量显著降低;而在下层施肥灌水是一种节水节肥的水肥供应方式。但下层施肥灌水不利于植株的直立性。因为下层施肥灌水时根系主要分布在下层,在上层分布数量极少;而上层施肥灌水根系在上下两层中的分布无明显差异;下层施肥灌水的玉米植株,其N、P、K吸收量远高于上层施肥灌水的植株。     

3种典型河岸林土壤氮磷的空间分布格局及其影响因素

通过等距离梯度密集采样,结合主成分分析和相关性分析,研究了3种河岸林土壤全氮和全磷的空间分布及其影响因素。结果表明,3种河岸林全氮储量表层显著高于中层和底层;全磷储量层次性不明显。3种河岸林中,云杉河岸林土壤的氮磷储量最大,青杨辽东栎混交林次之,落叶松辽东栎最小。影响全氮分布的主要因子为有机质和植被盖度;影响全磷分布的主要因素为土层厚度和土壤容重。     

Use of flue gas desulfurization (FGD) by‐product gypsum on alfalfa

Abstract

Subsoil acidity in northeast United States has been associated with decreased yield and decreased water and fertilizer nitrogen (N) utilization by forages. Surface applications of gypsiferious products has been shown to reduce subsoil acidity largely caused by high levels of soluble aluminum (Al). Our objective was to test the effectiveness and safety of using FGD gypsum to increase dry matter (DM) yields of alfalfa (Medicago sativa L.). Four and one‐half, 9, and 18 mt/ha of either commercially available agricultural gypsum or two gypsum by‐products were applied to a Rayne soil (Fine‐loamy, mixed, mesic Typic Hapludult) with a strongly acid subsoil. Agricultural and FGD gypsum increased alfalfa DM yields by as much as 21 and 14%, respectively. Correspondingly, in the subsoil, soluble Al decreased and calcium (Ca) content and Ca:Al ratio increased. Heavy metal concentrations in either the alfalfa or soils were not increased by any treatment. However, S in the alfalfa grown at the highest treatments approached concentrations that are considered to be toxic to grazing animals.     

Movement of bacteria and nutrients from pit latrines in the boundary waters canoe area wilderness

In the Boundary Waters Canoe Area Wilderness, the movement of fecal bacteria, N, and P from pit latrines was studied, as well as the effectiveness of peat latrine liners in reducing this movement. When latrines are constructed where only a thin layer of permeable soil overlies bedrock or other impermeable material, fecal bacteria can be carried considerable distances by subsurface flow. Lining latrine pits with acid peat appears to reduce bacteria transport. Most soils strongly adsorb P and prevent its movement. In this study no movement of P from latrine pits was seen except at one site with very sandy soil. In such soil a peat liner appears to be of some value, if a peat with a high P adsorption capacity is used. A peat liner should be viewed as an additional protection against P and bacteria movement rather than as a substitute for proper soil conditions. Latrines should not be built in thin, rocky soils. Nitrogen appears to move readily from toilet pits, regardless of soil type or presence of peat liners. But, because of dilution, N is not likely to have a discernible impact on water quality.