Implications of municipal wastewater irrigation on soil health from a study in Bangladesh

This study evaluated soil health in fields of wheat (Triticum aestivum L. cv Shatabdi) and potatoes (Solanum tuberosum L.) irrigated by different blends of municipal wastewater (hereafter called wastewater). The crops were grown with and without added fertilizers over three consecutive years. The wastewater contained high concentrations of organic carbon (C), nitrogen (N), phosphorus (P), sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S), zinc (Zn) and boron (B). It also contained negligible concentrations of a few heavy metals. Irrigation by wastewater resulted in an increase in the porosity of the surface soil and thus a reduced bulk density. Wastewater enhanced the saturated hydraulic conductivity and water retention capacity of the soils. The organic carbon, total N, available P and S, and exchangeable Na, K, Ca and Mg of the soils increased proportionately with the quantity of applied wastewater. C, N and K increased significantly (α = 0.05) when fields were irrigated using raw wastewater after applied fertilizers; the other elements accumulated in the soil insignificantly under both fertility levels. Electrical conductivity (EC) and pH of the upper 0–20 and 20–40 cm soil layers increased with the application of wastewater; the increase was significant only under raw wastewater irrigation. In the 40–60 cm soil layer, both EC and pH remained unchanged. The applied inorganic fertilizers raised EC but reduced soil pH. The wastewater contained large counts of total coliform (TC: 17.2 × 10⁶ cfu/100 mL) and faecal coliform (FC: 13.4 × 10³ cfu/100 mL). Irrigation using municipal wastewater is proposed for improving soil fertility as well as for alleviating water scarcity with the exception of some crops whose edible parts come in direct contact with wastewater and/or are eaten uncooked.     

Changes in enzyme activities of spruce (Picea balfouriana) forest soil as related to burning in the eastern Qinghai-Tibetan Plateau

The effect of forest fire on soil enzyme activity of spruce (Picea balfouriana) forest in the eastern Qinghai-Tibetan Plateau was assessed. Six specific enzymes were chosen for investigation: invertase, acid phosphatase, proteinase, catalase, peroxidase and polyphenoloxidase. It was found that the activities of invertase and proteinase were reduced by burning, but the activities of acid phosphatase, polyphenoloxidase and peroxidase increased. Meanwhile, burning significantly (P < 0.05) resulted in the decrease of concentrations of available N and K of 0–20 cm depth layer soil, and significantly (P < 0.05) decreased concentrations of organic matter content, total N and P, as well as available N, P and K in soil at both 20–40 and 40–60 cm depths except for available P at 20–40 cm soil depth. These results illustrated that burning could influence the enzyme activities and chemical properties of soil not only of upper but also lower soil layers. Correlation analysis indicated that invertase activities in 0–20 cm depth layer soil were significantly positively correlated with organic matter, total N and P, as well as available N and P. Furthermore, all six enzymes studied were sensitive to fire disturbance, and thus could be used as indicators of soil quality. Our study also showed that soil enzyme activities were associated with soil depth, decreasing from top to bottom in both burned and unburned spruce forests. The distribution pattern of soil enzyme activities suggested that the rate of organic matter decomposition and nutrient cycling depended on soil depth, which had important structural and functional characteristics in nutrient cycling dynamics and implications in plantation nutrient management. The finding that burning effects on enzyme activities and soil properties between different soil layers were homogenized was attributed to the 8-years’ regeneration of forest after burning.     

Soil P and cation availability and crop uptake in a forage rotation under conventional and reduced tillage

Long‐term conservation tillage can modify vertical distribution of nutrients in soil profiles and alter nutrient availability and yields of crops. This study aimed to evaluate the effect of 14 yr of conventional (CT) and reduced tillage (RT) on soil macronutrient availability (0–5, 5–15, 15–30 cm) and uptake by Italian ryegrass and maize in a forage rotation under a temperate–humid climate (NW Spain). Soil contents of total C, plant available Ca, Mg, Na, K and P and their uptake by plants were evaluated over 2 yr. The three‐way ANOVA showed that tillage and its interactions with soil depth and sampling date have little influence on soil C and macronutrients contents (<13% of variance explained). In the topsoil layer, all studied variables (except K) increased in RT compared with CT, but they remained unchanged (C, Ca and Na) or decreased (Mg, K and P) in deeper layers. Crop yields were greater with RT than CT during the year with soil‐water‐deficit periods, while limited tillage effect was found in the other year. Whereas no differences were obtained for maize, nutrient concentration (Mg, Na, K and P) in ryegrass increased under RT. Conservation tillage improved surface soil fertility, maize yield and ryegrass nutrient content.     

严重侵蚀退化马尾松林地植被恢复土壤养分的制约性因子

[目的]揭示马尾松(Pinus massoniana)林地植被恢复的土壤养分制约性因子,为严重侵蚀退化马尾松林地植被恢复提供理论依据。[方法]通过在福建省长汀县河田镇花岗岩风化红壤区,植被恢复差异较大的4种马尾松样地的0—5,5—20,20—40cm的土壤养分试验分析。[结果](1)恢复较差的马尾松林地的有机质、全氮、全磷、速效磷、全钾、速效钾含量均较低,土壤保肥能力差,养分易随土壤侵蚀而流失。(2)所有样地的有机质、全氮、全磷、速效磷,速效钾含量变化规律基本上为:恢复较差恢复中等恢复较好恢复好。(3)有机质、全氮、全磷、速效磷,速效钾极显著正相关(p0.01),且在第1主成分上的载荷分别为0.921,0.931,0.974,0.906,0.874。(4)4种恢复样地土壤表层全钾差异不显著,其他层土壤规律不明显,植被恢复好的样地的pH值最小,但是马尾松林下植被生长良好。[结论]有机质、全氮、全磷、速效磷、速效钾植是马尾松林地植被恢复主要制约因子,全钾、pH值不是马尾松林地植被恢复制约性因子。     

Changes in soil aggregate‐associated enzyme activities and nutrients under long‐term chemical fertilizer applications in a phosphorus‐limited paddy soil

Paddy soils in subtropical China are usually deficient in phosphorus (P) and require regular application of chemical fertilizers. This study evaluated the effects of chemical fertilizers on the distribution of soil organic carbon (SOC), total nitrogen (N) and available P, and on the activity of the associated enzymes in bulk soil and aggregates. Surface soils (0–20 cm) were collected from a 24‐yr‐old field experiment with five treatments: unfertilized control (CK), N only (N), N and potassium (NK), N and P (NP), and N, P and K (NPK). Undisturbed bulk soils were separated into >2, 1–2, 0.25–1, 0.053–0.25 and <0.053 mm aggregate classes using wet sieving. Results showed that both NP‐ and NPK‐treated soils significantly increased mean weight diameter of aggregates, SOC, available P in bulk soil and aggregates, as compared to CK. Most SOC and total N adhered to macro‐aggregates (>0.25 mm), which accounted for 64–81% of SOC and 54–82% of total N in bulk soil. The activities of invertase and acid phosphatase in the 1–2 mm fraction were the highest under NPK treatment. The highest activity of urease was observed in the <0.053 mm fraction under NP treatment. Soil organic carbon and available P were major contributors to variation of enzyme activities at the aggregate scale. In conclusion, application of NP or NPK fertilizers promoted the formation of soil aggregates, nutrient contents and activities of associated enzymes in P‐limited paddy soils, and thus enhanced soil quality.     

Pasture degradation impacts soil phosphorus storage via changes to aggregate-associated soil organic matter in highly weathered tropical soils

Maintaining the productivity of tropical pastures is a major challenge for the sustainable management of tropical landscapes around the globe. To address this issue, we examined linkages between soil organic matter (SOM), aggregation, and phosphorus (P) dynamics by comparing productive vs. degraded pastures in the deforested Amazon Basin of Colombia. Paired plots of productive (dominated by planted Brachiaria spp.) vs. degraded pasture were identified on nine farms in the Department of Caquetá and sampled during the rainy season of 2011. Aboveground pasture biomass production and nutrient content were measured. Surface soils (0–10 cm) were also fractionated by wet sieving, and C, ¹³C, N and P contents were analyzed for the bulk soil and various aggregate size classes. Productive pastures yielded more than double the aboveground biomass compared to degraded pastures (during a 35 day regrowth period following cutting), with over 60% higher N and P contents in this material. Similar trends were observed for the standing litter biomass and nutrient contents. Soil aggregate stability was found to differ between pasture types, with a mean weight diameter of 3590 vs. 3230 μm in productive vs. degraded pastures, respectively. Productive pastures were found to have 20% higher total soil C and N contents than degraded pastures. While there was no difference in total P content between pasture types, organic P was found to be nearly 40% higher in soils of productive vs. degraded pastures. Differences in total SOM between pasture types were largely explained by a higher C content in the large macroaggregate fraction (>2000 μm), and more specifically in the microaggregates (53–250 μm) occluded within this fraction. These findings confirm the role of microaggregates within macroaggregates as a preferential site for the physical stabilization of SOM, and furthermore, suggest that it may serve as a useful diagnostic fraction for evaluating management impacts on SOM in tropical pasture systems. Similar to trends observed for C and N, total P content was 25% higher in the microaggregates within large macroaggregates of productive vs. degraded pasture soils. This correspondence between C and total P contents in large macroaggregate fractions, along with elevated levels of organic P in productive pastures, suggests that this P is likely in an organic form and that there is a close link between soil structure, SOM dynamics and the maintenance of organic P in these soils. Given the potential relevance of organic P for efficient P cycling in these soils, our findings offer critical new insight for the management of SOM and aggregate-associated P pools in tropical pasture systems.     

陕北黄土区衰退沙棘人工林改良土壤的作用

为研究衰退沙棘人工林对土壤的改良功能,对陕北黄土区衰退沙棘人工林分轻度、中度、重度3种衰退类型进行了研究。结果表明:(1)3种衰退类型沙棘人工林0—60cm土层土壤速效磷、速效钾含量较对照均有提高。(2)轻度衰退沙棘人工林对40—60cm土层土壤有效氮,0—20cm速效磷含量有显著提高作用。对20—40cm土层土壤有效氮含量有极显著提高作用(由14.23mg/kg增至22.39mg/kg)。中度衰退沙棘人工林对20—60cm土壤有机质、有效氮有显著提高作用。重度衰退沙棘人工林对0—20cm土壤全氮含量的提高作用显著低于对照坡面。(3)3种衰退类型沙棘人工林对20—40cm土层速效磷含量的作用表现为中度衰退沙棘人工林最大,其次是轻度衰退沙棘林。其他土层则表现为随着衰退程度加深,沙棘人工林对土壤改良作用减弱。     

Restoration Affect Soil Organic Carbon and Nutrients in Different Particle‐size Fractions

Desertification is reversible and can often be prevented by adopting measures to control the causal processes. Desertification has generally decreased in most of the arid and semiarid areas of China during the last few decades because of the restoration of degraded vegetation and soil nutrients. However, little is known about the responses of soil nutrients in different particle‐size fractions to the restoration process and about the importance of this response to the restoration of bulk‐soil nutrients. In this study, we separated bulk‐soil samples in different sieve fractions: coarse‐fine sand (2·0–0·1 mm), very fine sand (0·10–0·05 mm) and silt + clay (<0·05 mm) fractions. Soil organic carbon (SOC), N, P and K contents stored in the silt + clay were greater than the contents of non‐protected nutrients in the coarser fractions. During the restoration of desertified land, the content and stability of bulk‐soil SOC, total N and P and available N, P and K increased with increasing nutrient contents in all fractions. Topsoil nutrients stored in coarse‐fine sand and very fine sand fractions were more sensitive than those stored in the silt + clay fraction to the fixation of mobile sandy lands and vegetation recovery. The changes of bulk‐soil nutrients and their stability were decided by the soil nutrients associated with all particle‐size fractions. Path analysis revealed that SOC and total nutrients in very fine sand and available nutrients in coarse‐fine sand were the key factors driving the soil recovery. These results will help us understand soil recovery mechanisms and evaluate the degree of recovery. Copyright © 2015 John Wiley & Sons, Ltd.     

Estimates of variation for measurements of selected soil parameters on slash‐and‐burn fields in northern Laos

Abstract

Monitoring changes in soil fertility is an important component in the evaluation of land‐use systems. This research was undertaken to estimate short‐range soil variability of selected soil parameters in slash‐and‐burn systems of Northern Laos as a prerequisite for planning long‐term experiments. Coefficient of variation for the top interval (0–3 cm) was 10.4, 8.7, 20.7, 12.8, 75.8, and 44.8% for pH, total nitrogen (N), organic carbon (C), total phosphorus (P), available P, and available potassium (K), respectively (averaged over two sites). Variation generally decreased with increasing depth of soil interval, except for soil organic matter, where coefficient of variation was 14.1, 13.4, 14.6, 18.2, and 26.9% for intervals of 3–10, 10–25, 25–50, 50–75, and 75–100 cm, respectively. The number of sub‐samples required to document changes in available P and K will be unrealistically high if high confidence levels are required. Correlation between pH and available P and K was high for the 0–3 cm interval.     

退化演替对高山草地植被和土壤理化特性影响

[目的]分析3种不同草地退化阶段(轻度退化,中度退化和重度退化)草地植被和土壤理化特性的变化规律,为类似区域退化草地植被恢复提供有效途径。[方法]野外植被调查、土壤取样和室内分析。[结果]草地退化不同阶段草地植物群落组成和物种多样性均有差异,退化对草地土壤理化特性有明显影响。重度退化草地土壤容重显著高于轻度退化草地(p0.05)。轻度和中度退化样地0—10cm土壤空隙度显著高于重度退化草地。重度退化草地的土壤有机质、全碳、全钾、全磷和有效钾均明显小于轻度退化草地(p0.05),但土壤pH值和有效氮含量没有显著变化。[结论]高山草地退化演替对该区土壤物理特性具有显著影响。     

西藏中部退化农田土壤肥力的变化特征及其重建

通过田间定位试验 ,就西藏中部退化土壤化学和生物学肥力的变化等进行了研究。结果表明 ,无肥状态下土壤养分的变化具有极大的不平衡性 ,不同土层全钾、有效钾的下降速率均甚显著。有机肥 ,特别是有机—无机肥在促进土壤细菌繁殖和土壤有机质形成、改善腐殖质结构等方面具有显著作用 ,CEC、交换性盐基总量以及土壤氮、磷库容及其有效性亦呈明显提高 ,全钾、有效钾的亏缺程度逐渐下降 ,土壤氮、磷、钾的年均平衡量与其年均变化量间均呈不同程度的正相关 ,但土壤微生物区系仍处于极不协调的状态。在有机肥持续投入的基础上 ,增施氮肥、适施磷肥、重施钾肥对退化土壤的肥力恢复与重建具有重要作用     

三江源区草地退化与人工恢复对土壤理化性状的影响

以三江源区不同退化程度的天然草地及不同恢复年限的人工草地为研究对象,系统分析土壤理化性质随取样深度的动态变化。结果表明:(1)人工草地土壤含水量及全氮、全钾、全磷、速效钾、速效磷的含量随恢复年限均表现出先减小后增大的"V"形变化趋势;(2)随着退化程度增加,退化草地土壤中含水量逐渐降低,全氮、全钾、有机质、速效钾含量未表现出逐渐降低趋势,而草地的裸斑面积、土壤及养分的流失量逐渐增加;(3)人工草地及退化草地土壤中全氮、速效钾、有机质含量均随着取样深度增加而逐渐降低,草地恢复年限和退化程度基本不影响养分在土壤中的空间分布;(4)人工草地建设使退化草地有机质、全氮、全钾的含量增加,尤其有利于0-4cm的土壤养分增加。因而,人工草地建设可以作为三江源区退化草地土壤恢复的措施之一。     

Soil chemical properties after long‐term n fertilization of bromegrass: Nitrogen rate

Abstract

Nitrogen (N) fertilizers increase yield and quality of grass forage, and may also alter soil chemical properties. A field experiment was conducted in south‐central Alberta to determine the effect of long‐term application of ammonium nitrate to bromegrass on concentration and downward mobility of soluble NO₃‐N, extractable NH₄‐N, P, Ca, Mg, and K, and total C and N in a Thin Black Chernozemic loam soil. The fertilizer was applied annually in early spring for 16 years at 0 to 336 kg N/ha. There was little accumulation of NO₃‐N in the soil at N rates of 112 kg/ha or less. However, at rates higher than 112 kg N/ha there was accumulation of NO₃‐N in the 15–30 and 30–60 cm layers, but very little in the 90–120 cm depth. The NH₄‐N accumulated in the 0–5 cm layer when the fertilizer was applied at rates between 168 to 280 kg N/ha and in the 5–10 cm layer at N rates exceeding 280 kg/ha. There was a decline in extractable P in soil with N application up to 84 kg N/ha rate, while it increased with high N rates. The increasing amounts of applied N resulted in a decline in extractable soil Ca, Mg and K, and this decrease was more pronounced in the 0–5,5–10,10–15, and 15–30 cm layers for K, 0–5 and 5–10 cm layers for Ca, and 0–5, 5–10, and 10–15 cm layers for Mg. There was a build‐up of total C and N in the surface soil with increasing rate of applied N.     

Soil properties and plant community in different aged Pinus halepensis Mill. plantations in arid Mediterranean areas: The case of southern Tunisia

In arid and semiarid Mediterranean areas, Pinus halepensis Mill. is one of the dominant forest species and is widely used in restoration programmes. We collected samples and investigated the understory plant species in an age sequence of 0‐, 5‐, 9‐, and 13‐year‐old P. halepensis plantations to assess the effect of the tree on soil properties and development of plant community. Soil samples were taken from two depths (0–10 and 10–30 cm) under tree canopy and in the associated open spaces. Results showed that tree establishment and development enhanced organic C, total N, and available P accumulation, and improved soil moisture content which increased significantly with increasing plantation age. At the same time, P. halepensis facilitated the colonization and development of understory vegetation. Indeed, the number of plant species, the total plant cover, and the perennial species density were more important under tree canopy and increased with increasing plantation age. The soil dynamic under 13‐year‐old P. halepensis plantations reflected two phase restoration sequence, characterized by nominal changes during tree establishment (0–5 years) and marked and rapid changes associated with the start of canopy closure (5–13 years). Our results provide that the introduction of P. halepensis with afforestation could be an effective and applicable measure to restore arid degraded areas. Copyright © 2010 John Wiley & Sons, Ltd.     

设施蔬菜大棚土壤氮磷钾养分富积降低土壤钙素的有效性

【目的】 随着种植年限的增加,设施农业缺钙性生理病害发生率迅速上升。设施土壤中氮磷钾元素的富积与土壤中钙素的形态及有效性有密切关系,进而影响植物对钙素的吸收。因此,本研究调查比较了不同种植年限设施菜地土壤钙素有效性的变化,及与N、P、K含量的关系,为提高土壤钙素有效性和减少缺钙性生理病害提供理论依据。 【方法】 在辽宁省海城市选取了38个设施蔬菜大棚,种植年限在3～30年不等,土壤均为棕壤,按照每三年为一个时间段,将大棚分为9组。采集了棚内0—20 cm的耕层土壤样品,同时采集棚外露地0—20 cm土壤样品作为对照。分析了有机质、氮、磷、钾养分含量,分别测定了土壤水溶性钙、交换性钙、酸溶性钙、非酸溶性钙含量,利用回归方法计算了氮磷钾含量与四种形态钙含量之间的关系。 【结果】 随着种植年限延长,设施土壤有机质、氮、磷、钾、总钙、酸溶性钙和非酸溶性钙含量逐年增加,水溶性钙和交换性钙分别在种植达到9～11年和12～14年时达到最大值104.1和611.9 mg/kg,之后呈下降趋势。总钙增加量的94.3%～96.4%属无效态的非酸溶性钙。土壤中氮、钾含量的提高促进了交换性钙的解吸,铵态氮和速效钾含量与交换性钙呈显著负相关 (r = –0.5451,P <0.01; r = –0.4809,P <0.01, n = 38)。土壤中磷含量的提高促进了难溶性磷酸钙盐的形成,磷酸高钙盐与无效性的非酸溶性钙呈极显著正相关(r = 0.5884,P <0.01, n = 38)。种植30年的设施土壤有效态钙含量与有效氮、磷、钾的比例比露地土壤下降了近70%。 【结论】 随着设施蔬菜种植年限的增加,土壤中的氮、磷、钾养分含量不断增加。氮和钾含量的增加促进了交换性钙的解吸,磷的增加促进了水溶态和交换态钙向无效的非酸溶性钙的转化。因此,土壤中氮磷钾的富积加剧了蔬菜土壤有效性钙的缺乏。      

Nutrient dynamics from surface-applied organic matter amendments on no-till orchard soil

Advancing conservation agriculture depends on understanding nutrient dynamics of organic matter amendments (OMA) on no-till soil. This field incubation study compared surface-applied composted dairy manure (CM), green waste compost (GWC) and an unamended control from March to September in 2015 and 2016 using a RCBD in a California almond (Prunus dulcis) orchard. Measurements included OMA nutrient release rates, changes in soil organic carbon (SOC), total N (TN) and inorganic N, P and K availability using in-season soil sampling and collection of ion exchange resin (IER) membranes from 0 to 10 cm depth, and cumulative N and P availability using soil IER cores from 0 to 50 cm depth. We hypothesized OMA sources with a lower initial C:N increase soil N availability, greater soluble phosphorus (P) and potassium (K) concentrations increase P and K availability, and all OMA sources increase SOC with the greatest N recovery in the TN pool. No differences were observed in C, N and P release rates, while the K release rate was the greatest. In-season N availability showed no effect but P and K availability differed as evidenced by greater IER adsorption and soil extractable P and K. Both OMA sources significantly increased in SOC and TN. Net N mineralization from OMA sources ranged from 0.7% to 8.0% of applied N and total N recovery in TN and inorganic N pools increased based on the initial C:N. These results advance our understanding of nutrient dynamics while conserving the soil due to the no-till practice of surface-applied OMA.     

人工管理措施改善了我国西部高寒沙化草甸土壤水分和碳、氮、磷含量

Regeneration of degraded grassland ecosystems is a significant issue in restoration ecology globally. To understand the effects of artificial management measures on alpine meadows, we surveyed topsoil properties including moisture, organic carbon (SOC), nitrogen (N), and phosphorus (P) contents five years after fencing and fencing + reseeding management practices in a sandy meadow in the eastern Qinghai-Tibetan Plateau, northwestern China. Both the fencing and fencing + reseeding management practices significantly increased soil moisture storage, SOC, total N, available N, total P, and available P, as compared to the unmanaged control. Fencing plus reseeding was more effective than fencing alone for improving soil C, N, and P contents. These suggested that rehabilitation by reseeding and fencing generally had favorable effects on the soil properties in degraded sandy alpine meadows, and was an effective approach for restoration of degraded meadow ecosystems of the Qinghai-Tibetan Plateau.     

Response of soil C:N:P stoichiometry,organic carbon stock,and release to wetland grasslandification in Mu Us Desert

Purpose

Wetlands in Mu Us Desert have severely been threatened by grasslandification over the past decades. Therefore, we studied the impacts of grasslandification on soil carbon (C):nitrogen (N):phosphorus (P) stoichiometry, soil organic carbon (SOC) stock, and release in wetland-grassland transitional zone in Mu Us Desert.

Materials and methods

From wetland to grassland, the transition zone was divided into five different successional stages according to plant communities and soil water conditions. At every stage, soil physical and chemical properties were determined and C:N:P ratios were calculated. SOC stock and soil respirations were also determined to assess soil carbon storage and release.

Results and discussion

After grasslandification, SOC contents of top soils (0–10 cm) decreased from 100.2 to 31.79 g kg^?1 in June and from 103.7 to 32.5 g kg^?1 in October; total nitrogen (TN) contents of top soils (0–10 cm) decreased from 3.65 to 1.85 g kg^?1 in June and from 6.43 to 3.36 g kg^?1 in October; and total phosphorus (TP) contents of top soils (0–10 cm) decreased from 179.4 to 117.4 mg kg^?1 in June and from 368.6 to 227.8 mg kg^?1 in October. From stages Typha angustifolia wetland (TAW) to Phalaris arundinacea L. (PAL), in the top soil (0–10 cm), C:N ratios decreased from 32.2 to 16.9 in June and from 19.0 to 11.8 in October; C:P ratios decreased from 1519.2 to 580.5 in June and from 19.0 to 11.8 in October; and N:P ratios decreased from 46.9 to 34.8 in June and changed from 34.9 to 34.0 in October. SOC stock decreased and soil respiration increased with grasslandification. The decrease of SOC, TN, and TP contents was attributed to the reduction of aboveground biomass and mineralization of SOM, and the decrease of soil C:N, C:P, and N:P ratios was mainly attributed to the faster decreasing speeds of SOC than TN and TP. The reduction of aboveground biomass and increased SOC release led by enhanced soil respiration were the main reasons of SOC stock decrease.

Conclusions

Grasslandification led to lowers levels of SOC, TN, TP, and soil C:N, C:P, and N:P ratios. Grasslandification also led to higher SOC loss, and increased soil respiration was the main reason. Since it is difficult to restore grassland to original wetland, efficient practices should be conducted to reduce water drainage from wetland to prevent grasslandification.

     

The effects of clear‐felling subalpine coniferous forests on soil physical and chemical properties in the eastern Tibetan Plateau

Establishing soil quality changes following clear‐felling is important for guiding the sustainable management of forests. In this study we identified changes after 4, 5, 10 and 17 yr in soil physical and chemical properties from clear‐felling in the eastern Tibetan Plateau. These properties were also compared with those of soil from an adjacent primary forest. The results show that: (i) bulk density at 0–20 and 20–40 cm soil layer continuously increased; (ii) soil C and total N in the 0–20 cm soil layer continuously declined following clear‐felling; and (iii) available soil nutrients and exchangeable cations were significantly influenced by clear‐felling. Almost all soil properties showed deteriorating trends within a short time from clear‐felling and subsequent seasonal grazing by cattle. Therefore, improved management is imperative for sustaining soil quality and maintaining the long‐term nutrient balance in clear‐cut stands. The cessation of anthropogenic activities such as grazing should be the main strategy for soil restoration in clear‐felled areas.     

长期不同施肥处理红壤旱地剖面养分分布差异

【目的】 研究长期不同施肥措施下红壤旱地的培肥效果、养分迁移特征以及环境风险,对制定红壤旱地合理的养分管理和培肥技术,促进畜禽粪便的循环利用具有重要意义。 【方法】 依托始于1986年的红壤旱地肥料定位试验,选取不施肥 (CK)、氮磷钾肥配施 (NPK)、2倍氮磷钾肥配施 (2NPK)、有机肥 (OM) 和有机肥和氮磷钾肥配施 (NPKM) 5个处理,采集0—10 cm、10—20 cm、20—40 cm、40—60 cm、60—80 cm、80—100 cm土壤样品,分析了pH值、有机质及氮磷钾养分含量。 【结果】 连续施肥28年后,红壤旱地土壤有机质、全氮、碱解氮、全磷、有效磷、速效钾等含量均随着土壤深度增加逐步降低。与对照相比,施用有机肥显著提高了0—40 cm土壤的pH值,其余处理pH有所下降。长期施用化肥后,红壤旱地土壤有效磷、全磷、碱解氮和全氮在0—20 cm耕层累积,土壤速效钾的累积则达到40 cm深;与化肥处理相比,有机肥和有机无机肥配施处理0—40 cm土壤的全氮、碱解氮、速效钾、有效磷和全磷的含量显著增加,土壤全氮和碱解氮的下移累积达到40 cm,而土壤全磷和有效磷的下移累积则达到了60 cm。红壤旱地长期施用猪粪等有机肥主要增加了0—40 cm耕层土壤的磷素累积,而在剖面80 cm以下未表现出明显累积现象。 【结论】 长期施用化肥 (28年)处理养分主要在0—20 cm红壤旱地耕层土壤累积,而长期施用有机肥或有机无机肥配施还可以明显提高20—40 cm土壤养分含量,养分下移累积作用明显。此外,红壤旱地长期施用有机肥可以缓解耕层土壤的酸化、提高耕层土壤肥力水平,是增加培肥深度的有效措施,但是长期施用猪粪导致的氮磷下渗深度增加可能引起的环境风险也应引起重视。