Impacts of land use/cover change on soil properties in the Mediterranean region of northwestern Jordan

This study was carried out to evaluate the effects of deforestation on physical and chemical properties of soils under native forest in the Mediterranean region of northwestern Jordan. Land use/cover maps of 1953, 1978 and 2002 were interpreted and analysed within GIS to quantify the shift from forest to rainfed cultivation. Six sites were sampled in a non‐changed forest and in cultivated fields, three for each. Different soil properties of texture, bulk density, organic matter, total nitrogen, pH, cation exchange capacity (CEC), phosphorous and potassium were analysed. Results showed that many forests were changed into cultivated lands at a rate more than the reforestation. Subsequently, adverse effects on the studied physical and chemical properties were observed. The most affected properties were particle size distribution, bulk density of surface soil and subsoil. Organic matter and CEC decreased in cultivated soil as compared to the forest soil. Cultivated soils were found to exhibit a significantly lower status in physical and chemical soil properties as compared to forest soils. This general decline in the soil physical and chemical properties, in turn, contributed to soil erosion, reduction of soil fertility and land degradation. There is an urgent need to improve soil quality by developing sustainable land use practices to reduce the rate of soil degradation and to ensure long‐term sustainability of the farming system in the study area and in similar biophysical settings. Copyright © 2008 John Wiley & Sons, Ltd.     

The effect of soil pH manipulation on chemical properties of an agricultural soil from northern Idaho

Abstract

Selected chemical properties of an artificially acidified agricultural soil from northern Idaho were evaluated in a laboratory study. Elemental S and Ca(OH)₂were used to manipulate the soil pH of a Latahco silt loam (fine‐silty, mixed, frigid Argiaquic Xeric Argialboll), which had an initial pH of 5.7. A 100 day incubation period resulted in a soil pH manipulation range of 3.3 to 7.0. Chemical properties evaluated included: N mineralization rate, extractable P, AI, Mn, Ca, Mg and K and CEC. N mineralization rate (assessed by anaerobic incubation) decreased with decreasing soil pH. Nitrification rate also decreased as NH₄ ⁺‐N accumulated under acid soil conditions. Sodium acetate extractable P was positively linearly correlated (R²= 0.87) with soil pH over the entire pH range evaluated. Potassium chloride extractable Al was less than 1.3 mg kg^‐1of soil at pH values higher than 4.4. Consequently, potential Al toxicity problems in these soils are minimal. Extractable Mn increased with decreasing soil pH. Soil CEC, extractable Mg, and extractable K all decreased with increasing soil pH from 3.3 to 7.0. Extractable Ca levels were largely unaffected by changing soil pH. It is likely that the availability of N and P would be the most adversely affected parameters by soil acidification     

Changes in the properties of a Mexican Fluvisol following 30 years of sugarcane cultivation

A study to evaluate the changes in the fertility of Fluvisols under continuous cultivation of sugarcane was conducted in the vicinity of the Santa Rosalía sugar refinery. About 4000 ha of Fluvisols have been under sugarcane cultivation for more than 30 years. Three representative plots under monoculture for 5, 10, 20 and 30 years, were selected under on-farm conditions. Several samples were obtained from crop row and inter-row zones, at 0–30 cm soil depth, and composited into four samples for each plot. Soil samples were analyzed for pH, organic matter, total organic C, total nitrogen, available phosphorus, exchangeable potassium, calcium and magnesium, cation exchange capacity, texture and bulk density. There were significant changes in the soil chemical properties due to 30 years of monoculture, except for OM, exchangeable K, Ca, Mg and CEC. Total soil organic C, total N and P declined by 17, 21 and 37%, respectively, by 30 years of monoculture of sugarcane. These losses mainly occurred during the first 20 years of cultivation. However, the adverse effect of decline in soil fertility was not reflected in the sugarcane yields. The 67% increase in yields observed between 5 and 30 years of monoculture may be attributed to the adoption of recommended cultural practices and to farmer's experience. Soil physical properties were not affected by the intensive sugarcane cultivation. A complete adoption of recommended practices by SR among farmers and a revision of the N and P fertilization rate are necessary to maintain the fertility of sugarcane soils.     

Changes in soil fertility and leaf nutrient concentration at a sugar cane plantation in Papua New Guinea

Abstract

Commercial sugar cane (Saccharum qfficinarum) cultivation in Papua New Guinea started in 1979 at a plantation in the Ramu valley where Udifluvents and Hapluderts are the dominant soil types. The sugar cane is not irrigated and receives only nitrogen (N) fertilizers (±90 kg N ha^‐1 y^‐1). Changes in soil chemical fertility were assessed by comparing soil fertility data from the mid‐1980s and 1990s and by comparing soil fertility data from sugar cane and adjoining natural grassland. Between the mid‐1980s and 1990s the topsoil pH had declined significantly (p<0.001) by 0.3 units and this was accompanied by a decline in cation exchange capacity (CEC) of 34 mmol_c kg^‐1. Total N levels in the topsoils declined (p<0.001) from 2.5 to 1.9 g kg^‐1 and available P from 36 to 27 mg kg^‐1 during the same period. Exchangeable potassium (K) also declined significantly (p<0.05) with 1.3 mmol_c kg^‐1, but changes in exchangeable calcium (Ca) and magnesium (Mg) were not significant. The decline in soil fertility was highest in the topsoil although significant changes occurred up to 0.6 m depth. Total N decreased in the 0–0.15 and 0.15–0.30 m soil horizons, but increased in the lower horizons, possibly because of nitrate leaching. A similar degree of soil fertility decline was observed when soils under sugar cane and adjoining natural grassland were compared. However, the interrow had a slightly lower fertility level in comparison to within sugar cane rows. The decrease in total N, available phosphorus (P) and exchangeable K in the soil coincided with a decrease in the leaf N, P, and K concentrations of the sugar cane over the past 10 years. It was concluded that soil fertility had markedly declined under sugar cane monocropping although levels remained favorable for sugar cane cultivation. For sustainable soil management, nutrient inputs as well as small applications of lime may eventually be needed.     

Soil property changes following conversion of acacia woodland into grazing and farmlands in the Rift Valley area of Ethiopia

Continued conversion of woodlands into grazing and farmland is seriously undermining the natural ecosystem of the dry and fragile Rift Valley areas of Ethiopia. This study investigated the effects of land‐use change on soil organic carbon (SOC), total nitrogen (N), pH, exchangeable bases, cation exchange capacity (CEC) and base saturation (per cent) in three adjacent land‐use types: controlled grazing, open‐grazing and farmland. A total of 81 soil samples were collected and analysed. Contents of SOC and total N decreased drastically in open‐grazing and farmland (p < 0·001), and were significantly higher in the top 0·2 m than in the subsurface soil layer. Compared with the controlled grazing, reductions in the contents of SOC and total N in the top 1 m soil layer were 22–30 and 19 per cent, respectively, due possibly to the decrease in plant biomass input into the soil and the fast decomposition of organic materials. Long‐term cultivation had significantly increased the concentration of exchangeable K. Exchangeable Na was high in the lower layers, while Mg was higher in the top surface soil. CEC also varied with soil depth (p = 0·016); it was higher in the topsoil than in the subsurface soil, which may be, among others, due to the differences in soil organic matter distribution with depth. Although these semi‐arid soils are known to have low organic carbon and CEC levels, the values from the current study area are critically low, and may indicate the further impoverishment of the soils under high agricultural and grazing pressures. Copyright © 2010 John Wiley & Sons, Ltd.     

Formula fertilization of nitrogen and potassium fertilizers reduces cadmium accumulation in Panax notoginseng

ABSTRACT

This study investigated the effect of nitrogen (N) and potassium (K) formula fertilization on cadmium (Cd) accumulation in P. notoginseng. Field investigations as well as formulated N and K fertilizers application experiments were conducted. Field investigations showed that Cd accumulation decreased PNS content in the main roots of P. notoginseng, while PNS content was promoted by soil available potassium (AK) and K in the main roots. The Cd content in P. notoginseng and the bioavailable Cd content in the soil decreased with the increasing of total K (TK) and AK in the soil. The increase of soil pH, total organic matter (TOM) and cation exchange capacity (CEC) values can reduce the bioavailable Cd content in soil, thus reducing the Cd accumulation in P. notoginseng. Under current fertilization in P. notoginseng cultivation, decreased N fertilization can alleviate the deterioration of soil physical and chemical properties. Under identical N fertilization, increasing K fertilization promoted the PNS accumulation (0.3–38.3%), also improved soil physical and chemical properties. Formulated N and K fertilizers application (1:2) experiments showed that reducing application of N and increasing K fertilization could reduce the bioavailable Cd content in soil, and the Cd content also decreased by 0.5–69.6% in P. notoginseng.

Abbreviation: PNS: P. notoginseng saponins; F(EXC): Exchangeable fraction; F(Carb): Bound to carbonates fraction; F(Fe-MnOX): Bound to iron and manganese oxides fraction; F(OM): Bound to organic matter fraction; F(RES): Residual fraction; AK: Available potassium; TK: Total potassium; CEC: Cation exchange capacity; TOM: Total organic matter     

城市不同利用区域绿地土壤酶活性特征--以上海市为例

选择上海市钢铁厂、造船厂、试剂厂、交通区和居民区5种城市绿地,分析了过氧化氢酶、碱性磷酸酶、脲酶和脱氢酶4种土壤酶活性并讨论了土壤理化性质和重金属含量对其活性的影响。结果表明:土壤酶活性受土壤理化性质和重金属含量影响;其中过氧化氢酶活性受土壤体积质量、pH、CEC和Cr的影响最大;碱性磷酸酶受有机质、水解性氮、Pb和Zn的影响最大;脱氢酶受CEC、pH、体积质量和水解性氮的影响较大;脲酶受水解性氮、CEC、pH和体积质量影响最大。土地利用方式不同土壤酶活性也不同:调查区域土壤中过氧化氢酶活性均较高,土壤碱性磷酸酶活性普遍较低,试剂厂和交通区土壤脲酶活性较高,交通区和试剂厂土壤脱氢酶活性最高。     

Alterations in Soil Chemical Properties Induced by Continuous Rice Cultivation: A Study on the Arid Nile Delta Soils of Egypt

Changes in soil chemical properties resulting from continuous rice (Oryza sativa) cultivation on the Nile Delta soils of Egypt were examined. The eight soil profiles characterized for this study were designated as 0 (crop rotation without rice), 1 (crop rotation with rice after every 2 years), and 2, 3, 4, 5, 6, and 7 representing continuous rice cultivation for 2, 4, 8, 12, 15, and 20 years, respectively. Sampling was conducted at 0–20, 20–40, 40–60, and 60–80 cm depths for each profile and samples analyzed for a suite of chemical properties. Soil pH, salinity indicators [electrical conductivity (EC), and exchangeable sodium percentage (ESP)], as well as soluble and exchangeable cations and anions such as chloride and sulfate, all tended to decrease with years of continuous rice cultivation, with a number of significant (p < 0·05) differences observed. Cation exchange capacity (CEC) increased with years of continuous rice cultivation, with a 12% increase observed between 2‐ and 20‐year continuous rice cultivation systems. Principal component analysis conducted on soil properties within the continuous rice cultivation systems (profiles 2–7) revealed two possible components, namely F1 (pH, EC, ESP, and soluble Na⁺, Mg²⁺, K⁺, Cl⁻, and SO₄⁻²) and F2 (clay, organic matter, and CEC), which could be broadly associated to soil salinity and soil fertility, respectively. Findings suggested possible alterations in soil chemical properties by continuous rice cultivation practices on these Nile Delta soils of Egypt, Africa. Copyright © 2015 John Wiley & Sons, Ltd.     

壳聚糖对土壤理化性状的影响

壳聚糖对土壤理化性状有较大的影响。当土壤中施入壳聚糖酸溶液后,土壤的团粒结构和渗透系数随壳聚糖施用量的增加而增加,而容重、CEC和pH则减小;在EC值上表现为先下降后上升的趋势。当壳聚糖施用量达到0.45‰[对干土平均质量(W/W)]后,土壤物理性状的变化趋于稳定。3种壳聚糖酸溶液处理的土壤物理性状的变化趋势一致,无明显差异。在壳聚糖酸溶液中,酸作为溶剂本身对土壤物理性状的影响不大。壳聚糖酸溶液对土壤化学性状的影响过程较复杂,表现出是由壳聚糖和酸对土壤共同作用的结果。溶剂酸是影响土壤pH主要因素,其酸性越强,壳聚糖酸溶液的酸性就越强,处理后土壤的pH就越小。土壤CEC、EC同时受壳聚糖用量和溶剂酸种类的影响。     

Soil quality assessment under shifting cultivation and forests in Northeastern Himalaya of India

The study aimed to evaluate the impact of shifting cultivation on soil quality, in Wokha district of Nagaland, using weighted soil quality index (SQIw). Four forest sites and three sites under shifting cultivation were selected and physical (texture and bulk density) and chemical (pH, electrical conductivity, cation exchange capacity, organic carbon, available N, P, K, exchangeable cations) parameters were analyzed. The SQIw was calculated on a minimum data set selected by principal component analysis, followed by varimax rotation algorithm and through subsequent normalization of the parameters using the linear scoring function. Significant (P < 0.05) variations in SQIw were found across the depth of the soil and land use according to severity of factors associated with land use. Three different classes of soil quality were also identified: high quality (SQIw > 0.70) for two forest soils (FS1 and FS2) and land under shifting cultivation (JH1), low quality (SQIw < 0.50), only to FS3, and intermediate quality (0.50 < SQI < 0.70) in all other soils. The approach used in this study proved to be sensitive to evaluate the soil quality, however further research is required to better understand the sustainability of shifting cultivation by including more physical, biological and chemical indicators.     

Land-use history and fire effects on soil fertility in eastern Spain

Changes in land use and fire directly affect the physico‐chemical properties of the soil. In an eastern Spanish area, we analysed the effects of land‐use history and fire frequency prior to fire on soil fertility 9 years after fire. The results showed that long‐term cultivation caused decreases in soil organic matter, total nitrogen (N) and C/N. Between 20 and 40 years after cropping ceased, soil organic carbon (C) and total N had generally not recovered values similar to those found in soils that were never cropped. Total phosphorus and available phosphorus contents were larger in the latest abandoned plots than in the earliest abandoned plots and the uncropped ones, which was interpreted as a result of fertilization. Increasing fire frequency from one to two fires generally caused a decrease in soil organic C, total N, C/N, total phosphorus and available phosphorus. We observed that the losses of organic C in the soil caused by fire were larger among the uncropped plots and hypothesized that fuel loads and thus fire intensities were larger in these ecosystems. Our results also suggested that both long‐term cultivation and fire would tend to separate C and P cycles.     

Soil chemical characteristics in relation to Fusarium wilts in banana crops of Gran Canaria Island (Spain)

Abstract

Several soil characteristics have been studied in relation to Fusarium wilts in field plots of banana plantations of Gran Canaria Island (Spain). Principal component analysis has been applied to soil chemical parameters, the aim being to determine the possible relationships between the apparition and development of the Fusarium wilts and soil characteristics. The results seem to indicate that there is a relationship between the disease incidence and the values of some parameters like pH, cation exchange capacity (CEC), sodium (Na) in solution, and iron (Fe); pH, CEC, and Na values were significantly smaller in areas affected by the disease. However, the values of Fe extracted with DTPA and Fe associated with fulvic acids were significantly higher in disease affected areas; the same tendency was observed in the values of total carbon (C) and nitrogen (N) in the different areas. Other parameters studied, like exchangeable cations, Fe‐oxalate, etc., have not showed either differences or general tendencies. These results seem to suggest that the absence and/or presence of disease could be controlled partly for the chemical characteristics of the different soil areas of the same field plot.     

Soil carbon and nutrient pools, microbial properties and gross nitrogen transformations in adjacent natural forest and hoop pine plantations of subtropical Australia

Background, Aims, and Scope  An improved understanding of important soil carbon (C) and nutrient pools as well as microbial activities in forest ecosystems is required for developing effective forest management regimes underpinning forest productivity and sustainability. Forest types and management practices can have significant impacts on soil C and nutrient pools as well as biological properties in forest ecosystems. Soil C and nutrient pools were assessed for adjacent natural forest (NF), first rotation (1R) (50-year-old), and second rotation (2R) (1-year-old) hoop pine (Araucaria cunninghamii Ait. ex D. Don) plantations in southeast Queensland of subtropical Australia. Materials and Methods  Five transects spaced 3 m apart with 9 sampling points along each transect were selected (9.6 m × 12.0 m each site), with 45 soil cores (7.5 cm in diameter) collected and separated into 0–10 and 10–20 cm depths. These soils were analysed for total C, total nitrogen (N), C (δ¹³C) and N (δ¹⁵N) isotope composition. The 0–10 cm soils were analysed for pH, CEC, exchangeable cations, total P and total K, and assayed for microbial biomass C and N, respiration, metabolic quotient, potential mineralizable N (PMN), gross N mineralization (M) and immobilization (I). Results  Total C and N in 0–10 cm soils were higher under NF and 1R plantation than under 2R plantation, while they were highest in 10–20 cm soils under NF, followed by the 1R and then 2R plantation. δ¹³C was lower under NF than under the plantations, while δ¹⁵N was higher under NF than under the plantations. Total P was the highest under NF, followed by the 1R and then 2R plantation, while total K was higher under the 2R plantation. No significant differences were detected for pH, CEC, exchangeable cations, microbial C and N, respiration and metabolic quotient among the 3 sites. PMN and M were higher under NF, while I was the highest under the 2R plantation, followed by the NF and then 1R plantation. Discussion  Soil total C and N in 0–10 cm depth were significantly lower under 2R hoop pine plantation than those under NF and 1R hoop pine plantation. There were significant reductions in soil total C and N from NF to 1R and from 1R to 2R hoop pine plantations in 10–20 cm depth. This highlights potential N deficiency in the 2R hoop pine plantations, and application of N fertilizers may be required to improve the productivity of 2R hoop pine plantations. There were no significant differences in other soil chemical and physical properties in 0–10 cm depth among the 3 sites under NF, 1R and 2R hoop pine plantations, except for soil total P and K. Soil microbial biomass C, CO₂ respiration and metabolic quotient did not differ among the 3 sites assessed, perhaps mainly due to these biological variables being too sensitive to variations in soil chemical and physical properties and thereby being associated with a larger variability in the soil biological properties. However, soil potential mineralizable N, gross N mineralization and immobilization were rather sensitive to the conversion of NF to hoop pine plantation and forest management practices. Conclusions  Total C and N in the top 20 cm soil were highest under NF, followed by 1R and then 2R hoop pine plantations, indicating that N deficiency may become a growth-limiting factor in the 2R hoop pine plantations and subsequent rotations of hoop pine plantation. The sample size for soil δ¹³C seems to be much smaller than those for soil total C and N as well as δ¹⁵N. The significant reductions in soil total P from NF to 1R and then from 1R to 2R hoop pine plantations highlight that P deficiency might become another growth-limiting factor in the second and subsequent rotations of hoop pine plantations. Soil microbial properties may be associated with large spatial variations due to these biological properties being too sensitive to the variations in soil chemical and physical properties in these forest ecosystems. Recommendations and Perspectives  Soil potential mineralizable N, gross N mineralization and immobilization were useful indices of soil N availability in response to forest types and management practices. The sampling size for soil δ¹³C was much smaller than the other soil chemical and biological properties due to the different patterns of spatial variation in these soil properties.     

Changes of chemical properties in an oxisol after clearing of native Cerrado vegetation for agricultural use in Vilhena, Rondonia State, Brazil

Native vegetation clearing in the Amazon Cerrado region for agricultural purposes may be modifying soil chemical characteristics. The extent of change depends on the management practices used. We evaluated changes in chemical properties of a clayey oxisol (dystrophic red yellow latosol) under no-tillage (NT) and conventional tillage (CT). Soil samples were taken randomly (n = 5) in July 2004 at 0–5 cm, 5–10 cm, 10–20 cm and 20–30 cm depths at six treatments: Cerrado with native vegetation, CT cultivated with rice for 1 year (1CT) and 2 years (2CT), and NT cultivated with soybean for 1 year (1NT), 2 years (2NT) and 3 years (3NT) in each case after a 2-year period of rice under CT. Soil pH (CaCl₂, KCl and water), ΔpH, total acidity (H⁺ + Al³⁺), total organic carbon (TOC), available P, exchangeable K, Ca, Mg, potential cation exchange capacity (CEC) and base saturation (V) were determined. The highest pH values were determined in topsoil layers at the older NT adoption. Under Cerrado pH was lower than under cultivation at all depths due to absence of lime application. Generally, negative values of ΔpH were observed at all sites in all layers indicating predominant presence of negative charges in the soil. Although not statistically significant it seems that the amount of negative charges was higher in deeper layers. Total acidity displayed the highest values throughout the soil profile under Cerrado and low pH and low concentrations of exchangeable bases. Cultivated systems with fertilizer generated considerable increases of P, K, Ca, and Mg compared to Cerrado. Soil macronutrient content and base saturation under NT gradually increased throughout the profile with time. Highest CEC values were calculated for the 0–5 cm and 5–10 cm layers under Cerrado and NT systems. For the 0–5 cm layer CEC was lower at the CT system compared to the Cerrado and the oldest year under NT system.

Alteration of TOC was more pronounced in the top 10 cm layer at all sites. The highest content was measured in the topsoil layer under Cerrado. Considering the future land use in Cerrado areas the NT system, if properly managed, appears to be the favourable management option of the existing croplands established after Cerrado clearing.     

Minimizing ammonia volatilization from urea,improving lowland rice (cv. MR219) seed germination,plant growth variables,nutrient uptake,and nutrient recovery using clinoptilolite zeolite

The anionic nature and high cation exchange capacity (CEC) of clinoptilolite zeolite can be exploited to reduce ammonia (NH₃) loss from urea and to improve soil chemical properties to increase nutrient utilization efficiency in lowland rice cultivation. A closed-dynamic airflow system was used to determine NH₃ loss from treatments (20, 40, and 60 g clinoptilolite zeolite pot^?1). Seed germination study was conducted to evaluate the effects of clinoptilolite zeolite on rice seed germination. A pot study was conducted to determine the effects of clinoptilolite zeolite on rice plant growth variables, nutrient uptake, nutrient recovery, and soil chemical properties. Standard procedures were used to determine NH₃ loss, rice plant height, number of leaves, number of tillers, dry matter production, nutrient uptake, nutrient recovery, and soil chemical properties. Application of clinoptilolite zeolite (15%) increased shoot elongation of seedlings and significantly reduced NH₃ loss (up to 26% with 60 g zeolite pot^?1), and increased number of leaves, total dry matter, nutrient uptake, nutrient recovery, soil pH, CEC, and exchangeable Na⁺. Amending acid soils with clinoptilolite zeolite can significantly minimize NH₃ loss and improve rice plant growth variables, nutrient uptake, nutrient recovery, and soil chemical properties. These findings are being validated in our ongoing field trials.     

Ecological study on the dynamics of soil organic matter and its related properties in shifting cultivation systems of Northern Thailand

Abstract

There is a large number of hill people in northern Thailand, who practices shifting cultivation. In order to analyze the soil ecological problems involved in the transition from traditional shifting cultivation to more intensive upland farming, the authors carried out comparative studies on the dynamics of organic matter and its related properties in soils both in the traditional shifting cultivation systems adopted by Karen people and more intensive upland farming practiced by Thai and Hmong people in the area. The contents of organic matter and available N in the surface 10 cm layers of soil from the fields continuously cultivated were lower than those in soils under prolonged fallow (more than 10 y) or natural forest. Based on the rate of soil respiration, the amount of organic matter decomposed within 1 y was estimated to reach nearly 10% of that stored in the upper 50 cm layers of the soil profile in the upland crop fields. These results indicate that the organic matter-related resources markedly decreased under continuous cropping. The contents of C, N, and P in the microbial biomass of the surface 10 cm layers of soil ranged from 0.37 to 2.09 mg C g^?l soil, from 22.7 to 188 µg N g^?l soil, and from 6.1 to 65.7 µg P g^?l soil, respectively. Since the contents of microbial C, N, and P in the surface soils were generally higher under prolonged fallow and natural forests than in the fields continuously cultivated, the microbial activity and/or the amounts of C, N, and P available for biological activity seemed to have declined under continuous upland farming. The incubation experiment to assess the N mineralization pattern showed two remarkable characteristics: 1) there was an initial time lag until active mineralization of N occurred in the soils from young fallow forest and 2) the soil burning effect was observed after burning in the fields under prolonged fallow. The active process of nitrification after N mineralization was always associated with a sharp fall in soil pH, suggesting that soil acidification was promoted and basic cations were lost from the soils. In conclusion, rapid deterioration of the soil organic matter-related properties in cropping fields can be considered to be one of the ecological reasons why upland fields must be returned to fallow again a few years after forest reclamation in traditional shifting cultivation systems. Therefore, in alternative farming systems with more intensive land use, it is essential to apply organic materials into soils to decrease the rate of soil degradation, or to improve the soil fertility, in avoiding soil acidification along with nitrification.     

Long-Term Cultivation Effects on Biological C and N Fractions in a Fluvaquentic Haplustolls of Semi-arid Region of the Northern Turkey

Conversion of a native ecosystem can impact the nature and dynamics of organic carbon (C) fractions. The goal of this study was to determine the effects of cultivation and monoculture wheat production on soil organic C and biological C fractions compared to a previously flooded native pasture in northern Turkey. Soil samples were collected from four randomly selected locations of each management system. Some soil chemical [pH, calcium carbonate (CaCO₃), total nitrogen (N), and organic C], physical (sand, clay, and silt), and biological properties [microbial biomass carbon (MBC), mineralizable C, and mineralizable N] were measured. Conversion of pasture to cultivated land slightly increased soil pH, but CaCO₃, total organic C (TOC), and N contents were significantly (P < 0.05) decreased with cultivation. Total organic C and N contents were more than three times less in cultivated soils compared to pasture. Microbial biomass C was significantly decreased (P < 0.05) with long-term cultivation, and the greater seasonal fluctuations were measured at the surface of both ecosystems. The greatest level of potentially mineralizable C was observed in the pasture rather than the cultivated soil, but the proportional distribution of mineralized C to TOC was greater in the cultivated soil. These results suggested that the long-term cultivation (15 years) of previously flooded native ecosystems increased C mineralization and resulted in 72% C loss at the surface soil. Cultivated soils have a greater potential to restore atmospheric carbon dioxide (CO₂) if proper cultivation and management systems are used.     

Effect of different types of organic fertilizers on the chemical properties and enzymatic activities of an Oxisol under intensive cultivation of vegetables for 4 years

The effects of different types of organic fertilizers on the chemical and enzymatic properties of an Oxisol were studied after being fertilized for four consecutive years (26 crops) in a greenhouse under intensive cultivation of vegetables. Seven treatments, consisting of five types of organic fertilizer treatments, one "sequential application" (SA) treatment, and a chemical fertilizer treated plot were compared. The organic fertilizers used were dairy cattle dung compost (DCDC), hog dung compost (HDC), chicken dung compost (CDC), pea residue compost (PRC) and soybean meal (SBM). After 4 years of cultivation, the soils were analyzed for their chemical properties and enzymatic activities. The microbial carbon (C) and nitrogen (N), basal respiration and nitrification rate were also measured. The results showed that the SBM significantly lowered the soil pH, and that the HDC and DCDC raised the soil pH. The SBM and CDC resulted in the lowest soil electrical conductivity. The SBM had no significant effect on soil organic C and total N contents when compared with the CF plot. However, the DCDC resulted in the highest contents of soil organic C and total N. The organic fertilizers applied did not significantly affect the soil available copper, zinc, cadmium, lead and nickel. The effects of the different organic fertilizers on soil enzymatic activities depended on the types of organic fertilizers applied. The SBM and CDC often resulted in a lower microbial C (or N) and respiration rate, while in contrast DCDC and PRC resulted in high measurements. Most of the measured soil enzymatic activities in the SBM treatment, except for acid phosphatase, were the lowest. Differing contents of different heavy metals in the organic fertilizers resulted in different Mehlich III extractable heavy metal contents in the soils. From the point of view of the soil chemical and enzymatic properties, SBM is not an appropriate organic fertilizer for continuous application to an Oxisol.     

不同种植年限设施地土壤养分和重金属含量的变化特征

为了解设施地土壤的理化性质,以江苏省苏北地区大棚土壤为例,研究种植年限分别为1,3,5,7 a大棚土壤含水量、全N、全P、全K和重金属含量的变化情况。结果表明,随着种植年限的增加,设施地土壤含水量显著降低,随着土层深度的增加,土壤含水量进一步降低。设施地土壤全N、全P和全K含量比大田高,特别是全N和全K积累量大,且分布于耕作层,随着土层深度的增加全N和全K含量变化较大;同时,随着种植年限增加,设施地土壤全N、全P和全K含量显著增加,7 a左右的设施地土壤20 cm耕作层中的全N含量分别为1.99,1.87,2.40 g/kg;全P含量分别为1.03,1.01,1.74 g/kg;全K含量分别为1.94,3.52,4.40 g/kg,且全N和全K含量随着土层深度的增加而逐渐降低,与土层深度的变化呈显著负相关关系。随着种植年限的增加重金属含量增加,7 a左右大棚种植年限扬州和连云港地区20 cm土层中的Pb含量分别为194,225 mg/kg;淮安地区不同种植年限20 cm土层的Cd含量分别为0.80,0.93,1.14,2.49 mg/kg;扬州和连云港地区无论种植年限多久,Cr含量均大于120 mg/kg;扬州地区As含量均大于25 mg/kg,Pb、Cr和As含量随着土层深度的增加而逐渐降低,与土层深度的变化呈显著负相关关系。所以设施地随着种植年限的增加,土壤理化性质会发生变化,应采取措施保持土壤含水量,防止土壤板结、盐渍化,消除重金属累积。     

The impact of land‐cover change on soil properties in northern Ghana

Effects of changes in land‐cover on soil quality parameters in an area in northern Ghana were studied. Land‐cover changes were derived from maps of the study area for 1984, 1992 and 1999. There were no significant differences between properties of soils under natural vegetation and soils put under cultivation from 1992, but permanently cultivated soils (1984–1999) showed significantly lower physical and chemical soil properties. Soils recently opened up since 1992 for cultivation in the last seven years (i.e. 1992–1999) were found to manifest significantly higher contents of organic C, N, Ca, Mg and ECEC than those under permanent cultivation, suggesting that continuous cropping is responsible for deterioration in soil quality. Minimum organic C contents necessary to meet critical levels of selected soil quality parameters were estimated. The organic C content of recently cultivated soils would need to be increased by about 7 t ha⁻ to replenish soil nutrient capital. This calls for a strategy to synchronize organic matter management with inorganic fertilizer application. Further research is also needed to develop farming systems that conserve organic matter and also improve the quality of organic matter in the study area. Copyright © 2004 John Wiley & Sons, Ltd.