Kinetics of phosphorus release from calcareous soils under different land use in Iran

The rate of phosporus (P) release from soils can significantly influence P fertility of soils. The objectives of this study were to investigate the effects of land‐use types on the kinetics of P release under different management practices and the relationship between kinetic parameters and soil physical and chemical properties from calcareous soils. The kinetics of P release in 0.01 M CaCl₂ was studied in surface samples of 30 calcareous soils planted to garlic, garden, pasture, potato, vegetables, and wheat. Trend in P‐release kinetics was similar between land‐use types. Significantly different quantities of P were released under different land use. The maximum amount (average of five soils) (46.4 mg kg^–1) of P was released in soil under potato and the minimum amount (10.4 mg kg^–1) under pasture. The kinetics of P release from soils can be described as an initial rapid rate followed by a slower rate. Different models were used to describe P release. In general, parabolic diffusion and power equation were found to be appropriate for modeling P release. The P‐release rate for the soils was estimated by parabolic equation for the studied land‐use types. The constant b was lower for pasture and wheat than for garlic and potato. The relationship between the rate of P release with Olsen‐P was linear, while it was curved with respect to the CaCl₂‐P, indicating that release of P was diffusion‐controlled. When the kinetic parameters of models were regressed on soil properties, CaCl₂‐P and CaCO₃ appeared to be the most important soil properties influencing P‐release rates in these soils.     

Density separation of soil organic matter across three land uses in calcareous soils of Iran

ABSTRACT

The aim of this study was to examine the usefulness of physical and chemical fractionation in quantifying soil organic matter (SOM) in different stabilized fraction pools. Soil samples from three land use types in Lorestan province, Southwest Iran were examined to account for the amount of organic carbon and nitrogen in different SOM fractions. Size/density separation and chemical oxidation methods were applied to separate the SOM fractions including particulate organic matter (POM), Si + C (silt and clay), DOC (dissolved organic C), rSOM (oxidation-resistant organic carbon and nitrogen) and S + SA (sand and stable aggregates). The values obtained for TOC, TN, and HWC were highest in forest lands followed by the range and agricultural lands. Among the SOM fractions, S + SA showed the highest values (5.75, 5.77 and 20.6 g kg^?1 for agriculture, range and forest lands respectively) followed by POM, Si + C, rSOM, and DOC. The concentrations of C and N in the labile fractions obtained the higher values than in the stabilized fractions. Forest lands had the highest amounts of organic C and N among all fractions whereas agricultural lands showed highest values for inorganic C content of soils in different fractions.     

土地整理对农田土壤碳含量的影响

土地整理对土壤的强扰动会影响土壤的碳循环平衡,为了研究土地整理对农田土壤碳含量的影响,通过间接采样和随机采样方法,采集了江苏3个土地整理区土地整理前后土样进行有机质测定,初步分析了不同土地整理区土地整理后的土壤碳含量变化及其变化差异原因。主要结论有：1）通过土地整理,3个土地整理区土壤碳含量都有得到提高。其中,苏南丹阳土地整理区碳质量分数提高了26.05%,碳密度提高23.87%,提高幅度最大,碳密度变化方向与碳含量变化具有一致性,但提高幅度低于碳含量。这与各整理区原有土质、土地整理工程施工方式、施工时间等因素密切相关。2）水田碳质量分数显著高于旱地碳质量分数,但是经过土地整理旱地碳含量提高幅度大于水田,水田在整理前后碳含量变化幅度不大。3）在土地整理项目实施前应制定适宜的土地整理规划,实施有利于土壤固碳的土地整理工程。     

Chemical fractionation of phosphorus in calcareous soils of Hamedan,western Iran under different land use

We investigated the effects of land uses on P distribution and availability in selected calcareous soils under different management practices. KCl‐P (labile P), NaOH‐P (Fe‐Al‐bound P), HCl‐P (Ca‐bound P), and residual P (Res‐P) fractions at 0–30 cm depth were determined for soils planted to garlic, orchard, pasture, potato, leafy vegetables, and wheat. Trends in P distribution between chemical fractions were similar between land uses. Ca‐bound P was the most abundant P fraction in the soils, constituting between 61% and 78% of the total P, whereas P associated with labile was less abundant (< 2%). Soils under leafy vegetables and wheat along with pasture presented the highest and lowest values in all fractions of P, respectively. Labile P generally was highest for leafy vegetables and potato. Labile P and Fe‐Al‐bound P comprised < 1.4% and 8% of total P, respectively. Residual P ranged from ≈ 14% (potato and garlic) to 31% (pasture). Long‐term fertilization increased P allocation to inorganic fractions, as Ca‐bound P contained 78% of total P for potato and garlic and 74% for leafy vegetables but 61% for pasture. A strong positive correlation between labile P and Fe‐Al‐bound P (r = 0.534, p < 0.01), labile P and Ca‐bound P (r = 0.574, p < 0.01), Ca‐bound P and Fe‐Al‐bound P (r = 0.504, p < 0.01), Olsen‐P and CaCl₂‐P (r = 0.821, p < 0.01) was found. Principal‐component analysis showed that the first four components accounted for most of the variation, 32.5%, 16.9%, 12.9%, and 7.9% of total variation, respectively.     

沙地整治下榆林土地利用及土壤有机质时空分异特征

毛乌素沙地是典型的生态脆弱区,近年来针对其在榆林境内的沙地整治利用取得显著成效,也对土壤环境产生了深刻影响。为了探究沙地不同整治利用方式对土壤有机质的影响,该研究选取榆林市显性沙地,利用多光谱遥感影像及相关光谱指数,结合沙地土地利用变化特征,通过XGBoost机器学习方法,反演1990-2020年土壤有机质含量;分析不同土地类型下土壤有机质含量变化,通过半变异函数揭示了其空间变异性,厘清人为因素和自然环境的影响程度。结果表明,30 a间榆林5 460 km2沙地中超过半数得到整治和利用,沙地-草地是最主要的地类转变方式,建设用地面积增长最迅速;沙区土壤有机质含量上升,但整体呈现先增加后降低的趋势,有机质均值由0.34%增长至0.79%,近10年降低至0.51%;榆林沙区土壤有机质具有较强的空间自相关性。起初,人为利用对其有积极作用,但随着沙地的利用强度增大,对土壤有机质产生负向作用,进而致使其含量下降,面临土地退化危机。建议加强退化林草的修复改良,放缓建设用地开发力度,研究以期为沙地整治提供理论和实践借鉴意义,保护榆林沙地土壤环境安全。     

Impacts of land use and salinization on soil inorganic and organic carbon in the middle-lower Yellow River Delta

Soil inorganic carbon (SIC) is an important reservoir of carbon (C) in arid, semi-arid, and semi-humid regions. However, knowledge is incomplete on the dynamics of SIC and its relationship with soil organic C (SOC) under different land use types in the semi-humid region, particularly in coastal zones impacted by soil salinization. We collected 170 soil samples from 34 profiles across various land use types (maize-wheat, cotton, paddy, and reed) in the middle-lower Yellow River Delta (YRD), China. We measured soil pH, electrical conductivity (EC), water-soluble salts, and SOC and SIC contents. Our results showed significant differences in both SOC and SIC among land use types. The dry cropland (maize-wheat and cotton) soils had significantly higher SOC and SIC densities (4.71 and 15.46 kg C m^-2, respectively) than the paddy soils (3.28 and 14.09 kg C m^-2, respectively) in the 0–100 cm layer. Compared with paddy soils, reed soils contained significantly higher SOC (4.68 kg C m^-2) and similar SIC (15.02 kg C m^-2) densities. There was a significant positive correlation between SOC and SIC densities over a 0–100 cm soil depth in dry cropland soils, but a negative relationship in the paddy soils. On average, SOC and SIC densities under maize-wheat cropping were 15% and 4% lower, respectively, in the salt-affected soils in the middle-lower YRD than the upper YRD. This study indicated that land use types had great influences on both SOC and SIC and their relationship, and salinization had adverse effect on soil C storage in the YRD.     

The influence of land use and fallow period on the properties of two calcareous soils in the humid tropics of southern Mexico

Calcareous soils are common in the humid tropics of Mexico, but little is known about their productivity and resistance to changes in land use. The influence of land use and duration of fallow on physical and chemical properties were investigated in (a) a loamy Rendzina (at Site A) rich in organic matter and limited in depth by calcareous gravel, and (b) a deeper Calcaric Phaeozem (at Site B) with a more clayey texture throughout. Plots at different successional stages within farmers' shifting cultivation systems were selected on both soils: cropland/young fallow (zero years fallow length), shrub-fallow and tree-fallow at Site A, and cropland/young fallow and forest at Site B. Changes in soil properties suggested a process of recovery with fallow length, in which organic matter, total N and CEC increased with time. The increase in organic matter was remarkably large, on average 0.5–0.6% per year. The Rendzina contained more organic matter than the Calcaric Phaeozem, probably because of its greater carbonate content, which is presumed to protect organic matter against decomposition. The differences in soil properties were mostly greater over time than between treatments.     

有机管理对不同土地利用方式下土壤质量的影响

许多研究发现有机管理可以改善农田土壤质量,但是否不同土地利用方式下都存在此结论尚未明确。为探究有机管理对不同土地利用方式土壤质量的影响,本研究基于一个多土地利用方式的有机管理农场及其附近常规管理农田进行土壤质量调查,对比不同管理措施及大棚菜地、果园、露天菜地、农田边界、稻田田埂5种土地利用方式下农田土壤质量的差异,并对不同管理措施下农田土壤养分含量、重金属含量、动物数量共计20个指标进行方差分析和主成分分析。研究发现虽然总体上(综合5种土地利用方式的均值)有机管理的土壤pH显著高于常规农田;但针对一种土地利用方式,只有露天菜地和农田边界的土壤pH显著提高。总体上有机管理下土壤全磷、全钾、有效磷含量显著降低,但露天菜地土壤有机质和全氮含量均显著高于常规管理农田。有机管理在总体上显著降低了土壤Cr、Cu、Ni、Zn含量;但针对一种土地利用方式,只显著降低了大棚菜地土壤Cr、Ni、Zn含量,果园和稻田田埂土壤Cu含量,露天菜地和农田边界土壤Zn含量。有机管理虽然总体上均显著增加了土壤中蜘蛛目、倍足纲、步甲、蚯蚓的数量;但针对一种土地利用方式,只显著增加了露天菜地地表蜘蛛目、倍足纲、步甲,稻田田埂地表步甲、土壤蚯蚓以及果园倍足纲数量。主成分分析结果表明,不同管理方式下土壤质量差异明显,有机管理下蜘蛛目、倍足纲、步甲和蚯蚓等土壤动物较多,土壤pH较高,土壤P含量较低,重金属Cu、Pb、Zn、Cr含量较低,但并非在所有土地利用方式下都成立。由此可见,有机管理虽然总体上可以改善土壤质量,但受具体管理措施、人为投入品数量和有机种植时间等因素影响,并非在所有土地利用方式下效果都显著,且在不同土地利用方式下显著改善的指标也各不相同,因此需要针对不同土地利用方式和不同指标采取针对性的改善措施。     

A study of the effects of land use changes on soil physical properties and organic matter

Changes in land use can significantly affect soil properties. This study was conducted in the Taleghan watershed of Tehran Province, Iran, to determine the effects of land use changes on soil organic matter (SOM) and soil physical properties including soil aggregate stability, saturated hydraulic conductivity, infiltration rate, available water content, total porosity and bulk density (BD). In the present study, two sites contained adjacent land uses of natural pasture and dryland farming were selected. Soil samples were taken from depths of 0–15 and 15–30 cm for each land use. The results indicated that the conversion of natural pasture to dryland farming led to a significant decrease in SOM at 0–30 cm in the first and second sites (24.7 and 44.2%, respectively). In addition, a significant increase in BD was observed at a depth of 0–30 cm in dryland farm soils (1.39 g cm^–3) compared to pastureland (1.20 g cm^–3) at the first site. An increase in BD was also observed at the same depth of dryland farm soils (1.46 g cm^–3) and pastureland soils (1.42 g cm^–3) at the second site. In addition, total porosity, mean‐weight diameter of aggregates, saturated hydraulic conductivity, available water content and estimated final infiltration rate showed significant differences between land uses. The results showed that the conversion of natural pasture to dryland farming alters soil properties that negatively affect soil productivity and erodibility. Copyright © 2010 John Wiley & Sons, Ltd.     

Soil organic matter quantity and quality in mountain soils of the Alay Range, Kyrgyzia, affected by land use change

 Changes in soil management practices influence the amount, quality and turnover of soil organic matter (SOM). Our objective was to study the effects of deforestation followed by pasture establishment on SOM quantity, quality and turnover in mountain soils of the Sui Checti valley in the Alay Range, Kyrgyzia. This objective was approached by analysis of total organic C (TOC), N, lignin-derived phenols, and neutral sugars in soil samples and primary particle-size soil fractions. Pasture installation led to a loss of about 30% TOC compared with the native Juniperus turkestanica forests. The pasture soils accumulated about 20% N, due to inputs via animal excrement. A change in land use from forest to pasture mainly affected the SOM bound to the silt fraction; there was more microbial decomposition in the pasture than in the forest silt fraction, as indicated by lower yields of lignin and carbohydrates, and also by a more advanced oxidative lignin side-chain oxidation and higher values of plant : microbial sugar ratios. The ratio of arabinose : xylose was indicative of the removal of carbohydrates when the original forest was replaced by pasture, and we conclude that this can be used as an indicator of deforestation. The accumulation of lignin and its low humification within the forest floor could be due to the extremely cold winter and dry summer climate. Received: 10 March 1999     

Assessing scale effects on modelled soil organic carbon contents as a result of land use change in Belgium

This paper explores the influence of spatial scale on modelled projections of soil organic carbon (SOC) content. The effect of land use change (LUC) on future SOC stocks was estimated using the Rothamsted Carbon model for a small area of southern Belgium. The study assumed no management change and used a single climate change scenario. Three model experiments were used to identify how data scale affects predicted SOC stocks: (i) using European LUC datasets at a resolution of 10′ and assuming equal distribution of change within the study area, (ii) using more accurate regional data aggregated to the 10’ resolution, and (iii) using the regional data at a spatial resolution of 250 m. The results show that using coarse resolution (10′) data is inappropriate when modelling SOC changes in the study area as only the methods using precise data predict a change in SOC stocks similar to those reported in the literature. This is largely because of differences in model parameterisation. However, precisely locating LUC does not significantly affect the results. The model, using either pan‐European or region‐specific precise data predicts an average SOC increase of 1 t C ha^?1 (1990–2050), mainly resulting from afforestation of 13% of agricultural land.     

土地利用规划修编中粮食产量预测方法比较

为探索提高土地利用总体规划修编中粮食产量预测精度的方法,该文应用1988-2005年晋城市粮食产量相关数据的分析,对线性回归模型、灰色GM(1,1)模型和灰色多元线性回归组合模型3种粮食产量预测方法进行了研究.首先,运用灰色关联分析对影响粮食产最的影响因素作出关联因子排序;其次,在灰色关联分析的基础上选取主要影响因子;再次,利用灰色GM(1,1)模型得到主要影响因素的预测值,同时,利用原始数据建立多元线性回归模型;最后,将灰色GM(1,1)模型的预测结果作为多元线性回归模型的输入值,得到灰色多元线性回归组合模型.通过比较这3种粮食产量预测方法的预测结果,得出灰色多元线性回归组合模型最适宜于晋城市粮食产量的预测.该研究可提高土地利用总体规划编制的科学性.     

Responses of soil organic matter and greenhouse gas fluxes to soil management and land use changes in a humid temperate region of southern Europe

We studied the effects of soil management and changes of land use on soils of three adjacent plots of cropland, pasture and oak (Quercus robur) forest. The pasture and the forest were established in part of the cropland, respectively, 20 and 40 yr before the study began. Soil organic matter (SOM) dynamics, water-filled pore space (WFPS), soil temperature, inorganic N and microbial C, as well as fluxes of CO₂, CH₄ and N₂O were measured in the plots over 25 months. The transformation of the cropland to mowed pasture slightly increased the soil organic and microbial C contents, whereas afforestation significantly increased these variables. The cropland and pasture soils showed low CH₄ uptake rates (<1 kg C ha⁻¹ yr⁻¹) and, coinciding with WFPS values >70%, episodes of CH₄ emission, which could be favoured by soil compaction. In the forest site, possibly because of the changes in soil structure and microbial activity, the soil always acted as a sink for CH₄ (4.7 kg C ha⁻¹ yr⁻¹). The N₂O releases at the cropland and pasture sites (2.7 and 4.8 kg N₂O-N ha⁻¹ yr⁻¹) were, respectively, 3 and 6 times higher than at the forest site (0.8 kg N₂O-N ha⁻¹ yr⁻¹). The highest N₂O emissions in the cultivated soils were related to fertilisation and slurry application, and always occurred when the WFPS >60%. These results show that the changes in soil properties as a consequence of the transformation of cropfield to intensive grassland do not imply substantial changes in SOM or in the dynamics of CH₄ and N₂O. On the contrary, afforestation resulted in increases in SOM content and CH₄ uptake, as well as decreases in N₂O emissions.     

Role of soil organic matter in stabilization of water-stable aggregates in Soils under different types of land use

Three Andosols (used as grassland, upland field, and paddy field) and two Gray Lowland soils (used as upland field and paddy field) were examined to study the role of organic matter in the stabilization of soil aggregates. It was found that prolonged use of Andosols as grassland or as upland field enabled to maintain a higher level of soil organic carbon than use as paddy field. However, paddy soil exhibited a greater aggregate stability (determined by wet-sieving procedure) than soil under upland field or grassland management. Comparison between two Gray Lowland soils also showed that aggregates in the paddy soil were more stable than in the upland field soil. Among organic constituents examined (such as sodium pyrophosphate (SPP)-extractable organic matter and carbohydrates), only the contents of hot water (HW)-extractable carbohydrates of the soils were significantly correlated with aggregate stability. Paddy soils which showed a greater aggregate stability contained a larger amount of HW -extractable carbohydrates in the soils, and a larger amount of HW -extractable carbohydrates regardless of the size of their aggregates compared with other soils. These findings suggest that HW -extractable carbohydrates which represents easily decomposable organic materials may be of special importance for the stabilization of aggregates in the soils.     

土地利用和地形因子影响下的西藏农业产值空间化模拟

农业产值空间化模拟是客观评价农业生产效率的基础,是科学制定农业发展政策的依据。该文综合运用地统计学方法和地理信息系统空间分析功能,根据海拔高度与农业产值不同的拟合关系将西藏划分为Ⅰ型和Ⅱ型地区,分析了两类区域土地利用和地形因子与农业产值的关系。在此基础上,以土地利用为指示性因子,综合考虑地形因子对农业产值空间分布的影响,运用因子相乘的方法实现了多源数据的融合,建立了西藏农业产值空间化模拟模型。分析模拟结果：Ⅰ、Ⅱ型12个检验样本中共有8个县相对误差小于30%,模拟结果比较理想。同时,该模拟结果能够较好地反映西藏农业整体发展水平低,80%以上的农业用地每平方公里产值低于5400元, “一江两河”流域和昌都地区农业产值相对较高的实际情况。这有助于正确认识西藏的农业发展状况,为区域可持续发展服务。     

县域土地利用程度评估模型构建及应用研究

在新形势下回顾和总结了以往土地利用率衡量土地利用程度的优缺点，并从利用广度、强度和深度3个层次全面阐述土地利用率的内涵，由此提出衡量区域土地利用程度应当从种植制度、有效生物产出、经济产出3个方面来综合评估，土地利用率复种指数、产出指数和效益指数三者各有侧重。研究结果表明，曲周县全县土地利用程度高的区域分布较为典型，集中分布在3个区域：一是以四疃为中心科技辐射点的北部区域；二是依托邯临公路两侧的带状区域；三是以城关镇为中心高投入辐射面的东部区域。     

不同利用方式下土壤有机质和全磷的可见近红外高光谱反演

以太湖流域直湖港小流域稻田、桃园和菜地的土壤样本为研究对象,研究了不同光谱建模方法和土地利用方式对土壤有机质和全磷高光谱反演的影响。结果表明:(1)偏最小二乘回归分析(Partial least squarer egression,PLSR)模型的建模和预测精度较高且稳定;人工神经网络中广义回归神经网络(Generalized regression neural network,GRNN)网络预测精度较高但易出现过拟合现象,反向传播神经网络(Back propagation neural network,BPNN)网络比较稳健但精度略低;偏最小二乘与人工神经网络相结合则可综合两者优点,改善复杂样本下的预测精度。(2)土壤有机质的光谱反演结果优于全磷。3种土地利用方式中,稻田的预测效果总体优于桃园和菜地。在当前研究区域内土地利用方式对土壤有机质光谱反演影响不大,但对全磷反演影响较大。今后利用光谱对土壤全磷反演时需分土地利用方式对模型进行校准。     

Landscape and land use effects on soil resources in a Himalayan watershed

Sustainable land management decisions at all scales require solid, science-based information. Soil quality assessment can provide this regarding soil physical, chemical, and biological characteristics and the ability to provide ecosystem and societal services. Our objective was to make a regional assessment of soils in the Garhwal Himalayas to determine their ability to perform various functions and respond to external influences. Five functional categories were assessed using 13 soil parameters focused on ecological sustainability. Human land use effects on soils were referenced to natural woodlands at each landscape position. Within upper-slope regions, flora and fauna habitat, moisture retention, organic matter and nutrient cycling, air and water infiltration and resistance to erosion were decreased 35, 27, 24, 24, and 9%, respectively. At mid-slope positions the order and magnitude of decrease were organic matter and nutrient cycling, flora and fauna habitat, and moisture retention (26, 22, and 16%, respectively). Changes within the valley were lowest, averaging − 3% for flora and fauna habitat and − 13% for organic matter and nutrient cycling. We conclude that the minimum data set (MDS) used provided a representative assessment of soil quality and could serve as a basis for assessment in similar tropical watersheds.