A comparative study on chemical characteristics of tropical soils from volcanic material under forest and agriculture

Abstract

An investigation was conducted to compare differences in chemical characteristics of Costa Rica soils under continuous cultivation and under forest vegetation. Inceptisols from young volcanic material under forest, sugar cane, coffee and pasture, respectively, were sampled in the San Carlos region of Costa Rica, and analysed for pH, organic matter, N, Ca, Mg, K, Na, Al, Fe, Zn and Mn contents. Indications were obtained that continuous cropping for 1 to 22 years with sugar cane resulted in a decrease in Ca and Mg content and an increase in acid extractable Al concentrations, compared to amounts found in forest soils. In soils under coffee the only significant changes were a reduction in soil organic matter, N and Al contents. Exchangeable bases decreased slightly during the first two years, but in fields 15 years under coffee, the content of exchangeable bases was affected slightly, except for a relatively marked decrease in amounts of Mg. Conversion into pasture maintained soil fertility at a level comparable to that found in the forest soil ecosystem. It was concluded that differences in vegetational ecosystems caused soil chemical changes, but deforestation in the tropics did not necessarily result in rapid soil degradation processes. The magnitude of the data showed that the soil in the San Carlos region of Costa Rica had been cultivated for at least 10 to 20 years without producing evidence of excessive deterioration.     

The pH of bodenburg silt loam soil as related to forest cover and time under cultivation

Abstract

Soil pH's were evaluated at three time intervals following land clearing at two locations in the Matanuska Valley. Seasonal fluctuations of pH values over a seven‐year period as determined in water (pH_w,) and 0.01 M CaCl₂ (pH_s) were additionally evaluated at these locations. A statistical rise in soil pH occurred at both locations with clearing and subsequent cultivation. Soil reaction differences related to season and year were not consistent and were not related to a definite pattern. No relationship between monthly or seasonal precipitation and the soil reaction was found. The correlation coefficient between pH_w and pH_s was highly significant. Work of other investigators is discussed in the interpretation of the data collected.     

The Langmuir parameters of orthophosphate and pyrophosphate sorption for ammoniated tropical soils

Abstract

The Langmuir parameters of orthophosphate (OP) and pyrophosphate (PP) sorption for the ammoniated tropical soils were determined. Positive linear relationships between OP and PP sorption maxima and amounts of anhydrous NH₃ added were noticed. Indexes of bonding energy of OP and PP increased exponentially as ammoniation level of the soils increased from 33 to 100% of ammonia retention capacity.     

The effect of water and acid‐washing soil treatment on the measurement of pH,delta pH and zero point of charge in some variable charge soils

Abstract

This study was undertaken to determine the effect of previous water and acid‐washing soil treatment on soil pH, Delta pH and Zero Point of Charge of soil surface samples of three Hawaii soils, Molokai (Typic Torrox), Wahiawa (Tropeptic Eutrustox), and Hilo (Typic Hydrandept).

The acid‐washing treatment lowered the soil pH and shifted the Zero Point of Charge to lower pH values. The effect was greater in the Wahiawa and Molokai soils that are dominated by oxidic materials. Whereas the acid‐washing treatment did not change the magnitude of the negative charge in the Wahiawa and Molokai soils, it overestimated the magnitude of the positive charge in the Hilo soil. This phenomena probably was enhanced by the dominance of variable charge clay minerals in the Hilo soil. The results indicated that the acid‐washing treatment changed the nature of the charge characteristics of the soils, hence it should not be recommended in the characterization of the net charge in variable charge soils.     

Estimation of Saturated Paste Extracts’ Electrical Conductivity from 1:5 Soil/Water Suspension and Gypsum

Texture and salt type influence the relationships between saturated paste electrical conductivity (EC_e) and EC of other soil/water ratios. The objectives of this study were to develop and validate relationships between EC_e and EC_1:5 suspension for soils in Yazd Province and evaluate the effects of soil texture and gypsum on those relationships. Three hundred twenty-two soil samples were collected, of which 272 (all data) were used to develop the models and 50 were used to validate them. The soils were divided into two general textural categories of coarse and fine and two categories of with (G) and without gypsum (NG). Gypsum content had a stronger impact on the accuracy of the suspension method in predicting EC_e than texture. The EC_e = 5.60 EC_1:5 ? 4.37 and EC_e = 5.37 EC_1:5 + 0.57 models are recommended for soils with and without gypsum, respectively. The methodology can be implemented in other regions, particularly if gypsum is present.     

Increase in the Capacity of Interlayer Sites in a Paddy Soil as a Possible Factor Affecting the Dynamics of Fixed Ammonium at the Initial Stage of Anaerobic Incubation

To evaluate whether the capacity of interlayer sites affects the dynamics of fixed ammonium (NH₄⁺) in a paddy soil, a combination of potassium (K)–saturation treatment and stepwise extraction of nonexchangeable K with 0.01 mol L^?1 hydrochloric acid was applied to a soil incubated anaerobically up to 70 days. The capacity of interlayer sites increased with an increase of weakly fixed NH₄⁺ during the initial 28 days (r = 0.78, P < 0.01), and remained stable thereafter. On the other hand, the concentration of exchangeable NH₄⁺ increased curvilinearly during the whole incubation period, which was correlated with an increase of weakly fixed NH₄⁺ (r = 0.85, P < 0.01). These results suggested that the dynamics of weakly fixed NH₄⁺ in a paddy soil is regulated not only by the chemical equilibrium between exchangeable and weakly fixed NH₄⁺ but also by the capacity of interlayer sites within a few weeks after flooding.     

基于土壤微波辐射布儒斯特角反演土壤含水率

在利用被动微波遥感技术进行裸露地表土壤含水率（Soil Moisture Content,SMC）的反演中,土壤粗糙度是制约反演精度的最关键因素。该研究利用改进的积分方程模型（Advanced Integral Equation Model,AIEM）进行地表多角度微波发射率的模拟,探索地表微波辐射多角度信息用于提高地表SMC反演精度的可行性。基于不同SMC和不同粗糙度地表多角度V极化发射率数据的变化趋势提取土壤介质布儒斯特角,结果表明,土壤布儒斯特角对SMC具有较高的敏感性,C波段（6.6 GHz）不同含水率土壤的布儒斯特角分布在60°～80°范围内。基于AIEM模拟数据的分析发现,土壤布儒斯特角正切值与SMC具有较好的线性关系,线性拟合决定系数为0.94,均方根误差为0.027 cm3/cm3,并得到了基于布儒斯特角的裸露地表SMC反演算法。基于模拟数据的算法验证结果表明,算法的SMC预测值与理论值的决定系数为0.95,均方根误差为0.024 cm3/cm3。算法在不同土壤粗糙度自相关函数下均表现出稳健的特性,SMC预测精度最大均方根误差为0.027 cm3/cm3,最小为0.023 cm3/cm3。基于布儒斯特角的SMC反演算法利用的是多角度土壤发射率的相对变化而非其绝对数值,该研究为SMC的多角度被动微波遥感提供了一种不同的研究思路。     

基于危险度与风险格局的土地盐碱化监测区优先级评价

为提高盐碱化监测和防治的针对性和精准性,该文选取与盐碱化形成有关的土壤质地、蒸降比、地下水矿化度、土地利用程度、盐碱化历史敏感性,以及与盐碱化扩散有关的地貌、数字高程(digital elevation model, DEM)、植被指数(normalized difference vegetation index, NDVI)、坡度、土壤质地等因子,借助BP神经网格、最小阻力模型、灰色关联度、叠加法和空间分析法,开展黑龙江省土地盐碱化监测区域识别,研究结果表明,1)黑龙江盐碱地监测区面积为2 981.72万hm~2,占研究区的67.10%,其中高、中、低级别监测区占区域面积的20.18%、14.68%、32.23%;2)盐碱地监测级别总体呈现西部东部中部、北部、南部,高级别和中级别监测区主要分布在松嫩平原西部、西南部和北部以及三江平原东北部地区,低级别监测区主要分布在松嫩平原东部、三江平原南部、东南部山地区。研究结果及过程为土地盐碱化监测与防治提供了科学依据和方法参考。     

The rice soils of Cambodia. II. Statistical discrimination of soil properties by the Cambodian Agronomic Soil Classification system (CASC)

Abstract. A novel agronomic system of soil classification for managing rice soils in Cambodia (CASC) was developed recently. It integrates local knowledge about the soil with its conceptual and taxonomic understanding by soil scientists. Using quantitative soil survey data we evaluated the agronomic efficacy of the classification system. Although the CASC is based on simple field criteria it explained 25 to 44% of the variation in soil prop-erties relevant for agronomic decision making. It failed, however, to differentiate soil types based on pH (6% of variances explained). Despite its simplicity it performed as well or better than the most widely used soil map in Cambodia (Crocker, 1962), and unlike this small-scale soil map it allows classification on a field-specific basis. The average values of soil properties were often significantly different between groups. Organic carbon, clay content and plant available magnesium and calcium contributed most to the discrimination of CASC soil groups. The predictive accuracy when allocating new samples on the basis of quantitative survey data to soil groups of the CASC was 50% to 100%, except for soil groups Kein Svay (0%) and Kampong Siem (20%). The CASC is valuable for managing Cambodian rice soils and may also be used for up-scaling and mapping of soil information.