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1.
Cultivation of irrigated desert soils in Central Iran is one way of utilizing under‐exploited land to produce more food. This study explores the value of soil quality indicators as measures when converting desert to croplands. Soil samples from unfarmed desert, wheat and alfalfa sites in the Abarkooh Plain (Central Iran) were taken from 0–10, 10–20 and 20–30 cm depths. Soil quality indicators including organic carbon, total nitrogen, carbohydrate, particulate organic carbon (POC) in aggregate fractions, and aggregate water‐stability were determined. The desert soils contained organic carbon of 0·26–0·56 g kg−1, total nitrogen of 0·05–0·08 g kg−1 and carbohydrate of 0·03–0·11 g kg−1 at 0–30 cm depth. Across this depth, the contents of organic carbon, total nitrogen and carbohydrate in wheat were about 3–7, 2–3 and 6–26‐times higher than those of desert soils, respectively. These values for alfalfa were 5–12, 3–4 and 7–35 times, respectively. The POC (near zero in desert soils) and generally other soil quality indicators showed greater improvement in alfalfa than in wheat fields. The results indicated a significant decrease in proportion of the fraction <0·05 mm in cultivated soils, whereas the proportion of the large aggregate size classes (2–4 and 1–2 mm) was increased by irrigation and cultivation. A significant improvement in aggregate water‐stability was observed in cultivated soils. At all depths, a large portion of the total soil organic carbon was stored in the fractions <0·05 mm for desert and macroaggregates (0·25–2 mm) for cultivated soils. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

2.
Recent evidences from some irrigated areas worldwide, such as Central Asia, suggest that water used for irrigation contains magnesium (Mg2+) at levels higher than calcium (Ca2+). Excess levels of Mg2+ in irrigation water and/or in soil, in combination with sodium (Na+) or alone, result in soil degradation because of Mg2+ effects on the soil's physical properties. More than 30 per cent of irrigated lands in Southern Kazakhstan having excess levels of Mg2+ are characterized by low infiltration rates and hydraulic conductivities. The consequence has been a gradual decline in the yield of cotton (Gossypium hirsutum L.), which is commonly grown in the region. These soils require adequate quantities of Ca2+ to mitigate the effects of excess Mg2+. As a source of Ca2+, phosphogypsum—a byproduct of the phosphorous fertilizer industry—is available in some parts of Central Asia. In participation with the local farming community, we carried out a 4‐year field experiment in Southern Kazakhstan to evaluate the effects of soil application of phosphogypsum—0, 4·5, and 8·0 metric ton per hectare (t ha−1)—on chemical changes in a soil containing excess levels of Mg2+, and on cotton yield and economics. The canal water had Mg2+ to Ca2+ ratio ranging from 1·30 to 1·66 during irrigation period. The application of phosphogypsum increased Ca2+ concentration in the soil and triggered the replacement of excess Mg2+ from the cation exchange complex. After harvesting the first crop, there was 18 per cent decrease in exchangeable magnesium percentage (EMP) of the surface 0·2 m soil over the pre‐experiment EMP level in the plots where phosphogypsum was applied at 4·5 t ha−1, and a 31 per cent decrease in EMP in plots treated with phosphogypsum at 8 t ha−1. Additional beneficial effect of the amendment was an increase in the soil phosphorus content. The 4‐year average cotton yields were 2·6 t ha−1 with 8 t ha−1 phosphogypsum, 2·4 t ha−1 with 4·5 t ha−1 phosphogypsum, and 1·4 t ha−1 with the control. Since the amendment was applied once at the beginning, exchangeable Mg2+ levels tended to increase 4 years after its application, particularly in the treatment with 4·5 t ha−1 phosphogypsum. Thus, there would be a need for phosphogypsum application to such soils after every 4–5 years to optimize the ionic balance and sustain higher levels of cotton production. The economic benefits from the phosphogypsum treatments were almost twice those from the control. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

3.
In the Far West Texas region in the USA, long‐term irrigation of fine‐textured valley soils with saline Rio Grande River water has led to soil salinity and sodicity problems. Soil salinity [measured by saturated paste electrical conductivity (ECe)] and sodicity [measured by sodium adsorption ratio (SAR)] in the irrigated areas have resulted in poor growing conditions, reduced crop yields, and declining farm profitability. Understanding the spatial distribution of ECe and SAR within the affected areas is necessary for developing management practices. Conventional methods of assessing ECe and SAR distribution at a high spatial resolution are expensive and time consuming. This study evaluated the accuracy of electromagnetic induction (EMI), which measures apparent electrical conductivity (ECa), to delineate ECe and SAR distribution in two cotton fields located in the Hudspeth and El Paso Counties of Texas, USA. Calibration equations for converting ECa into ECe and SAR were derived using the multiple linear regression (MLR) model included in the ECe Sampling Assessment and Prediction program package developed by the US Salinity Laboratory. Correlations between ECa and soil variables (clay content, ECe, SAR) were highly significant (p ≤ 0·05). This was further confirmed by significant (p ≤ 0·05) MLRs used for estimating ECe and SAR. The ECe and SAR determined by ECa closely matched the measured ECe and SAR values of the study site soils, which ranged from 0·47 to 9·87 dS m−1 and 2·27 to 27·4 mmol1/2 L−1/2, respectively. High R2 values between estimated and measured soil ECe and SAR values validated the MLR model results. Results of this study indicated that the EMI method can be used for rapid and accurate delineation of salinity and sodicity distribution within the affected area. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

4.
Saline‐sodic water is a by‐product of coalbed natural gas (CBNG) production in the Powder River Basin of Wyoming, USA and is being beneficially used in places as irrigation water. This study evaluated effects of 2 years of natural precipitation on soil properties of a hay field after the cessation of managed irrigation with CBNG water. The hay field had been irrigated with only CBNG water [CBNG(NT)], CBNG water amended with gypsum [CBNG(G)] or gypsum plus sulfur via a sulfur burner [CBNG(GSB)] in combination with soil amendments—gypsum ( +G ), elemental sulfur ( +S ), and both ( +GS ). Results indicated that infiltration rates were the lowest on fields irrigated with CBNG(NT), followed by CBNG(G) and CBNG(NT) +G treatments (12·2, 13·2, and 13·5 cm h−1, respectively). The CBNG(GSB) +GS treatment had the highest infiltration rates (33·5 cm h−1). By the second year, salinity and sodicity of treated soils had decreased in the A‐horizon of most CBNG‐water irrigated plots, whereas in Bt1‐ and Bt2‐horizons salinity generally decreased but sodicity increased; S and GS soil amended plots had higher profile salinities compared with NT and G soil treatments. Although Na+ leaching was observed in all fields that received soil and/or water amendments, CBNG(GSB) +GS plots had the lowest sodicity in the A‐ and Bt1‐horizons. Effective managed irrigation requires knowledge of site‐specific soil properties, plant suitability, water chemistry, and amendments that would be needed to treat the CBNG waters and soils. This study indicates the greatest success was realized when using both soil and water amendments. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

5.
Problems of frequent drought stress, low soil organic carbon (SOC) concentration, low aggregation, susceptibility to compaction, salinization and accelerated soil erosion in dry regions are accentuated by removal of crop residues, mechanical methods of seedbed preparation, summer clean fallowing and overgrazing, and excessive irrigation. The attendant soil degradation and desertification lead to depletion of SOC, decline in biomass production, eutrophication/pollution of waters and emission of greenhouse gases. Adoption of conservation agriculture, based on the use of crop residue mulch and no till farming, can conserve water, reduce soil erosion, improve soil structure, enhance SOC concentration, and reduce the rate of enrichment of atmospheric CO2. The rate of SOC sequestration with conversion to conservation agriculture, elimination of summer fallowing and growing forages/cover crops may be 100 to 200 kg ha−1 y−1 in coarse‐textured soils of semiarid regions and 150 to 300 kg ha−1 y−1 in heavy‐textured soils of the subhumid regions. The potential of soil C sequestration in central Asia is 10 to 22 Tg C y−1 (16±8 Tg C y−1) for about 50 years, and it represents 20 per cent of the CO2 emissions by fossil fuel combustion. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

6.
The effects of compost application on soil carbon sequestration potential and carbon budget of a tropical sandy soil was studied. Greenhouse gas emissions from soil surface and agricultural inputs (fertiliser and fossil fuel uses) were evaluated. The origin of soil organic carbon was identified by using stable carbon isotope. The CO2, CH4 and N2O emissions from soil were estimated in hill evergreen forest (NF) plot as reference, and in the corn cultivation plots with compost application rate at 30 Mg ha−1 y−1 (LC), and at 50 Mg ha−1 y−1 (HC). The total C emissions from soil surface were 8·54, 10·14 and 9·86 Mg C ha−1 y−1 for NF, HC and LC soils, respectively. Total N2O emissions from HC and LC plots (2·56 and 3·47 kg N2O ha−1 y−1) were significantly higher than from the NF plot (1·47 kg N2O ha−1 y−1). Total CO2 emissions from fuel uses of fertiliser, irrigation and machinery were about 10 per cent of total CO2 emissions. For soil carbon storage, since 1983, it has been increased significantly (12 Mg ha−1) under the application of 50 Mg ha−1 y−1 of compost but not with 30 Mg ha−1 y−1. The net C budget when balancing out carbon inputs and outputs from soil for NF, HC and LC soils were +3·24, −2·50 and +2·07 Mg C ha−1 y−1, respectively. Stable isotope of carbon (δ13C value) indicates that most of the increased soil carbon is derived from the compost inputs and/or corn biomass. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

7.
Due to increased population and urbanization, freshwater demand for domestic purposes has increased resulting in a smaller proportion for irrigation of crops. We carried out a 3‐year field experiment in the Indus Plains of Pakistan on salt‐affected soil (ECe 15·67–23·96 dS m−1, pHs 8·35–8·93, SAR 70–120, infiltration rate 0·72–0·78 cm h−1, ρ b 1·70–1·80 Mg m−3) having tile drainage in place. The 3‐year cropping sequence consisted of rice (Oryza sativa L.) and wheat (Triticum aestivum L.) crops in rotation. These crops were irrigated with groundwater having electrical conductivity (EC) 2·7 dS m−1, sodium adsorption ratio (SAR) 8·0 (mmol L−1)1/2 and residual sodium carbonate (RSC) 1·3 mmolc L−1. Treatments were: (1) irrigation with brackish water without amendment (control); (2) Sesbania (Sesbania aculeata) green manure each year before rice (SM); (3) applied gypsum at 100 per cent soil gypsum requirement (SGR) and (4) applied gypsum as in treatment 3 plus sesbania green manure each year (GSM). A decrease in soil salinity and sodicity and favourable infiltration rate and bulk density over pre‐experiment levels are recorded. GSM resulted in the largest decrease in soil salinity and sodicity. There was a positive relationship between crop yield and economic benefits and improvement in soil physical and chemical properties. On the basis of six crops, the greatest net benefit was obtained from GSM. Based on this long‐term study, combined use of gypsum at 100 per cent soil gypsum requirement along with sesbania each year is recommended for soil amelioration and crop production. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
Reforestation of saline sodic soil is increasingly undertaken as a means of reclaiming otherwise unproductive agricultural land. Currently, restoration of degraded land is limited to species with high tolerances of salinity. Biochar application has the potential to improve physical, biological and chemical properties of these soils to allow establishment of a wider range of plants. In a glasshouse trial, we applied biochar made from Acacia pycnantha (5 Mg ha−1) or no biochar to either a low (ECe 4·75 dS m−1, ESP 6·9), a moderate (ECe 27·6 dS m−1, ESP 29·3) or a high (ECe 49·4 dS m−1, ESP 45·1) saline sodic soil. The regional common reforestation species Eucalyptus viminalis and Acacia mearnsii were planted as tubestock in to the soils. Early establishment indicators, including growth, plant condition and nutrition, were assessed at the end of a simulated growing season, 108 days after biochar application. Application of biochar increased height, and decreased root : shoot and the concentration of Mn, N and S in plants of E. viminalis when grown in the highly saline sodic soil. Biochar application increased the concentration of B in leaves of E. viminalis and increased the concentration of P, K and S in leaves of A. mearnsii when grown in the low saline sodic soil. The results confirm that there is potential for biochar to assist in reforestation of saline sodic soils. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

9.
Reclamation of disturbed soils is done with the primary objective of restoring the land for agronomic or forestry land use. Reclamation followed by sustainable management can restore the depleted soil organic carbon (SOC) stock over time. This study was designed to assess SOC stocks of reclaimed and undisturbed minesoils under different cropping systems in Dover Township, Tuscarawas County, Ohio (40°32·33′ N and 81°33·86′ W). Prior to reclamation, the soil was classified as Bethesda Soil Series (loamy‐skeletal, mixed, acid, mesic Typic Udorthent). The reclaimed and unmined sites were located side by side and were under forage (fescue—Festuca arundinacea Schreb. and alfa grass—Stipa tenacissima L.), and corn (Zea mays L.)—soybean (Glycine max (L.) Merr.) rotation. All fields were chisel plowed annually except unmined forage, and fertilized only when planted to corn. The manure was mostly applied on unmined fields planted to corn, and reclaimed fields planted to forage and corn. The variability in soil properties (i.e., soil bulk density, pH and soil organic carbon stock) ranged from moderate to low across all land uses in both reclaimed and unmined fields for 0–10 and 10–20 cm depths. The soil nitrogen stock ranged from low to moderate for unmined fields and moderate to high in some reclaimed fields. Soil pH was always less than 6·7 in both reclaimed and unmined fields. The mean soil bulk density was consistently lower in unmined (1·27 mg m−3 and 1·22 mg m−3) than reclaimed fields (1·39 mg m−3 and 1·34 mg m−3) planted to forage and corn, respectively. The SOC and total nitrogen (TN) concentrations were higher for reclaimed forage (33·30 g kg−1; 3·23 g kg−1) and cornfields (21·22 g kg−1; 3·66 g kg−1) than unmined forage (17·47 g kg−1; 1·98 g kg−1) and cornfield (17·70 g kg−1; 2·76 g kg−1). The SOC stocks in unmined soils did not differ among forage, corn or soybean fields but did so in reclaimed soils for 0–10 cm depth. The SOC stock for reclaimed forage (39·6 mg ha−1 for 0–10 cm and 28·6 mg ha−1 for 10–20 cm depths) and cornfields (28·3 mg ha−1; 32·2 mg ha−1) were higher than that for the unmined forage (22·7 mg ha−1; 17·6 mg ha−1) and corn (21·5 mg ha−1; 26·8 mg ha−1) fields for both depths. These results showed that the manure application increased SOC stocks in soil. Overall this study showed that if the reclamation is done properly, there is a large potential for SOC sequestration in reclaimed soils. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

10.
Irrigation with treated wastewater (TWW) may affect soil structure and stability and the characteristics of dissolved organic matter (DOM) of the soil solution. The objectives of our study were (i) to evaluate the impact of TWW irrigation, as compared with fresh water (FW) irrigation, on aggregate stability and saturated hydraulic conductivity (indices of soil structure stability) and (ii) to determine whether these indices can be associated with the chromophoric indicators of water‐extractable DOM in TWW‐ and FW‐irrigated soils. We studied aggregate stability and soil hydraulic conductivity (HC) of four different soil types irrigated with either TWW (for at least 5 years) or FW. The results were linked to earlier published data on the concentration scores of fluorescent chromophoric DOM components (obtained from excitation‐emission matrices of flouorescence coupled with parallel factor analysis), dissolved organic carbon (DOC) concentration and absorbance at 254 nm (Abs254). These were all obtained from water extracts of the same soils as those used in the current study. Irrigation with TWW decreased aggregate stability, in comparison to irrigation with FW, in the sandy clay and clay soils, while in the loamy sand TWW increased aggregate stability. The apparent steady state HCs in the TWW‐irrigated samples in the loamy sand, sandy clay and clay soils were similar to, or significantly less than, those obtained in the FW‐irrigated samples. In the sandy loam the opposite trend was noted. Results of principal component and classification analyses showed that the aggregate stability indices were directly associated with soil organic matter and DOM attributes in the coarse‐textured soils, while in the fine‐textured soils inverse associations were noted. Only in the fine‐textured soils were the HC attributes associated (directly) with some of the DOM characteristics. Our results suggest that structural indices of fine‐textured soils are more sensitive than those of coarse‐textured soils to the composition of water extractable DOM.  相似文献   

11.
Usage of alkaline and saline groundwater with elevated concentrations of fluoride (F−) for irrigation of pastures requires an assessment of the mobility of F− within the plant-water-soil continuum. Factors influencing F− sorption and desorption in 95 Australian soils were examined. Pronounced differences in F− sorption were observed across the soils, but these differences could not be explained by differences in soil pH, electrical conductivity or organic carbon. Rather, sorption was correlated with the content of Fe/Al hydrous oxides and kaolinite in soil. Sorption of F− onto soils increased the solution pH and the ratio of (F− adsorbed) to (OH− desorbed) was consistently below 1, thereby indicating that adsorption of F− results in the release of water and hydroxyl groups from, or co-adsorption of protons to, the sorbent surface. Maximum sorption occurred at pH values of approximately 5–6, whilst sulphate slightly increased (<5%) F− sorption. Desorption was slightly decreased (~3%–7%) in presence of sulphate anions. Hence, it is unlikely that irrigation of soil with alkaline and saline groundwater, in combination with soil applications of gypsum and sulphur to limit pH fluctuations, would increase mobility of F− in soil. Finally, the irrigation of soil columns with 1200–1500 mm of alkaline and saline groundwater containing 0.18 mM F−, as would commonly occur in irrigation systems using coal seam gas associated water in Australia, resulted in a F− concentration of 0.05 mM at 10 cm depth and the measured values were in excellent agreement with modelled F− movement based on sorption parameters. Thus, sorption parameters can be used to identify soils which minimize movement of F− because of their strong F− sorption. Based on these results, safe limits for irrigation of soil can be established which avoid F− toxicity risks to plants, animals and contamination of water resources.  相似文献   

12.
Temporal changes in soil chemical and nutritional properties were evaluated in a long-term experiment conducted on Alfisols in West Africa. Effects of land use and cropping duration on soil chemical properties at 0–5 cm and 5–10 cm depths were evaluated for five treatments: (1) alley cropping with Leucaena leucocephala established on the contour at 4-m intervals; (2) mucuna (Mucuna utilis) fallowing for 1 year followed by maize (Zea mays)-cowpea (Vigna unguiculata) cultivation for 2 years on severely degraded land; (3) fallowing with mucuna on moderately degraded soils; (4) ley farming involving growing improved pastures for 1 year, grazing for the second year, and growing maize-cowpea for the third year on severely degraded land; (5) ley farming on moderately degraded soils. Soil chemical properties were measured once every year from 1982 through 1986 during the dry season, and included pH, soil organic carbon (SOC), total soil nitrogen (TSN), Bray-P, exchangeable cations, and effective cation exchange capacity (CEC). Regardless of the cropping system treatments, soil chemical quality decreased with cultivation time. The rate of decrease at 0–5 cm depth was 0·23 units year−1 for pH, 0·05 per cent year−1 for SOC, 0·012 per cent year−1 for TSN, 0·49 cmol kg−1 year−1 for Ca2+, 0·03 cmol kg−1 year−1 for Mg2+, 0·018 cmol kg−1 year−1 for K+, and 0·48 cmol kg−1 year−1 for CEC. Although there was also a general decrease in soil chemical quality at 5–10 cm depth, the trends were not clearly defined. In contrast to the decrease in soil properties given above, there was an increase in concentration at 0–5 cm depth of total acidity with cultivation time at the rate of 0·62 cmol kg−1 year−1, and of Mn3+ concentration at the rate of 0·081 cmol kg−1 year−1. Continuous cropping also increased the concentration of Bray-P at 0–5 cm depth due to application of phosphatic fertilizer. Trends in soil chemical properties were not clearly defined with regards to cropping system treatments. In general, however, soil chemical properties were relatively favorable in ley farming and mucuna fallowing treatments imposed on moderately degraded soils. Results are discussed in terms of recommended rates of fertilizer use, in view of soil test values, expected yields, and critical limits of soil properties.  相似文献   

13.
Food and fodder shortage in arid and semi‐arid regions force farmers to use marginal quality water for meeting the water requirement of crops which result in low quality, reduced production and an adverse impact on soil properties. A field study on loamy‐sand (Hyperthermic Typic Ustipsamments) saline soil was conducted during 1999–2001 at Central Institute for Research on Buffaloes, Hisar. This involved assessment of effects of conjunctive use of saline water, EC = 4·6–7·4 dSm−1, SAR = 14–22 ((mmol−1)½ with good quality water on five fodder crop rotations: oat‐sorghum (Avena sativa‐–Sorghum bicolor), rye grass–sorghum (Loleum rigidum—Sorghum bicolor), Egyptian clover—sorghum (Trifoleum alexandrinum—Sorghum bicolor), Persian clover—sorghum (Trifoleum resupinatum—Sorghum bicolor) and Indian clover–sorghum (Melilotus indica—Sorghum bicolor) and certain soil properties associated with it. Leguminous winter fodder crops were more sensitive to poor quality water use. Reductions in fodder yield with use of saline water alone throughout season were 85, 68, 54, 42, 36 and 26 per cent in Indian clover, Egyptian clover, Persian clover, oat, rye grass and sorghum respectively as compared to good quality water. Leguminous fodder crops produced protein rich (12–14 per cent) and low fibre (18–20 per cent) fodder as compared to poor quality grassy fodder under good quality water irrigation but their quality deteriorated when saline water was used. These leguminous crops accumulated proportionately higher Na+ (1·58 per cent) resulting in adverse impact on their growth as compared to grassy fodder crops. Higher soil salinity (12·2 dSm−1), SAR = 20 (mmol−1)½ was recorded with saline water irrigation; and slight adverse impact was noticed on infiltration rate and contents of water dispersible clay. Alternate cyclic use of canal and saline water could be an option for fodder production under such conditions. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

14.
In the oldest sections of Burkina Faso's largest irrigation scheme in the Sourou Valley (13° 10′ N, 03° 30′W) rice (Oryza sativa L.) yields dropped from about 5 to 6 t ha−1 in the early 1990s, shortly after establishment of the scheme, to 2 to 4 t ha−1 from 1995 onwards. Farmers blamed this yield decline on the appearance of 2 to 20 m diameter low productive spots. According to farmers and field measurements, the low productive spots decreased yields by 25–50 per cent. The low productive spots are caused by Zn deficiency. Low Zn availability is related to the very low DTPA‐extractable Zn content of the soil (0·08–0·46 mg kg−1), the alkaline‐calcareous character of the soil, the non‐application of Zn fertilizers, and a relatively large P fertilizer dose (21 kg P ha−1). Farmers were correct in relating the calcareous nature of the soil to the presence of the low productive spots. They were instrumental in identifying application of decomposed organic resources (e.g. rice straw at 5 t ha−1) as a short‐term solution that increases yields by 1·5 to 2·0 t ha−1. Application of Zn fertilizer (10 kg Zn ha−1) in 29 farmer fields in the 2001 dry season eradicated the low productive spots and increased yields from 3·4 to 6·0 t ha−1. Although application of Zn fertilizer is strongly recommended, it is not yet available in Burkina Faso. Based on a comparison of fertilizer prices on the world market and the local market, we expect that the use of Zn fertilizers will be highly profitable (cost/value ratio ≫ 2). Despite the relatively recent introduction of irrigated rice cropping, most farmers showed a good understanding of cropping constraints and possible solutions. Both farmers and researchers mutually benefited from each other's knowledge and observations. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

15.
《Biosystems Engineering》2003,84(3):315-329
A model for fan-ventilated greenhouse cooling is presented in which the primary heat transfer surfaces (cover/structure, canopy and floor) are represented as three parallel planes. Validation of the model was accomplished using data collected over 14 days. Agreement was good, with canopy temperatures over-predicted by only 0·1%, air temperatures in the canopy under-predicted by 0·5%, humidity of the canopy air under-predicted by 1·6% and transpiration rates under-predicted by 1·4%. Simulation runs suggest that when evaporative pad cooling is not used, little advantage is derived from increasing airflow rates beyond about 0·05 m3 m−2 s−1. When evaporative pad cooling is used, however, both air and canopy temperatures decline with increasing airflow rates up to 0·13 m3 m−2 s−1, the highest level considered. Increasing canopy size is predicted to be more influential in reducing air temperatures when evaporative pad cooling is used than when it is not, but its effect on canopy temperature is expected to be approximately the same whether or not evaporative pad cooling is used. With no evaporative pad cooling, the evapotranspiration coefficient (i.e., the ratio of energy used for transpiration to incoming solar energy) is predicted to range from 1·75 for an outside temperature of 36·8°C and an outside humidity ratios of 3·3 g kg−1 to 0·8 for an outside humidity ratio of 29·9 g kg−1 at the same temperature. With evaporative pad cooling, the coefficient is predicted to range from 0·6 to 0·8 at the same outside temperature and the same range of outside humidity ratios.  相似文献   

16.
Water dispersible clay (WDC) can influence soil erosion by water. Therefore, in highly erodible soils such as the ones in eastern Nigeria, there is a need to monitor the clay dispersion characteristics to direct and modify soil conservation strategies. Twenty‐five soil samples (0–20 cm in depth) varying in texture, chemical properties and mineralogy were collected from various locations in central eastern Nigeria. The objective was to determine the WDC of the soils and relate this to selected soil physical and chemical attributes. The soils were analysed for their total clay (TC), water‐dispersible clay (WDC), clay dispersion ratio (CDR), dispersion ratio (DR), dithionite extractable iron (Fed), soil organic matter (SOM), exchangeable cations, exhangeable sodium percentage (ESP) and sodium adsorption ratio (SAR). Total clay contents of the soil varied from 80–560 g kg−1. The USLE erodibility K ranges from 0·02 to 0·1 Mg h MJ−1 mm and WEPP K fall between 1·2 × 10−6–1·7 × 10−6 kg s m−4. The RUSLE erodibility K correlated significantly with CDR and DR (r = 0·44; 0·39). Also, a positive significant correlation (r = 0·71) existed between WEPP K and RUSLE K. Soils with high clay dispersion ratio (CDR) are highly erodibile and positively correlates (p < 0·51) with Fed, CEC and SOM. Also, DR positively correlates with Mg2+ and SOM and negatively correlate with ESP and SAR. Principal component analysis showed that SAR, Na+ and percent base saturation play significant role in the clay dispersion of these soils. The implication of this result is that these elements may pose potential problem to these soils if not properly managed. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

17.
Saline–sodic and sodic soils are characterized by the occurrence of sodium (Na+) to levels that can adversely affect several soil properties and growth of most crops. As a potential substitute of cost‐intensive chemical amelioration, phytoremediation of such soils has emerged as an efficient and low‐cost strategy. This plant‐assisted amelioration involves cultivation of certain plant species that can withstand ambient soil salinity and sodicity levels. It relies on enhanced dissolution of native calcite within the root zone to provide adequate Ca2+ for the Na+ Ca2+ exchange at the cation exchange sites. There is a lack of information for the Na+ balance in terms of removal from saline–sodic soils through plant uptake and leaching during the phytoremediation process. We carried out a lysimeter experiment on a calcareous saline–sodic soil [pH of saturated soil paste (pHs) = 7.2, electrical conductivity of the saturated paste extract (ECe) = 4.9 dS m−1, sodium adsorption ratio (SAR) = 15.9, CaCO3 = 50 g kg−1]. There were three treatments: (1) control (without application of a chemical amendment or crop cultivation), (2) soil application of gypsum according to the gypsum requirement of the soil and (3) planting of alfalfa (Medicago sativa L.) as a phytoremediation crop. The efficiency of treatments for soluble salt and Na+ removal from the soil was in the order: gypsum ≈ alfalfa > control. In the phytoremediation treatment, the amount of Na+ removed from the soil through leaching was found to be the principal cause of reduction in salinity and sodicity. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

18.
Abstract

More than 50% of the irrigated soils in the Sultanate of Oman is in the coastal plains of the Batinah area. Intensive agriculture and groundwater depletion have led to seawater intrusion and soil salinization. As a prerequisite to combat this problem, basic studies on some soil properties were done and are presented. The textural classification ranged from sand and loamy sand to fine‐textured silt loams, and the soil moisture characteristics (0.1–15 bars) revealed field capacities (0.3 bar) and permanent wilting point (15 bars) ranges of 40 to 2%, respectively. The soils are generally calcareous with about 40% calcium carbonate (CaCO3), but low in gypsum [calcium sulfate (CaSO4) content]. The EC1:5 values disclosed the extent of salinization with increasing values of up to 16 dS/m towards the coastal areas of the fine‐textured soils. This was coupled with high sodium (Na) adsorption ratios of up to 30 indicating saline‐sodic conditions.  相似文献   

19.
In semi‐arid Mediterranean soils, water availability is the most limiting factor, negatively affecting the organic matter (OM) degradation. The aim of this work is to study under controlled laboratory conditions how three sources of OM [municipal solid waste (MSW), sheep manure (SM) and cow manure (CM)] behave when they are applied to an agricultural soil subjected to a severe year‐long drought. In order to apply the same concentration of OM to the soil (16·92 Mg OM ha−1), 2 kg of soil was mixed with 30, 67·41 and 55·25 Mg ha−1 (dry matter) of MSW, CM and SM, respectively. Two levels of irrigation were employed: (i) watered soils and (ii) non‐watered soils. Soil's chemical properties [water soluble carbon (WSC), humic acids, fulvic acids and protein mass distribution], biological properties (soil microbial biomass carbon and o‐diphenoloxidase activity) and solid‐state 13C cross‐polarisation magic angle spinning nuclear magnetic resonance spectroscopy were determined. In watered soils, the soil microbial biomass carbon was higher in the SM than in CM and MSW treatments (9·9% and 23·1%, respectively). The WSC was significantly higher in SM than in CM (55·7%) and MSW (78·7%) treatments. A decrease in the content of O‐alkyl C and an increase in alkyl C, aromatic C and carboxyl C were observed. In non‐watered soils, the biochemical properties and alkyl C and alkyl/O‐alkyl ratio decreased, whereas WSC content and O‐alkyl C increased. These results indicated that the evolution of OM and the activity of the microbial community in non‐watered soils were very different to those in the watered soils. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

20.
Biochar has the potential to decrease salinity and nutrient loss of saline soil. We investigated the effects of biochar amendment (0–10 g kg−1) on salinity of saline soil (2.8‰ salt) in NaCl leaching and nutrient retention by conducting column leaching experiments. The biochar was produced in situ from Salix fragilis L. via a fire-water coupled process. The soil columns irrigated with 15 cm of water showed that biochar amendment (4 g kg−1) decreased the concentration Na+ by 25.55% in the first irrigation and to 60.30% for the second irrigation in sandy loam layer over the corresponding control (CK). Meanwhile, the sodium adsorption ratio (SAR) of soil after the first and second irrigation was 1.62 and 0.54, respectively, which were 15.2% and 49.5% lower than CK. The marked increase in saturated hydraulic conductivity (Ks) from 0.15 × 10–5 cm s−1 for CK to 0.39 × 10–5 cm s−1, following 4 g kg−1 of biochar addition, was conducive to salt leaching. Besides, biochar use (4 g kg−1) increased NH4+-N and Olsen-P by 63.63% and 62.50% over the CK, but accelerated NO3–-N leaching. Since 15 cm hydrostatic pressure would result in salt accumulation of root zone, we would recommend using 4 g kg−1 of biochar, 30 cm of water to ease the problem of salt leaching from the surface horizon to the subsoil. This study would provide a guidance to remediate the saline soil in the Yellow River Delta by judicious application of biochar and irrigation.  相似文献   

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