Stretching Soil Sampling to Watershed: Evaluation of Soil‐Test Parameters in a Semi‐arid Tropical Watershed

Soil sampling is an integral component of fertility evaluation and nutrient recommendation for efficient use of nutrients in crop production. Little attention has been devoted to evaluating methodology for sampling watersheds under dryland agriculture. A stratified random sampling methodology for sampling the Appayapally watershed in Mahabubnagar district of Andhra Pradesh state in the semi‐arid tropical region of India was adopted and evaluated. The watershed has an area of about 500 ha, with gentle sloping lands (<1% slope), and 217 farmers own land in the watershed. The soils are Alfisols. A total of 114 soil samples were collected from the top 15‐cm layer to represent the entire watershed. Each sample was a composite of 7–8 cores, randomly collected from the area represented by a crop and group of farmers. The soil samples were air dried, ground, and analyzed for pH, electrical conductivity (EC), organic carbon (C), total nitrogen (N), and extractable phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), sulfur (S), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), and boron (B). Statistical analysis of the results on soil fertility parameters showed that the mean‐ or median‐based results of soil tests performed in the study did not differ significantly when the sample set size varied from 5 to 114 (100% of the population). Our results indicate that farmers' fields in the Appayapally watershed are uniform in the chemical fertility parameters studied, and even a small sample set size can represent the whole population. However, such a sampling strategy may be applicable only to watersheds that are very gently sloping and where fertilizer use is very low, resulting in an overall low fertility in the whole watershed.     

Water Treatment Residuals and Biosolids Co‐applications Affect Phosphatases in a Semi‐arid Rangeland Soil

Co‐application of biosolids and water treatment residuals (WTR) land has not been extensively studied but may be beneficial by sorbing excess biosolid‐borne or soil phosphorus (P) onto WTR, reducing the likelihood of off‐site movement. Reduction of excess soil P may affect the role of specific P‐cleaving enzymes. The research objective was to understand the long‐term effects of single co‐applications and the short‐term impacts of repeated co‐applications on soil acid phosphomonoesterase, phosphodiesterase, pyrophosphatase, and phytase enzyme activities. Test plots were 7.5 × 15 m with treatments consisting of three different WTR rates with a single biosolids rate (5, 10, and 21 Mg WTR ha^?1; 10 Mg biosolids ha^?1) surface co‐applied once in 1991 or reapplied in 2002. Control plots consisted of those that received no WTR–biosolids co‐applications and plots that received only 10 Mg biosolids ha^?1. Plots were sampled to a 5‐cm depth in 2003 and 2004, and soil phosphatases and phytase enzyme activities were measured. Soil phosphodiesterase activity decreased in WTR‐amended plots, and pyrophosphatase activity decreased with increasing WTR application rates. In contrast, acid phosphatase and phytase activity increased with WTR addition, with WTR application possibly triggering a deficiency response causing microorganisms or plants to secrete these enzymes. Biosolids and WTR co‐applications may affect enzymatic strategies for P mineralization in this study site. Reductions in phosphodiesterase activity suggest less P mineralization from biomass sources, including nucleic acids and phospholipids. Increased acid phosphatase and phytase activities indicate that ester‐P and inositol‐P may be important plant‐available P sources in soils amended with WTR.     

Re‐analysis of the Relationship between Organic Carbon and Loss‐on‐Ignition in Soil

The suitability of loss‐on‐ignition (LOI) as an alternative to direct measurement of organic carbon (OC) has been debated for decades without resolution. The literature contains an abundance of different linear regression models to describe the LOI–OC relationship, most based on untransformed values of LOI and OC. Such regression is suspect because the variables are unable to occupy Euclidean space. Logratio transformation—based on relative rather than absolute differences—eliminates this constraint. Re‐analysis of the relationship on new and 10 previously published datasets using logratio techniques reveals that the relationship is nonlinear and that the profusion of regression models is in part a function of the range of LOI. Although LOI may offer a crude estimate of OC at high LOI levels, OC/LOI ratios when LOI is less than about 25% are too variable for reliable OC estimation, and interstudy comparisons remain dubious. Direct measurement of OC is recommended.     

Influence of Tillage and Nutrient Sources on Yield Sustainability and Soil Quality under Sorghum–Mung Bean System in Rainfed Semi‐arid Tropics

The crop production in rainfed semi‐arid tropical (SAT) Alfisols is constrained by low soil organic matter, poor soil fertility, soil structural infirmities, and scarce moisture availability. To offset some of these constraints, a long‐term study of tillage [conventional (CT) and reduced (RT)] and conjunctive nutrient‐use treatments was conducted in SAT Alfisol at Hyderabad, India, under sorghum–mung bean system. The order of performance of the treatments in increasing the sorghum yield was 2 Mg gliricidia loppings + 20 kg nitrogen (N) through urea (T4) (93.2%) > 4 Mg compost + 20 kg N through urea (T3) (88.7%) > 40 kg N through urea (T2) (88.5%) > 4 Mg compost + 2 Mg gliricidia loppings (T5) (82.2%). In the case of mung bean, where half as much N was applied as was to the sorghum, the order of performance of the treatments in increasing the grain yields was T3 (63.6%) >T5 (60.3%) >T4 (58.0%) >T2 (49.6%). Tillage significantly influenced the hydraulic conductivity only, whereas the conjunctive nutrient‐use treatments significantly influenced the predominant physical, chemical, and biological soil‐quality parameters. Among the conjunctive nutrient‐use treatments, T5 was found to be superior in influencing the majority of the soil‐quality parameters and increased the organic carbon by 21.6%, available N by 24.5%, dehydrogenase activity by 56.1%, microbial biomass carbon by 38.8%, labile carbon by 20.3%, and microbial biomass nitrogen by 38.8% over the unamended control and proved superior most in improving soil quality.     

Forms of Iron and Their Association with Soil Properties in Four Soil Taxonomic Orders of Arid and Semi‐arid Soils of Punjab,India

Profiles of arid and semi‐arid zones soils of Punjab, northwestern India, were investigated for different forms of iron (Fe): total Fe, diethylenetriamine penta‐acetic acid (DTPA)–extractable Fe, soil solution plus exchangeable Fe, Fe adsorbed onto inorganic sites and oxide surfaces, and Fe bound by organic sites. Irrespective of the different fractions of Fe present, its content was higher in the fine‐textured Alfisols and Inceptisols than in the coarse‐textured Entisols and Aridisols. Lower content of total Fe was observed in the surface horizon and then increased in the subsurface horizons, whereas no set pattern was observed in Entisols. Also, irrespective of the soil orders, the contents of different forms of Fe were higher in the surface horizon and then decreased by depth. None of the forms of Fe exhibited any consistent pattern of distribution.

Organic matter and the content of clay and silt fractions had a strong bearing on the distribution of forms of Fe. Based on a linear coefficient of correlation, the soil solution plus exchangeable Fe adsorbed onto inorganic sites and DTPA‐extractable Fe increased with increase in soil organic carbon but decreased with increase in soil pH and calcium carbonate content. Total Fe increased with increase in cation exchange capacity (CEC) and clay and silt content. The results also revealed that there was equilibrium in different fractions of this element. Among the different Fe forms, Fe bound by organic sites, water‐soluble plus exchangeable Fe, and Fe adsorbed onto oxides (amorphous surfaces) were positively correlated with the DTPA‐extractable Fe. Though some forms are interrelated, none of the forms had any relationship with the total Fe.     

Distribution of Forms of Zinc and Their Association with Soil Properties and Uptake in Different Soil Orders in Semi‐arid Soils of Punjab,India

Abstract

Profiles of semi‐arid–zone soils in Punjab, northwest India, were investigated for different forms of zinc (Zn), including total, diethylenetriamine penta‐acetic acid (DTPA)-extractable, soil solution plus exchangeable (Zn), Zn adsorbed onto inorganic sites, Zn bound by organic sites, and Zn adsorbed onto oxide surfaces. Irrespective of the different fractions of Zn present, its content was higher in fine‐textured Alfisols and Inceptisols than in coarse‐textured Entisols. In general, the higher content of Zn was observed in the surface horizon and then decreased in the subsurface horizons. However, none of the forms of Zn exhibited any consistent pattern of distribution. Organic matter and size fractions (clay and silt) had a strong influence on the distribution of different forms of Zn. Based upon the linear coefficient of correlation, the soil solution plus exchangeable Zn, adsorbed onto inorganic sites, and DTPA‐Zn increased with increase in organic carbon but decreased with increase in pH and calcium carbonate content. Total Zn increased with increase in clay and silt content. Among the different forms, Zn bound by organic sites, water soluble plus exchangeable Zn and Zn adsorb onto oxide (amorphous surfaces) were all correlated with DTPA extractable Zn. The uptake of Zn was more in recent floodplain Entisols than very fine textured Alfisols and Inceptisols. Among the different forms soil solution +exchangeable and DTPA‐extractable Zn was positively correlated with total uptake of Zn.     

Decomposition and Nutrient Release from Litter Fall in the Semi‐arid Tropics of Sudan

In Sudan, tree plantations remain the first choice and are widely used in protecting arable lands from sand movement. Decomposition and nutrient changes from leaves of some agroforestry trees (Eucalyptus microtheca, Ficus spp., and Leucaena leucocephala) and litter fall from guava (Psidium guajava) and mango (Magnifera indica) were monitored (in a 12‐week litter‐bag experiment). Rate of dry‐matter weight loss from guava (0.098 wk^?1) was significantly (P < 0.01) faster than from mango residues (0.04 wk^?1). Corresponding values for Leucaena, Eucalyptus, and Ficus were 0.0533, 0.0524, and 0.0438 wk^?1, respectively. In general, micronutrients tend to accummulate during a decomposition period. Potassium (K) was the only element found to be consistently lost by leaching very rapidly from all litters. Nitrogen (N) was released at a significantly (P < 0.03) higher rate from Leucaena (0.0558 wk^?1) compared to Ficus (0.0399 wk^?1) and Eucalyptus (0.0301 wk^?1). Mobility of nutrients from the litters was in the order of K > phosphorus (P) = N > calcium (Ca) > magnesium (Mg). It is concluded that ficus and mango leaves are suitable for improving quality of arid soils through buildup of soil organic matter and supplying easily released organic sulfur (S) (environmentally sound management practice) whereas litter from guava is suitable for temporary nutrient correction. Mixing of guava and mango residues may slow fast decomposition of the former.     

Relationship between Soil‐Test Boron and Lentil Yields in the Inland Pacific Northwest

Abstract

Critical soil‐test boron (B) levels and consequent fertilizer recommendations for lentils have been traditionally based on values (0.5 µg/g) developed for alfalfa, sweet clover, and other legumes commonly grown in the inland Pacific Northwest. The purpose of this study was to define the relationship between soil‐test B values and lentil yields. Fifty‐nine field studies using B were conducted between 1980 and 2003 on Mollisols and Alfisols in northern Idaho and eastern Washington. Based on the results of these studies, the critical soil B value for optimum lentil yields is 0.4 µg/g. These studies found that the traditionally used critical soil‐test B values were higher (0.5 µg/g) than needed to achieve optimum yield. Even though this newly established critical B value is lower, about 50% of the soils in the region are too low in B to produce optimum lentil yields.     

Heavy‐Metal Contamination of Soil and Vegetables in Wastewater‐Irrigated Agricultural Soil in a Suburban Area of Hanoi,Vietnam

The To Lich and Kim Nguu Rivers, laden with untreated waste from industrial sources, serve as sources of water for irrigating vegetable farms. The purposes of this study were to identify the impact of wastewater irrigation on the level of heavy metals in the soils and vegetables and to predict their potential mobility and bioavailability. Soil samples were collected from different distances from the canal. The average concentrations of the heavy metals in the soil were in the order zinc (Zn; 204 mg kg^?1) > copper (Cu; 196 mg kg^?1) > chromium (Cr; 175 mg kg^?1) > lead (Pb; 131 mg kg^?1) > nickel (Ni; 60 mg kg^?1) > cadmium (Cd; 4 mg kg^?1). The concentrations of all heavy metals in the study site were much greater than the background level in that area and exceeded the permissible levels of the Vietnamese standards for Cd, Cu, and Pb. The concentrations of Zn, Ni, and Pb in the surface soil decreased with distance from the canal. The results of selective sequential extraction indicated that dominant fractions were oxide, organic, and residual for Ni, Pb, and Zn; organic and oxide for Cr; oxide for Cd; and organic for Cu. Leaching tests for water and acid indicated that the ratio of leached metal concentration to total metal concentration in the soil decreased in the order of Cd > Ni > Cr > Pb > Cu > Zn and in the order of Cd > Ni > Cr > Zn > Cu > Pb for the ethylenediaminetetraaceitc acid (EDTA) treatment. The EDTA treatment gave greater leachability than other treatments for most metal types. By leaching with water and acid, all heavy metals were fully released from the exchangeable fraction, and some heavy metals were fully released from carbonate and oxide fractions. The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in the vegetables exceeded the Vietnamese standards. The transfer coefficients for the metals were in the order of Zn > Ni > Cu > Cd = Cr > Pb.     

Diagnosis of Secondary and Micronutrient Deficiencies and Their Management in Rainfed Agroecosystems: Case Study from Indian Semi‐arid Tropics

Rainfed agriculture in the semi‐arid tropical (SAT) regions of India is greatly influenced by water shortages caused by low, highly variable, and erratic rainfall. However, apart from water shortages, crop productivity in these regions is also affected by low fertility. Little effort has been devoted to diagnosing and managing the nutrient‐related problems in farmers' fields in the SAT regions of India. The ongoing integrated watershed management program by the International Crops Research Institute for the Semi‐arid Tropics and its partners provided the opportunity to diagnose the soil infertility‐related problems by soil testing, develop nutrient management protocols, and determine on‐farm crop responses to fertilization in the SAT zone of India. This article discusses examples from recent research on the diagnosis of multinutrient deficiencies and on‐farm crop responses to fertilization. Results of analyses of soil samples from farmers' fields in several districts of Andhra Pradesh, Karnataka, Tamil Nadu, Rajasthan, and Madhya Pradesh states and Junagarh district, Gujarat, showed that almost all farmers' fields had low organic carbon (C), low to moderate available phosphorus (P), and generally adequate extractable potassium (K). However, the widespread deficiencies of sulfur (S), boron (B), and zinc (Zn) were most revealing; their deficiencies varied with nutrient, district, and state. On‐farm trials conducted during three seasons (2002–2004) in three districts of Andhra Pradesh showed significant yield responses of maize, castor, groundnut, and mung bean to the applications of S, B, and Zn over farmer's input treatment, and the yield responses were larger when these nutrients were added along with nitrogen (N) and P. It is concluded that the deficiencies of nutrients such as S, B, and Zn are widespread and are holding back the potential of rainfed production systems. Clearly, nutrient deficiencies can be diagnosed by soil testing.     

Response of Sunflower to Sources and Levels of Sulfur under Rainfed Semi‐arid Tropical Conditions

Sulfur (S) is one of the severely limited nutrients in rainfed semi‐arid tropical Alfisols. Its application plays an important role in improving the yield and quality of oilseed crops. To identify the optimum level of sulfur for greater yield and oil content in the sunflower crop (MSFH‐8) through suitable sources, a field experiment involving varying levels of S through two sources (gypsum and elemental S) in combination with standard levels of nitrogen (N) and phosphorus (P) was conducted on a sandy loam soil (Typic Haplustalf) at Hayathnagar Research Farm of Central Research Institute for Dryland Agriculture, Hyderabad, situated at an altitude of 515 m above mean sea level and on 78° 36′ E longitude and 17° 18′ N latitude. The response to S application in sunflower crop in terms of growth parameters, yield components, nutrient uptake, and seed oil content was conspicuous. The application of graded levels of sulfur at rates of 20, 40, and 60 kg ha^?1 applied through elemental S significantly increased the seed yield of the sunflower crop over the control by 5.4, 10.7, and 18.1% respectively, whereas the corresponding increases in case of gypsum (CaSO₄·2H₂O) were 25.1, 28.8, and 33.9% respectively. The greatest seed yield of sunflower (1175 kg ha^?1) and percentage oil content (39.7%) was obtained with 60 kg S ha^?1 through gypsum under rainfed conditions. Our study clearly indicated that the application of S at relatively high levels significantly increased the uptake of N, P, and S. The percentage oil content in seed recorded a positive and highly significant relationship with the uptake of N (r = 0.958**), P (r = 0.967**), and S (r = 0.951**), signifying the importance of balanced nutrition in influencing the oil content of seed in sunflower. The application of S through gypsum at rate of 60 kg S ha^?1 along with 40 kg N and 30 kg P₂O₅ ha^?1 was most superior in enhancing the seed yield and percentage oil content in seed.     

Application of Near Infrared Reflectance Spectroscopy for the Assessment of Soil Quality in a Long‐Term Pasture

Abstract

The objective of the present study was to assess the ability of near infrared reflectance spectroscopy (NIRS) to analyze chemical soil properties and to evaluate the effects of different phosphorus (P) and potassium (K) fertilization rates on soil quality in different layers of a long‐term pasture. The NIRS calibrations were developed for humus, total Kjeldahl nitrogen (N_Kjeldahl), and several humic substances (HA1, “mobile” humic acids fraction; ΣHA, sum of humic acids; FA1, “mobile” fulvic acids; ΣFA, sum of fulvic acids, etc.) using soil samples of rather heterogeneous origin, collected during 1999–2003. Different spectral preprocessing and the modified partial least squares (MPLS) regression method were explored to enhance the relation between the spectra and measured soil properties. The equations were employed for the quality prediction of a sod gleyic light loam (Cambisol) in five PK fertilization treatments. The soil was sampled in 2000 and 2003 in three field replicates at depths of 0–10, 10–20, 20–30, and 30–50 cm, n=60 samples yr^?1. The best coefficients of correlation, R², between the reference and NIRS‐predicted data were as follows: for N_Kjeldahl, 0.965; humus, 0.938; HA1, 0.903; HA2, 0.905; HA3, 0.924; ΣHA, 0.904; and FA1, 0.911; and ΣFA, 0.885. Our findings suggest that it is feasible to use NIRS for the assessment of the effects of the inorganic PK fertilizer on the soil quality in different depths of a long‐term pasture.     

Tillage Effects on Soil Quality Indicators and Nematode Abundance in Loessial Soil under Long‐Term No‐Till Production

Abstract: Soil quality indicators and nematode abundance were characterized in a loessial soil under long‐term conservation tillage to evaluate the effects of no‐till, double‐disk, chisel, and moldboard plow treatments. Indicators included soil electrical conductivity (EC), soil texture, soil organic matter (SOM), and total particulate organic matter (tPOM). Nematode abundance was positively correlated with EC, silt content, and total POM and negatively correlated with clay content. Clay content was the main source of variation among soil quality indicators and was negatively correlated with nematode abundance and most indicators. The gain in SOM in the no‐till system amounted to 10887 kg over the 24 years or 454 kg ha^?1 year^?1, about half of this difference (45%) resulting from soil erosion in plowed soils. The balance of gain in SOM with no till (249 kg ha^?1 year^?1) was due to SOM sequestration with no till. No‐till management reduced soil erosion, increased SOM, and enhanced soil physical characteristics.     

Relationship between soil‐test P and K and yield response of runner peanuts to fertilizer

Abstract

Direct fertilization of peanuts (Arachis hypogaeaL.) with P and K has generally shown few yield responses, resulting in only limited information concerning critical soil‐test levels of P and K. The purpose of the experiments in this report was to determine the critical soil‐test levels of P and K for runner peanuts using the double‐acid extraction procedure. Fertilizer experiments were conducted on farmers’ fields from 1973 to 1986. Site selection was based on soil test data that indicated “medium”; or “low”; levels of available P or K but “high”; in Ca and Mg. Phosphorus and potassium were applied together at all sites at rates of 20 and 74 kg/ha, respectively, as concentrated superphosphate and potassium chloride.

There were yield increases to fertilizer in 6 of the 39 experiments. Soil‐test P for these six ranged between 4 and 53 kg/ha; soil‐test K ranged between 10 and 31 kg/ha. Delineating the yield effect into their P and K components with the aid of multiple regressions of yield on soil test values showed that yield increases were due to the K component of the fertilizer. The critical soil‐test K value was calculated to be 37 kg/ha. Sound mature kernels (SMK) were generally unaffected by fertilizer.     

Land‐Use Effects on Soil Nutrient Cycling and Microbial Community Dynamics in the Everglades Agricultural Area,Florida

Soil subsidence has become a critical problem since the onset of drainage of the organic soils in the Everglades Agricultural Area (EAA), which may impair current land uses in the future. The objectives of this study were to characterize soil microbial community‐level physiology profiles, extracellular enzymatic activities, microbial biomass, and nutrient pools for four land uses: sugarcane, turfgrass, pasture, and forest. Long‐term cultivation and management significantly altered the distribution and cycling of nutrients and microbial community composition and activity in the EAA, especially for sugarcane and turf fields. The least‐managed fields under pasture had the lowest microbial biomass and phosphorus (P) levels. Turf and forest had more microbial metabolic diversity than pasture or the most intensively managed sugarcane fields. Land‐use changes from sugarcane cropping to turf increased microbial activity and organic‐matter decomposition rates, indicating that changes from agricultural to urban land uses may further contribute to soil subsidence.     

Depth and Width of the Wetted Zone in a Sandy Soil after Leaching Drip‐Irrigation Events and Implications for Nitrate‐Load Calculation

Abstract

The quantitative assessment of nitrate‐nitrogen (NO₃‐N) leaching below the root zone of vegetable crops grown with plasticulture (called load) may be done using 150‐cm‐deep soil samples divided into five 30‐cm‐long subsamples. The load is then calculated by multiplying the NO₃‐N concentration in each subsample by the volume of soil (width×length×depth, W×L×D) wetted by the drip tape. Length (total L of mulched bed per unit surface) and D (length of the soil subsample) are well known, but W is not. To determine W at different depths, two dye tests were conducted on a 7‐m‐deep Lakeland fine sand using standard 71‐cm‐wide plasticulture beds. Dye tests consisted of irrigation lengths of up to 38 and 60 h, digging transverse sections of the raised beds at set times, and taking measurements of D and W in 30‐cm‐deep increments. Most dye patterns were elliptically elongated. Maximum average depths were similar (118 and 119 cm) for both tests despite differences in irrigation duration and physical proximity of both tests (100 m apart in the same field). Overall, D response (cm, both tests combined) to irrigation volume (V, L/100 m) was quadratic (D_comb.avg=?2×10^?7 V²+0.008 V+34), and W responses (using maximum and mean values at each 30‐cm increment depth, W_max and W_mean, respectively) to D (cm) were linear (W_max=?0.65D+114 and W_mean=?0.42D+79). Predicted W_max were 104, 84, 64, 44, and 25 cm in 30‐cm depth increments. Load calculations using NO₃‐N concentrations of 7.2, 5.0, 3.9, 3.0, and 2.9 µg/kg for the 15, 46, 77, 107, and 137 cm depths, respectively, were 21.2, 37.6, 28.2, and 39.1 kg/ha for W values of 40 cm, bed width (71 cm), W_mean, and W_max, respectively. These load calculations ranged from simple to double based on the choice of W estimate used, which illustrates the importance of knowing W accurately when load is calculated from field measurements. These W_max and W_mean values may be used for load calculations on sandy soils but are likely to overestimate load because they were determined without transpiring plants and may need to be adjusted for different soil types.     

Denitrification activity in the vadose zone beneath a sludge‐amended semi‐arid soil

Abstract

Soil cores were collected to a depth of 14 m from a Southwest semi‐arid soil amended with either anaerobically digested sludge or inorganic fertilizer. Twenty sections partitioned from each core were characterized for their physical and chemical properties. Denitrification potential was estimated in each core section in the laboratory using the acetylene reduction method. The sludge‐amended soil had significantly higher denitrification rates within and below the root zone than the fertilizer‐amended soil. Additionally, significant correlation values were obtained in both cores between denitrification rates and particle size distribution, moisture, and total organic carbon (C). Sludge applications in semi‐desert soils may add much needed organic C in the soil profile. This additional soluble organic C may help control nitrate (NO₃) ground water pollution by providing substrate C for denitrifying bacteria below the root zone.     

The Relationship Between pH Value and Magnetic Susceptibility of Soil——A Case Study of Mountain Red Soil and Red Limestone Soil

通过对昆明西山山原红壤和红色石灰土的pH值和磁化率测试研究发现,山原红壤的pH值在4.0～5.8之间,呈酸性,质量磁化率在56 × 10-8～ 174× 10-8 m3/kg之间,pH值与磁化率呈明显的正相关关系;而红色石灰土pH值在6.0～8.4之间,磁化率为752× 10-8 ～5056×10-8m3/kg,pH值和磁化率呈负相关关系.该研究表明,在我国西南地区,土壤pH值和磁化率既存在明显的负相关关系也存在正相关关系.结合前人在其他地区的研究资料,进一步发现,土壤的酸碱环境可能是决定这些关系的重要因素.     

Can a Single and Unique Cu Soil Quality Standard be Valid for Different Mediterranean Agricultural Soils under an Accumulator Crop?

The validity of the soil quality standard for copper (Cu) established by the Spanish legislation (Spanish Royal Decree 9/2005) is evaluated in representative agricultural Mediterranean soils under an accumulator crop (Lactuca sativa L. var. Romaine cv. Long Green), considering both the effect of the metal on crop growth (biomass production) and its accumulation in the edible part of the plant. For saline soils, such a soil quality standard seems not to be valid taking into account both of the aspects evaluated. For non-saline soils, the soil quality standard also seems not to be valid since, considering the metal accumulation in the edible part of the plant, the soil quality standard should be above such standard; but considering the productivity function of soil (biomass production), the standard should be much below, meaning that this function is being greatly affected by the presence of high concentrations of Cu. The soil quality standard for each soil considered should correspond to a value between its respective EC₅₀ and EC₁₀ values (effective concentrations of added Cu causing 50% and 10% inhibition on the biomass production), depending on the politicians and/or farmers' compromise with yield production and, therefore, with soil productivity. These threshold values were greater for the soil having more organic matter and clay content, showing that Cu toxicity also depends on these properties. Further research in other agricultural areas of the region would improve the basis for proposing adequate soil quality standards as highlighted by the European Thematic Strategy for Soil Protection.     

Relationship between signaling and metabolic pathways of grapevines under temperature and light stresses—a review

Depending on plant genotype–environment interactions, cell signal transduction, and thereby gene expression, disruptive or promotive effects on grapevine physiology, metabolism, and, consequently, fruit quality and yield may occur. This review article aims to evaluate the effects of temperature and light stress on grapevine signaling and metabolic pathways to provide insights into breeding/engineering strategies for designing grapevines with improved quality, yield and tolerance. The modifications of signaling and metabolic pathways are discussed to assist geneticists with designing tolerant grape cultivars with high capacity of producing bioactive compounds and, thereby health-promoting effects in grapevines and humans.