Methods of measuring available nutrients in West Indian soils

Summary Methods of measuring available N have been compared using response and uptake data from maize grown on 155 West Indian soils in greenhouse experiments. Total soil N and Cornfield's alkaline hydrolysable N gave best estimates of available N when all soils were considered together. Correlations between test data and N uptake were best for acid soils, for soils with large cation exchange capacities and for soils with between 80 and 99 per cent base saturation. Differences between correlations for soils from different islands could usually be related to these soil properties.     

Methods of measuring available nutrients in West Indian soils

Summary Total K, exchangeable K (NH₄OAc method), CH₃COOH, cold H₂SO₄ and boiling HNO₃ extractable K were compared with dry matter yield response and K uptake from maize grown on 155 Commonwealth Caribbean soils in greenhouse experiments.Correlation coefficients for soil test values with percentage yield and K uptake were calculated using data from all the soils together and also when the soils were grouped according to pH (< 5.5, 5.5–7.0 and > 7.0), per cent base saturation (< 60, 60–79, 80–99 and 100 per cent), cation exchange capacity (< 10, 10–30 and > 30 me per 100 g) and texture (clays, clay loams and loams and sands). In general, correlations of soil test value with K uptake were superior to those with percentage yield. Total K gave no significant correlations in any of the comparisons. The NH₄OAc (exchangeable K) and cold H₂SO₄ were the most successful methods overall and the least sensitive to changes in soil properties. The CH₃COOH extract in general was the least effective. The differing behaviour and the ability of the methods to extract K is discussed in relation to the mineralogy and genesis of the soils which make up the various groups when divided according to the soil properties listed above.     

Chlorophyll compounds and nitrogen availability in West Indian soils

Summary The amounts of chlorophyll-type compounds extracted by 90 per cent aqueous acetone from 70 West Indian soils were inversely correlated with soil pH; chlorophyll compounds decomposed when soils were limed to pH 7. Chlorophyll compounds were only significantly correlated with nitrogen used by maize in pot experiments and with mineralizable nitrogen for soils in the pH 5.0 to 5.9 range. Chlorophyll may persist in acid soils because micro-organisms are less active or because the chlorophyll molecule is altered, possibly by the isomorphus replacement of magnesium by reduced iron or manganese.     

Arsenic affects mineral nutrients in grains of various Indian rice (Oryza sativa L.) genotypes grown on arsenic-contaminated soils of West Bengal

The exposure of paddy fields to arsenic (As) through groundwater irrigation is a serious concern that may not only lead to As accumulation to unacceptable levels but also interfere with mineral nutrients in rice grains. In the present field study, profiling of the mineral nutrients (iron (Fe), phosphorous, zinc, and selenium (Se)) was done in various rice genotypes with respect to As accumulation. A significant genotypic variation was observed in elemental retention on root Fe plaque and their accumulation in various plant parts including grains, specific As uptake (29–167 mg kg^?1 dw), as well as As transfer factor (4–45%). Grains retained the least level of As (0.7–3%) with inorganic As species being the dominant forms, while organic As species, viz., dimethylarsinic acid and monomethylarsonic acid, were non-detectable. In all tested varieties, the level of Se was low (0.05–0.12 mg kg^?1 dw), whereas that of As was high (0.4–1.68 mg kg^?1 dw), considering their safe/recommended daily intake limits, which may not warrant their human consumption. Hence, their utilization may increase the risk of arsenicosis, when grown in As-contaminated areas.     

Methods for measuring amounts of energy available from banksia inflorescences

Several methods have been used to remove nectar from banksia inflorescences to measure amounts of energy available, but these methods have been poorly described in the literature. Each method has advantages and disadvantages with respect to the proportion of nectar removed and the time taken to remove nectar. Power-driven aspirators probably remove the most nectar, followed by syringes and capillary tubes. However, it often takes more than 20 min to sample an inflorescence using these methods. Centrifuging inflorescences by placing them in plastic bags and swinging them by hand on a rope takes only about 5 min anil allows many more inflorescences to be sampled per time. Centrifuging. however, removes only about 70% of the nectar so that the benefits gained by faster sampling are countered by reduction in accuracy. Nevertheless, amounts of nectar extracted by centrifuging provide a reliable index of the amounts present, and so it is possible to make Qualitative comparisons of inflorescences sampled at different times, from different locations, or from different experimental treatments.     

土壤速效养分空间变异的尺度效应

在GIS技术支持下,运用经典统计学和地统计学的方法,从经典统计分析、变异函数和Kriging插值图等方面探讨了禹城市耕地土壤速效磷(AP)、速效钾(AK)在县级和镇级两个不同采样尺度下的空间变异特征.结果表明:在两个采样尺度下,AP、AK都服从对数正态分布,它们的变异系数范围为26.5%～36.6%,均属中等变异强度,随着采样尺度的缩小,土壤AP、AK的变异系数都增大.两个采样尺度下,土壤AP和AK均在一定范围内存在空间相关关系,县级采样尺度下土壤AP和AK的空间自相关距离较大,分别为9.0 km和26.5 km,镇级采样尺度下土壤AP和AK的空间自相关距离明显变小,分别为1.7 km和2.8 km.两个采样尺度下的土壤AP和AK受结构性因素和随机性因素的影响,表现出明显不同的分布规律.     

On available forms of chemical compounds in soils

Different methods are used to study available forms of chemical compounds in soils. The sequential extraction method is described in detail. Also, a comparative overview is given of the most frequently extracted fractions of chemical elements (water-soluble, exchangeable, specifically sorbed, carbonate, bonded to organics, Fe and Mn oxides/hydroxides, and aluminosilicates), as well as of relevant extractants. Advantages and disadvantages of various extractants are discussed, and ways to improve their selectivity are proposed. It is also shown that the content of available forms of chemical compounds in soil can be used for estimating the extent of industrial soil pollution.     

Method of measuring invertase activity in soils

Summary Invertase (-D-fructofuranoside fructohydrolase, EC [Enzyme Commission] 3.2.1.26) is the enzyme that catalyzes the hydrolysis of sucrose and yields glucose and fructose. The activity of this enzyme was monitored by systematically developing a sensitive and rapid method to detect reducing sugars with the precision of 1.4 to 6.1% C.V. The method involves the colorimetric determination of reducing sugars which react with 3,5-dinitrosalicylic acid when soil is incubated with buffered sucrose solution and toluene at 37°C for 24 h. The detection limit for the method described is 100 g of reducing sugar per ml of soil extract. The color intensity remained constant up to 24 h. Comparative studies showed that the method described was in good agreement to other invertase assay procedures reported in the literature.Studies on the stability and distribution of invertase in soils by using the method described showed that air-drying of field-moist soil samples resulted in decreased activity ranging from 15.3 to 23.7% (avg.=19.8%). Statistical analyses indicated that invertase activity was significantly correlated with total N (r=0.78^***) and organic C (r=0.70^***) in the topsoil of 19 diverse samples. There was no significant correlation between invertase activity and soil pH, cation exchange capacity, percentage of clay and percentage of sand. The activity of this enzyme was concentrated in surface soils and decreased with profile depth. Regression analyses showed that invertase activity was significantly correlated with organic carbon content of three soil profiles examined.     

Chemical methods of estimating plant available manganese in soils

Summary Twelve different chemical extraction procedures for extracting soil manganese were used. Soil test values determined for fourteen representative soil samples of Rajasthan State with manganese uptake by six crop species have shown that of the extractants used, 3N ammonium dihydrogen orthophosphate can be best used for estimating plant available soil manganese.     

Evaluation of suitable extractant for available lead in soils

Summary Four extractants were used to extract Soil-Pb from alluvial soils and the amounts of Pb extracted was correlated with Pb concentration in wheat crop. Of all the reagents, the Grigg's reagent was found to extract maximum amount of Pb from soils and the N NH₄OAc the least. A highly significant correlation (r=0.295) was observed between Grigg's reagent extractable Pb and Pb concentration in wheat plants followed by ammonium acetate (r=0.238). While 0.02M EDTA did not show any significant correlation, a negative significant correlation was observed with 0.1N HCl. re]19750512     

Effects of prescribed burning on plant available nutrients in dry heathland ecosystems

Heathland management is an important tool with which to modify ecosystem impacts caused by atmospheric nutrient deposition. Since changes in nutrient availability as a result of management measures affect the outcomes of heathland succession and species competition, studies on this issue are important from both a nature conservation and management point of view. This study reports the effects of prescribed burning on nutrient availability in dry heathland soils and the nutrient content of the two competing heathland species Calluna vulgaris and Deschampsia flexuosa, with particular reference to N and P. We hypothesise that winter prescribed burning leads to additional N availability, which enhances the importance of P in the context of nutrient limitation in heathland ecosystems. In the nature reserve “Lueneburg Heath” (NW Germany) we examined the availability of nutrients in the humus horizons and in the leachate as well as the relevant C:element ratios in Calluna and Deschampsia before and after a burning experiment. Our results show that prescribed burning resulted in drastically increased NH₄⁺ availability in the O-horizon. We observed only short-term effects (for NO₃⁻, PO₄³⁻, Mg) and insignificant effects on the availability of other nutrients (K, Ca). As a consequence of an increased nutrient availability in the humus horizons and a limited nutrient uptake by plants after burning, leaching increased significantly for N, Ca, K, and Mg after burning treatment. No significant changes were found in the foliar C:N ratios for either species after prescribed burning, although Deschampsia showed an increased deficiency for all the other nutrients, particularly for P, as expressed by increased foliar C:P and N:P ratios. By contrast, the nutrient content of Calluna did not change significantly, suggesting that prescribed burning favours the competitive capacity of Calluna as against Deschampsia. We assume that water shortage as a result of changes in the microclimate was mainly responsible for the deterioration of the nutrient content of Deschampsia. This gives Calluna a competitive advantage, enabling it to out-compete Deschampsia on burned heathlands, with respect to the key factor P-limitation.     

Measurement of available phosphate content of some Spanish soils

Summary Eight Spanish and seven English soils were used to examine methods of determining available soil phosphate. The reference value for the amount of phosphate available was that taken up by six successive cuts of ryegrass grown in a pot experiment.The L-value had the best overall correlation (r=0.94) but is a lengthy determination. Its laboratory analogue, the E-value, was more rapid and equivalent, with the exception of high-clay soils where it gave anomalous values. An anion-exchange resin technique was most suitable for routine measurement and predicted available phosphate (r=0.88) satisfactorily. re]19730122     

Spatio-temporal patterns of soil available nutrients following experimental disturbance in a pine forest

Although disturbance is known to alter soil nutrient heterogeneity, it remains unclear whether spatial patterns in soil nutrients after disturbance follow predictable temporal changes that reflect underlying processes. This study examined the effects of tree harvesting and girdling on overall variability, geostatistical patterns, and resource congruence of soil available nutrients in a mature Pinus elliottii Engelm. forest. The two disturbances led to different patterns of vegetation removal, forest floor redistribution, and revegetation, but showed similar post-disturbance changes in overall soil nutrient variability. Soil nutrient variability increased after both disturbances by more than 5-fold, and then decreased, returning to the undisturbed level in 4 years. Spatial structures assessed using geostatistics did not show predictable temporal trends. However, girdled plots showed more persistent spatial structures in soil nutrients than harvested plots, and had semivariogram ranges mostly equal to or less than 10 m, reflecting effects of persistent and spatially stable patches of undisturbed hardwoods that had an average patch size of 10 m. Resource congruence examined with Spearman rank correlations was nil before disturbance, increased after disturbance and then became nil again by the 4th year post-disturbance. The timing of the increase was related to treatment, occurring in the 1st year after disturbance in the girdled plots, but not until the 2nd year in the harvested plots. These two patterns of congruence were potentially caused by different rates of nutrient patch formation and resource uptake by plants during early succession. Although temporal changes in soil heterogeneity have been documented previously, the present study indicates that temporal trends in nutrient variability after disturbance may be predictable, and that the marked changes in spatio-temporal patterns of soil nutrients as a result of disturbance are ephemeral.Electronic Supplementary Material Supplementary material is available in the online version of this article at     

Occurrence and distribution of rhizobiophages in Indian soils.

Soil samples from 30 fields in neighbouring districts of Varanasi were screened for rhizobiophages on 60 Rhizobium strains. Plaques were observed on five strains: P1, P5, SU391 (R. leguminosarum), CB756 and 32H1 (Rhizobium sp.). Rhizobiophages infective on one or more of the five strains were present in all fields. There seems to be no correlation between presence of phage and the standing crop or the pH (7.1-8.2) of the soil. Eight distinct rhizobiophages have been isolated and characterized for host specificity, plaque morphology and maximum titer in broth.