摘要:

The Mehlich‐III method used for the determination of available P in 82 Quebec soils was compared to five other chemical methods (Bray‐II, Bray‐I, Mehlich‐II, Mehlich‐I and Olsen) and to two anion exchange resin techniques (F‐and HCO‐3) In general, very good correlations were found between Mehlich‐III, Bray‐II and Bray‐I methods on acid soils (r=0.95** and 0.98**). The Mehlich‐III‐P content is somewhat the same as that determined by Bray‐I and corresponds approximately to 80% of Bray‐II‐P. The Mehlich—III extractant was found to be more reliable than Bray‐II and Bray‐I on very acid spodosols having high P‐sorption capacity. The Bray methods, with high NH4F concentration, extracted strongly fixed Al‐P in these soils and may overestimate the available P. In some acid soils containing apatite and in calcareous soils, the Bray‐II and Mehlich‐I (double acid) easily dissolved these Ca‐P compounds and gave exaggerated high P values. The Mehlich‐III and the other methods were less vigourous for these compounds and were more accurate in estimating available P in these soils. On moderately calcarous soils, the Bray‐I and Mehlich‐I are partially neutralized by the free carbonates in the soil and become less effective in extracting soil P. The Mehlich‐III reactant is more buffered and less affected by carbonates in these soils. The Mehlich‐III and the Mehlich‐II were highly correlated for all soils having diverse properties (r=0.98**) and the amount of P extracted by Mehlich‐III was 117% of that extracted by Mehlich‐II.

ISSN:0010-3624    

DOI:10.1080/00103629009368212

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Mehlich 1‐Ca is used as an index to predict the Ca requirement for peanut (Arachis hypogaeaL.) fruit development in major peanut growing states. Recently, some concern has been raised about the inadequacy of Mehlich 1 extractable Ca for that purpose. Possible use of alternative extractants for soil Ca has been suggested. In this study, relationships among Mehlich 1, 0.2 M NH4Cl and 0.01 M NaNO3extractable Ca were examined in several Coastal Plain soils to which gypsum or lime had been applied. Variability in extractable Ca was much greater following lime treatment than following gypsum treatment. In Bonifay soil, the quantity of Ca extractable by the three extractants was similar in a gypsum treatment, but in a lime treatment (at an application rate equivalent to the gypsum treatment) Mehlich 1‐Ca was 2 and 5‐fold greater than NH4Cl‐ and NaNO3‐Ca, respectively. In Greenville soil, Mehlich 1‐Ca was 3 to 4‐fold greater than NaNO3‐Ca regardless of gypsum or lime amendment.

ISSN:0010-3624    

DOI:10.1080/00103629009368213

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Broccoli (Brassica oleraceavaritalicacv. Premium Crop) plants were germinated in soil, transferred to vermiculite three weeks later and grown in the greenhouse, supplied continuously with boron concentrations ranging from 0.0 to 12.5 mg L‐1. At commercial maturity, the partitioning of nitrogen into soluble (nitrate, ammonium, amino acids) and insoluble components of the foliage (young and old leaves) and the florets was investigated. Both boron deficiency and toxicity increased the per cent soluble nitrogen, particularly as nitrate. Boron toxicity, but not deficiency, consistently affected the concentration and relative composition of amino acids. The actual nitrogen partitioning, including the relative amino acid composition, was dependent upon the developmental stage and of the plant organs, and whether boron was present in deficient or toxic levels. Together with information about the composition of transport fluids from a previous study, the data are interpreted as evidence for a reduction in the availability of carbon under conditions of boron stress.

ISSN:0010-3624    

DOI:10.1080/00103629009368214

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Treble superphosphate (TSP) was applied at 0 and 120 kg P/ha to a highly weathered Oxisol which had received various levels of a sewage sludge 5 years earlier. Lettuce (Lactuca sativaL.) was grown as a test crop.

ISSN:0010-3624    

DOI:10.1080/00103629009368215

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A spectrophotometric method is described for the determination of aluminium in sodium dithionite extracts of soils using catechol violet (CV) at wavelength 585 nm following nitric/sulfuric acid digestion and neutralization. The detection limit is 5 mg/kg Al in soil. Evaluations undertaken were: contributions to blank value of digestion and neutralization reagents; interferences from iron; effects of storage of acid digests; and stability of sodium dithionite extracts. All digest and neutralization reagents contributed to the blank value with lowest values found for ultra‐pure neutralizing reagents. Soil extracts were stable for up to 90 days when stored at 4°C and ‐12°C.

ISSN:0010-3624    

DOI:10.1080/00103629009368216

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The water requirement for corn root expansion growth was studied by directly relating root extension to tissue water potential. Root growth rate was accurately measured over a short period (5–15 min) with a radial variable displacement transformer. Root tissue total and osmotic water potential was then immediately determined with an isopiestic thermocouple psychrometer. Roots experiencing a single water deficit of short duration (0–20 min) exhibited a nearly linear proportional response of growth rate (0 to 1.6 mm hr‐1) to tissue water potential over the range of about ‐1 to ‐10 MPa. Expansion ceased at at ‐10 MPa, defining this as the root's permanent wilting point. Roots experiencing longer periods of water deficit (6–7 hr) also exhibited the linear relationship but their osmotic potentials shifted to lower values in the process (osmoregulated).

ISSN:0010-3624    

DOI:10.1080/00103629009368217

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Fertilizer placement was studied in an extensive series of experiments on sweet corn (Zea maysL.), snapbeans (Phaseolus vulgarisL.), tomatoes (Lycopersicon esculentumMill) and cabbage (Brassica oleraceaL.,Capitatagroup), each at 4–9 production sites in Pennsylvania during 1981–3. Treatments were 1 increment banded or broadcast, 2 increments banded, broadcast, banded/ broadcast or banded/sidedressed, 4 increments broadcast, and a check. Fertilizer increments applied were NP, each at 28 kg/ha (sweet corn and snapbeans) or NPK, each at 56 kg/ha (transplants of tomato and cabbage) as urea, triple superphosphate and muriate of potash. Banding involved a single band 5 cm to the side of seed and 5 cm deep (sweet corn and snapbeans) or double bands 10 cm to each side of plants and 10 cm deep (tomatoes and cabbage). Yields were similar when single increments were banded or broadcast except with cabbage where banded yielded higher. With double increments, banding or combinations involving banding yielded higher than double and at least equal to quadruple increments broadcast. The most efficient treatments were double increments banded for sweet corn, banded/broadcast for tomatoes and banded/sidedressed for snapbeans and cabbage. Leaf N and K were variable with banding and broadcasting. Leaf P was enhanced by banding double increments when compared to broadcasting except with sweet corn. Leaf Ca and Mg were increased by banding over broadcasting with sweet corn and snapbeans. Banding resulted in consistently higher leaf Mn with all crops.

ISSN:0010-3624    

DOI:10.1080/00103629009368218

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A simple and precise method for determination of surface charge density of soils is described. It involves saturating the negative and positive exchange sites with NH+4and NO‐3ions, respectively, removing the excess solution by centrifugation, and determining the ions on the exchange sites by a steam distillation method. Results showed that the concentration and type of saturating ions and the extractant used significantly affected the surface negative charge densities. The average value of surface negative charge densities of 10 surface soils from Iowa, Chile, and Costa Rica by the proposed method agreed closely with that obtained by the original method proposed by Schofield in 1949 (14.6 vs. 13.7 cmol(‐) kg‐1soil). The advantages of the proposed method are no need for the laborious extraction steps and simplicity of the steam distillation method for determination of NH+4and NO‐3in soil samples.

ISSN:0010-3624    

DOI:10.1080/00103629009368219

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Crop response to fertilizer nitrogen (N) is dependent upon tillage management. This study was conducted to determine how tillage rotation influences non‐irrigated crop growth, N uptake and yield. The effects of tillage rotation, N rate and N timing schedule on early season dry matter production and N uptake, ear leaf N concentration at silking, and yield of corn [Zea mays(L.) Pioneer 3378] were investigated at Painter, VA, on an Altavista loam (fine‐loamy, mixed, thermic Aquic Hapludult). In 1986, maximum yields achieved in the 6‐year continuous no till (NT) [5.82 Mg/ha] and first year no till (AT) [5.64 Mg/ha] were significantly greater than that of the 6‐year continuous conventional till (CT) [3.67 Mg/ha], but no yield differences were obtained in the drier 1987 season. A higher rate of N fertilizer was required to obtain maximum yield in the first year no till (168 kg N/ha) than in the NT (112 kg N/ha) during 1986. Early 1986 N uptake and growth response with and without N at planting increased in the order CT < AT = NT and AT < CT < NT, respectively, indicating greatest immobilization of soil N occurred in the newly established no till soil. Lack of differences in critical ear leaf N values developed for NT and CT in each year imply that plant norms developed for one tillage system may accurately assess N status of corn grown under different tillage practices.

ISSN:0010-3624    

DOI:10.1080/00103629009368220

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Nitrogen fertilization and tillage practices may influence the availability and uptake of essential plant nutrients other than N. This study was conducted to assess the interactive effects of N rate and timing and tillage practices on uptake and concentration of P, K, Ca and Mg in corn grown under dryland conditions. Potassium accumulations in no till (NT) soils were greater than in conventional till (CT) near the surface and lower than CT in the subsoil. Phosphorus and Ca levels decreased with soil depth, while Mg tended to accumulate in the subsoil. Phosphorus uptake and concentration of 5‐leaf stage corn was increased as tillage intensity decreased. Nitrogen rate at planting increased 5‐leaf P uptake but reduced P concentration; however, by silking no effect of tillage or N fertilization practice on ear leaf P concentration was obtained. Increases in 5‐leaf corn K uptake and concentration as tillage intensity decreased may have reduced Mg and Ca concentrations via cation antagonism. Ear leaf Mg and Ca concentrations were increased by N rate, probably as a result of solubilization of Ca and Mg and improved crop growth. Distribution of essential elements in the soil due to tillage in combination with varying N fertilization practices can influence temporal nutrient uptake, thereby altering plant nutrient diagnosis.

ISSN:0010-3624    

DOI:10.1080/00103629009368221

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor