Timing of phosphorus fertilizer application within an irrigation cycle for perennial pasture

Irrigated pastures are significant contributors of phosphorus (P) to inland watercourses, with much of the P coming from applied fertilizer. It was hypothesized that the timing of P fertilizer application relative to irrigation regulates P concentrations in runoff and infiltrating water. To test this hypothesis, a two-by-two factorial experiment was conducted on twelve 8- x 30-m border-irrigated bays growing perennial pasture. Phosphorus fertilizer in the form of single superphosphate (44 kg P ha(-1)) was surface-broadcast onto the bays when the nominal change in soil water deficit reached 0 or 50 mm (U.S. Class A pan evaporation minus rainfall). Following fertilizer application, the bays were again irrigated when the nominal soil water deficit between fertilizing and the subsequent irrigation reached either 0 or 50 mm. The volume of water applied, runoff volume, and changes in soil water content were recorded for the three irrigations following fertilizer application. Total phosphorus (TP) and filtrable reactive phosphorus (FRP, <0.45 microm) concentrations in runoff and at depths of 0.1, 0.3, and 0.6 m in the soil were also measured. Soil water content at fertilizer application had less effect on P concentrations in runoff and soil water than the additional time between fertilizing and irrigating. By allowing a deficit of 50 mm between fertilizer application and irrigation, the average concentration of P in runoff and moving below a soil depth of 0.1 m was approximately halved. To maximize fertilizer use efficiency and minimize environmental effects, a delay should occur between applying P fertilizer and irrigating perennial pasture.     

A GROUND WATER RESOURCES STUDY OF A PACIFIC OCEAN ATOLL - TARAWA,GILBERT ISLANDS1

ABSTRACT: The geology and fresh ground water lens development in a typical Pacific atoll are described together with a method for hydrogeological investigation. The fresh water resources of such lenses are investigated using Tarawa as an example. It is shown that simple steady state solutions cannot be realistically applied, and that despite the paucity of hydrogeological data, which is considered typical of such islands, practical nonsteady state solutions allow resource assessments. The susceptability of lens resources to drought conditions is demonstrated.     

Cadmium availability from granulated and bulk-blended phosphate-potassium fertilizers

Recent field experiments have shown that high chloride (Cl) in irrigation waters can increase soil cadmium (Cd) uptake by crops because of the formation of soluble ion-pair complexes of Cd with Cl in soil solution. The present study was aimed at testing a hypothesis that KCl in granulated PK fertilizers may enhance Cd uptake by crops from Cd-containing P fertilizers because of close contact between Cd and Cl in the same granules. Less effect would be expected if the same granular PK fertilizers were bulk-blended because of separation of Cd and Cl in different granules. A single superphosphate (SSP) containing 32 mg Cd kg(-1) was granulated by the compaction process with KCl at a P to K ratio = 1:1. Granular KCl was also bulk-blended with granular SSP or Cd-free monocalcium phosphate (MCP) at the same P to K ratio. An acid Ultisol (pH 5.2) was treated with PK fertilizers at 400 mg kg(-1) each for P and K. Upland rice (Oryza sativa L.) and soybean [Glycine max (L.) Merr.] were grown to maturity, and signalgrass (Brachiaria decumbens Stapf.) was cut four times during the study. The results showed that the agronomic effectiveness in increasing crop yield was the same with SSP and MCP whether granulated or bulk-blended with KCl. Concentrations of Cd in plant tissue samples of all crops were much lower for MCP than for SSP. In all the plant tissue samples, except grain samples of upland rice, Cd concentrations obtained with granulated (SSP + KCl) were significantly higher than that with bulk-blended (SSP) + (KCl).     

Day-of-week patterns in toxic air contaminants in southern California

Day-of-week mean ambient concentrations were computed for six high-cancer-risk toxic air contaminants (TACs): 1,3-butadiene, benzene, acetaldehyde, formaldehyde, carbon tetrachloride (CCl4), and perchloroethylene. Data from six urban sites in southern California, from 1989 through 2001, were analyzed. Graphical displays were used to search for repeated patterns. Benzene and 1,3-butadiene, emitted mainly by mobile sources, exhibit distinctly lower concentrations on Sundays and slightly lower concentrations on Saturdays and Wednesdays. Acetaldehyde and formaldehyde show some trace of a weekly pattern similar to that of benzene and 1,3-butadiene, but the pattern is not strongly marked. Perchloroethylene, used primarily as a dry-cleaning solvent, is also distinctly lower on Sundays. CCl4 does not show a day-of-week pattern.     

A test and refinement of the equity sensitivity construct

This paper reports results from two studies that test a refinement of the equity sensitivity construct first in an experimental setting and second in a field setting. Results from Study 1 show that benevolents express tolerance for both overreward and underreward relative to entitleds and equity sensitives and that benevolents report relatively high levels of satisfaction regardless of reward condition. Study 1 results also show that manipulation of outcomes produce a more dramatic effect on satisfaction than does manipulation of inputs. Results from Study 2 reveal significantly different exchange ideologies for benevolents and entitleds and show that entitleds place more importance on pay whereas benevolents place more importance on the work itself. For both benevolents and entitleds, there is a positive correlation between assessments of distributive justice and job satisfaction. Implication of the findings both for equity theory research and the practice of management are discussed.     

Adsorption, desorption, soil mobility and aqueous persistence of fensulfothion and its sulfide and sulfone metabolites

Soil/water interactions with the insecticide fensulfothion and its sulfide and sulfone metabolites and described. Adsorption to, and desorption from four soils were studied. There was a general inverse relationship between water solubilities of the three chemicals and their adsorption K values. Order of adsorption was f. sulfide greater than f. sulfone greater than fensulfothion. Adsorption K values correlated significantly with soil organic content. Desorption of fensulfothion and the sulfone were similar whereas the less soluble sulfide desorbed to a lesser extent. To facilitate comparison of desorption tendencies of the three compounds of desorption index was developed. Mobilities through the soils were directly related to the water solubilities of the three chemicals. Mobilities in decreasing order were - fensulfothion greater than f. sulfone greater than f. sulfide. Persistence of fensulfothion was similar in both sterile and non-sterile natural water - about 50% remaining at the end of the 16 wk experiment. Under reducing conditions fensulfothion disappeared from water in 8-12 wk with almost complete conversion to the sulfide.     

A method for estimating dietary intake of environmental trace contaminants: Cadmium — a case study

Variations in either food content or dietary habit affect dietary intake of trace contaminants. Trace contaminants enter the human food chain through many environmental pathways, including contamination of water used for drinking or irrigation, sludge used on cropland, fertilizers and other agricultural chemicals, chemicals leached from disposal sites to water, or airborne deposition on soil, water, or crops. A flow chart (Fig. 1) summarizes these pathways.Dietary exposure to environmental trace contaminants places some segments of the U.S. population at substantially higher risk than others. A methodology to calculate population distribution curves for dietary intake of trace contaminants is presented in this report, using cadmium (Cd) as the specific example. This methodology can be applied both to calculate the distribution of daily individual intake of trace contaminants, as well as to estimate the size of the potentially at-risk population. The methodology is developed with both a stochastic approach and a matrix approach. The matrix approach is coded as program SCOPE, and the stochastic as program MONTE.The dietary habits of the U.S. population were determined by using computer codes to analyse and synthesize an array of dietary data. The 15- to 20-yr-old male population was selected for analysis because this group has the largest gram-caloric intake of any age-sex classification. Data from the U.S. Department of Agriculture and the Food and Drug Administration were analyzed to define Cd concentration distribution for 34 food categories, into which 1880 food items were classified. Food consumption frequency histograms were generated with this information, using data synthesis routines and SCOPE.A 1974 FDA survey of metal concentrations in selected foods at 71 U.S. sampling sites yielded tabular, truncated frequency histograms for Cd concentrations in 32 of the food categories studied. Histograms were then constructed by integrating consumption and Cd concentration for each food category for the total diet.The World Health Organization (WHO) recommended in 1972 a tolerable limit of Cd intake of approximately 70 μg per day. A comparison of SCOPE and MONTE total diet Cd intake frequency histograms indicates the likelihood of high Cd intake, at-rick populations. SCOPE results predict that approximately 13% of the 15- to 20-yr-old males studied ingest Cd at a rate greater than 70 μg per day. MONTE predicts that 14%, with a 12–17% range, ingest amounts greater than the WHO-recommended limit on a daily basis. This percentage represents a potential at-risk population. The actual at-risk population would be those persons who consistently ingest more than 70 μg/day.The percentage of the population projected to ingest more than 70 μg of Cd per day needs to be defined by geography, ethnicity, race, and dietary preference in order to fully evaluate Cd intake risks and to set parameters for epidemiological surveys needed for confirmation. Assuming validity for this methodology, there is justification for preventing significant increases in Cd dietary intake by way of man's activities.