Nitrate-Nitrogen Leached Below the Root Zone During and Following Alfalfa

The nitrate-nitrogen (NO?-N) contribution to subsurface drainage water by irrigated alfalfa (Medicago sativa L.) in crop rotations was evaluated by measuring the soil water flux and NO?-N concentration below the root zone of alfalfa and crops following alfalfa with and without additional nitrogen fertilization. Under alfalfa grown on Portneuf silt loam (Durixerollic Calciorthid) with a permeable hardpan, 44 kg NO?-N ha-1 year-1 moved below the root zone at concentrations between 3 and 15 ppm. During the growing season following alfalfa, 85-96 kg NO?-N ha-1 year-1 moved below the root zone under nonfertilized bean (Phaseolus vulgaris) crops at concentrations between 1 and 83 ppm. The second growing season after alfalfa, 17-29 kg NO?-N ha-1 year-1 at 3-15 ppm NO?-N moved below the root zone of nonfertilized bean and wheat (Triticum aestivum L.) crops. A field planted to corn (Zea mays L.) and fertilized with 200 and 170 kg N ha-1 the first and second year after alfalfa lost 153 and 108 kg NO?-N ha-1, respectively, from leaching. Leachate N concentrations varied from 1 to 64 ppm. Unfertilized corn lost 60 and 17 kg NO?-N/ha the first and second year after alfalfa, respectively, at leachate concentrations of 1-31 ppm. The NO?-N concentration in the soil solution below only slightly permeable hardpan areas was between 13 and 67 ppm, but only 10-23 kg ha-1 year-1 moved below the root zone because of the lower water flux through the hardpan. Comparing these results with previous data for the same area suggests that considerable denitrification and/or dilution takes place at the water table interface since 5.2 ppm NO?-N was the highest concentration measured in the subsurface drainage water with an average of 3.2 ppm NO?-N. The NO?-N contributed by alfalfa in the crop rotation was estimated to equal just half of that accounted for in the subsurface drainage in a previous study on the same irrigated trac

Conservation and Use of Sediment in Irrigation Runoff

CONTROLLING sediment entering natural streams in irrigation return flow is a major economic and ecological challenge. A landowner often has little control over the management practices of his upstream neighbors. But he may be able to use sediment from runoff draining onto his land to improve the land's topography. In so doing he may reduce erosion on his land and simultaneously lower the downstream sediment load

Selectivity Coefficients for Calcium-Magnesium-Sodium-Potassium Exchange in Eight Soils

The six selectivity coefficients for simultaneous Ca-Mg-Na-K exchange were calculated from soil extract cation activities and exchangeable cation concentrations for eight salt affected soils. These values were compared with selectivity coefficients calculated from solution cation concentrations and the exchangeable cations for the same soil samples. The lyotropic series for these soils in order of replaceability ease was Na ? Mg > Ca > K, whereas the generally accepted series is Na > K > Mg > Ca. The selectivity coefficient values varied between soils, but did not vary with depth in each soil. Potassium exchange selectivity coefficients have not previously been available for use in exchange models and are reported here for eight soils With these data, models can include K exchange in high K soils and soils irrigated with high K waters. Exchangeable sodium percentage (ESP) can be calculated on a programmable hand-held calculator for a soil using the chemical data and these selectivity coefficients. All ionic strength and ion pair corrections and selectivity calculations for this study were carried out on a programmable hand-held calculator

Selenium Concentrations in Phosphorus Fertilizer Materials and Associated Uptake by Plants

The Se concentration of seven Florida Land Pebble deposit phosphate rocks ranged from 0.7-7.0 ppm. The range was 1.4-1.78 ppm Se in seven samples from the western phosphate field. The Meade Peak phosphatic shale member of the Phosphoria formation contains more Se than rock from other phosphatic formations. Normal and concentrated superphosphates made from phosphatic rocks containing 100 ppm Se can be expected to contain about 60 and 40 ppm Se, respectively. Laboratory-prepared concentrated superphosphate containing 23 ppm Se applied to an alkaline soil that normally produced alfalfa (Medicago sativa L.) low in Se at a rate of 156 ppm P increased Se concentration in alfalfa above the minimal requirements to protect livestock from white muscle disease. Concentrated superphosphate and single superphosphate prepared from phosphate rock containing 178 ppm Se and applied at a rate of 80 ppm P increased the Se concentration in alfalfa compared to the same amount of P applied as Se free concentrated superphosphate. Normal phosphate fertilizer practices can provide required Se for livestock provided the fertilizer is prepared from phosphate rock containing sufficient Se

Salt Outflows from New and Old Irrigated Lands

Three water application treatments with low salt water were applied to previously nonirrigated soil and to a similar soil which had been irrigated for 67 years. The total soluble salt content of these soils initially, and after one and two seasons of treatment, was measured to determine salt outflow. Residual soluble salts were essentially removed from the previously nonirrigated soil after 30 cm of water/m depth of soil had passed from the soil as leachate, regardless of the number of sea/ions required for that amount of leaching. The total quantity of residual salt removed from soil 5 m deep was 70 metric tons/ha, with about 38 metric tons/ha being leached out by the first 14 cm of leachate. After the residual salt was removed, the salt content of the newly irrigated soil was the same as that of the soil which had been irrigated for 67 years. Subsequent salt outflow from the soil was directly related to the quantity of water leaching through the soil, indicating that more minerals dissolved with more leaching. Soils irrigated for many years and then not irrigated for up to 10 years had no measurable reaccumulation of soluble salts during the period of nonirrigation. Results of these investigations provide a basis for estimating salt outflows from newly developed and old irrigated lands, and for assessing the impact of these salts on surface and groundwater supplies

The statistics of single molecule detection: An overview

An overview of our recent results in modeling single molecule detection in fluid flow is presented. Our mathematical approach is based on a path integral representation. The model accounts for all experimental details, such as light collection, laser excitation, hydrodynamics and diffusion, and molecular photophysics. Special attention is paid to multiple molecule crossings through the detection volume. Numerical realization of the theory is discussed. Measurements of burst size distributions in single B-phycoerythrin molecule detection experiments are presented and compared with theoretical predictions

Water Soluble NO3-Nitrogen, PO4-Phosphorus, and Total Salt Balanced on a Large Irrigation Tract

Return flow from a 82,030-ha (202,700-acre) tract of calcareous silt loam soils irrigated with water diverted from the Snake River in southern Idaho increased the downstream total soluble salt and NO?-N loads, but decreased the downstream PO?-P load. Under the existing water management practice, 50% of the total input water returned to the Snake River as subsurface drainage. Net total soluble salt output was 2.4 metric tons/ha (1.0 English ton/acre) and, on the average, was considerably greater than necessary to maintain a salt balance. Net NO?-N output was 33 kg/ha (30 lb/acre). Only about 30% as much PO?-P left the tract via drainage water as entered the tract in irrigation water. As water passed through the soil, PO?-P was removed by chemical reactions in the soil, thus decreasing the concentration in the subsurface drainage water and decreasing the downstream PO?-P load. Applied P fertilizer was not leached into the drainage water

Effect of Phosphorus Fertilization on the Selenium Concentration in Alfalfa (Medicago sativa)

A study was conducted to determine the effect of P fertilization on the Se concentration in alfalfa. Adding P to the soil increased the Se concentration in alfalfa grown in the greenhouse on six of 14 soils from the northwestern United States. The Se concentration increase in alfalfa resulting from P addition was noted on some alkaline and some acid soils. Phosphorus addition increased the availability to alfalfa of both native and applied Se in the Portneuf silt loam. Applying 160 kg P/ha either as H?PO? or concentrated superphosphate to Gooding sandy loam in the field increased the Se concentration in alfalfa from a level marginal for animal requirements to an adequate level

Total Salt, Specific Ion, and Fertilizer Element Concentrations and Balances in the Irrigation and Drainage Waters of the Twin Falls Tract in Southern Idaho

Public interest in environmental quality has aroused concern and speculation about the effects of irrigation and the application of fertilizers on the quality of surface and ground waters. The Environmental Pollution Panel of the President's Science Advisory Committee, and other groups, have recommended that high priority be given to investigating the sources of total salts, specific ions, and nutrients that enter surface and ground waters. One source is drainage from irrigated areas or irrigation return flows. More information is needed about the quality of irrigation return flows under various management systems and climatic environments and on representative soil types. Such information is basic for determining practices to improve the quality of return flows and in planning new irrigation projects. The NO?-N, PO?-P, and total salt concentrations were measured in irrigation and drainage waters on the Twin Falls Canal Company irrigation tract in southern Idaho. This information was combined with a water balance to estimate input-output balances for these components, and results have been reported. The input-output balances for other specific ionic components have been computed for the irrigation and drainage waters of that tract. Results from these investigations and detailed information on specific ion concentrations, temperature and flow characteristics of drainage tunnels, tile-relief well complexes, and large surface drains are reported herein

Selenium Concentrations in Alfalfa from Several Sources Applied to a Low Selenium, Alkaline Soil

Two laboratory-prepared ferric hydroxy bi-selenites and CuSeO? applied to Portneuf silt ham in the field provided slowly available Se to alfalfa, resulting in Se concentration adequate but nontoxic for livestock. These materials have potential as Se fertilizers at low application rates. The ferric hydroxy bi-selenites offer little or no advantage over CuSeO?. Se from BaSeO? alone, BaSeO?—BaSO? mixtures, and CuSeO? was absorbed by alfalfa in concentrations toxic to livestock. A small fraction of applied elemental Se was available immediately after application, providing adequate Se to alfalfa for livestock. The remaining elemental Se was rather inert, and supplies only slightly more Se to alfalfa than did the untreated soil the year following application