A set of drop size distribution data is presented covering a wide range of sprinkler types including single nozzle impact sprinklers with straight bore and square nozzles, and sprayheads with various types of deflector plates. Drop sizes were measured by the laser-optical method and comparisons with other types of drop size measurement techniques are presented. Distributions are parameterized with an exponential function, and a method is provided to estimate the parameters given the sprinkler type, nozzle size, and pressure head. Keywords. Irrigation, Sprinklers, Drop size. S prinkler irrigation can be defined as any irrigation system which distributes water as discrete droplets through the air. The variety of sprinkler devices available has increased dramatically in recent years, from the conventional single or double nozzle impact sprinkler with many types of nozzles to various types of deflection-plate sprinklers which influence the drop sizes and water distribution patterns over a wide range of flow rates and pressures. Accurate knowledge of drop size distributions for sprinklers is important because evaporation and drift losses are controlled by the extreme small size ranges and drop impact energy on the soil is determined primarily by the largest size ranges. Selection of a specific sprinkler package for a sprinkler system operating on particular soil, slope, crop, and climate conditions will be aided by knowledge of the drop sizes. Several articles have been published describing the drop size distributions of specific types of sprinklers (Kohl, 1974; Kohl and DeBoer, 1984; Solomon et al., 1985; Kohl and DeBoer, 1990). The reported data were collected using pellet, stain, and photographic methods. This article presents additional data using a laser-optical method compared with some distributions determined by some of the previously used methods, so that the entire body of published data is more comparable. The main objective is to parameterize the data and present a method to predict the parameters as a function of nozzle size and pressure.

Kinetic energy contained in water drops as they impact the soil surface affects soil erosion and infiltration processes. Bubenzer and Jones (1971) found that splash of several silt loam soils was approximately proportional to drop kinetic energy to the 1.5 power, and intensity to the 0.5 power. Kinnell (1982) found that, for sand, splash loss per drop varied with the square of the drop mass. Thompson and James (1985) found that the hydraulic resistance of the surface seal formed on a silt loam soil by impacting water drops increased with drop kinetic energy. Mohammed and Kohl (1987) found that infiltration rates on a loam soil decreased more rapidly as water was applied with increased kinetic energy per unit volume. Moldenhauer and Long (1964) found that infiltration rates decreased and soil loss increased as the energy in the applied water increased. Moldenhauer and Kemper (1969) noted how the shearing action of water drops removes soil particles from large clods, causing severe sealing and crusting in depressions on the soil surface. Kincaid et al. (1990) noted how reservoir tillage increases infiltration rates and surface storage initially, but gradually degrades in Article was submitted for publication in May 1995; reviewed and approved for publication by the Soil and Water Div. of ASAE in January 1996. Presented as ASAE Paper No. 93-2103.Trade names and company names are included for the benefit of the reader and do not imply any endorsement or preferential treatment of the product listed by the USDA-Agricultural Research Service.The authors is Dennis C. Kincaid, ASAE Member Engineer, Agricultural Engineer, USDA-Agricultural Research Service, 3793 N 3600 E, Kimberly, ID 83341; effectiveness as water drops impact and degrade the dikes and ridges. Crust formation due to drop impact is also a problem in seedling emergence of crops like sugar beets. These studies point out the importance drop sizes and drop energy on breaking down the soil surface aggregates. Although natural rainfall and crop cover can overshadow the sprinkler drop energy effects on a seasonal basis, in areas where crops are established primarily by irrigation, sprinkler drop energy can be important.Existing sprinkler irrigation technology does not allow us to directly control drop sizes, so therefore, it is important to know the drop characteristics of a variety of sprinkler types in order to make intelligent choices in sprinkler system design. Several articles have been published describing the drop size distributions of specific types of sprinklers (Kohl, 1974;Kohl and DeBoer, 1984;Solomon et al., 1985;Kohl and DeBoer, 1990). Unfortunately, these data were collected using several different types of measurement methods, and some of the data may not be comparable, particularly in the upper and lower ends of the drop size spectra.This article presents sprinkler drop energy calculations using a consistent set of drop size data collected by the laser-optical method (Kincaid et al.,1996). The objective was to determine the kinetic energy (volume ...

A vacuum applied to soil water percolation samplers permits collection of both macro-and matrix-pore liquids. Performance of these field samplers is improved when the extraction vacuum is adjusted in accordance with the tension in the surrounding soil. This is particularly important when monitoring a network of spatially distributed samplers and for samplers installed in medium to fine textured soils. We designed a vacuum extraction system to more efficiently collect vadosezone soil solution samples. A single vacuum pump, vacuum tank, and air dryer provided a vacuum supply for 12 soil water sampling sites via a branching polyethylene pipe network. A vacuum controller containing two inexpensive pressure transducers, a voltage regulator, relay, and solenoid valve was developed and tested for field installation. Data loggers operated the controllers, monitored extraction vacuum and ambient soil water potential, and adjusted relative vacuum at each percolation sampling site. The automated vacuum controllers successfully maintained sampler extraction pressures at levels proportional to ambient soil water potential and provided the added benefit of recording the pressure values for use in subsequent data interpretation.

Center pivot sprinkler irrigation is increasing in popularity in the United States due to the low labor requirement and ability to irrigate large fields. The main problem associated with pivots continues to be the inherently high application rates and tendency for runoff and erosion on medium-and fine-textured soils and rolling topography. Recently developed sprinklers or spray heads can produce high application uniformity with controlled drop sizes and medium sized pattern widths at medium to low pressures. A method is presented to predict the average and peak application rates at any point along a center pivot lateral for a particular type of sprinkler. The method can be incorporated with infiltration and center pivot design models to predict when runoff might occur. A computer program is available to aid in the design process and compare alternative configurations.

Furrow irrigation systems have a greater application capacity, are less costly, and use less energy than sprinkler systems but furrow irrigation produces greater runoff, erosion, and deep percolation losses. Phosphorus (P) and nitrogen (N) losses are associated with runoff sediment, and can be minimized by eliminating irrigationinduced erosion. Excessive leaching of inorganic and organic solutes commonly occurs at the inflow region of furrow irrigated fields where infiltration opportunity times are longer. In one conservation practice, a high molecular weight, anionic polyacrylamide (PAM) is applied to advancing furrow stream flows at a concentration of 10 mg L Ϫ1 . Because PAM stabilizes furrow soil and flocculates suspended sediment, we hypothesized that this treatment would reduce runoff losses of sediment, molybdate reactive P (MRP), total P, NO 3 -N, and chemical oxygen demand (COD). Polyacrylamide treatment may increase furrow infiltration in some soils. However, we hypothesized that because it permits higher initial inflows, PAM would not increase NO 3 -N or Cl leaching rela- www.dekker.comThis article is a U.S. government work, and is not subject to copyright in the United States.tive to conventional, constant inflow irrigation. To test the first hypothesis, all treatments had the same inflow regime. For hypothesis two, control inflows were a constant 15 L min Ϫ1 ; PAM treated inflows were cut back from 45 to 15 L min Ϫ1 after furrow advance. Irrigation runoff and percolation waters were sampled and analyzed. Polyacrylamide increased infiltration and decreased runoff, particularly early in the irrigations. Mean cumulative runoff sediment loss over 12 h was 11.86 kg for each control furrow vs 1.15 kg for PAM-treated furrows. The PAM reduced 12-h cumulative sediment losses in runoff by 90%, MRP by 87%, total P by 92%, and COD by 85%, relative to control furrows. Polyacrylamide had no field-wide, season-long effect on cumulative amounts of water, NO 3 -N or Cl leached. The PAM-technology effectively prevented soil nutrient losses, increased nutrient-use efficiency, and decreased N and P loads in irrigation return flows and receiving surface waters.