An Instrument for in situ Measurements of Soil Moisture Flow and Suction

A soil moisture flux transducer was built and tested in the laboratory under steady-state conditions in a column of Portneuf silt loam soil. Initial data indicate that the instrument may be developed into a useful field research tool. Its principal advantage is that measurements of moisture flow may be made without any prior information concerning the unsaturated hydraulic conductivity of the soil. Rather, one needs to know only a soil moisture convergence factor which is dependent on the state of the soil and the design of the transducer. While this convergence factor is dependent upon the soil moisture content, the dependence appears to be nearly an order of magnitude less than the dependence of hydraulic conductivity on soil moisture content. It may prove possible to develop the unit for installation in the field to provide continuous measurements of the unsaturated soil moisture flow in the tensiometer range with errors no greater than those arising from the natural heterogeneity of the soil

Freezing Point Method

Research in soil-plant water relations during the last two decades has successfully addressed itself to the problems of expressing water status in soils and plant tissues in terms of free energy. The initial impetus was provided by Spanner (1951} in his classical work on the psychrometer. During the ensuing years the science of water relations was provided with a new theoretical approach based on thermodynamic principles and terminology. This was complemented by a substantial amount of research on basic techniques. The result has been a rather sophisticated technology which provides a means of describing the free energy status of water in natural systems in quantitative terms consistent with modern thermodynamic theory. This marks a significant turning point, because now we are capable of expressing the flow of water in the soil-plant continuum in meaningful terms of energy status. The recent comprehensive review by Barrs (1968) cites over 50 references on the use of the Spanner psychrometer and related vapor exchange methods, and a great many other useful references on various techniques for evaluating other aspects of plant water status. However, with this and other reviews (Boyer, 1969; Brown, 19TH; Pack 1968,. 1969; Rawins, 1966) there still appears to be a need for a practical guide on the use of thermocouple psychrometers and other methods of measuring water potential and its components

Punch Planting to Establish Lettuce and Carrots Under Adverse Conditions

It was observed in both the greenhouse and field that lettuce and carrots may be established by planting single seeds in holes punched through the soil crust. When the holes are not back-filled, seeds planted as deep as 60 mm will produce healthy plants in a few days. Preliminary experiments indicate that in some climatic regions a practical field management system could be developed which will eliminate emergence problems arising from soil crusting and premature drying of shallow seedbeds. The open hole punch method may also prove useful in controlling the temperature and salinity adjacent to the seed and in reducing initial tillage and irrigation requirements

Double Cropping Dry Peas and Forage in Southern Idaho

Dry peas grown as a cash crop in southern Idaho are usually harvested by the first of August, which leaves the land bare and unproductive for the last third of the growing season, unless the peas were used as a nurse crop to establish alfalfa. This raises the question: Could August, September and the early part of October be utilized for forage production from plants other than alfalfa

Relations Between CO2 Exchange Rate, CO2 Compensation, and Mesophyll Resistance from a Simple Field Method

An equation is developed that relates apparent photosynthesis to CO? light compensation values, resistance to CO? diffusion in air, and the apparent mesophyll resistance to CO? transport. The equation also yields values for total photosynthesis and light respiration from measurements of apparent photosynthesis. A simple method for measuring leaf CO? exchange rates in the field with a hand-operated syringe is described. Results obtained with this device and data published in recent literature are used with the new equation to show that photosynthesis may be limited more by mesophyll resistance than by photorespiration

Vapor Pressures of an Air-Water Interface During Evaporation

Low evaporation rates from soil caused solutes in the soil solution to accumulate at the air-water interface and reduce the vapor pressure. Nearly tenfold increases in concentration at the interface were observed with ZnSO? in a cool moist soil. CaCll?, AICI?, sucrose, and hexadecanol accumulated to lesser degrees, depending on the evaporation rate and the temperature. The small amount of water movement required to develop this increase suggests the phenomena may also occur next to semipermeable membranes, such as plant roots

Experimental Measurements of Soil-Moisture Hysteresis and Entrapped Air

A moisture-release curve may be determined by removing, stepwise, increments of water and measuring the steady-state soil-moisture suction that develops. A soil-moisture-adsorption curve may be determined in the same way, except that increments of water are allowed to enter the sample. The failure of these two curves to coincide is commonly known as soil-moisture hysteresis (see, for example, figs. 3 to 6)

Potato Tubers and Soil Aeration

Potato plants are more sensitive to soil oxygen stress than many other common crops. Some recent literature suggests this may be due to a relatively high oxygen requirement for tuber growth, rather than a greater requirement for the roots per se. Consequently, the oxygen consumption of growing potato tubers (Solanum tuberosum cv. Russet Burbank) was measured in the field on a Portneuf silt loam (coarse-silty, mixed, mask Durixerallic Calciorthid). Typical rates were 15 µg O2 cm-2 hr-1. A simple method for measuring soil oxygen diffusion rates in the laboratory was then devised, utilizing an oxygen meter and a stream of N2 gas. Soil conditions such as texture, bulk density, compaction around expanding tubers, oxygen sinks and water contents were studied with respect to their relative effects on limiting oxygen uptake by tubers. The minimum soil oxygen diffusion coefficient required for adequate tuber aeration is quite sensitive to the soil respiration rate and the depth of soil covering the tubers. Water contents of "field capacity" or a little wetter were found to not necessarily inhibit tuber aeration in loamy sand, silt loam, and silty clay soils provided the bulk densities were not excessive; i.e., greater than 1.6 or 1.7 Mg m-3 in the silt loam. Reduced aeration due to compaction around growing tubers is a possibility in the silty clay, but probably not in well drained silt loam or loamy sand. The criteria for a minimum acceptable soil oxygen diffusion coefficient must be based on tuber periderm permeability, soil ethylene generation, and other anaerobic soil reactions, as well as tuber respiration per se

Here's How Frost Damages Seedlings

HOW MANY TIMES have you stepped out in your field or garden after a cold night and seen a row of beans or tomatoes with wilted, black, and dead seedlings intermingled with plants that show no sign of frost damage? Do freezing temperatures really vary that much in the row, or are some seedlings more frost resistant; and if so, why don't agronomists select these plants and develop new varieties? Direct answers to questions like these are not simple, but we are beginning to understand why frost affects tender seedlings in a variety of different ways

Irrigating Row Crops from Sod Furrows to Reduce Erosion

Kentucky bluegrass (Poa pratensis L.) sod furrows were established to stabilize the soil. The furrows were used to irrigate corn (Zea mays L.), wheat (Triticum aestivum L.), barley (Hordeum vulgaris L.), beans (Phaseolus vulgaris L.), and sugar beets (Beta vulgaris L.). The sod strips containing the furrows were 0.3-m wide and managed as a permanent living entity. A strip mowing machine and a miniature rotary ditcher were developed to maintain the sod furrows. Crops were grown in clean tilled strips 0.9-m wide between the sod strips. Normal use of fertilizer, herbicides, and cultivation was utilized for the crop rows in the clean tilled strips. This management system eliminated soil erosion, at least doubled the infiltration rate of irrigation water, and allowed the production of satisfactory yields of wheat, barley, dry beans, and corn for silage. Sugar beet production was unacceptable due to competition from the sod