All Issues

The question of herbicide residues, and possible effects on succeeding crops, is one of great importance to agriculture, particularly with increasing use of such chemicals to minimize hand labor requirements as well as soil compaction from weed cultivation equipment. This study, involving tests with 13 herbicides, used under typical field conditions at six locations in California, showed great differences in residual characteristics. At high rates (approaching four times the amounts normally used for weed control), simazine, bromacil, and trifluralin caused soil residue problems. Location of the tests also affected the amounts of residue for different herbicides.

Greenchopping forage requires the frequent use of heavy equipment including tractors, choppers, and bank-out wagons—operating in fields that may vary from rather dry to quite wet. Such equipment may weigh from 16,000 lbs empty to nearly 25,000 lbs loaded, and this weight is unequally distributed among many wheels. The width of cut of the chopper, the axle widths of all units, and the positions of hitches determine the area of stubble run over by the wheels in successive rounds during field harvesting. Tests with typical greenchop equipment indicated that up to 80 per cent of the ground area was run over by wheels. Some wheels exactly track the preceding wheels and others partially cover areas run over in previous harvest rounds— thus there is no uniform wheel load treatment applied to the crop stubble or ground surface.

1. Results of field experiments indicate that it is more efficient and effective to apply nitrogen to the crop than to previous crop residues months ahead of planting the crop. 2. The increase in water infiltration rate resulting from various green manures or crop residues was inversely related to the nitrogen content at the time of incorporation. Low-nitrogen residues had a longer-lasting effect than legumes or other high-nitrogen residues. 3. The beneficial effect of barley crop residues on infiltration was significantly reduced by nitrogen application to the residue. 4. Addition of straw, along with fertilizer nitrogen, greatly reduced the uptake of fertilizer nitrogen by the succeeding crops. 5. The time required for cycling fertilizer nitrogen through the soil organic fraction and back into available form apparently involves a matter of years, or perhaps decades, rather than weeks or months. 6. Fine shredding and early incorporation of crop residues into a moist soil are key factors in handling residues to avoid interference with planting operations.

Harland Barley, a new population-variety available in 1968 in California, offers definite (and continuing) yield advantages over other feed barleys in commercial use. The new barley is the result of a 40-year breeding program at the Davis campus of the University of California. It shows yield advantages not only over Atlas barley, the traditional standard of comparison, but also over all of its own ancestors. Harland barley was named in acknowledgment of two of its co-developers, H. V. Harian and Harland Stevens. It is a product of joint research of the University and the Agricultural Research Service of the U. S. Department of Agriculture.

No evidence was found in these tests of real differences in performance between clay, concrete, or bituminous-fiber tiles. Differences in tile outflow were due primarily to soil variation and not to tile performance. Little actual change in salinity resulted from the leaching operation in the body of soil between the tiles. In most cases as much, and often more, water was lost through seepage as was removed by the tile. Much of the water which moved through the soil followed the disturbed trench above the tile, as evidenced by the much lower salinity in that trench. Electrical conductivity of the tile effluent was inversely related to both rate and duration of tile flow. Each tile showed a unique relationship between electrical conductivity, rate, and duration of flow—probably a reflection of a unique combination of hydraulic conductivities along each tile line.

Cytology (the branch of biology dealing with studies of cell structure and function under the microscope) is important to both plant and animal scientists, because cytological studies disclose useful information on cell organization and behavior under both normal and artificially induced conditions. Plant physiologists in the Department of Horticultural Science, Riverside, are actively engaged in research on herbicides, with special emphasis on selective elimination of weeds from plantings of crop plants. In some experiments, the effects of herbicides become immediately apparent in either the weeds or the crop plants, or in both. In other experiments, damage to both weeds and crop plants remains concealed for a long time before it becomes evident. Such variable and often unpredictable behavior explains the interest of weed control physiologists in the mode of action of selective herbicides upon the species under study. One of the more promising approaches to mode-of-action studies is the cytological examination of herbicidal effects upon individual cells, especially dividing cells in root tissues.

A severe leaf yellowing, or chlorosis problem, has occurred in chrysanthemums at several commercial greenhouses in the San Francisco Bay Area. The disorder was found to be magnesium deficiency caused by high annual applications of potassium. Magnesium fertilization, even at high rates, was not effective in correcting the problem. Elimination of potassium fertilization gave immediate control.

It appears that phosphorus deficiency in plants drastically affects the ability of leaf stomata to open universally in all plant species, but in varying degrees. Failure of the stomata to open results in greatly decreased water use, and in elevated leaf temperatures. These studies indicate that the increased temperature is the cause of at least some phosphorus-deficiency symptoms.