California Agriculture, July-August 1994
Volume 48, Number 4
Clearing the air: agriculture and air pollution
peer-reviewed research articles
Studv demonstrates ozone uptake by SJV crops
by David A. Grantz , J. Ian MacPherson , William J. Massman , James Pederson
The California Ozone Deposition Experiment, using Instruments mounted In an airplane and on the ground, shows that agricultural land in the San Joaquin Vailey removes large amounts of ozone from valley air. The most active pathway Is uptake through sto-mata In plant leaves, the process leading to crop yield losses. Other pathways, Including ozone destruction on leaf, stem and soil surfaces, are slower but very important on a valley-wide basis. Ozone deposition to crops may have a slgnlflcant Impact on air qualify, and should be considered when farmland Is converted to urban uses that contribute more to ozone production and less to ozone removal.
Early irrigation cutoff has little effect on French prune production
by David A. Goldhamer , G. Steven Sibbett , Rebecca C. Phene , Donald G. Katayama
In a 4-year study conducted on a deep, well-drained soil, irrigation cutoffs ranging from 12 to 45 days before harvest had only minor effects on prune production. Soluble solids tended to be higher and dry ratios lower with early cutoffs. There were no differences in fruit drop. It appears that prune trees are relatively tolerant of moderate to severe water stress for several weeks before harvest.
Early harvest prevents internal browning in Asian pears
by Carlos H. Crisosto , David Garner , Gayle M. Crisosto , G. Steven Sibbett , Kevin R. Day
Brown discoloration of the core, carpels and flesh of ‘Ya Li’ and ‘Seuri’ Chinese pears during storage depends on harvest date, not storage temperature. In this trial, fruit harvested no later than 180 days after full bloom showed no signs of browning. Browning occurred only in fruit that had been harvested when skin color had already changed from green to light green-yellow. Thus, skin color can be used to determine harvest date to avoid internal browning.
Alternate-year walnut pruning can boost yields, cut cost
by William H. Olson , David E. Ramos , Ronald G. Snyder
Annual pruning was compared to nonpruning for 8 years and to two alternate-year pruning treatments for 4 years in a mature, full-canopied ‘Ashley’ walnut orchard. Pruning increased light penetration and subsequent nut distribution throughout the canopy. Nut size and percent edible kernel wen? consistently lower in nonpruned trees than in trees pruned annually or biennially. However, annual pruning did not improve yield over that of nonpruned trees because fruitful spurs were removed. Alternate-year pruning resulted in yields comparable to those for nonpruned and annually pruned trees in the year following pruning. Biennially pruned trees yielded more than annually or nonpruned trees during the year pruning was not performed. Alternate-year pruning produced the highest income per acre even when the cost of pruning was considered.
Livina mulches suppress aphids in broccoli
by Michael J. Costello , Miguel A. Altieri
A living mulch combines an annual crop with a cover crop to provide pest control and soil protection. Results of a study in the Salinas Valley show cabbage aphid infestation can be lowered on broccoli grown in living mulches compared to clean cultivation, possibly because light reflectance patterns are less attractive to incoming aphids. Early and intense mowing of the cover crop and adequate irrigation maintained broccoli yield in living mulches relative to clean cultivation. Lack of specialized equipment is the main limitation to the commercial application of living mulches at this time.
On-farm nitrogen tests improve fertilizer efficiency, protect groundwater
by Timothy K. Hartz , Richard F. Smith , Kurt F. Schulbach , Michelle LeStrange
Nitrogen fertility of high-value vegetable crops must be carefuiiy managed to prevent contamination of groundwater while meeting agronomic goals. New on-farm techniques of monitoring nitrogen are simple, quick and fairiy reiiable. Routine field monitoring in conjunction with periodic testing by conventional laboratory anaiysis can save time and money.
Field procedure helps calculate irrigation time for cracking clay soils
by Mark E. Grismer , I. C. Tod
Available soil moisture and low soil salinity are difficult to maintain in clay soils of arid regions due to the clay's low permeability. However, a simple procedure has been developed for estimating the duration of flood irrigation needed to saturate the cracked profile in these soils, while improving water conservation through limiting excess runoff. Using a worksheet, the irrigator makes a few measurements, then calculates how long to irrigate each border.
On some tree species, annual sprays may control western poplar clearwing moth
by Walter J. Bentley , John F. Karlik , Woody Affleck
The western poplar clearwing moth, a serious pest to many species of western ornamental trees, can cause limb breakage or tree death in severe cases. In a study of three'species of ornamentals, the moth's development and infestation levels were measured in trees treated with carbaryl or chlorpyrifos. In heavily infested trees, annual insecticide applications provided control.
editorial, news, letters & science briefs
PM-10 - the unknown compound
by Robert G. Flocchini
Research update: Researchers try to arrest fugitive dust