ROOT DEPTH STUDIES WITH DESERT hymenelytra

S.B. CLARK . J. LETEY, JR. * 0. R. LUNT . A. WALLACE

~~~~~~ ~~~~~~~~~ tem which can forage for water from a light. A wooden plug with drain holes Atriplex hymenelytra (Torr.) Wats. (desert large soil volume. may also be- was inserted at the bottom. holly), a highly drought-resistant desert , come partially dormant during periods Three water treatments were imposed. was used as a test plant to study root be- of extreme water stress and may reju- One treatment consisted of wetting the havior in wet and dry soils. Roots did not venate during rain. entire soil column initially and then add- penetrate dry soil, but continued to grow A study of the effect of various water ing water twice weekly to maintain a wet profusely in soil having adequate soil mois- regimes on rate and depth of root pene- condition. In the second trwtment the ture. Roots extracted water from soil pro- tration was conducted on desert holly soil was initially wet throughout the col- gressively downward. They dried soil to -60 (Atriplex hymenelytra (Torr.) Wats.) . umn, but no further water was applied bars even though more water was available The growth containers were 10 cm in after plants were transplanted. The third ata greater depth. diameter and 300 cm deep. A black treatment consisted of wetting the soil Plexiglas tube drainline pipe was used column to a depth of approximately 100 for the container. Sections were cut out cm. Water was periodically added to at seven positions over the length of the maintain a relatively high water content LANTS CROWING in arid regions have column for root observation. The cut-out in the upper 100 cm, but not enough to P developed ways of surviving condi- section was then replaced and taped in penetrate beyond 100 cm. Each treat- tions of low soil water content. One sur- place for support. The entire column was ment was replicated. vival mcchanism is an extensive root sys- wrapped with aluminum foil to reflect Tensiometers were installed at 30 and 100 cm in the weekly irrigated treatment to indicate resultant soil water potentials. DEPTH OF ROOT PENETRATION WITH TIME OF ATRIPLEX HYMENELYTRA SUBJECTED TO THREE Thermocouple psychrometers were in- DIFFERENT TYPES OF IRRIGATION stalled slightly above and slightly below the wet/dry interface in the treatment where the upper_- 100 cm were maintained wet. Thermocouple psychrometers were initially installed at 15 cm for the treat- ment which had no watering after the initial profile soaking. When the soil water potential at 15 cm fell below -60 bars, psychrometers were moved to 30

- "0...... , '.O.. cm and then to 100 cm. !z '4 c Oxygen diffusion rate measurements I- -.,\ '0.... , W Y .-..o-...... o...... , were made by the platinum micro-elec- 5 150- Normal irrigation (weekly) Y, trode technique immediately after irri- a '.\ gation on the biweekly irrigated treat- I- ., 0 '. 0 ment. ASoil wetted to 100 cm only -.., cL 200- 0, I '. Root penetration k The average depth of root penetration W --. n ..-*. at various dates following transplanting 250- OSOil thoroughly wetted, with no further irrigation "-... is indicated in the figure. The rate of -growth was somewhat independent of I I I I I I treatment for the first two or three weeks. 0 20 40 60 80 100 Roots grown in containers irrigated bi- weekly essentially stopped elongation be- DAYS tween the 28th and 43rd day. Readings

16 CALIFORNIA AGRICULTURE, AUGUST, 1974 on the tensiometer indicated that water ample water to zones of inadequate water S. B. Clark is a former Research Asso- was being applictd when the potential at supply. The roots immediately above the ciate of the University of California, Los $0 CIII rcached hctween -50 and -20 dry layer were growing profusely, but Angeles. 0. K. Lunt is Director of tfie C\t%Lik&XS &wA .;%&%k%& hetwecx -5 axd &id nQ

RESIDUAL EFFECTS OF LETTUCE HERBICIDES ON FOLLOWING CROPS

D. W. CUDNEY . K. S. MAYBERRY

G. WORKER, JR.

CI I UCK is ‘rIiE most important vege- L,’table% crop grown in California’s Imperial Valley, grossing up to $73,000,- 000 annually. Nearly all lettuce in the valley is treated with herbicides-mostly with Ralan (benefin) . Balan has a broad weed spectrum ; however, growers have known for some time that Balm residues may cause damage to sorghum plantings that follow lettuce crops. Kerb (prona- midc) has now been released for use on Icttucc, and has been found to be an ex- cellcnt herbicide against weeds in the mustard group, such as London Rocket, normally not controlled with Balan. Little information was available, however, about residual effects of Kerb under des- rr; conditions, except that it could dam- age cereal crops planted after lettuce. The experiment reported here was de- signed to evaluate the effect of Balan ad Reduction in stand and growth is shown for the 4 Ib (twice label rate) of Kerb. Crops were planted 84 Kerb on 13 crops which could be planted days after a treatment to a lettuce crop which “failed.”

CALIFORNIA AGRICULTURE, AUGUST, 1974 17