Irrig Sci (1991) 12:193-198 Irrigation clence

�9 Springer-Verlag 1991

Irrigation of seed carrots on a sandy loam soil

J. E. Ayars t, R. B. Hutmacher 1, J. J. Steiner 2, A. B. Mantel 3, and S. S. Vail 1

1 USDA/ARS, Water Management Research Laboratory, 2021 S. Peach Ave., Fresno, CA 93727, USA 2 USDA/ARS, National Forage Seed Protection Research Center, 3450 S. W. Campus Way, Corvallis, OR 97331-7102, USA 3 Institute of Soils and Water, Volcani Center, Bet Dagan, Israel

Received January 17, 1991

Summary. Little research has been reported which quan- tifies the response of a carrot (Daucus carrota L. var sativa DC.) seed crop to water management. While the area of seed product ion of this crop in the United States is less than 3 000 ha, the return ranges from US $2 000 to $10 000 h a - 1. Because of the need to mature and dry the seed on the plant, carrot seed is generally grown in areas with negligible summer rain and thus depends on irriga- tion to supply the crop water requirement. A study was conducted to determine the effect of irrigation water management on seed production and crop water use of carrots grown by the root-to-seed method. Two carrot types (Nantes and Imperator) were evaluated in 9 irriga- tion treatments over a three year study period. Irrigation treatments which replaced a percentage of the calculated crop evapotranspiration on either a daily basis or when a soil water depletion reached 30 mm were used. A trickle irrigation system with the laterals placed on the carrot bed was used to apply a uniform and accurate amount of water. There was a marked difference in the crop re- sponse to the water management of the two carrot types used. The Nantes type exhibited a positive response to moderate water deficits in terms of improved pure live seed (PLS) yield while the Imperator achieved its maxi- mum yield when it was not stressed. Higher irrigation applications in the Nantes type resulted in reduced yields while the Imperator was not affected after its non-stress water requirement was met. Soil water data indicated that the most active zone of extraction of water was to a depth of 1.5 m in the soil profile. As the depth of applied water approached the crop water requirement, the depth of extraction was reduced. Increasing the frequency of irrigation also tended to reduce the depth of extraction of soil water. A total crop water use of approximately 550 to 620 mm was needed to achieve the best PLS yield which is roughly equal to potential evapotranspiration in the San Joaquin Valley, during the time that the crop water use was calculated. In such a climate, the irrigation inter-

Offprint requests to: J. E. Ayars

val should not exceed 3 to 5 days depending on the time of year.

Carrot (Daucus carrota L. var. sativa DC.) is the most important member of the Umbelliferae family, which also includes other commercially-grown species such as celery, parsnip, parsley, and dill. Although seed produc- tion acreage is relatively small compared to many crops, the crop value per unit area ranges from US $ 2 000 to $10 000 h a - 1. Seed product ion is generally restricted to regions with negligible summer rainfall, where suitable conditions can be provided for the seed to reach maturity and to dry properly. For this reason carrot seed is often grown in areas where irrigation is required.

George (1985) stated that "very little work has been done investigating the effects of soil moisture deficit on seed yield and quality", concurring with Hawthorn and Pollard (1954) who wrote over 30 years earlier that "far too little is known concerning the relationship of soil moisture to production of vegetable- and flower-seed crops. "Knowledge of the seed crop physiological re- sponse to water management has recently been described by Hutmacher et al. (1990) and Steiner et al. (1990).

MacGillivray and Clemente (1949) used the root-to- seed method [carrots grown to maturity from root trans- plants (stecklings)] and concluded that when winter rains were sufficient to fill a 1.8 m loam soil profile to field capacity, additional irrigation water of about 200 to 300 mm was adequate for carrot seed production. There was no effect of irrigation depth on seed size and germi- nation percentage. Soil water extraction was observed to a depth of 1.5 to 1.8 m, but soil water extraction was generally restricted to the upper 1.0 to 1.2 m of the pro- file.

Hawthorn (1952) examined the interactions between soil water, applied nitrogen, and plant spacing in a seed- to-seed carrot crop (carrots grown to maturity from a direct-seeded field). Different degrees of soil water deple- tion prior to irrigation were tested. There was a trend

194

t o w a r d h i g h e r t o t a l s eed y ie ld a t m e d i u m to l ow soi l w a t e r levels r a t h e r t h a n w i t h h i g h e r w a t e r levels . S a l t e r a n d G o o d e (1967) r e v i e w e d a n u m b e r o f i n v e s t i g a t i o n s o n i r r i g a t i o n o f c a r r o t s ( m a i n l y f o r f r e s h m a r k e t use) a n d s t a t e d t h a t " f r o m t h e s m a l l a m o u n t o f d a t a a v a i l a b l e t h e r e is n o c o n s i s t e n t e v i d e n c e t h a t t h e r e a r e m o i s t u r e - s e n s i t i v e s t a g e s d u r i n g c a r r o t g r o w t h , e v e n w h e n t h e p l a n t s a r e g r o w n t h r o u g h t h e f l o w e r i n g p e r i o d fo r seed p r o d u c t i o n " .

T h e o b j e c t i v e o f t h i s r e s e a r c h w a s to d e t e r m i n e t he e f fec t o f i r r i g a t i o n w a t e r m a n a g e m e n t o n seed p r o d u c - t i o n a n d c r o p w a t e r u s e o f a r o o t - t o - s e e d c a r r o t c r o p .

Materials and methods

Experiments were conducted in 1985, 1986 and 1988 in Fresno, Ca. on a deep Hanford fine sandy loam soil (Typic Xerorthents) which had a total available water capacity of approximately 150 mm in the top 2.0m. The volumetric soil water content at 10 kPa and 1 500 kPa matric potential were approximately 20% and 5%, re- spectively in the upper 1.0 to 1.2 m of the profile and 13 to 15% and 4% respectively in the 1.2 to 2.0 m zone. Furrow irrigations in excess of 200 mm applied prior to planting filled the soil water profile to a depth of 2 to 2.5 m. Soil samples were collected each year to a depth of 2 m prior to planting and were analyzed for total N, P, and K content. Based upon these analyses, all plots were side dressed with 32 g(N) m -2 as ammonium nitrate in 1985 and 1986 at first bolting. In 1988, a total of 4.8 g (N) m -2 as ammonium nitrate was applied at first bolting.

In all three years metham was applied 4 weeks prior to planting at a rate of 10.6 ml m -z active ingredient for both pathogen and weed control. Also, trifluralin was applied at a rate of 23 ml m -z active ingredient and incorporated into the top 0.1 m of soil prior to transplanting for weed control. Carrot stecklings of the type Nantes were transplanted 16 January 1985, and stecklings of the type Imperator were transplanted 9 February 1986. Both types were used in the 1988 experiment and were transplanted 21-22 January. The type was changed in 1986 because no Nantes stecklings were available at this location in 1986. Because of differences in the response of the types to the water management regimes in 1985 and 1986, it was decided to use both types in the experiment in 1988 for comparison purposes.

The stecklings were transplanted on a spacing of 0.1 to 0.12 m between plants on beds 1 m wide. Final average plant population was 9.1 plants m -z. Each plot was 5 beds wide by 15 m in length in 1985 and 1986. In 1988 the plots were split such that 2 beds were planted to Imperator and 3 beds to Nantes. The plot length was 15 m. Linuron was applied for weed control approximately 3 weeks after t ransplanting at a rate of 45 mg m - z active ingredient.

Uniform applications of water were made with sprinklers prior to initiating the differential irrigation to insure a good stand and to re-fill the soil profile at the start of differential treatments. In the interval between transplanting the stecklings and the initiation of differential irrigation treatments, a total of 88 mm, 161 mm and 83 rnm of rainfall occurred in 1985, 1986 and 1988 respectively. Sprinkler irrigation during the same period was 138, 99 and 110 mm in 1985, 1986 and 1988, respectively.

Irrigation water was applied by a manually operated surface trickle system consisting of laterals placed on the center of each bed, with in-line turbulent-flow emitters spaced every 0.5 m along the lateral, each discharging 2 liters per hour. Water applications were measured twice weekly using 19 mm water meters. A non-saline water (0.1 dS m-1 ) was used for irrigation.

Soil water content change in each plot was monitored weekly to bi-weekly in 1985 and before and after each irrigation in 1986 and 1988 using a neutron probe calibrated in-situ. Measurements were taken at 0.3 m increments between 0.15 and 1.95 m in one tube which had been centered in the plant row between two emitters. In

1988, soil samples for gravimetric water content determinations were taken monthly from January to April to a depth of 2.25 m in one randomly selected pot of each treatment.

Differential irrigation treatments began on April 19, April 30, and May 2 in 1985, 1986 and 1988, respectively. These times corre- spond to the beginning of bolting of the primary umbel each year. Irrigation was terminated on July 5, June 29 and July 4 in 1985, 1986 and 1988, respectively. Irrigations were terminated when most second order carrot umbels were mature to permit in-field drying of the plants for harvest.

Crop evapotranspiration was estimated using a modified Pen- man method described by Howell et al. (1984) to determine grass reference evapotranspiration (ETo) in combination with a locally- developed crop coefficient (Kc). Climatic data needed for the Et 0 calculation were taken from a weather station located 250 m from the experimental site. In 1985 crop coefficients were developed which consisted of straight line segments which increased Ko from 0.4 to 1.0. The Kc was adjusted weekly based on changes in mea- sured soil water in the 100% treatments. The use of the K c began with the start of the differential irrigation treatments with the max- imum value of Kr being attained between day 130 and 140 in each year of the experiment. The value of K c remained at 1.0 until the termination of irrigation.

In 1985, six irrigation treatments were established in a random- ized complete block design with 4 replicates. One treatment was irrigated when 30 mm of accumulated crop evapotranspiration (ETc) occurred, and plants in that treatment received 100 percent of the calculated water use. This treatment was identified as treatment 100-L. Four additional treatments were irrigated at the same fre- quency as treatment 100-L, but with quantities equal to 40, 60, 80, and 120% of acumulated ETc. These treatments were identified as 40-L, 60-L, 80-L, and 120-L, respectively. During the irrigation season, the frequency of water application was every 3 to 5 days. The sixth treatment (100-D) was irrigated daily with amounts equal to 100% of the previous day's estimated ET c .

In 1986, eight irrigation treatments were established in a ran- domized complete block design with three replicates. One treatment (100-L) was irrigated after each 30 mm of accumulated ETc with an amount adequate to replace 100%o of the calculated ETc. Three additional treatments were irrigated at the same frequency as the 100-L treatment, but 60, 80, or 120% of ET c was applied in treat- ments 60-L, 80-L, and 120-L, respectively. Daily irrigations in amounts equivalent to 80, 100 and 120 percent of ET c were applied in treatments 80-D, 100-D, and 120-D, respectively. One additional treatment (120-2L) in 1986 was irrigated with an amount equivalent to 120% of ET c after each 55 to 60 mm of accumulated ET c.

In 1988, nine irrigation treatments were established in a ran- domized complete block design with four replications. Each of the treatments used in 1986 were repeated with the addition of treat- ment 40-L which had been used in 1985. Additionally, treatments 60-L, 80-L, 100-L, and 100-D were split and both types of carrots were grown in three replications of these treatments.

Six meters of row within each plot were harvested by hand on 16 July 1985, 25 July 1986 and 18 July 1988 to determine total seed yield. Umbels from four orders (primary, secondary, tertiary, qua- ternary) were harvested separately, dried to uniform moisture con- tent ( < 10%), threshed, and cleaned. Seed germination was evaluat- ed according to AOSA (Association of Official Seed Analysts, 1978) rules. Pure live seed (PLS) yields were determined for each umbel order by multiplying the cleaned seed weight by the germination percentage. Regression analysis was used to analyze the quantita- tive variable series for the irrigation treatments. Single degree of freedom contrasts were used to determine irrigation treatment dif- ferences (SAS Institute, 1985).

Results and discussion

T h e c r o p w a t e r b a l a n c e w a s c a l c u l a t e d ( H o w e l l e t al. 1983) for t h e p e r i o d o f d i f f e r en t i a l w a t e r a p p l i c a t i o n s a n d

Table 1. Water balance in seed carrots for the period of differential irrigation application at Fresno, CA in 1985, 1986, and 1988

195

Treat- Trickle applied irrigation (ram) Decrease in soil water content Water use (mm)a ment in 2.10 m profile (mm)

1985 1986 1988 1988 1985 1986 1988 1988 Nantes Imperator Nantes Imperator Nantes Imperator Nantes Imperator

1985 b 1986 1988 c 1988 c Nantes Imperator Nantes Imperator

80-D # 346 356 # # 59 46 # # 405 473 # 100-D 517 482 444 444 77 11 36 39 604 493 551 554 120-D # 572 532 # # 44 10 # # 616 613 #

40-L 206 # 180 # 99 # 77 # 315 # 328 # 60-L 309 349 270 270 92 58 85 92 418 407 426 433 80-L 412 455 360 360 100 66 58 61 522 521 489 492

100-L 517 560 450 450 70 72 38 51 597 632 559 572 120-L 620 665 540 # 65 --15 -- 6 # 695 650 605 # 120-2L # 651 540 # # 85 - 4 # # 736 607 #

a Between days 102 and 186, 118 and 182 and 108 and 197 in 1985, 1986, and 1988, respectively. Does not include rainfall and irrigation water applied prior to the initiation of differential irrigation b Includes 10 mm of precipitation which fell after the start of differential irrigation treatments c Includes 71 mm of precipitation which fell after the start of differential irrigation treatments # Treatment not included in study or neutron access tubes not present in treatment

was used to charac te r i ze the seed yield response to the differential i r r iga t ion t rea tments . Runof f f rom ind iv idua l p lo ts was p reven ted a n d deep p e r c o l a t i o n losses were a s sumed to be negligible. W i t h the poss ib le excep t ion of the 120-L t r ea tmen t this a s s u m p t i o n shou ld be va l id since small a m o u n t s of wa te r were be ing app l i ed in a soil wi th the solid wa te r con ten t genera l ly be low field capaci ty . Tota l wa te r use du r ing the pe r iod of differential t rea t - ments was defined as the sum of the t r i ck le -app l i ed i r r iga- t ion wa te r plus the change in soil wate r s to rage in a 2.1 m profi le f rom the s ta r t of the different ial t r ea tmen t s to the end of the g rowing season. Even t h o u g h dr ip i r r iga t ion was used in all years a n d runoff was prevented , inf i l t ra- t ion p r o b l e m s deve loped mid - sea son in 1986 which creat - ed p o n d e d cond i t ions in some t r ea tmen t s (i.e., 100-D, 120-D, 100-L, 120-L). U n d e r these p o n d e d cond i t ions less of the app l i ed wa te r was ava i l ab le for d i rec t c rop use.

The ca lcu la ted grass reference e v a p o t r a n s p i r a t i o n (ET0) was 532 m m from d a y 109 to d a y 186 in 1985, 486 m m from d a y 120 to d a y 182 in 1986 and 520 m m from d a y 108 to day 197 in 1988. These days c o r r e s p o n d to the beg inn ing of differential i r r iga t ion and harves t of the c rop in the respect ive years. The to ta l e s t ima ted wa te r use in ind iv idua l t r ea tmen t s du r ing these same pe r iods r anged f rom 315 to 695 mm, 405 to 736 m m and 328 to 613 m m in 1985, 1986 a n d 1988, respect ively (Table 1). W a t e r use inc reased as a p p l i c a t i o n a m o u n t s increased. The average to ta l wa te r use for the 80-D t r ea tmen t was a p p r o x i m a t e l y equa l to the to ta l wa te r use in the 60-L t r ea tmen t r a the r t han be ing equa l to the to ta l wa te r use in t r e a tmen t 80-L, which w o u l d be expected. Whi l e the 80-D t r e a t m e n t had more i r r iga t ion wa te r app l i ed t han the 60-L t rea tment , the a d d i t i o n a l wa te r used in the 60-L t r ea tmen t was de r ived f rom s to red soil water . This sug- gests tha t the h igher f requency i r r iga t ion (daily) l imi ted the c rop roo t zone and thus the c rop rel ied m o r e heavi ly on i r r iga t ion wate r t han d id the t r ea tmen t which was i r r iga ted less f requent ly. I t is therefore poss ib le tha t in this coa r se - t ex tu red soil p lan t s receiving the low i r r iga t ion

Table 2. Significant differences in soil water depletion by Nantes type seed carrots grown at Fresno, California in 1988 from day of year 108 to 197 as determined using single degree of freedom con- trasts (SAS Institute, 1985)

40-L 60-L 80-L 100-L 120-L 80-D 100-D 120-D

40-L - NS ** ** ** ** ** ** 60-L - ** ** ** ** ** ** 80-L - ** ** ** ** **

100-L - ** NS NS ** 120-L - ** ** * 80-D - * **

100-D - **

NS -- non-significant *' ** = significant at 0.05, 0.01, respectively

f requency t r ea tmen t deve loped m o r e extensive r o o t sys- tems to ex t rac t wa te r f rom deeper in the soil profile.

The wate r use (WU) and t r ickle a pp l i ed wa te r ( A W ) presen ted in Table 1 were p lo t t ed in Fig. 1. A l inear re- gress ion was fit t h r o u g h the data . The s lope of the regres- s ion e q u a t i o n indica tes tha t a b o u t 78% of the app l i ed wate r resul ted in d i rec t increases in wa te r use.

The decrease in soil wa te r f rom the beg inn ing to the end of the differential i r r iga t ion was c o m p a r e d by i r r iga- t ion t r ea tmen t (Table 2) using single degree of f r eedom con t ra s t s (SAS Inst i tu tes , 1985). These con t ra s t s conf i rm tha t there was a s ignif icant difference be tween the ext rac- t ion by i r r iga t ion t r ea tmen t s b o t h by dep th app l i ed a n d f requency of app l ica t ion , i.e., 80-L ex t r ac t ed more soil wate r t han 80-D a n d 60-L ex t r ac t ed m o r e than 80-L.

The changes in the to ta l s to red wa te r in a 2.1 m profi le and the wate r d i s t r i bu t ion in the soil profi le for the 60-L, 80-L, 100-L and 120-L t r ea tmen t s for the N a n t e s type du r ing the 1988 season will be used to fur ther descr ibe the soil wate r ex t r ac t ion p a t t e r n of the crop. S imi la r t r ends were observed dur ing the 1985 and 1986 seasons, a l though in 1986 the inf i l t ra t ion p r o b l e m s inf luenced wa te r dis t r i - b u t i o n dur ing mid to late season.

196

E

(D

9O0

80O

700

600

500

400

300

200

100

0

0

+ 85 Nantes D

~, 85 Nantes L

O 86 Imper . L / ~ ~

4. 86 Imper. L ~ ~ ~ ,

�9 86 Imper . 2L 2 ~ I ' ~ T O

�9 88 Nantes D

v 88 Nantes L M O

o 88 Nantes 2L ~ ( ~

o 88 Imper . D

WU = 1 85 .5 + 0 . 7 8 4 ~ A W r 2 = 0,92 "

I I I I I I I

1 O0 200 300 400 500 600 700

Trickle applied water (mm)

800

Fig. 1. Water use (WU) by Nantes and Imperator type seed carrots grown under nine irrigation treatments (80-D, 100-D, 120-D, 40-L, 60-L, 80-L, 100-L, 120-L, t20-2L) at Fresno, CA, in 1985, 1986, and 1988 as a function of ap- plied trickle irrigation water (AW)

. . . . . . . . 60-L 380 - - 80-L

. . . . 100-L / - -~ - - - - 1 2 0 - L / / | \

/ / / \

-=5 . . . . . "" - - _

200 ~ i I i ~ l z ~ t i i I = i P ,

120 135 150 165 180 195

Day of year

Fig. 2. Total soil water content in a 2.10 m profile for seed carrot irrigation treatments 60-L, 80-L, t00-L and 120-L for the Nantes type grown at Fresno, CA, in 1988. Standard errors for each data point are shown as vertical lines

E E v 320

-~ 2 6 0

The change in total soil water s torage in a 2.1 m profile for the per iod just after the start of differential irrigation to harvest is given in Fig. 2. The da ta show that soil water decreased as the depth of appl icat ion was reduced relative to the evapo t ransp i ra t ion (ETc) demand. As the depth of irr igation increased f rom 60 to 120% of ETc, the total soil water s tored was increased such that when irrigation was terminated, the final value in the 120% treatment was greater than the water content at the beginning of the season. The increase in water content noted in all treat- ments between days 172 and 187 cor responded with the late season decline in viable leaf area and t ranspirat ional conduc tance (Hu tmache r et al. 1990; Steiner et al. 1990). Dur ing this per iod the c rop coefficient (Kc) was main- tained at 1.0 and apparen t ly resulted in a greater applica- t ion of water than the plants could use in all 4 measured t reatments (Fig. 2), (Hu tmacher et al. 1990).

o~

t -

O o o

E

18F a

6 ~ -F . . . . . . May 2 - - - July 15

0 ~" i i i i i J [ i ~ 1 i i i

1218 I t . . . . . - - - ~ . . . . . .

~ 0 i i I i i i i i i i i i L

,sic 12 -= . . . . . . . " ! - - -

6

0 i i i i i i i i i i I I i i

12

6

0 L I I 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1

Depth (m) Fig. 3a-d. Soil water content profiles on 2 May 1988 and 15 July 1988 for irrigation treatments 60-L (a), 80-L ~), 100-L (e), and 120-L (d) for the Nantes type seed carrots grown at Fresno, CA. Standard errors for each data point are shown as vertical lines

The max imum amoun t of soil water was extracted by the 60-L t reatment a m o n g treatments 60-L, 80-L, 100-L, and 120-L (Fig. 3a) th rough 3d, respectively). In 1988 more water was extracted by 60-L than 80-L, 120-L or 120-2L (Fig. 3). Water was extracted to a depth in excess of 1.5 m. The volume and depth of water extracted was reduced as the irrigation t reatments progressed f rom 60 to 100% of ET c . The 120% treatment data show some water extract ion to a depth of 0.9 m and increased water

i Nantes R Imper. ~ Nantes ~ Imper.

o~ 9 6 E O) v "O

�9 -~ 72

"O

03

._> 48

ta

24

r,4,a i

80-D 100-D

120

1985 1986

t 120-D 40-L 60-L 80-L

1988 1988

100-L 120-L 120-2L

I rr igat ion t reatment

197

Fig. 4. Pure live seed yield (g m- 2) for irrigation treatments (80-D, 100-D, 120-D, 40-L, 60-L, 80-L, 100-L, 120-L, 120-2L) for Nantes and Imperator type carrots grown for seed at Fresno, CA, in 1985, 1986, and 1988. Standard error of the mean shown by the bar.

content from 0.9 to 2.1 m. The change in soil water data for each treatment over the course of the growing season indicates that the water extraction was limited primarily to the first 1.5 m of depth in the soil profile and that as the depth of application was increased, the zone of maximum change in soil water content became shallower (Figs. 3 a - d). Similar data for Nantes type in 1985 and the Impera- tor type grown in 1986 (data not shown) exhibited the same general response, with the greatest extraction occur- ring in the first 1.5 m of the soil profile and increasing water applications reducing the depth of extraction.

The pure live seed (PLS) yield data for all treatments and all years is given in Fig. 4. PLS yields are the product of total seed yields multiplied by the 14 day results of a standard evaluation of germination percentage; therefore, they reflect a composite measure of both quantity and seed viability.

It is not necessarily valid to compare the PLS yield responses of each individual irrigation treatment across all three years because in 1985 and 1986 two different carrot types were grown, while both types were grown in 1988. Some generalizations can be made, however, in comparing relative seed responses to trickle irrigation management. Among the treatments irrigated at the low frequency (L) level, pure live seed yield (PLS) in the Nan- tes type increased to a maximum yield in the 80-L treat- ment and then decreased as additional water was added in both 1985 and 1988. The peak yield in the Nantes type was in the 120-D treatment in 1988 and in the 100-D treatment in 1985. The PLS yield of the Nantes 80-D treatment in 1988 was greater than the 100-D treatment in 1985. In 1985, the yield in the 100-D treatment was greater than the 100-L treatment but the opposite was the case in 1988.

The PLS yield of the Imperator type increased to its maximum level within a treatment at 120% of ETo in both the daily and 30 mm treatments in 1986 and in the daily treatment in 1988. The maximum yield in the daily treatment for the Imperator type in 1988 occurred in the 100-L treatment not the 120-D as was the case in 1986. In

1988 the highest yields for both types of carrots was in the 120-D treatment for the Nantes type. The yields for the daily irrigation treatments in the Imperator type were nearly equal across the 80, 100 and 120% irrigation amounts in 1988 while they were increasing in 1986. The extremely low pure live seed yields of the Imperator type carrots in 1986 when compared to the 1988 yield data were a result of reduced seed set rather than low germina- tion percentage (Steiner et al. 1990). While total above- ground phytomass was not significantly different across years, the quantity of seed produced was highly variable (Hutmacher et al. 1990).

The PLS in both types responded to water manage- ment in each of the years grown, albeit the response was different between types. The PLS yield data from both 1985 and 1988 indicate that the Nantes type will tolerate and even thrive with moderate stress induced by reduced water application while Imperator does not and has a minimum total water use requirement after which addi- tional water does not adversely affect yield. Excess water can reduce PLS yields of Nantes. This is demonstrated in Fig. 5.

The 1988 PLS data for the low frequency and daily irrigation treatments for both types of carrot seed were plotted in Fig. 5 relative to the water applied by the 100-L treatment. The plot shows the maximum yield of the Nan- tes type occurring at the 0.80 level and then decreasing as the water application increases while the yield of the Im- perator type increases and then levels off. The exception to pattern was the 120-D treatment for the Nantes type, which had the highest value of yield of all treatment in 1988. A total water use of 550 to 620 mm during the period of time from primary umbel appearance through harvest appears to result in the maximum yields in each of the types.

The water use efficiency expressed as the ratio of PLS yield to water use and single degree of freedom contrasts of 1988 W U E data for Nantes (only) are given in Table 3. In 1988, the highest efficiencies in the Nantes type oc- curred in the 40-L, 60-L, 80-L and 120-D treatments

198

d-" E O~

v

-O

{D (D

( / ) d /3_

120 -

100

8O

6O

40

2O

0

Nantes- daily (1988) (r 2 = 0.56) .=

t

Nantes-low (1988) / ~ _ - ~ ,

/ / O (R'-- 0.94)

,MP-,ow (1988) o ,e,2 . . . . . ~ Nantes-I~ ~ ~ ~ . . . . . . . J / (1985)

/ (R" = 0.85*) O

i i i i i l i I i I J i i

0.2 0.4 0.6 0.8 1.0 1.2

Relative t r ick le-appl ied water (relative to treatment 100-L)

Fig. 5. Pure live seed yield (g m-2) for low frequency and daily irrigation treatments for the Nantes type seed carrots grown at Fresno, CA, in 1988. Linear (r 2) and quadratic (R z) coefficients of determination marked with (*) are significant at P<0.05

Table& Water use efficiency during period of differential irrigation of seed carrots grown at Fresno, CA in 1985, 1986, and 1988 and single degree of freedom contrast (SAS Institute, 1985) of WUE data for 1988 Nantes (only)

Treatment 1985 1986 1988 1988 Nantes Imperator Nantes Imperator

(g/m 3)

80-D # 65 93 # 100-D 120 65 138 141 120-D # 69 171 #

40-L 87 # 170 # 60-L 153 68 154 111 80-L 123 51 171 161

100-L 86 48 139 148 120-L 66 51 118 #

120-2L # 34 106 #

# Treatment not included in study or neutron access tubes not present in treatment

40-L 60-L 80-L 100-L 120-L 80-D 100-D 120-D

120-2L ** ** ** * NS NS * ** 40-L NS NS ** ** ** * NS 60-L - NS * ** ** NS NS 80-L - * ** ** ** NS

100-L - NS ** NS * 120-L - * NS ** 80-D - ** **

100-D - *

NS = non-significant *' ** =significant at 0.05, 0.01, respectively

while the h ighest W U E for the I m p e r a t o r type occur red in the 80-L and 100-L t rea tments . In the low f requency (L) t r ea tmen t s the h ighes t values of W U E in bo th types oc- cur red in the 80-L t r ea tmen t . F o r the N a n t e s type as the dep th of a p p l i c a t i o n inc reased a b o v e the 80-L t rea tment ,

the yields declined, which when coupled with increased wate r app l ica t ion , resul ted in lower W U E . Pure live seed yields for I m p e r a t o r type were cons tan t above the 80-L t r ea tmen t and with add i t i ona l i r r iga t ion wate r the W U E values were reduced. The high W U E in the 120-D t rea t - ment was the result of high yields coup led with the add i - t ional i r r iga t ion water. The re la t ively high seed yields and W U E no ted in 80-L t r ea tmen t s in 1985 and 1988 ind ica t - ed a favorab le response to mi ld wate r deficits in bo th types.

Conclusions

A three year s tudy of the wate r requ i rements of seed car- rot g rown from steckl ings de t e rmine d tha t the zone of m a x i m u m of ex t rac t ion of soil wa te r ranged f rom 0.90 to 1.50 m depend ing on the f requency of i r r igat ion. As the f requency increased the dep th of ex t rac t ion decreased. A to ta l wate r use of 550 to 620 m m is a d e q u a t e in this coar - se- tex tured soil to achieve m a x i m u m P L S yield in any given year. The N a n t e s type r e s p o n d e d with best yield to s l ightly stressed cond i t ions and had reduced P L S yields when over- i r r iga ted . P L S yields for I m p e r a t o r type were highest at a m i n i m u m non-s t ress level and were no t affect- ed by increased i r r igat ion. The best W U E in bo th types was in the 80-L t rea tment .

The results of this s tudy conf i rm prev ious research ( M a c G i l l i v r a y and Clemente 1949) which ind ica ted tha t s ignif icant wate r use by seed ca r ro t c rops was genera l ly res t r ic ted to the u p p e r 1 .0 -1 .2 m of the soil profi le (M a c G i l l i v r a y and Clemente 1949).

References

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