Subsurface Drip Irrigation For Native Wildflower

Seed Production

Clint Shock, Erik Feibert, and Lamont Saunders,

Malheur Experiment Station

Oregon State University

Ontario, OR 2007

Nancy Shaw

U.S. Forest Service

Rocky Mountain Research Station

Boise, ID

Introduction

Native forb seed is needed to restore rangelands of the Intermountain West. Commercial seed production is necessary to provide the quantity of seed needed for restoration efforts. A major limitation to economically viable commercial production of native forb seed is stable and consistent seed productivity over years. Variations in spring rainfall and soil moisture result in highly unpredictable water stress at flowering, seed set, and seed development. Excessive water stress during flowering, seed set, and seed development is known to compromise yield and quality of other seed crops.

Native forbs are not competitive with crop weeds. Both sprinkler and furrow irrigation could promote seed production, but risk encouraging weeds. Furthermore, sprinkler and furrow irrigation can lead to the loss of plant stand and seed production due to fungal pathogens. By burying drip tapes at 12-inch depth, and avoiding wetting of the soil surface, we hope to assure flowering and seed set without encouraging weeds or opportunistic diseases. This trial tested the effect of three irrigation intensities on the seed yield of seven native forb species.

Materials and Methods

Plant Establishment
Seed of the seven intermountain west forb species (Table 1) was received in late November in 2004 from the Rocky Mountain Research Station (Boise, ID). The plan was to plant the seed in the fall of 2004, but due to excessive rainfall in October, the ground preparation was not completed and planting was postponed to early 2005. To ensure germination the seed was submitted to a cold stratification treatment. The seed was soaked overnight in distilled water on January 26, 2004. After soaking, the water was drained and the seed soaked for 20 minutes in a 10 percent by volume solution of 13 percent bleach in distilled water. The water was drained and the seed placed in a thin layer in plastic containers. The plastic containers had lids with holes drilled to allow air movement. The seed containers were placed in a cooler set at approximately 34°F. Every few days the seed was mixed and, if necessary, distilled water added to maintain moist seed. In late February, seed of Lomatium grayi and Lomatium triternatum had started sprouting.

Table 1. Forb species planted at the Malheur Experiment Station.

Species	Common name
Eriogonum umbellatum	Sulfur buckwheat
Penstemon acuminatus	Sand penstemon
Penstemon deustus	Hotrock penstemon
Penstemon speciosus	Royal or Sagebrush penstemon
Lomatium dissectum	Fernleaf biscuitroot
Lomatium triternatum	Nine leaf desert parsley
Lomatium grayi	Gray's lomatium
Sphaeralcea parvifolia	Small flower globe mallow
Sphaeralcea grossularifolia	Gooseberry leafed globe mallow
Sphaeralcea coccinea	Red globe mallow
Dalea searlsiae	Seals' prairie clover
Dalea ornata	Western prairie clover
Astragalus filipes	Basalt milkvetch

In late February, 2005, drip tape (T-Tape TSX 515-16-340) was buried at 12-inch depth between two rows (30 inch rows) of a Nyssa silt loam with a pH of 8.3 and 1.1 percent organic matter. The drip tape was buried on alternating inter-row spaces (5 ft apart). The flow rate for the drip tape was 0.34 gal/min/100 ft at 8 PSI with emitters spaced 16 inches apart, resulting in a water application rate of 0.066 inch/hour.

On March 3, seed of all species was planted in 30 inch rows using a custom made plot grain drill with disk openers. All seed was planted at 20-30 seeds per foot of row. The Eriogonum umbellatum and the Penstemon sp. were planted at 0.25 inch depth and the Lomatium sp. at 0.5 inch depth. The trial was irrigated with a minisprinkler system (R10 Turbo Rotator, Nelson Irrigation Corp., Walla Walla, WA) for even stand establishment from March 4 to April 29. Risers were spaced 25 ft apart along the flexible polyethylene hose laterals that were spaced 30 ft apart and the water application rate was 0.10 inch/hour. A total of 1.72 inches of water was applied with the minisprinkler system. Eriogonum umbellatum, Lomatium triternatum, and Lomatium grayi started emerging on March 29. All other species, except Lomatium dissectum, emerged by late April. Starting June 24, the field was irrigated using the drip system. A total of 3.73 inches of water was applied with the drip system from June 24 to July 7. Thereafter the field was not irrigated.

Plant stands for Eriogonum umbellatum, Penstemon sp., Lomatium triternatum, and Lomatium grayi Lomatium dissectum did not emerge. None of the species flowered in 2005. In early October, 2005, more seed was received from the Rocky Mountain Research Station for replanting. The Eriogonum umbellatum and Penstemon sp. plots had the blank lengths of row replanted by hand. The Lomatium sp. plots had the entire row lengths replanted using the planter. The seed was replanted on October 26, 2005. In the spring of 2006, plant stand of the replanted species was excellent, except for Penstemon deustus. were uneven.

Flowering, harvesting, and seed cleaning in 2006.
Eriogonum umbellatum flowering started on May 19, peaked on June 24, and ended on July 28. Penstemon acuminatus flowering started on May 2, peaked on May 10, and ended on May 19. Penstemon speciosus flowering started on May 10 and peaked on May 19. Penstemon deustus flowering started on May 10, and peaked on May 22.

The Eriogonum umbellatum and Penstemon sp. plots produced seed in 2006, probably because they had emerged in the spring of 2005. In these plots, only the lengths of row that had consistent stand and seed production were harvested. The plant stand for Penstemon deustus was too poor to result in reliable seed yield estimates. The middle two rows of each plot were harvested using a Wintersteiger Nurserymaster small plot combine. Penstemon acuminatus was harvested on July 7, P. speciosus was harvested on July 13, E. umbellatum was harvested on August 3, and P. deustus was harvested on August 4.

Eriogonum umbellatum seeds did not separate from the flowering structures in the combine. Eriogonum umbellatum unthreshed seed was taken to the U.S. Forest Service Lucky Peak Nursery and run through a dewinger to separate seed. The seed was further cleaned in a small clipper seed cleaner.

Penstemon deustus seed pods were too hard to be opened in the combine. Penstemon deustus unthreshed seed was pre cleaned in a small clipper seed cleaner and then seed pods were broken manually by rubbing the pods on a ribbed rubber mat. The seed was then cleaned again inthe small clipper seed cleaner.

Penstemon acuminatus and Penstemon speciosus threshed in the combine and the seed was further cleaned using a small clipper seed cleaner.

Expansion and fertilization of the trials.
On April 11, 2006, seed of three globe mallow species (Sphaeralcea parvifolia, S. grossularifolia, S. coccinea), two prairie clover species(Dalea searlsiae, D. ornata), and basalt milkvetch (Astragalus filipes) was planted at 30 seeds/ft of row. The field was sprinkler irrigated until emergence. Emergence was poor. In late August of 2006 seed of the three globe mallow species was harvested by hand. On November 9, 2006 the six forbs were flailed. On November 10, 2006 the six forbs were replanted.

On October 27, 2006, 50 lb P/acre and 2 lb Zn/acre were injected through the drip tape to all plots of Eriogonum umbellatum, Penstemon sp., and Lomatium sp. On November 11, 100 lb N/acre as urea was broadcast to all Lomatium sp. plots. On November 11, the Penstemon deustus plots were replanted at 30 seeds/foot of row. On November 17, all plots of Eriogonum umbellatum, Penstemon sp. (except P. deustus), and Lomatium sp, had Prowl at 1 lb ai/acre broadcast on the soil surface.

Irrigation for seed production in 2006
In April, 2006, the field was divided into plots 30 ft long. Each plot contained 4 rows of each of Eriogonum umbellatum, P. acuminatus, P. speciosus, P. deustus, L. dissectum, L. triternatum, and L. grayi. The experimental design was a randomized complete block with 4 replicates. The three irrigation treatments were: a non irrigated check, one inch per irrigation for a total of 4.8 inches, and 2 inches per irrigation for a total of 8.7 inches. Four irrigations were applied approximately every 2 weeks starting on May 19. The amount of water applied to each plot was measured by a water meter for each plot and recorded after each irrigation (Table 3). At the first irrigation on May 19, Penstemon acuminatus had ended flowering, Penstemon deustus and Penstemon speciosus were flowering, and Eriogonum umbellatum was just starting flowering.

Soil volumetric water content was measured by neutron probe. The neutron probe was calibrated by taking soil samples and probe readings at 8-, 20-, and 32- inch depths during installation of the access tubes. The soil water content was determined volumetrically from the soil samples and regressed against the neutron probe readings, separately for each soil depth. The regression equations were then used to transform the neutron probe readings during the season into volumetric soil water content.

Irrigation for seed production in 2007
In March of 2007, the drip irrigation system was modified to allow separate irrigation of the species due to differing growth habits. The three Lomatium sp. were irrigated together and Penstemon deustus and P. speciosus were irrigated together, but separately from the others. Penstemon acuminatus and Eriogonum umbellatum were irrigated individually. In early April, 2007, the three globe mallow species, two prairie clover species, and basalt milkvetch were divided into plots with a drip irrigation system to allow the same irrigation treatments as the other forbs. Soil volumetric water content was measured in 2007 as in 2006.

On April 5, irrigations for the three Lomatium sp. were started. On April 19, irrigations for Penstemon deustus and Penstemon speciosus were started. On May 2, irrigations for Penstemon acuminatus and Eriogonum umbellatum were started. Irrigation treatments were the same as in 2006. The three globe mallow species, two prairie clover species, and basalt milkvetch were irrigated together according to the treatments starting on May 16. Inadvertently, irrigation treatments were not stopped after 4 irrigations were applied, as in 2006. Irrigation treatments for all species were continued until the last irrigation on June 24.

Cultural practices, harvest, and seed cleaning in 2007.
Penstemon acuminatus and Penstemon speciosus were sprayed with Aza-Direct^® at 0.0062 lb ai/acre on May 14 and May 29 for lygus bug control.

Lomatium grayi seed was hand harvested on May 30 and June 29. Lomatium triternatum was hand harvested on June 29 and July 16. The seed was separated from the stalks by hand and cleaned with a small clipper seed cleaner. Since the seed harvest and cleaning varied by species, the details are reported in Table 2.

The three Sphaeralcea species were hand harvested on June 20, July 10, and August 13. The harvested seed pods were threshed in the small plot combine with an alfalfa seed concave. The two prairie clover species were hand harvested on June 20 and July 10.

Penstemon acuminatus was harvested on July 9 with the small plot combine with an alfalfa seed concave. The seed was further cleaned with a small clipper seed cleaner. Penstemon speciosus was hand harvested on July 23. Hand harvest for Penstemon speciosus was necessary due to poor seed set. Penstemon speciosus seed was separated by hand and cleaned with a small clipper seed cleaner.

Eriogonum umbellatum was harvested on July 31 using the small plot combine with a dry bean concave. The seed was threshed by hand and cleaned with a small clipper seed cleaner.

Table 2. Seed harvest and cleaning by species in 2007. Malheur Experiment Station, Oregon State University, Ontario, OR.

Species	Number of harvests	Harvest method	Pre cleaning	Threshing method	Cleaning method
Eriogonum umbellatum	1	combinea	none	dewingerd	mechanical
Penstemon acuminatus	1	combineb	none	combine	mechanical
Penstemon deustus	1	combinea	mechanicalc	hande	mechanical
Penstemon speciosusf	1	combineb	none	combine	mechanical
Lomatium dissectum	0
Lomatium triternatum	2	hand	hand	none	mechanical
Lomatium grayi	2	hand	hand	none	mechanical
Sphaeralcea parvifolia	3	hand	none	combine	none
Sphaeralcea grossularifolia	3	hand	none	combine	none
Sphaeralcea coccinea	3	hand	none	combine	none
Dalea searlsiae	2	hand	none	dewinger	mechanical
Dalea ornata	2	hand	none	dewinger	mechanical

^adry bean concave
^balfalfa seed concave
^cclipper seed cleaner
^dspecialized seed threshing machine at U.S.D.A. Lucky Peak Nursery. In 2007, due to travel constraints, an adjustable hand driven corn grinder was used to thresh seed.
^ehard seed pods were broken by rubbing against a ribbed rubber mat.
^fharvested by hand in 2007 due to poor seed set.

Results and Discussion

Precipitation in the fall of 2005 and spring of 2006 was higher than normal at the Malheur Experiment Station (Fig. 1). Precipitation from October 2005 through June 2006 was 15.9 inches. The 64-year average precipitation from October through June is 9.1 inches. Precipitation from March through June was 6.4 inches in 2006. The 64-year average precipitation from March through June is 3.6 inches. The wet weather could have attenuated the effects of the irrigation treatments in 2006 (Shock et al., 2007). Of the 7 species tested, only Eriogonum umbellatum and Penstemon speciosus showed seed yield responses to irrigation rate in 2006 (Table 4).

Precipitation from October 2006 through June 2007 was 6.2 inches, lower than the 64-year average. Precipitation from March through June was 2.0 inches in 2007. The total amount of water applied to the forbs was higher than planned in 2007 (Table 3). The biweekly irrigations were continued until June 24, instead of being terminated after four irrigations. The soil volumetric water content responded to the irrigation treatments (Fig. 2 to 6).

Emergence for the two prairie clover (Dalea sp.) species in the spring of 2007 was again poor. Emergence for Penstemon deustus and for basalt milkvetch (Astragalus filipes) was extremely poor. Astragalus filipes produced negligible amounts of seed in 2007.

Flowering and seed set in 2007
Lomatium grayi started flowering in late March and ended in mid May. Lomatium triternatum started flowering in mid April and ended in early June. Lomatium dissectum did not flower. Penstemon acuminatus and P. deustus started flowering in early May and ended in late June. P. speciosus started flowering in early May and ended in late June. Eriogonum umbellatum started flowering in early May and ended in late July. The three Sphaeralcea species (globe mallow) started flowering in early May and continued flowering through September. The two Dalea species (prairie clover) started flowering in early May and ended in late June.

The three Sphaeralcea species (globe mallow) showed a long flowering period (early May through September). Multiple harvests were necessary because the seed falls out of the pods once the pods are mature.

Penstemon acuminatus and Penstemon speciosus had poor seed set partly due to a heavy lygus bug infestation that was not adequately controlled by the applied insecticides. Poor seed set for P. acuminatus and P. speciosus was also related to poor vegetative growth in 2007 compared to 2006.

Seed yields
In 2006, seed yield of Eriogonum umbellatum was highest with the 2-inch irrigation rate (Table 4). In 2007, seed yield of E. umbellatum with the 1-inch irrigation rate was significantly higher than with the non-irrigated check. Seed yield with the 2-inch rate was not significantly higher than with the 1-inch rate.

Seed yields of Penstemon acuminatus and P. speciosus in 2007 were substantially lower than in 2006, possibly due to poor vegetative growth and lygus bug damage to flowering structures (Table 4). There was no significant difference in seed yield between irrigation treatments for P. acuminatus in 2006. In 2007, seed yield of P. acuminatus was highest with the 1 inch irrigation rate. Seed yields with either the 2 inch irrigation rate or the non-irrigated check were similar and substantially lower.

For P. speciosus in 2006 and 2007, seed yields were increased with the 1 inch irrigation rate compared to the non-irrigated check. Seed yields with the 2-inch irrigation rate were lower, but not significantly different than for the 1-inch rate.

There was no significant difference in seed yield between irrigation treatments for P. deustus in 2006 and 2007. For P. deustus, the replanting of the low stand areas in October of 2005 and the replanting of the whole area in October 2006 resulted in very poor emergence and in plots with very low and uneven stand.

Of the three Lomatium species, L. grayi had the most vigorous vegetative growth in 2007. Lomatium grayi and Lomatium triternatum showed a trend for increasing seed yield with increasing irrigation rate in 2007. The highest irrigation rate resulted in significantly higher seed yield than the non-irrigated check. The much greater Lomatium growth in 2007 shows promise for higher seed yields in future years. L. dissectum had the poorest vegetative growth in 2006 and 2007 and did not flower in either year.

There was no significant difference in seed yield between irrigation treatments for the three Sphaeralcea species, with Sphaeralcea parvifolia having the highest seed yield. The Sphaeralcea species seed yields ranged from 279 to 1062 lb/acre in 2007 without irrigation.

There was no significant difference in seed yield between irrigation treatments for the two Dalea species, with Dalea ornata having the highest seed yield. Emergence for the two Dalea species was poor with plots having poor and uneven stand.

Summary and comparison of 2006 and 2007
Precipitation from March through June was 6.4 inches in 2006 and 2.0 inches in 2007. The 64-year average precipitation from March through June is 3.6 inches.

For Eriogonum umbellatum, seed yield was maximized with the 2-inch irrigation rate in 2006 and with the 1- or 2-inch irrigation rate in 2007. For Penstemon acuminatus, seed yield was not responsive to irrigation in 2006 and was maximized with the 1-inch irrigation rate in 2007. For P. speciosus, seed yields were maximized with the 1-inch irrigation rate in 2006 and 2007. For P. deustus, seed yield was not responsive to irrigation in 2006 and 2007. None of the three Lomatium species flowered in 2006. Lomatium dissectum has been very slow to develop on the experimental site and has not flowered. Seed yield for Lomatium triternatum and L. grayi were maximized by the highest irrigation rate of 2-inches in 2007. The three Sphaeralcea species and the two Dalea species were not responsive to irrigation in 2007.

The poor emergence and resulting poor stand cast doubt on the accuracy of the seed yield response to irrigation for Penstemon deustus, the three Sphaeralcea species, and the two Dalea species.

Conclusions

Subsurface drip irrigation (SDI) systems are being tested for native seed production because SDI has two potential strategic advantages; a). low water use, and b). the buried drip tape provides water to the plants at depth, out of reach of stimulating weed seed germination on the soil surface and away from the plant tissues that are not adapted to a wet environment.

Knowledge about native forb seed production would help make commercial production of this seed feasible. Irrigation methods are being developed at the Oregon State University Malheur Experiment Station to help assure reliable seed production with reasonably high seed yields. Growers need to have economic return on their seed plantings, but forbs may not produce seed every year. Due to the arid environment, supplemental irrigation may be required for successful flowering and seed set many years because soil water reserves may be exhausted before seed formation. The total irrigation water requirements for these arid land species has been shown to be low, but varied by species.

Acknowledgments

The work reported here was supported in part by the USDA Forest Service Great Basin Native Plant Selection & Increase Project.

Figure 1. Monthly precipitation from October of the previous year through July for the last three years. Malheur Experiment Station, Oregon State University, Ontario, OR, 2007.

Table 3. Irrigation treatments and actual amounts of water applied to native forbs in 2006 and 2007. Precipitation from March through June was 6.4 inches in 2006 and 2.0 inches in 2007. The 64-year average is 3.6 inches. Malheur Experiment Station, Oregon State University, Ontario, OR.

			Actual amount of water applied
Date		Irrigation rates (inches per irrigation)	Lomatium sp.	Penstemon deustus, P. speciosus	Penstemon acuminatus, Eriogonum umbellatum	Sphaeralcea sp., Dalea sp.
		------------------------------ acre inches/acre -----------------------------
2006
19-May	2		2.23	2.23	2.23
19-May	1		1.31	1.31	1.31
2-Jun	2		2.16	2.16	2.16
2-Jun	1		1.23	1.23	1.23
20-Jun	2		2.04	2.04	2.04
20-Jun	1		1.23	1.23	1.23
30-Jun	2		2.26	2.26	2.26
30-Jun	1		1.12	1.12	1.12
total	2		8.69	8.69	8.69
total	1		4.89	4.89	4.89
2007
5-Apr	2		2.00
5-Apr	1		1.28
19-Apr	2		2.78	2.78
19-Apr	1		1.34	1.34
2-May	2		2.70	2.70	2.70
2-May	1		1.40	1.40	1.40
16-May	2		2.62	2.62	2.62	2.62
16-May	1		1.42	1.42	1.42	1.42
30-May	2		2.49	2.49	2.49	2.49
30-May	1		1.22	1.22	1.22	1.22
10-Jun	2		2.46	2.46	2.46	2.46
10-Jun	1		1.09	1.09	1.09	1.09
24-Jun	2		2.59	2.59	2.59	2.59
24-Jun	1		1.41	1.41	1.41	1.41
total	2		17.6	15.6	12.9	10.2
total	1		9.2	7.9	6.5	5.1

^aareas of low stand replanted by hand in October 2005.
^b areas of low stand replanted by hand in October 2005 and whole area replanted in October 2006.Yields in 2006 are based on small areas with adequate stand. Yields in 2007 are based on whole area of very poor and uneven stand.
^cWhole area replanted in October 2005.
^dWhole area replanted in November 2006.
^epoor and uneven stand
^f LSD (0.10)