Land Retirement Demonstration Project

THE PRE-IRRIGATION TRIAL

Overview

In this trial, the utility of pre-irrigating lands prior to imprinting was investigated. Pre-irrigation is a common weed-control practice in agriculture (Lanini et al. 2003), and is a recommended approach in hedgerow installation (Earnshaw 2004). Hence, it appeared that this technique might also have some utility in the ecological restoration of retired agricultural lands.

Pre-irrigation entails irrigating the land before the start of the growing season (i.e., the initiation of winter rainfall in late fall-early winter) in order to promote germination of the 'winter weeds.' The weeds are then removed, either chemically, by tillage, or by burning, and the crop is seeded. In this manner, the seeded species hopefully have a competitive advantage over any additional weeds that germinate later in the growing season.

The area designated for the trial had been dominated by a variety of weeds during the preceding year, and the area had been disked for weed control during the winter of 2001-02. Plots were ca. 0.2 ha (0.5 ac) in size; a complete random block design was applied with treatments replicated four times. A single treatment factor (pre-irrigation) was evaluated (Figure 1).

Figure 1. Experimental design of the Growth-form and Herbicide Trial.

Site preparation was initiated on 3 September, 2002. The soil was disked and trenches were installed for flood irrigation. In order to account for the effects of site preparation on vegetation establishment, the control plots received the same preparation as the treatment plots (i.e., trenches were also dug in the control plots but these were not flooded). The pre-irrigated plots were sprinkler-irrigated (cf. Lee & Dyer 1997) from September 7-9. After the winter weeds had germinated, all plots (treatment and control) were disked (14 October, 2002).

Following disking, a mixture containing seed of eight native species (Table 1) was imprinted in all plots (19 November, 2004). Data were collected from 12 quadrats (35 x 70 cm) per plot. Vegetation monitoring was conducted on 29 April, 2003.

---

Table 1. Species imprinted in the Pre-irrigation Trial, including family, common name, life-form, and seeding rate. Seeding rates are expressed as pure live seeds per square foot (PLS/ft²).

Taxon	Family	Common Name	Life-form	Seeding Rate
Allenrolfea occidentalis	Chenopodiaceae	iodine bush	shrub	7.01
Atriplex polycarpa	Chenopodiaceae	allscale saltbush	shrub	2.44
Frankenia salina	Frankeniaceae	alkali heath	perennial herb	2.51
Hemizonia pungens	Asteraceae	common spikeweed	annual herb	2.45
Lasthenia californica	Asteraceae	California goldfields	annual herb	7.81
Sesuvium verrucosum	Aizoaceae	western sea-purslane	perennial herb	2.68
Suaeda moquinii	Chenopodiaceae	bush seepweed	sub-woody perennial	18.31
Vulpia microstachys	Poaceae	small fescue	annual herb	7.81

---

References

Earnshaw, S. 2004. Hedgerows for California Agriculture. A Resource Guide. Community Alliance With Family Farmers, Davis, CA.

Lanini, W. T., S. Fennimore and T. Stevenson. 2003. Pre-irrigation followed by cultivation or flaming to deplete the weed seed bank prior to crop planting. U. C. Davis, Davis, CA.

Lee, J. and D. A. Dyer. 1997. Organic Processing Tomatoes in Yolo County: Moving Towards Sustainability. TN-PLANT MATERIALS-48. USDA-NRCS Lockeford Plant Materials Center, Lockeford, CA.

Page created: March 1, 2005; Last updated: April 3, 2005