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