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Water Use
Water Requirements. The amount of water available to safflower is a key factor in determining yield. Safflower is thought to be a drought resistant crop. While it tolerates high temperatures and requires low atmospheric humidity, safflower will not produce a satisfactory crop without adequate soil moisture. Because it can explore a large, deep soil volume to recover water, it is able to grow when other crops with less aggressive root systems cannot. However, safflower is a C31 crop like tomatoes and cotton. To grow and produce an economic yield, approximately the same amount of water is required per unit of dry matter produced as required by other C3 crops experiencing comparable conditions.
Temperature and atmospheric humidity determine the water requirement of safflower and the amount of green leaf area maintained by the crop over the period it grows and develops. Together these factors will vary somewhat from season to season and especially by location. A safflower leaf canopy experiencing hot, dry conditions will require more water to produce an equivalent amount of plant or seed biomass than a plant experiencing cooler, less arid conditions. This amount can equal as much as one-half inch per day (12 mm) for a crop with a complete leaf canopy.
The moisture available to the crop during the season is dependent on soil depth, stored soil moisture, soil physical properties and whether or not the crop will be irrigated. Safflower grows best in soils well supplied with moisture, but will survive and produce a low yield if it can transpire a minimum of 16 to 18 inches (400 to 460 mm) of water, provided plants have not developed a large leaf canopy early and exhausted soil reserves before the seed maturation period begins. In countries where subsistence farming is practiced, however, safflower production is attempted and low yields achieved on lesser amounts of available water. In California, experience indicates that a total of about 20 to 25 inches (500 to 630 mm) of available water is required for economic yields (approximately 2,000 lbs per acre) under non-irrigated conditions. Under irrigation in the Central Valley, 25 to 44 inches (630 to 1,100 mm), including water derived from rainfall, will be used by a high yielding crop due to the larger leaf canopy that tends to develop and a longer period of growth. Depending on the efficiency of the irrigation system used and the amount of precipitation or stored soil moisture present, a larger amount of water than the amount transpired must be applied to account for irrigation losses, including an amount needed for a leaching fraction under saline conditions. An approximate relationship between yield and evapotranspiration (ET) in the Central Valley is 100 pounds of seed per inch of ET (4.4 kg per mm)-(figure 5).
Figure 5. Estimated yield and evapotranspiration in the San Joaquin Valley. Yield (lb/acre) = 105.2 ET. Average Boswell data. Source: Adapted from Fisher, Yamada, and Pomeroy 1967.
Some of the highest yields experienced in California are obtained in locations where subirrigation from shallow groundwater occurs, such as the Sacramento-San Joaquin Delta and the Tulare Lake Basin, and on deep soils storing moisture to a depth of 6 to 12 feet (2 to 4 m) from winter rainfall, pre- or early season irrigation. Where there is no shallow water table, soils must be capable of storing the majority of this water since in California's Mediterranean climate, rainfall usually ceases by the time the crop begins to grow. The low yields of some fields appear to be associated with the presence of continuously dry soil starting at a depth of 3 to 4 feet (1 to 1.1 m). Shallow, upland soils in the coastal and valley foothills have not produced large yields because of insufficient reserves of moisture in the subsoil. In upland farming conditions without irrigation (dry farming), yields of safflower have been much better following a fallow year than on continuously cropped land. On deep soils in the Sacramento Valley, safflower can be grown without irrigation and without a fallow period if rainfall fills the soil profile or previously irrigated crops have not fully used available soil moisture to safflower's rooting depth. On clay soils which restrict root growth, however, safflower may not be able to recover all the moisture present.
Sometimes plants fail to produce a satisfactory seed crop even though large, vigorous plants have developed. This can be caused by depletion of available soil moisture by the time flowering occurs. Hot dry weather at flowering may also cause seed set failure, though it is likely that this is due to moisture stress rather than any special sensitivity of safflower blossoms to high temperatures.
Damage from excess moisture. If safflower is irrigated, the soil need not store as much moisture, but irrigating safflower can be risky, especially late in the crop's development. Standing water or saturated soil near the base of the plant can lead to infection with Phytophthora, a damaging root rot. During the summer when soil temperatures are high and safflower has developed a stem or has flowered, it can be killed quickly by standing water or waterlogged soil. Young plants may withstand temporary water logging if the soil temperature is 60° F (15.5° C) or lower.
1 C3 refers to the first products of the photosynthetic pathway formed in some plant species. These are 3 carbon molecules. C4 species produce 4 carbon molecules as the first products of photosynthesis. Cotton, wheat, tomatoes, sugarbeets, and most vegetable and tree crops are C3 species. Corn (maize) and sorghum are prominent C4 species. The difference is important in this context because C4 species tend to be more efficient in the use of water than C3 species, and most C3 species have comparable water requirements per unit of dry matter produced.
Safflower Contents | Soils [6]
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Modified: 7 Jun 1999
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