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Soils suitable for safflower

Soil series. High yields of safflower are produced on deep, fertile, and well-drained soils. Class I and II soils characteristically produce good yields, while Class III and IV soils are problematic and crop stands are more likely to experience root rot losses, as well as available water limitations (figure 6). Sandy soils may not have sufficient water-holding capacity to produce good yields of safflower, unless irrigated frequently during the growing season.

Figure 6. Safflower soil moisture use and depth for selected Sacramento Valley soils. Both soil profiles were estimated to contain approximately 100% of their potential available soil moisture at the start of measurement. The Yolo soil is a Class I soil; the Capay soil is regarded as a Class III. Source: Adapted from Henderson 1981.

Salinity. Safflower tolerates salinity better than many other crops, however, it is more sensitive to salinity at germination than at later growth stages. Salinity in soils and drainage water has diverse effects on safflower. It reduces the rate and percent of germination. Salt affected plants are smaller and more succulent. Transpiration rates are lowered, leaf cell structure is altered, and stomatal numbers are reduced. Flowering is hastened, seed yield is reduced in flower heads, particularly in those that develop late (tertiary flower heads) (plate 1). To a lesser degree, oil percent in seeds may be reduced. Lower oil content in seeds likely is related to shortened seed development (faster physiological maturity). A similar phenomenon occurs with grain crops and bushel weights (thousand grain weights). Because seeds develop less well, the hull percentage increases.

Plate 1. Safflower damaged by high-salinity soils (left) and undamaged by low-salinity soils (right) on plots receiving equivalent amounts of water.

Varying tolerance to salinity among safflower varieties has been reported. There appears to be some genetic variation in tolerance, and the effects of other interacting factors including climate and weather, irrigation management and technology, soil physical factors, soil fertility, and the growth stage of the crop cause crop performance to deviate from predictions made based on results from experiments under controlled conditions.

In experiments conducted by the USDA Salinity Laboratory at Riverside in which increasingly saline irrigation water was applied to different, non-saline plots, a salt concentration (measured as electrical conductivity of a saturated paste extract or ECe) in the top 12 inches of soil equal to 7 dS m-1 reduced yield 10 to 15 per cent. An EC of 11 dS m-1 reduced yield about 25 per cent, however, a sharp drop off in yield occurred with irrigation water of 12 dS m-1 or greater. Crop maturity was hastened at the rate of one week per 3 to 4 dS m-1 increase in irrigation water salinity, compared to the control. More recent estimates of safflower's tolerance of saline irrigation water predict that a 50% yield reduction will occur in soils with an ECe of 9.9 dS m-1.

Germination and emergence are more sensitive to salinity than subsequent crop growth. In laboratory trials, at 6.8 dS m-1, time to emergence was doubled for all the varieties tested, suggesting that safflower may be twice as sensitive to salinity at that stage than subsequently. Final germination was reduced by 10% at 8.3 dS m-1.

In the Tulare Lake area in the southern San Joaquin Valley, safflower grows on saline soils with shallow, perched water tables. It uses water from this saturated soil zone for a substantial portion of its growth and is thought to lower the depth of perched water from 3 to 4 feet (0.9 to 1.2 m) to as much as 10 feet (3 m) during the growing season. The shallow groundwater used by safflower in this region typically varies over the range of 6 to 12 dS m-1 and soil extracts vary between 5 to 8 dS m-1 at 3 to 5 feet (0.9 to 1.5 m) in depth. Safflower yields under these conditions can be among the highest in the state.

In experiments conducted on these soils, saline irrigation water was applied to cotton for two successive years and followed by safflower in the third year, grown largely without irrigation. This cycle was repeated three times. In the first cycle, yields were largely unaffected in plots that had received irrigation water ranging from approximately 1 to 7 dS m-1 in the previous two years, but fell by approximately 40% from control plot levels in plots that had been treated with 11.6 dS m-1 irrigation water. Plant density was also reduced by approximately 30% over the same range of irrigation treatments. In later cycles, safflower yields were affected significantly at higher salinity levels, in part because plant numbers were reduced by poor germination and emergence under very saline conditions.

Sodium, distinct from overall salinity, has been shown to stimulate vegetative growth and improve safflower yields under controlled conditions. The adverse effects of salinity are unrelated to Na content per se. But if soils are sodic, with poor structure, or salts concentrations are high (ECe > 9.9 dS m-1), Na may lower safflower yields indirectly. Boron injury has been observed in some varieties. When injury occurs, leaf margins turn brown, and the affected areas enlarge until the entire leaf is killed. On relatively high boron content soils (3 to 5 ppm B) in Yolo County, however, safflower has consistently produced yields of one to two tons per acre (2200 to 4400 kg per ha) with irrigation.

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Modified: 7 Jun 1999 Comments to webmaster@agric.ucdavis.edu