| Abstrakt: |
In order to study the drought sensitivity of pea ( Pisum sativum L. cv. Bodil) during different growth phases, a field experiment was conducted in 1985 and 1986 on coarse textured sandy soil with low water-holding capacity. Drought occurred naturally or was imposed by shelters during the vegetative, the flowering and the pod filling growth phase, respectively. Drought sensitivities were assessed as the ratio between relative yield decrease (1 − Y/Y) and relative evapotranspiration deficit (1 − ET/ET) of the individual growth phases, where Y and ET are the actual yield and evapotranspiration, respectively, of a drought stressed plot and Y and ET are the maximum yield and evapotranspiration of the fully irrigated treatment. Root growth was followed by measuring root density ( L) in 10 cm soil layers to a depth of 50 cm. The leaf osmotic potential at full hydration (Ψ) was measured in the last fully developed leaf during the growing season. The available water capacity was estimated to be 42-50 mm on the basis of a plot of ET/ET versus soil water deficit measured by the neutron moderation method or direct measurement of the root depth. The root zone with L>0.1 cm only reached a depth of 35 cm at the end of the flowering phase and a depth of 45-50 cm at maturity. Root growth continued during the drought periods. The drought sensitivity of pea was high during the flowering phase, especially in 1986 when water stress developed rapidly, and considerably lower during the pod filling phase. The yield reduction caused by drought in the flowering phase was mainly the result of a lower number of pods per stalk. Severe drought did not occur during the vegetative phase. The leaf osmotic potential ( Ψ) declined from c. -0.75 MPa to c. -1.30 MPa during the growing season. Osmotic adjustment was largest during drought in the early growth phases; in 1985 Ψdecreased 0.5 MPa under relatively slow drought development during the flowering phase while in 1986, when drought stress developed rapidly, Ψonly decreased 0.2 MPa. Osmotic adjustment may have caused the lower drought sensitivity in 1985 than in 1986 and mediated the continued root growth during drought. [ABSTRACT FROM AUTHOR] |
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