Emergence response of subterranean clover to dissolved gypsum in relation to soil properties and evaporative conditions

Abstract

Using small plots set in the earthen floor of an open glasshouse, the emergence response of subterranean clover to dissolved gypsum has been determined on 10 soils covering a range of clay and exchangeable sodium levels. The response on a loam soil of low exchangeable sodium percentage (E.S.P.) has been examined at three times of differing evaporative potential. For loams and clay loams, the appearance of a response depends on the severity of evaporative conditions as well as on the E.S.P. On clay soils not naturally self mulching, some response is probably always obtained but, in general, the higher the clay content and the higher the E.S.P. and evaporative potential, the more likely is an emergence response to dissolved gypsum. Emergence was found to be highly correlated with the matric potential of the surface 1/2 in. at the time emergence began. From a consideration of the relationships between emergence and moisture status, the most significant effect of the gypsum treatment seems to be the delay of several days it causes in the air drying of the surface soil, probably because of improved transmission of moisture from beneath. Parallel effects on surface soil temperature to those on moisture can be explained in terms of differences in amount of evaporative cooling. Relationships found between emergence and emergence response to gypsum on the one hand and clay content and E.S.P. on the other are presumably a reflection of the relationship of these soil properties to porosity and moisture transmission.