SOME SPECTRAL PROPERTIES OF SEVERAL SOIL TYPES - IMPLICATIONS FOR PHOTOMORPHOGENESIS

Abstract. Light transmission through several sands, soils and size classes of glass beads was investigated. The glass beads served as a highly reflective model system for the sands. Light penetration was significantly better through sands than through either sandy or silty loams. For sandy soils, there was a shift in the spectrum leading to a change in the red‐to‐far‐red photon ratio with increase in depth: this ratio dropped by more than 30% in the first few millimetres, and in some cases increased again with further increases in depth. The depths at which these changes occurred in the soil profile were specific for a given soil type. Similar spectral changes were obtained when sample depth for a sandy soil was held constant, and particle (ped) size of that soil was decreased. No such changes, either with sample depth or ped size, were observed with loams. Per cent transmittance in the blue (442 nm) was more than three orders of magnitude lower than in the red (632.8 nm) for sandy soils. When dry sandy soils were water‐saturated, their transmittance increased by up to three orders of magnitude, and the red far‐red ratios in the transmitted light increased in all cases. By contrast, water‐saturated loams were essentially opaque. The possible significance of these spectral properties of soils in seed germination and seedling photomorphogenesis is discussed. Copyright © 1990, Wiley Blackwell. All rights reserved