Characteristic moisture curves and maximum water content of two crop residues

Abstract

Limited data are available relating water potential (Ψ) to crop residue water content (Θ), although this relationship is important to study decomposition and moisture retention of the residue layer in no-till systems and other agricultural situations where residues are used. The objectives of this study were (i) to determine the characteristic moisture curves of rye (Secale cereale L.) and clover residues (Trifolium incarnatum L.), and (ii) to determine residue characteristics that can predict maximum water content of crop residues. Air-dried residues were separated into leaves and stems, cut into 0.5 cm length pieces and saturated with distilled water. Pieces of the drained residues were dried to various water contents in the laboratory and then transferred into thermocouple psychrometer chambers. Characteristic moisture functions of the type Ψ = a ċ Θ^−b, where a and b are empirical constants, were fitted to the data. The characteristic moisture curves had a similar shape to that of a Cecil sandy loam soil used as an example; however, while plant residues were able to retain up to 4.3 g H₂O g⁻¹, the mineral soil retained only 0.22 g H₂O g⁻¹. Soluble carbohydrate concentration can be used as a practical index to estimate maximum water content of residues, given the good relationship between both variables (R ² = 0.92).