Tissue density determines the water storage characteristics of crop residues

The water storage properties of plant residues play an important role in the regulation of water retention and water transport in no-till agricultural soils. The objective of this work was to understand how the characteristics of crop residues determine their water absorption and retention properties. A range of eleven undecomposed crop residues and maize stem residue of different particle sizes at three stages of decomposition were characterized regarding their physical and chemical features. Water immersion for varying periods of time was used to determine the kinetics of water absorption and the maximal water storage for each type of residue. The immersion time required to reach an equilibrium moisture content varied greatly according to the residue type, ranging from 6 to 30 h at 20 A degrees C. The maximal water content ranged from 1.28 to 3.81 g H2O g(-1) dry residue for undecomposed residues and increased with increasing decomposition. The proportions of cellulose, hemicellulose and lignin in the plant cell walls did not explain the water storage capacities. Differences in porosity, resulting from different tissue densities and the creation of pores during decomposition, were highly correlated with differences in water storage properties. The tissue density of plant residues, which can be inferred from simple characteristics of residue mass and volume, is a relevant criterion for explaining the maximal water storage capacity of plant residues.