Hydraulic properties of sphagnum peat moss and tuff (scoria) and their potential effects on water availability

Abstract

The potential rate of water and nutrient supply to plant roots depends on the hydraulic properties of the container medium (growth medium, substrate), primarily on its unsaturated hydraulic conductivity, which is a measure of the medium's resistance to water flow. Water availability to plants grown in containers is usually being evaluated using criteria based exclusively on water characteristic curves of the medium in which the plant is grown. This approach is challenged in the present paper. We hypothise that the coarse structure of peat moss as well as of other container media may result in a sharp decrease in hydraulic conductivity, as the water content of peat is reduced. Transient changes in unsaturated hydraulic conductivity may result in reduced water uptake by plant roots. The objectives of this research were to determine the hydraulic properties of sphagnum peat moss and to evaluate their potential effects on water availability. Tuff (granulated volcanic ash) and its mix with peat were also tested for comparison. Water characteristic curves (drying and wetting cycles) and saturated hydraulic conductivity were measured. A predictive mathematical model was used to calculate the unsaturated hydraulic conductivity of the media. Measured water retention and saturated hydraulic conductivity data were used to estimate model parameters by a nonlinear least-squares curve-fitting technique. Model predictions of unsaturated hydraulic conductivity were validated by direct measurements. Results showed that~sharp variations in hydraulic conductivity occur in a very narrow suction range (0-2.5 kPa). In this range a decrease of more than three orders of magnitude in the unsaturated hydraulic conductivity was observed for peat. A similar trend was observed for the other media tested. This suggests that the approach that has been commonly used for determinations of water availability and for irrigation scheduling in container media may provide inaccurate predictions as to potential plant response.

Hydrological Behavior of Peat- and Coir-Based Substrates and Their Effect on Begonia Growth

“…As shown, a sharp decrease of the unsaturated hydraulic conductivity was observed within this range of water pressure heads (0 to −100 cm). Similar results have also been reported by other researchers (e.g., [20,44,45]). Comparing the unsaturated hydraulic conductivity values of the substrates A 70 :Ps 24 : P6 , C 75 :P 25 , and Ps 50 :P 50 characterized as "ideal" (Figure 4), it is apparent that remarkable differences exist among them (Table 5).…”

Tomato sap flow, stem and fruit growth in relation to water availability in rockwool growing medium

“…The water retention curve of the used rockwool substrate corresponded fairly well with what has been reported earlier in literature (Table 1; da Silva et al 1993;Raviv and Lieth 2008). Our estimated value of θ s differed, however, from the one reported by Bougoul et al (2005), who reported θ s values much lower than the porosity of rockwool.…”

“…In our study θ s approximated 95% of the porosity which is in general agreement with standard observations. In accordance with da Silva et al (1995), the rockwool substrate in our study was characterized by a very high water content at saturation (h=0), which decreased sharply with decreasing h, approaching zero at −5 kPa (da Silva et al 1993;da Silva et al 1995;Jones 1992). Additionally, K rel was shown to decrease rapidly with decreasing h. As a result, K rel was approximately zero when h was −1.5 kPa.…”

Effects of the physical properties ofsphagnumpeat on the nursery growth of containerizedpicea marianaandpicea glaucaseedlings

“…The negative correlation found in this study between air volume and seedling diameter in white spruce indicates that aeration was not a limiting factor. In unsaturated peat, hydraulic conductivity is very low (Örlander & Due 1986, da Silva et al 1993, resulting in large negative water potentials within the seedling (Bernier 1992). The high porosity caused by the exclusion of fine particles might have enhanced this negative aspect of the peat to the point of limiting seedling growth even with regular watering.…”