Influence of rate and grading of sugar beet lime (SBL) waste on the properties and yield potential of a peat based mushroom casing

Sugar beet lime (SBL) was sieved to a number of particle sizes (No grading, <= 4.75, <= 2.00, and <= 0.25 mm) and incorporated at different rates (50, 75, 100 and 125 kg m(-3)) into peat casing. The SBL was stored under cover, aerobically composted and aged 12 months before use. A sandbox apparatus was used to determine the volumetric water content of the treatment casing blends gravimetrically, over a range of suction pressures (between 0 and -100 hPa). The data were used to determine a range of physical properties for each casing blend. Quality parameters for harvested mushrooms, mushroom dry matter and colour were also determined. Tensiometers were used in situ to evaluate the effect of rate and particle size of SBL on the matric potential of the treatment casings. Increasing the rate of SBL in the casing from 50 to 125 kg m(-3) lowered organic matter content, reduced total pore space and water holding capacity and increased ash content, pH and electrical conductivity. Reducing the particle size across the four rates of incorporation increased bulk density, electrical conductivity, pH and percentage ash and reduced pore space over the range of SBL incorporation rates. Water retention properties of casing increased and matric potential decreased as rate and grade of the SBL was reduced over the course of the crop cycle. Casing blends incorporating SBL at the rate of 75 kg m(-3) and graded to <= 0.25 mm produced significantly higher mushroom yields and whiter mushrooms with lower dry matter.