Evaluation of gypsum and organic matter additions for improving soil structure in a radiata pine nursery at Benalla, Victoria

Abstract

A randomized block experiment was carried out in a radiata pine nursery at Benalla where the soil is weakly aggregated and slakes severely on wetting. Sunflower hulls or sudax ST6 hay or gypsum/dolomite were added during one cycle of a summer green crop, winter cover crop and a pine crop. Plots were also split for a deep ripping treatment. The aim was to improve soil conditions for the growth of pine seedlings. The addition of 170 t/ha of sunflower hulls reduced bulk density (P<0.01) and surface crust resistance (P< 0.05) and markedly increased infiltration capacity (P<0.01). Water-stable aggregation was not statistically affected by any of the treatments because the soil has a clay content of only 18%, though there was an encouraging trend of more water-stable aggregates within the size range 0.25-2 mm following the application of sunflower hulls. Germination of the pine crop was unaffected by treatments as the seed was covered with coarse sand. Seedling survival was low (range 41.1 -47.6%), due in part to saline conditions following fertilizer application. Early growth of seedlings was greater (P<0.05) where additional organic matter was incorporated, but differences between treatments were not statistically significant at harvest. We conclude that soil conditions can be improved for pine growth by adding a large quantity of organic matter, reducing cultivation and maintaining an intensive green cropping program.