Soil-structure changes in a long-term citrus experiment.

Abstract

Data are given on the changes induced in the physical properties of the soil in a factorial experiment in which cultural, irrigation, and nitrogen treatments are being tested on citrus. Apart from an increase in the non-capillary porosity of the surface layer to the depth of cultivation, there is no difference to be noted in porosity between the cultivated plots with the addition of organic matter and the uncultivated bare-surface plots where no organic matter is added. Under permanent sod the total non-capillary porosity is reduced but larger pores are present, 44 per cent. being in the form of insect burrows 2 mm. and more in diameter. The initial infiltration rates of the cultivated plots reflect the high porosity of the surface layer, but there is no difference in the final infiltration rates for these and the bare-surface plots. The infiltration rate of the sod plots is four times as high as in the other treatments, and is attributable to the effective hydraulic area of the faunal burrows. Cultivation has reduced aggregate stability as compared with uncultivated bare-surface and sod treatments, and the sod plots are considerably better in this respect than the bare-surface plots. This is not reflected in the soil organic carbon contents. Aggregate stability increases with increasing ammonium sulphate applications regardless of the cultural treatments. This is associated with increasing soil acidity, which, incidentally, may influence structure through its effect on microflora and exchangeable cations.