Biochemical changes in a yellow-brown loam and a central gley soil converted from pasture to maize in the Waikato area

Abstract

Some biochemical properties of topsoil samples oftwo soils—Horotiu silt loam (yellow-brown loam) and Puniu silty clay loam (central gley soil)—in the Waikato area, that had been under pasture for at least 50 years and cropped with maize for 8 years were compared. Organic C contents of the Horotiu and Puniu pasture samples were 10.1 and 7.8 percent respectively, and total N contents 0.97 and 0.70 percent respectively. Under maize, organic C contents had declined by 40 percent In Horotiu soil and 54 percent in Puniu soil. Carbon dioxide production, net production of mineral N, microbial biomass (as measured by biomass C, mineral N flush, and ATP contents), and enzyme activities (urease, phosphatase, sulphatase, invertase, amylase, cellulase, and hemicellulase) had all declined appreciably more with cropping than had organic C contents; they would therefore provide more sensitive indicators than organic matter to changes in soil with management.

All biochemical activities (except urease and, to a lesser extent, invertase), when expressed on a soil organic C or total N basis, were lower in Horotiu than Puniu samples. Together with the organic C changes, they suggest that some stabilisation of organic matter had occurred in the allophanic Horotiu soil.

Generally, Horotiu soil that had been under maize for 11 years differed little in its biochemical activities from that under maize for 8 years.

Keywords:

• Horotiu silt loam
• Puniu silty clay loam
• gley soils
• allophanes
• Gramineae
• Zea mays
• maize
• soil micro-flora
• soil composition
• soil biochemical properties
• organic composition
• biomass
• soil enzymes
• pastures
• crop sequence