The pattern of dry matter and nutrient content changes in native pastures at Katherine, N.T

Abstract

At Katherine, N.T., changes in the above ground dry matter yield and nitrogen and phosphorus content of native pasture under a low open forest canopy were followed over three seasons, 1959-1962, by fortnightly sampling. Substantial increases in dry matter yield at the start of the season took place on4 when two or more inches of rain had fallen in the previous fortnight. Within four weeks of the cessation of rain at the end of the season, moderate to sharp falls in dry matter yield were recorded. Nitrogen and phosphorus contents remained in an approximately constant ratio of 14 : 1 throughout the sampling period. Both increased sharply during the first fortnight in which two or more inches of rain fell, declined rapidly in the next four to six weeks, and thereafter fell at a slow and steady rate. Maximum nitrogen and phosphorus yields were attained at the same time as, or shortly before, maximum dry matter yield was attained. Immediately after the attainment of maxima, there was a sharp fall in nitrogen and phosphorus yield. More detailed sampling at the end of the 1961 -62 season indicated that this was largely due to losses of nitrogen and phosphorus from the leaves.