Changes in pH, bicarbonate-extractable-P, carbon and nitrogen in soils under pasture over 7 to 27 years

We examined changes in soil pH and total carbon (C), nitrogen (N) and bicarbonate phosphorus (bicarbonate-P) in resampled sites under grazed pastures, using two data sets on commercial farms. These were a soil quality (SQ) data set (0–10 cm soil depth; samples collected along transects) and a soil profile data set from National Soils Database (NSD) sites. For 158 topsoils from the SQ data set, the number of sites increasing and decreasing in pH was almost equal, and the mean pH increased slightly after about 7 years. Soil C increased under drystock, especially in hill country, but there was no significant change under dairying; the C:N ratio decreased more rapidly in soils under drystock than under dairy. Although there was no strong direct relationship between pH and C loss or gain, those sites decreasing in pH had significant gains in C, whereas sites increasing in pH had no significant gains in C. Bicarbonate-P increased in flatter land, but not in hill country. Resampling of 89 NSD soil profiles after...