Long-term fertiliser application and fertility of hill soils

Abstract

<jats:p>Application of phosphatic fertiliser to legume/grass pastures, and increased stocking rate, is commonly assumed to increase soil organic matter (estimated from soil carbon) content, to lower soil pH, and to increase soil Olsen P status. Changes in these variables in soils derived from sedimentary parent material were monitored over 16 years, in a longterm grazing experiment on southern North Island hill country. There were 2 fertiliser treatments, principally high (capital applications followed by 375 kg/ha/year) and low (125 kg/ha/year) superphosphate application. There was a net loss of soil C of approximately 200 kg/ha/year in both treatments, although annual C inputs to the soil were greater (by 1000 kg/ha) in the high fertiliser soils. Soil pH increased slightly; and Olsen P status reflected P application, although it was less responsive to P application (13 kg P/ha applied above maintenance for 1 Olsen P unit increase) than has commonly been assumed is the case (4-7 kg P/ha per unit). The most likely reason for net loss of soil C is increased decomposer activity in the soil, and the greater proportion of plant-fixed C ingested by grazing animals as a result of intensification. The lack of a decline in soil pH may have been related to the declining soil organic matter level lowering hydrogen ion-supplying power. The lower-than-expected responsiveness of Olsen P to fertiliser P application was probably because the experimental area had a very poor fertiliser application history, in comparison with previous experiments against which Olsen P was calibrated. Keywords: carbon, fertiliser application, hill country, Olsen P, organic matter, pH, soils</jats:p>

Dissolved organic matter leaching in some contrasting New Zealand pasture soils

“…The magnitude of such losses suggests that, rather than being at steady state, the soil organic matter (SOM) content in developed pastures continues to change in response to the balance of inputs and losses. Earlier work by Ghani et al (1996) and Lambert et al (1998) also found losses in SOC in pasture soils that would otherwise be regarded as still developing and accumulating SOC. It is important to consider the consequences of losses of SOC of the magnitude reported by Schipper et al (2007).…”

New-generative agriculture – based on science, informed by research and honed by New Zealand farmers

“…Long-term trials undertaken in New Zealand hill country support the fact that SOM can be increased with fertiliser application (Lambert et al 1996;Parfitt et al 2003). When the plots were grazed hard, however, SOM was lost -more from the high-fertiliser plots than the low-fertiliser plots due to increased activity of soil decomposers, but SOM was still higher on the high-fertiliser plots (Lambert et al 1998), as found in the Khan et al (2007) research.…”