Large losses of soil C and N from soil profiles under pasture in New Zealand during the past 20 years

Abstract

The conversion of two-thirds of New Zealand's native forests and grasslands to agriculture has followed trends in other developed nations, except that pastoral grazing rather than cropping dominates agriculture. The initial conversion of land to pasture decreased soil acidity and elevated N and P stocks, but caused little change in soil organic C stocks. However, less is known about C and nutrient stock changes during the last two decades under long-term pastoral management. We resampled 31 whole soil profiles in pastures spanning seven soil orders with a latitudinal range of 36-461S, which had originally been sampled 17-30 years ago. We measured total C, total N, and bulk density for each horizon (generally to 1 m) and also reanalyzed archived soil samples of the same horizons for C and N. On average, profiles had lost significant amounts of C (À2.1 kg C m À2 ) and N (À0.18 kg N m À2 ) since initial sampling. Assuming a continuous linear decline in organic matter between sampling dates, significant losses averaged 106 g C m À2 yr À1 (P 5 0.01) and 9.1 g N m À2 yr À1 (P 5 0.002). Removal of C through leaching and erosion appears too small to explain these losses, suggesting losses from respiration exceed the inputs of photosynthate in the soil profile. These results emphasize that resampling soil profiles provide a robust method for detecting soil C changes, and add credence to the suggestion that soil C losses may be occurring in some temperate soil profiles. Further work is required to determine whether these losses are continuing and how losses might be extrapolated across landscapes to determine the implications for New Zealand's national CO 2 emissions and the sustainability of the implied rates of soil N loss.

Evaluating the lingering effect of livestock grazing on functional potentials of microbial communities in Tibetan grassland soils

“…As a result, the magnitude of soil carbon (C) and nitrogen (N) pools could be altered by reallocating C and N between roots and shoots, or by recycling C and N through the animal excreta pathway (Hamilton and Frank 2001;Ruess and Mcnaughton 1987). Soil C stock has been shown to decrease significantly in temperate grassland during 20 years of grazing, which might be owing to loss from respiration (Schipper et al 2007). However, another analysis found that C stock was unchanged in grazed tussock grassland and increased in grazed hill country soil (Schipper et al 2010).…”

Contributions of secondary forest and nitrogen dynamics to terrestrial carbon uptake

“…Furthermore, cultivation also removed ecosystem N due to crop consumption and export. Schipper et al (2007) indicates that significant amount of soil C and N is lost from soils under pasture in New Zealand during 20 years time period. Therefore it is expected that regrowing forest would very likely be nitrogen limited.…”

Effects of organic matter amendments on net primary productivity and greenhouse gas emissions in annual grasslands

“…The sustainability and profitability of rangelands is largely a function of forage quality and quantity (Briske et al 2011). However, these ecosystems have, to varying degrees, experienced degradation of vegetation and soils due to overgrazing, plant invasions, and climate change (Asner et al 2004, Schipper et al 2007, Bai et al 2008. Thus, management practices aimed at enhancing plant production may have considerable potential to restore or increase grassland C storage and feed back on the global C cycle (Schimel et al 1990, Conant et al 2001, Follett 2001, Schuman et al 2002, Derner and Schuman 2007.…”