2 results for Power, I.L.

  • Trends in soil carbon and nutrients of hill-country pastures receiving different phosphorus fertilizer loadings for 20 years

    Schipper, Louis A.; Dodd, M.B.; Fisk, L.M.; Power, I.L.; Parenzee, Jacinta; Arnold, Greg (2010)

    Journal article
    University of Waikato

    There are few records of long-term trends in soil C and N in grazed pasture systems but recent measurements have demonstrated unexplained losses on New Zealand lowlands. To determine whether losses were also occurring in hill country pastures, we analyzed archived soil samples collected between 1983 and 2006 from two slope classes (steep and easy) at the Whatawhata Research Centre. Soils were Ultic Hapludand and Typic Haplohumult on the easy slopes (10–20°), and Typic Haplohumult on the steeper slopes (30–40°). Soil samples (0–75 mm) had been collected from paddocks that were fertilized with six different loading rates of P (ranging from 0 to 100 kg P ha⁻¹ year⁻¹ since 1985). This range of P loadings allowed us to determine whether P inputs would regulate trends in soil C and N. While there were significant temporal trends in C and N (P < 0.05), these were not unidirectional and trends were not dependent on P loading rate. On average, soil C initially increased during the first 6 years of the trial at 0.270% C year⁻¹ (1.56 t ha⁻¹ year⁻¹) and 0.156% C year⁻¹ (1.06 t ha⁻¹ year⁻¹) on easy and steep slopes, respectively. Subsequently, there was no significant trend in soil C on the easy slopes but soil C declined at −0.066% year⁻¹ (0.45 t ha⁻¹ year⁻¹) on the steep slopes. Similarly, soil N increased between 1983 and 1989 at 0.025% N year⁻¹ (144 kg ha⁻¹ year⁻¹) and 0.012% N year⁻¹ (82 kg ha⁻¹ year⁻¹) on easy and steep slopes, respectively. Post-1989, small but significant losses of total N were measured on the steep slopes of 0.004% year⁻¹ (27 kg N ha⁻¹ year⁻¹) (P < 0.05) with no trend on the easy slopes. Two potential causal factors for these decadal-scale patterns were identified, operating via changes in primary productivity. These were lower S inputs from 1989 due to a change in fertilizer type, and a series of relatively dry summers during the 1990s. These significant inter-annual trends in soil C and N complicate attempts to measure long-term changes in soil organic matter associated with land use change and management practices. This study has demonstrated the potential error associated with infrequent soil sampling to determine long-term trends in soil C and N; large gains or losses could have been detected at Whatawhata depending on when sampling started and finished. Understanding these long-term trends in soil organic matter dynamics and driving factors requires more long-term sampling trials.

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  • Rates of accumulation of cadmium and uranium in a New Zealand hill farm soil as a result of long-term use of phosphate fertilizer

    Schipper, Louis A.; Sparling, Graham P.; Fisk, L.M.; Dodd, M.B.; Power, I.L.; Littler, Ray A. (2011)

    Journal article
    University of Waikato

    In New Zealand, phosphate (P) fertilisers used in agriculture are the main sources of the potentially toxic elements cadmium (Cd) and uranium (U), which occur as unwanted contaminants. New Zealand is developing draft soil guideline values (SGV) for maximum concentrations of Cd. To assess when soils under pasture for sheep production might reach a particular SGV, we analysed archived soil samples from a 23 yr P fertiliser trial. The pasture sites were at Whatawhata, North Island, New Zealand, and had received P fertiliser at the rates of 0, 30, 50 and 100 kg P ha⁻¹ yr⁻¹. From 1983 to 1989, P was applied as single superphosphate, from 1989 to 2006, P was applied as triple superphosphate. Soils from replicate paddocks were sampled annually to a depth of 75 mm on easy (10–20°) and steep (30–40°) slope classes. Total P, Cd and U were analysed by ICP-MS after acid digestion. Data were analysed by fitting trend lines using linear mixed models for two slope classes and for two sampling periods 1983–1989 and 1989–2006 when the soil sampling method and fertiliser type had been changed. The changes in total P, Cd and U were directly related to the type and amount of P fertiliser applied, the control treatment showed no significant change in P, Cd or U. At 50 and 100 kg P ha⁻¹ yr⁻¹ there were generally linear increases in total P and total U, and the same trend line applied to both time periods, but the rate of increase in P was greater on the easy slope class. For Cd, a “broken stick” model was needed to explain the data. Pre-1989, Cd increased in the 50 and 100 kg P ha⁻¹ yr⁻¹ treatment (0.036–0.045 mg kg⁻¹ yr⁻¹, respectively): post 1988 the rate of increase declined markedly on those two treatments (0.005–0.015 mg kg⁻¹ yr⁻¹, respectively), and declined absolutely in the 30 kg P ha⁻¹ yr⁻¹ treatments. The maximum content of Cd was in the 100 kg P ha⁻¹ yr⁻¹ treatment which reached 0.931 mg Cd kg⁻¹ on the easy slope. For U there were steady linear increases for the 30, 50 and 100 kg P ha⁻¹ treatments, and no significant difference between the steep and easy slopes, nor the two sampling periods, the maximum concentration obtained was 2.80 mg U kg⁻¹ on the 100 kg P ha⁻¹ treatment. The results suggest that at rates of P fertiliser likely to be applied to hill farms (<50 kg P ha⁻¹ yr⁻¹ ), and using P fertiliser with low Cd content, then the Cd concentration in this soil will never reach a SGV of 1 mg kg⁻¹.

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