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

authors: Schipper, Louis A.

subjects: soil carbon

abstract: 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.

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

year: 2010

title: TDR size and quantity

authors: Park, Simon

abstract: Simon Park has been contracted by BoPRC for several years to provide advice on land use and management in the Rotorua Lakes catchment. Since 2012 this has included working with LWQS and the Farmer Collective on collaborative solutions for Lake Rotorua, especially regarding farm nutrient losses. He is the secretariat support person for the Lake Rotorua Catchment Stakeholder Advisory Group (StAG). Simon has an MSc in Earth Sciences from Waikato University. He has previously worked at MfE on sustainable land use policies and has processed resource consents at regional and district council levels.

text: TDR size and quantity Simon Park has been contracted by BoPRC for several years to provide advice on land use and management in the Rotorua Lakes catchment. Since 2012 this has included working with LWQS and the Farmer Collective on collaborative solutions for Lake Rotorua, especially regarding farm nutrient losses. He is the secretariat support person for the Lake Rotorua Catchment Stakeholder Advisory Group (StAG). Simon has an MSc in Earth Sciences from Waikato University. He has previously worked at MfE on sustainable land use policies and has processed resource consents at regional and district council levels.

year: 2013

title: Spot sampling of nutrient concentrations in the Puarenga catchment, Rotorua

authors: Abell, Jonathan Michael

subjects: New Zealand

abstract: The Centre for Biodiversity and Ecology Research was approached by Tūhourangi Tribal Authority for assistance with measuring water quality in streams in the Puarenga Stream catchment. Water sampling was subsequently undertaken on 18 July 2011 and samples were analysed to determine concentrations of total and dissolved fractions of nitrogen and phosphorus. 
Nitrogen and phosphorus are both essential plant nutrients which, when present in excess, can cause eutrophication and associated water quality decline of freshwaters. High concentrations of dissolved forms of nitrogen can also be toxic to aquatic organisms. Excessive nitrogen and phosphorus concentrations are typically the result of pollution due to human activities, although groundwater in the Central Volcanic Plateau region can have elevated concentrations of phosphorus arising from natural geological sources.
This report summarises the methods used, presents the results and places measured concentrations in context by drawing comparisons with both guideline and regional mean values.

text: Spot sampling of nutrient concentrations in the Puarenga catchment, Rotorua The Centre for Biodiversity and Ecology Research was approached by Tūhourangi Tribal Authority for assistance with measuring water quality in streams in the Puarenga Stream catchment. Water sampling was subsequently undertaken on 18 July 2011 and samples were analysed to determine concentrations of total and dissolved fractions of nitrogen and phosphorus. 
Nitrogen and phosphorus are both essential plant nutrients which, when present in excess, can cause eutrophication and associated water quality decline of freshwaters. High concentrations of dissolved forms of nitrogen can also be toxic to aquatic organisms. Excessive nitrogen and phosphorus concentrations are typically the result of pollution due to human activities, although groundwater in the Central Volcanic Plateau region can have elevated concentrations of phosphorus arising from natural geological sources.
This report summarises the methods used, presents the results and places measured concentrations in context by drawing comparisons with both guideline and regional mean values.

year: 2011-09