Phosphorus and nitrate run‐off in hill pasture and forest catchments, Taita, New Zealand

Abstract

Phosphorus and nitrogen were measured in stream run-off from the four catchments of the Taita Experimental Basin (41° 11´ S, 174° 58´ E). The land is used as exotic conifer forest, native forest, and hill pasture. Multiple regression analysis was used to estimate chemical losses per unit area in floods and at low flows.At low flows, the hill pasture (fertilised with lime at 630 kg·ba -1 ·y -1 , and superphosphate at 380 kg·ha -1 ·y -1 ) tended to lose more phosphorus and nitrate than the forested land, but differences were small, and not always significant. During large floods, the hill pasture (No. 5 Catchment) lost about 3 times as much reactive phosphate and 2-5 times as much total phosphorus as the forested land, and 130-190 times as much nitrate as land in the Exotic Forest and Native Forest 2 Catchments. Nitrate losses from land in the No. 4 Catchment (mainly native forest) were as high as those from the hill pasture, so high nitrate loss is not associated solely with agriculture.Losses of total phosphorus via the catchment streams were estimated as: No. 5 Catchment (hill pasture), 293 g·ha -1 ·y -1 ; Native Forest 2 Catchment, 201 g·ha -1 ·y -1 ; No. 4 Catchment, 124 g·ha -1 ·y -1 ; Exotic Forest Catchment, 71 g·ha -1 .y -1 . Nitrate-N losses were estimated to have been 1356 g·ha -1 ·y -1 , 11.5 g·ha -1 ·y -1 , 1436 g·ha -1 ·y -1 , and 44 g·ha -1 ·y -1 respectively. Phosphorus and nitrate concentrations were similar in the Exotic Forest and Native Forest 2 streams, but the Exotic Forest tended to lose smaller amounts because it yielded about 50% less water per unit area.Over the 2-y study, an estimated 47-70% of phosphorus losses and up to 83% nitrate losses occurred in large floods; 31% and 48% respectively were apparently lost from the hill pasture catchment in a single flood. Less than 20% of estimated phosphorus losses and as little as 1% of nitrate losses occurred at low flows.Run-off of phosphorus and nitrate was spasmodic, and this should be considered in assessing the impact of surface run-off on the biology and chemistry of receiving waters.

Nitrogen, Phosphorus and Potassium Losses in a Grazing System with Different Stocking Rates in a Volcanic Soil

“…Overall P losses were low compared with results of P transfer from grazed land in Europe (Haygarth and Jarvis, 1997) and New Zealand (McColl et al, 1977). Values found in the present study are lower than those for P transfer found in forestry catchments in Chile (650 g ha -1 yr -1 ; Oyarzun et al, 1997).…”

“…Peaks of RP concentration were measured associated to spring P fertilizer application during all years and were greater than those reported by McColl et al (1977) for grasslands on volcanic soils. The high RP concentrations after TSF addition was probably due to the direct transport of fertilizers granules in runoff after the application and because TSP granules were rapidly solubilized by surface runoff (Heathwaite et al, 1998).…”

Phosphorus losses in surface run‐off from grazed permanent pastures on a volcanic soil from Chile

“…Peaks of TP and RP concentrations in run‐off were associated with spring P fertilizer application during both years and were greater than those reported by McColl et al. (1977) for grasslands on volcanic soils.…”

Model analysis of dissolved inorganic phosphorus exports from the Yangtze river to the estuary

“…It is defined as the fraction of TP exported from the landscape to the rivers as DIP. Plotlevel and regional studies have generally found that about 0.1-3.3% of the P applied as fertilizer or manure was lost as DIP via surface runoff transport (Burwell et al 1997;McColl et al 1977;Nicholaichuk and Read 1978;Sharpley and Syers 1979;McDowell and McGregor 1984;Sharpley et al 1995;Bennett et al 1999;Baker and Richards 2002;Cao and Lin 2006). However, Harrison et al (2005) believed that the fractional loss as DIP was underestimated in watersheds with high runoff; therefore, they allowed the fraction to vary between 1 and 10%.…”