Open AccessPotential for nitrate leaching from different land uses in the Pukekohe area
Author(s) -
J. R. Crush,
S.N. Cathcart,
P. C. Singleton,
R. D. Longhurst
Publication year - 1997
Publication title -
proceedings of the new zealand grassland association
Language(s) - English
Resource type - Journals
eISSN - 1179-4577
pISSN - 0369-3902
DOI - 10.33584/jnzg.1997.59.2266
Subject(s) - leaching (pedology) , environmental science , agronomy , topsoil , nitrate , groundwater , nitrogen , crop , soil water , agriculture , dry matter , chemistry , biology , ecology , soil science , organic chemistry , geotechnical engineering , engineering
Nitrogen balances (inputs minus outputs) were calculated for 5 dairy farms, 5 orchards and a range of crops. All the balances were positive, i.e., surplus N was present and a proportion of this N will eventually reach the groundwater as nitrate. On a per ha basis, the greatest N surplus was from early potatoes > winter cabbage, winter lettuce and squash > dairying, kiwifruit, summer cabbage and summer lettuce > pumpkins, onions and main crop potatoes > dry stock farming. The area in each activity was multiplied by the surplus N factor to obtain the potential contribution of N to groundwater in the Pukekohe area. Early potatoes (217 t N), contribute much more than onions (105 t N), dairying (59 t N) or dry stock farming (57 t N). Other activities contributed < 30 t N each. Winter crops had higher surplus N levels than the same crop grown in summer because winter crops had higher fertiliser N inputs and lower crop off-take of N. Management practices contributing to the N surpluses include high rates of N fertiliser used on some crops; a long history of cultivation, which has reduced soil organic matter contents and the ability of these soils to immobilise mineral N; and nil to intermittent use of cover crops to retain N in the topsoil. Keywords: aquifers, dairying, fertiliser, groundwater, land use, management, nitrate, nitrogen balance, nitrate leaching, vegetables.