Nitrogen leaching losses under a less intensive farming and environment (LIFE) integrated system

Abstract

Less Intensive Farming and Environment (LIFE) management is a form of integrated farming which aims to meet farming's economic and environmental requirements. We used a farm-scale LIFE demonstration to measure nitrogen (N) leaching losses over a 6 year period (1995±2001) using ceramic suction cups and a meteorological model to give estimates of drainage volumes. Losses from the system averaged 49 kg N ha ±1 , with an average drainage nitrate concentration of 15.5 mg N L ±1 . Rainfall and its distribution strongly in¯uenced the loss, and drainage N concentration only fell below the nominal target of 11.3 mg N L ±1 (the EU limit for potable water) in the two wettest seasons. Crop type did not have a signi®cant effect on either postharvest mineral N (PHMN) in soil or the leaching loss in the subsequent winter. However PHMN and overwinter N leaching declined with increasing crop yield. Overwinter crop N uptake increased with early sowing: leaching loss was only 5 kg N ha ±1 under grass sown in early September. Measurements of PHMN, crop sowing date and drainage data were used to construct simple equations to predict average drainage N concentration under various scenarios. The large N loss from our site is partially attributable to soil type (shallow over limestone), indeed on similar soil the loss from a conventional farm nearby was greater. The LIFE practices of postharvest harrowing and late cereal sowing will minimize the need for agrochemical use but they stimulate mineralization and reduce plant N uptake in autumn, leaving more N at risk to leaching. Some assessment of all environmental impacts is needed if the bene®ts of integrated practices such as those used in LIFE are to be quanti®ed.

Nitrous oxide emissions after application of inorganic fertilizer and incorporation of green manure residues

“…In integrated farming systems maximum use is made of crops that contribute positively to soil fertility, such as green manures, to reduce the environmental impact of conventional arable production (Eltiti 1992;Webster et al 2003), while maintaining crop yields and pro®ts (Jordan et al 1997). Over-wintering green manures and cover crops have been shown to retain up to 60 kg N ha ±1 over their growing period (Christian et al 1992;Shepherd and Lord 1996), thereby reducing NO 3 ± leaching and the potential for loss of N as N 2 O.…”