Organic farming has been proposed as a means of reducing leaching and improving the use efficiency of plant nutrients in agriculture. In such systems, nutrient inputs originate from various organic sources or from naturally occurring minerals with low solubility. In this study, measurements of leaching and crop uptake of N, P, and K and determinations of mineral N in soil were conducted in tile-drained plots during a 6-yr period in two organic crop rotations, one with and one without addition of animal manures. In the latter, N was provided by green manures. For comparison, two conventional systems in which mineral fertilizers and pesticides were used (one with cover crops) were also included. Leaching loads of N were smallest in the conventional system with cover crops, on average 25 kg N ha 21 yr 21 over the 6-yr period. The corresponding amounts in the other systems were 39 (organic with animal manure), 34 (organic without animal manure), and 38 (conventional) kg N ha 21 . Phosphorus-leaching loads were small overall in all systems (,0.25 kg ha 21 yr 21 ). Potassium-leaching loads reached on average 27 kg ha 21 yr 21 over the 6 yr in the conventional systems and 16 kg ha 21 yr 21 in the organic systems. When N leaching was expressed as a percentage of total N removal during the 6-yr period (leaching plus harvested N with crops), it represented 59% in the organic system without animal manure, 33% in the conventional system, and 22% in the conventional system with cover crops. These results clearly suggest that N use efficiency is improved if inorganic N fertilizers are used rather than green manures, especially in combination with cover crops. The superior system from all considerations was the conventional system with a cover crop.

In this study, three types of cropping systems with different nutrient management strategies were studied on a clay soil with the aim of comparing leaching of N, P and K and obtaining knowledge on nutrient budgets. A conventional cropping system with cereals and application of mineral fertilizers (CON) was compared with two organic cropping systems, one without animal manure in which green manure crops were used for N supply (OGM) and one where animal manure (cattle slurry) was applied (OAM). Leaching and crop uptake of N, P and K, and soil mineral N were measured in pipe-drained plots over a 6-year period.The mean annual leaching loads of N were moderate and did not differ significantly (P > 0.05) between treatments; 13 kg N ha )1 in CON, 11 kg N ha )1 in OGM and 7.4 kg N ha )1 in OAM. Average annual P leaching showed greater variation than N leaching and was significantly greater in OGM (0.81 kg ha )1 year )1 ) than in CON (0.36 kg ha )1 ) and OAM (0.41 kg ha )1 ). For all cropping systems, removal in harvested crops was the most important export of nutrients from the field and constituted between 80 and 94% of total N outputs (harvested and leached N). Yields of cereals in the organic systems were considerably less (15-50%) than in the CON system, leading to a less efficient use of N than in the conventional system.

Abstract. Results are presented from three years (1992‐1995) of a field leaching experiment on a sandy soil in south‐west Sweden. Plots of spring cereals, either with or without an undersown perennial ryegrass catch crop, were compared for nitrogen leaching and nitrogen status in soil. Both treatments were ploughed in spring, and other tillage regimes were also identical. Measurements of nitrogen leaching from drains, nitrogen uptake in crops and mineral nitrogen in the soil were made. Two coupled, simulation models, which describe water flow and nitrogen transformations and transport in soil, were used to interpret data and to calculate the nitrogen budget and nitrogen mineralization in the soil. Nitrogen leaching was 40 50% less in the catch crop treatment compared with the control during years when the establishment of the catch crop succeeded. In the third year of the experiment nitrogen leaching was actually greater in the catch crop treatment (7 kg N/ha). This increase was caused by a poorly established catch crop coinciding with enhanced mineralization of previous catch crop residues. There was no simulated change in soil organic nitrogen in either of the treatments. Simulations showed increased nitrogen mineralization during April‐July after incorporation of plant material in spring, especially in the catch crop treatment. However, the increased nitrogen mineralization probably occurred too late for the released nitrogen to be fully available to the main crop.

One measure used in Sweden to mitigate eutrophication of waters is the construction of small wetlands (free water surface wetland for phosphorus retention [P wetlands]) to trap particulate phosphorus (PP) transported in ditches and streams. Th is study evaluated P retention dynamics in a newly constructed P wetland serving a 26-ha agricultural catchment with clay soil. Flow-proportional composite water samples were collected at the wetland inlet and outlet over 2 yr (2010)(2011) and analyzed for total P (TP), dissolved P (DP), particulate P (PP), and total suspended solids (TSS). Both winters had unusually long periods of snow accumulation, and additional time-proportional water samples were frequently collected during snowmelt. Infl ow TP and DP concentrations varied greatly (0.02-1.09 mg L −1 ) during the sampling period. During snowmelt in 2010, there was a daily oscillation in P concentration and water fl ow in line with air temperature variations. Outfl ow P concentrations were generally lower than infl ow concentrations, with net P losses observed only in August and December 2010. On an annual basis, the wetland acted as a net P sink, with mean specifi c retention of 69 kg TP, 17 kg DP, and 30 t TSS ha −1 yr −1 , corresponding to a reduction in losses of 0.22 kg TP ha −1 yr −1 from the agricultural catchment. Relative retention was high (36% TP, 9% DP, and 36% TSS), indicating that small constructed wetlands (0.3% of catchment area) can substantially reduce P loads from agricultural clay soils with moderately undulating topography.

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