Nitrogen turnover and leaching in cropping systems with ryegrass catch crops

This thesis deals with perennial ryegrass (Lolium perenne L.) catch crops and their short- and long-term effects on nitrogen leaching and nitrogen turnover in soils. Results are presented from three field experiments on a sandy soil in south-west Sweden, where undersown catch crops were used in cropping systems with and without applications of liquid manure. The effects of different tillage practices on soil mineral nitrogen and leaching were also studied. Two coupled simulation models, which describe water flow and nitrogen transformations and transport in soil, were used for calculations of nitrogen mineralization and soil nitrogen balances. A more detailed study of the residual effects of ryegrass on the nitrogen supyly to the subsequent crops and nitrogen leaching was performed in lysimeters, using 'N-labelled ryegrass. Undersown catch crops efficiently reduced nitrogen losses when mineral fertilizer or manure was applied at normal rates (90-1 10 kg Nha). Over five years, undersown catch crops reduced nitrogen leaching by 60%, on average, compared with soil which was conventionally tilled in August-September. Incorporation of catch crops affected nitrogen mineralization mainly during the first growing season following incorporation, when approximately 20-30% of catch crop nitrogen was released. The results emphasize the importance of an early onset of nitrogen mineralization in spring after incorporation of catch crops. This is necessary in order to overcome the soil-depletion effect of nitrogen uptake induced by the catch crop. Simulations showed that incorporation of catch crop material in late autumn instead of spring can result in a time distribution of nitrogen mineralization more suitable for a subsequent cereal crop, but this was not verified by the results of the lysimeter experiment. It seems important to obtain further knowledge of how to improve the degree of synchronization between nitrogen mineralization after incorporation of catch crops and nitrogen demand of the subsequent crops. According to simulations, the main part of the catch crop nitrogen contributed to a long-term accumulation of soil organic nitrogen (+I0 kg N per hectare and year), while it slowly declined in autumn-tilled soil given mineral fertilizer (-30 kg N per hectare and year). However, the accumulation of soil organic nitrogen due to the catch crops was very modest compared with the total amount of organic nitrogen in the soil

Identification of key factors for reducing N and P leaching from organic crop rotations

Leaching of nitrogen (N) and phosphorus (P) for different 6-year organic crop rotations was examined in separately tile-drained field plots on two different sites in southwest Sweden. On each site, two different farming systems, one with dairy cows and one without stock, were evaluated to identify parts of the crop rotations with the greatest risks of N and P leaching and to examine the scope for improvement. Although organic farming methods themselves already led to a reduction in nutrient leaching, critical periods in the crop rotation could nevertheless be identified for the two soil types. While P leaching is of major importance on clay soils, sandy soils are strongly susceptible to N leaching. From the present study it could be concluded, that key factors for reducing N and P leaching from clay soils are late ploughing, avoidance of early incorporation of clover-grass leys in order to sow a winter cereal, the use of undersown crops and an even distribution of nutrients within the crop rotation. For the sandy soil, where measures like undersown crops and spring tillage were already integrated in the studied crop rotation, potato cultivation and application of farmyard manure were identified as the main sources of N losses to the drainage water

Phosphorus load in outdoor areas for laying hens and capacity of phosphorus retaining materials to reduce the environmental impact

This study investigated manure loads in outdoor paddocks for laying hens and the capacity of two phosphorus (P) retaining materials for reducing leaching from manure in areas with high hen density. Inventories on two commercial farms during 2 years (2017 and 2018) of the impact of hens (groups of 3000 hens) on vegetation, as a proxy for land use by hens, showed that 16-21% of outdoor area in grassland paddocks and 22-39% of area in a forest paddock were used by the hens. Sand and limestone were tested as P retention materials in areas with high manure load in a field study during the outdoor season for laying hens (May 1 to October 31 in 2018). The materials were placed on the ground (0.2 m deep bed, 3.3 m wide) outside the pop-hole in paddocks with 76 hens. The average numbers of hens outdoors were recorded at 9 am and 3 pm daily. There was no significant difference between the materials concerning distribution of hens, and they seemed not to prefer any material more than the other. When cylinders containing the spent materials were exposed to simulated rainfalls in a laboratory study, the P concentrations in drainage water were high for all materials, including a control with gravel (58-136 mg PO4-P L-1 and 130-197 mg total-P L-1). On average, 14% of manure P retained in the sand and limestone materials was leached after 100 mm of simulated rainfall. Thus, these materials may act as physical filters for P in manure, but to reduce the risk of P losses to waters during the following winter, they need to be removed from the paddocks and preferably used as potential P fertilizers on arable land

Managing multi-functional peri-urban landscapes: Impacts of horse-keeping on water quality

Eutrophication assessments in water management to quantify nutrient loads and identify mitigating measures seldom include the contribution from horse facilities. This may be due to lack of appropriate methods, limited resources, or the belief that the impact from horses is insignificant. However, the recreational horse sector is growing, predominantly in multi-functional peri-urban landscapes. We applied an ecosystem management approach to quantify nutrient loads from horse facilities in the Stockholm Region, Sweden. We found that horses increased the total loads with 30-40% P and 20-45% N, with average area-specific loads of 1.2 kg P and 7.6 kg N ha-1 year-1. Identified local risk factors included manure management practices, trampling severity, soil condition and closeness to water. Comparisons of assessment methods showed that literature standard values of area-specific loads and water runoff may be sufficient at the catchment level, but in small and more complex catchments, measurements and local knowledge are needed

Mitigating phosphorus leaching from a clay loam through structure liming

Phosphorus (P) losses from clay soils can be mitigated by introducing measures for improving soil structure. These include structure liming, where a mixture of CaO or Ca(OH)2 and CaCO3 is added to the soil. In a field experiment with separately tile-drained plots on a clay loam in Sweden, we examined the effects of structure liming on leaching of total-P, phosphate P (PO4-P) and total nitrogen (N) during three years after initial application. The treatments included two application rates (8 and 16 t ha−1) of a common product in comparison with a control (no lime). Effects of structure liming emerged during the second and third year after application, with 45 and 38% lower total-P leaching than in the unlimed control. A significant effect of the application rate was found in the third year. Nitrogen leaching and crop yield were not affected. As expected, soil pH raised following structure lime addition. Measurements of aggregate stability did not confirm the reduction in P leaching, indicating that it is important to measure P concentrations in drainage water directly when assessing the effect of structure liming

Stocktake study of current fertilisation recommendations across Europe and discussion towards a more harmonised approach

The European Commission has set targets for a reduction in nutrient losses by at least 50% and a reduction in fertiliser use by at least 20% by 2030 while ensuring no deterioration in soil fertility. Within the mandate of the European Joint Programme EJP Soil 'Towards climate-smart sustainable management of agricultural soils', the objective of this study was to assess current fertilisation practices across Europe and discuss the potential for harmonisation of fertilisation methodologies as a strategy to reduce nutrient loss and overall fertiliser use. A stocktake study of current methods of delivering fertilisation advice took place across 23 European countries. The stocktake was in the form of a questionnaire, comprising 46 questions. Information was gathered on a large range of factors, including soil analysis methods, along with soil, crop and climatic factors taken into consideration within fertilisation calculations. The questionnaire was completed by experts, who are involved in compiling fertilisation recommendations within their country. Substantial differences exist in the content, format and delivery of fertilisation guidelines across Europe. The barriers, constraints and potential benefits of a harmonised approach to fertilisation across Europe are discussed. The general consensus from all participating countries was that harmonisation of fertilisation guidelines should be increased, but it was unclear in what format this could be achieved. Shared learning in the delivery and format of fertilisation guidelines and mechanisms to adhere to environmental legislation were viewed as being beneficial. However, it would be very difficult, if not impossible, to harmonise all soil test data and fertilisation methodologies at EU level due to diverse soil types and agro-ecosystem influences. Nevertheless, increased future collaboration, especially between neighbouring countries within the same environmental zone, was seen as potentially very beneficial. This study is unique in providing current detail on fertilisation practices across European countries in a side-by-side comparison. The gathered data can provide a baseline for the development of scientifically based EU policy targets for nutrient loss and soil fertility evaluation

Effects of spring and autumn tillage, catch crops, and pig manure application on long-term nutrient leaching from a loamy sand

A field experiment with separately tile-drained plots was established on a sandy loam soil in 1993 to investigate management practices that can reduce nutrient leaching. Practices tested included timing of tillage in autumn or spring (ploughing with or without preceding cultivation) and catch crops in systems with mineral fertilizer alone or in combination with pig manure. Drainage water from each plot was collected separately and analyzed for total nitrogen (tot-N), nitrate-N (NO3-N), total phosphorus (tot-P), phosphate-P (PO4-P), and potassium (K). Biomass of catch crops, soil mineral N content, and yield of the main crop were also determined. The experimental set-up was modified after 14 years, but the core research questions were the same and the results from the two periods (1993–2006, 2007–2021) were comparable. Spring tillage and undersown catch crops (perennial ryegrass, Lolium perenne L.) reduced tot-N leaching and concentrations in drainage water compared with autumn tillage. However, a combination of spring tillage and catch crop increased tot-P leaching and concentrations in drainage water compared with autumn tillage and no catch crop. Use of pig manure increased tot-N leaching and concentrations in drainage water compared with treatments without pig manure, both with and without a catch crop. Treatments without a catch crop showed substantial growth of biomass during autumn in terms of weeds and volunteer plants, but growing a catch crop resulted in more biomass in most years. A catch crop was more effective in reducing N leaching than only weeds and volunteer plants, probably mainly due to its ability to survive winter and take up and store N over a longer period. Leaching of K increased with a catch crop, while the other treatments did not influence K losses. Yield of main crops was not affected by the different treatments

Winter Runoff of Nitrogen and Phosphorus from a Rotational Pen Design with Suckler Cows

Keeping beef cattle outdoors during winter reduces costs and improves animal welfare, but increases the risk of nitrogen (N) and phosphorus (P) runoff losses. This study evaluated a rotational pen design on grassland with two groups of suckler cows given access to an expanding staying area and a new feeding area each week (72 cattle ha−1), with one month’s stay per pen. The spatial distribution of excreta and effects on N and P surface runoff was evaluated during six months. The total excreta loads corresponded to 500 kg·N·ha−1 and 50 kg·P·ha−1. New feeding areas did not distribute excretions evenly, which resulted in the highest proportion of excretions (31%) occurring in the first week’s sub-area. The topsoil had significantly higher amounts of mineral-N, mainly as NH4-N (29 - 81 kg·ha−1), than an unaffected area (13 kg·ha−1). Mean total runoff losses were similar for both groups (1.4 kg·P·ha−1 and 9.0 kg·N·ha−1). Around 78% of N and 70% of P runoff losses occurred during the month with cattle present. During the first two weeks with heavy rain, N and P runoff losses were 50% higher from an area with suckler cows than a corresponding vegetated sub-area without cows. The study design did not provide a sufficient distribution of excretions and a high animal density in combination with trampling resulted in unacceptable N and P run-off losses. An environmentally friendly design would need to include frequent moving of all equipment and access to larger areas

Losses of phosphorus, potassium and nitrogen from horse manure left on the ground

In this five-month Swedish field study, we examined losses of nutrients from horse manure over time, in order to examine how regularly manure should be cleared from paddocks in order to minimise the risk of nutrient leaching. Small heaps of manure (400 g) were placed in open cylinders outdoors and samples (five replicates) were taken on 12 occasions from December 2020 to May 2021. The samples were analysed for weight, dry matter content and concentrations of total nitrogen (N), ammonium N, total phosphorus (P), water-extractable P (WEP), potassium (K) and carbon (C). There was a fast decline in P and K concentrations and a strong correlation between accumulated precipitation and losses from the manure into the soil. The mean reduction in total-P was 11 mg P kg-1 manure dry weight per mm accumulated precipitation. Manure N was retained in the manure over the five-month period. In conclusion, this study demonstrated high mobility of P and K, indicating a need for strategies for rapid removal of manure from paddocks. Daily removal of manure from paddocks used year-round would, approximately, save 1.7 kg P and 5.5 kg K per horse per year, which could be recycled to replace non-renewable mineral fertilisers