Pig slurry application and irrigation effects on nitrate leaching in Mediterranean soil lysimeters

Mineral Fertilizer and Manure Effects on Leached Inorganic Nitrogen, Nitrate Isotopic Composition, Phosphorus, and Dissolved Organic Carbon under Furrow Irrigation

A better understanding of nutrient leaching in furrow irrigated agriculture is needed to optimize fertilizer use and avoid contamination of water supplies. In this field study (2003-2006), we measured deep percolation fluxes at 1.2-m depth and associated nutrient concentrations and mass losses from dairy manure nitrogen (N) or mineral N (urea, sodium nitrate [NaNO])-amended soils (372 kg available N ha in 4 yr) and nonamended controls and determined the δN-NO and δO-NO isotope ratios in the leached nitrate. Flow-weighted concentration means for individual irrigations varied widely, from near zero to as much as 250 mg L for NO-N, 480 μg L for dissolved reactive phosphorus (DRP), 43 mg L for dissolved organic C (DOC), and 390 mg L for chloride (Cl). Relative to other treatments, mineral fertilizer increased NO-N concentrations 2.6- to 3-fold and Cl concentrations 2.6- to 3.6-fold in deep leachate, particularly when NaNO was applied in 2004 and 2006, and produced maximum mean season-long NO-N and Cl losses. Manure and control treatments produced similar leachate nutrient mass losses, and for some irrigation periods, mineral fertilizer produced 85 and 97% lesser DRP losses and two times greater Cl losses compared with manure and control treatments. Four-year cumulative losses among treatments differed only for Cl. Isotopic composition of deep-leached nitrate indicates that both transformation and biologic cycling of mineral and manure N are rapid in these soils, which, with percolation volume, influence the amounts of NO-N and DOC leached. In light of the potential negative effects associated with either fertilizer type, and because even nonamended soils produced substantial amounts of leached NO-N (69.5 kg ha yr), management must minimize percolation water losses to limit nutrient losses from these fertilized, furrow-irrigated soils.

Vertical distribution of denitrification end-products in paddy soils

Knowledge of denitrification process and its end-product at various depths of paddy soil is very important for our understanding of its role in mitigating reactive N and indirect nitrous oxide (N₂O) emission. In this study, the end-products of denitrification were determined at four depths in a long-term field lysimeter experiment in southeast China over a rice season. Three treatments were included: (1) chemical fertilizer (NPK); (2) NPK plus pig manure (NPKM); and (3) NPK plus straw (NPKS). The concentration of dissolved N₂O increased with soil depth across all treatments and the highest concentration of excess dinitrogen (N₂) was observed at 0.2m depth, as was the highest dissolved organic carbon (DOC) content. Denitrification reduced the amount of nitrate by 48-54% in the paddy soil profile, especially at 0.2m depth (68-88%), whereas the lower reduction of NO₃^- (17-44%) in the subsoil (at 0.6 and 0.8m depth) was accompanied by a higher concentration of NO₃^-. Our results demonstrated that DOC was the major limiting factor of denitrification in the subsoil. The application of pig manure markedly increased the amount of DOC in the surface soil, resulting in a high rate of denitrification, whereas the addition of straw had no effect on denitrification. The indirect emission factors for N₂O (EF5-g, 0.001-0.006) were comparable with the default value (0.0025) reported by the Intergovernmental Panel on Climate Change. The low N₂O production was probably caused by the complete reduction of N₂O to N₂, as reflected by the lower N₂O/(N₂O+N₂) ratios in the paddy soil profile. Although the surface soil was identified as a hotspot for denitrification, a considerable amount of excess N₂ was observed in the subsoil for all three treatments. We therefore conclude that the loss of N through denitrification may be significantly underestimated if only the surface soil is considered.

Impact of chemically amended pig slurry on greenhouse gas emissions, soil properties and leachate

The effectiveness of chemical amendment of pig slurry to ameliorate phosphorus (P) losses in runoff is well studied, but research mainly has concentrated only on the runoff pathway. The aims of this study were to investigate changes to leachate nutrient losses, soil properties and greenhouse gas (GHG) emissions due to the chemical amendment of pig slurry spread at 19 kg total phosphorus (TP), 90 kg total nitrogen (TN), and 180 kg total carbon (TC) ha(-1). The amendments examined were: (1) commercial grade liquid alum (8% Al2O3) applied at a rate of 0.88:1 [Al:TP], (2) commercial-grade liquid ferric chloride (38% FeCl3) applied at a rate of 0.89:1 [Fe:TP] and (3) commercial-grade liquid poly-aluminium chloride (PAC) (10% Al2O3) applied at a rate of 0.72:1 [Al:TP]. Columns filled with sieved soil were incubated for 8 mo at 10 °C and were leached with 160 mL (19 mm) distilled water wk(-1). All amendments reduced the Morgan's phosphorus and water extractable P content of the soil to that of the soil-only treatment, indicating that they have the ability to reduce P loss in leachate following slurry application. There were no significant differences between treatments for nitrogen (N) or carbon (C) in leachate or soil, indicating no deleterious impact on reactive N emissions or soil C cycling. Chemical amendment posed no significant change to GHG emissions from pig slurry, and in the cases of alum and PAC, reduced cumulative N2O and CO2 losses. Chemical amendment of land applied pig slurry can reduce P in runoff without any negative impact on nutrient leaching and GHG emissions. Future work must be conducted to ascertain if more significant reductions in GHG emissions are possible with chemical amendments.

Modelling nitrogen leaching from sewage sludge application to arable land in the Lombardy region (northern Italy)

Sewage sludge can be used as fertiliser, offering the possibility of safely recycling this waste product as a resource in agricultural applications. As the environmental concerns related to waste recycling in agricultural applications are well-known, restrictions on the use of sewage sludge have been implemented by the EU and local authorities. This work aimed to evaluate the nitrogen leaching associated with the application of sludge and the effectiveness of the temporal restrictions on its application implemented to safeguard the environment in the Lombardy region of northern Italy (120 days in Nitrate Vulnerable Zones and 90 days elsewhere) using the CropSyst model which was first validated. The effects of fertilisation using four different sludge types on N leaching were simulated at five sites under cultivation with maize and rice crops; six different timing schemes for sludge application were tested, three of which involved dates that were in agreement (AT) with the regulation, while the other three were not in agreement (NAT). We detected a significant effect of the sludge type and application timing, whereas the effect of their interaction was never significant. The mean annual leaching was 22 to 154 kg N ha(-1). The higher the ammonium N content in the sludge was, the greater the potential for N leaching was found to be. For the maize crop, the distribution of sludge in the late fall period resulted in significantly greater N leaching (61 kg N ha(-1)) and led to lower yields (9 t DM ha(-1)) compared to late winter fertilisation (49 kg N ha(-1); 10 t DM ha(-1)), whereas no differences in N leaching or yield were detected between AT and NAT, which was also observed for the rice crop. Therefore, the applied temporal constraints did not always appear to be advantageous for protecting the environment from leaching.

Viability of Ascaris suum eggs in stored raw and separated liquid slurry

Separation of pig slurry into solid and liquid fractions is gaining importance as a way to manage increasing volumes of slurry. In contrast to solid manure and slurry, little is known about pathogen survival in separated liquid slurry. The viability of Ascaris suum eggs, a conservative indicator of fecal pollution, and its association with ammonia was investigated in separated liquid slurry in comparison with raw slurry. For this purpose nylon bags with 6000 eggs each were placed in 1 litre bottles containing one of the two fractions for 308 days at 5 °C or 25 °C. Initial analysis of helminth eggs in the separated liquid slurry revealed 47 Ascaris eggs per gramme. At 25 °C, egg viability declined to zero with a similar trend in both raw slurry and the separated liquid slurry by day 308, a time when at 5 °C 88% and 42% of the eggs were still viable in separated liquid slurry and raw slurry, respectively. The poorer survival at 25 °C was correlated with high ammonia contents in the range of 7.9-22.4 mM in raw slurry and 7.3-23.2 mM in liquid slurry compared to 3.2-9.5 mM in raw slurry and 2.6-9.5 mM in liquid slurry stored at 5 °C. The study demonstrates that at 5 °C, A. suum eggs have a higher viability in separated liquid slurry as compared to raw slurry. The hygiene aspect of this needs to be further investigated when separated liquid slurry is used to fertilize pastures or crops.

Belt separation system under slat in fattening pig housing: effect of belt type and extraction frequency

The efficiency of manure separation by a conveyor belt under a partially slatted floor for fattening pigs was determined for two types of belts, a flat belt with an incline of up to 6 degrees transversely and a concave belt with an incline of up to 1 degrees longitudinally. A 31.20% and 23.75% dry matter content of the solid fraction was obtained for the flat and concave belt, respectively. The flat belt was more efficient at 6 degrees than other slope angles. The residence time of the manure on the two belt types influenced the separation efficiency from a live weight of 63.00 kg upwards. The quantity of residue produced with this system was reduced to 25-40% with respect to a pit system under slat. This could mean a remarkable reduction in costs of storage, transport and application of manure.

Response of maize yield, nitrate leaching, and soil nitrogen to pig slurry combined with mineral nitrogen

The application of pig (Sus scrofa) slurry (PS) is a common fertilization practice that may affect nitrate concentrations and loads in drainage and receiving water bodies. To protect water resources, many agricultural areas are being designated as vulnerable to nitrate contamination, and there is a need for scientific data aiming at reducing nitrate exports from these vulnerable zones by optimizing N fertilization strategies. The objective of this work, conducted in drainage lysimeters in a 4-yr monoculture maize (Zea mays L.) crop, is to assess the effects of four fertilization strategies combining PS (30, 60, 90, and 120 t ha(-1)) and mineral N on yield, changes in soil mineral N, and concentration and mass of nitrate in drainage waters. Grain yield was not affected by treatments in the four experimental years, nor was the soil mineral N at the end of the experiment. Effects of fertilization strategies on nitrate concentration and mass in drainage waters were detected only after 3 yr of repeated PS applications. The mass of nitrate leached over the 4 yr was positively related to the total amount of N applied, either organic or mineral. In year 2003, precipitation in spring reduced N availability for the crop in treatments with rates > or = 60 t PS ha(-1). The N-budget revealed that the transport pathways for 25% of N inputs to the system are unknown. The presowing application of pig slurry at 30 t ha(-1) complemented with mineral N at side-dressing, was the most efficient from an environmental standpoint (4-yr average of 145 kg grain yield kg(-1) N leached).