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2. Materials & Methods In experiment one, five field trials were conducted to test the effect of soil properties on N2O emissions during the wheat growing season. The soils at each site differ in texture, carbon content (1.31-1.9% total organic C) and pH (5.3-7.4). On each field site, N-fertilizer was applied as calcium-ammonium-nitrate (CAN) at a rate of 220 kg N ha-1 in 3 split applications (80-70-70 kg N ha-1). In experiment two, we set up an incubation experiment under complete anoxic conditions with the soils that have been collected from each field site. The denitrification potential and respiration rate of soils were measured. Briefly, 1 kg moist soil was placed in PVC vessels with porous ceramic plates at the bottom, flooded with 15 mM KNO3 and drained to 20% gravimetric water content. The incubation atmosphere was replaced by helium (He) to remove atmospheric nitrogen. During the incubation period, fresh He was directed through an inlet in the lid with a flow rate of 15 ml vessel-1 min-1. Gas samples from the incubation vessels were automatically analyzed twice per day by ECD (N2O) and TCD (N2) detectors (gas chromatography, GC-450 Varian Inc., USA).
3. Results & Discussion In the field experiments, N2O emissions from soils with N-fertilizer application were significantly higher during the growing season than control (non fertilized) soils at all field sites (Fig 1). Cumulative N2O emissions ranged between 747 to 1078 g N2O-N*ha-1 (Figure 1). In this experiment, cumulative emissions at the Münster (loamy soil) sand Osnabrück (loamy sand soil) sites were significantly higher than at the other field sites. Soil at the Münster site had the highest total C content and that may have provided favourable conditions for both nitrification and denitrification. However, high N2O emission at the Osnabrück site was surprising, as the soil at this site had moderate carbon content when compared to the other soil types. In the incubation experiment, the denitrification rate of soils ranged between 0.15 to 0.3 mg N kg soil-1 hour-1. There was a weak correlation between the denitrification potential and the total organic carbon content (Figure 2A). Labile soil organic carbon compounds trigger denitrification by providing energy for the denitrifiers (Weier et al.,1993). However, soil organic matter is a heterogeneous mixture of various organic matter pools which may have different decomposition rate. Therefore total soil organic matter content is not a direct measure of labile carbon content of soil; thus we also measured respiration rate of each soil under standardized aerobic conditions. The denitrification potential of soils correlated significantly with the soil respiration rate (Figure 2B).
Figure 1. Cumulative N2O emissions in g N2O-N*ha-1 at different field sites in North Western Germany during the vegetation period of winter wheat.
Error bars show the standard error of the mean of each treatment (n=3).
There was a weak correlation between cumulative field N2O emissions and denitrification potential (Figure 2C). The weakness of the correlation may be due to other factors such as soil physical properties or differences in crop N uptake in different fields. Surprisingly, there was a significant positive relationship between denitrification potential and maximum mean daily field N2O fluxes (Figure 2D).
Figure 2. The relationship between total organic carbon content of soil (A) respiration rate (B), cumulative N2O emissions from field (C) and highest daily N2O emissions from field (D) with potential denitrification rate in five soils (ST=Steinfurt, Bil=Billerbeck, Lav=Lavesum, Os=Osnabrück, MS=Münster).
Error bars show the standard error of the mean of each treatment (n=3).
4. Conclusion Present field and incubation experiments showed that, a higher level of available carbon content of soils (rather than total soil organic matter content) induced higher N2O emission and denitrification rate. There was a weak correlation between potential denitrification rate and cumulative N2O emitted under field conditions over a whole season. However, maximum daily N2O fluxes correlate significantly with the denitrification potential of soils which may indicate that N2O emissions during high peak events were derived mainly from denitrification.
References Weier, K. L, Doran, J.W, Power, J.F. and Walters, D.T. 1993. Denitrification and the Dinitrogen/Nitrous Oxide Ratio as Affected by Soil Water, Available Carbon, and Nitrate. Soil Science Society of America Journal 57, 66Nitrogen Workshop 2012 Response of corn (Zea mays L.) to precision injected dairy slurry with focus on nitrogen Bittman, S., Hunt, D.E., Kowalenko, C.G.
a Pacific Agri-food Research Centre, Agriculture and Agri-Food Canada, Agassiz BC, Canada
1. Background & Objectives Despite a surplus of manure on many dairy operations, farmers supplement their corn (Zea mays L.) crops with mineral N and P fertilizer, usually applied as a starter with the planter. On-farm and research experiments in British Columbia (BC), Canada have shown that starter fertilizer is beneficial to the crop even when large amounts of manure is broadcast (Bittman et al., 2006;
Bittman et al., 2004). We have shown that injected dairy sludge placed near corn rows provides starter P to corn crops with no injury to the crop under cool moist spring conditions in coastal BC (Bittman et al., 2012). The objective of his study is to assess the response of silage corn to different rates of dairy slurry injected at 5-10 cm from the corn seed furrow relative to broadcast manure and chemical fertilizer.
2. Materials & Methods The study was conducted in 2010 and 2011 on silty loam soil at the Pacific Agri-Food Research Centre in south coastal BC, Canada. The dairy slurry, obtained from a commercial dairy farm with high-producing Holstein cows fed grass and corn silages and bedded with saw dust, was stored in a 3 m deep tank over winter. The slurry was injected at 75 cm spacing and 15 cm depth using offset disk tools at rates to give 80, 160 and 240 kg total N ha-1 (28.8, 57.6, 86.4 m3 ha-1); the furrows were manually covered soon after application to reduce ammonia loss. Broadcast manure was applied and immediately incorporated by hand. Corn (Pioneer 38B11RR) was planted approximately 7-10 days after manure injection to allow time for the slurry to soak into the soil.
Corn was planted at 75000 seeds ha-1 planted at 5-10 cm distance from the centre of the manure furrow with a conventional corn planter with or without starter N and P fertilizer at seeding. The starter was applied at 24 and 29 kg ha-1 of N and P, respectively, as a blend of urea and monoammonium phosphate. The experiment was arranged in 4 randomized compete blocks and we measured yield and uptake of nutrients. We sampled the middle 2 rows of 8-m long plots with 4rows.
3. Results & Discussion There was a curvilinear response of corn yield to applied mineral N at 29 kg P ha-1 with a peak of
18.5 t dry matter ha-1 at 160 N kg ha-1 of N (Figure 1). The crop responded to broadcast and incorporated slurry in a linear fashion with the low and high rates corresponding closely to the mineral N fertilizer without P treatment. Corn yield responded more to the injected manure treatment probably due to a greater concentration of nutrients near the seed (Bittman et al., 2012) and to less ammonia volatilization losses. The broadcast manure with starter (typical farm practice) yielded the same as the injected manure without starter. Yield with injected manure, having very low potential for volatilization losses, was lower than with mineral fertilizer except at the high rates.
At the high rates, more P was applied with manure but the convergence of yield was more likely due to the higher rate of available N as a high P fertilizer treatment (not shown) was similar to the 29 kg P ha-1 rate. Adding starter fertilizer to the injected manure minimized any difference in whole crop yield between injected manure and mineral fertilizer at equivalent rates of N. Likewise there was lower grain yield at harvest with injected manure than with mineral fertilizer and starter fertilizer application diminished any difference between the treatments (not shown). Grain
percentage and dry matter content in the whole crop was similar for injected manure and fertilizer treatments suggesting no delay in final maturity with injected manure.
Whole plant dry matter yield (t ha-1)
4. Conclusion This study shows corn responds better to slurry injected near corn seed than to broadcast and incorporated slurry. Starter fertilizer can be used to augment yield of manure-treated corn or, alternatively, higher rates of manure can be applied. The higher manure rates would lead to accumulation of P in the soil but would obviate the need for chemical fertilizer for intensive corn.
Where maximum corn yields are not needed, slurry may be injected at sustainable rates with no additional chemical fertilizer. Work is continuing on the effects of injected manure on nitrate leaching, emission of nitrous oxide and long term release of N.
References Bittman S., Hunt D.E., Kowalenko C.G., Wu X. and Forge T.A. 2004. Early phosphorus nutrition in corn and the role of mycorrhizae, In: Bittman S. and Kowalenko C.G. (eds.), Advanced silage corn management. Pacific Field Corn Assoc., Agassiz, BC. pp. 42–48. Available at http://www.farmwest.com/index.cfm?method=library.showPage&librarypageid=132 (veri. 29 Dec. 2011).
Bittman S., Kowalenko C.G., Hunt D.E., Forge T.A. and Wu. X. 2006. Starter P fertilizer and broadcast nutrients on corn with contrasting colonization by arbuscular mycorrhizae. Agronomy Journal 98, 394-401.
Bittman S., Liu A., Hunt D.E., Forge, T.A., Kowalenko C.G., Chantigny, M. and Buckley K. 2012. Precision Placement of Separated Dairy Sludge Improves Early Phosphorus Nutrition and Growth in Corn (Zea mays L.) Journal of Environmental Quality 41, (in press).
Nitrogen Workshop 2012
Role of soil organic matter content on nitrogen dynamics in volcanic ash soils Alfaro, M.a, Cárdenas, L.b, Salazar, F.a, Rosas, A.a, Vistoso, E.a, Hube, S.a, Ramírez L.a a INIA Remehue, Ruta 5 Sur, km 8, Osorno, Chile b Rothamsted Research, North Wyke, Okehampton, Devon EX20 2SB, UK
1. Background & Objectives Previous studies have shown that nitrogen (N) leaching losses are low in Chilean volcanic soils (Salazar et al., 2011), despite a high potential for available N production in the soil (Dixon et al, 2011). This could be related to the high soil organic matter content (SOM) of these soils, which could act as a buffer for N losses. The objective of this paper was to evaluate the fate of 15N added to soils with different SOM.
2. Materials & Methods A monolith lysimeter experiment was carried out between May 2010 and March 2011 to determine the fate of N applied as inorganic fertilizer to three volcanic ash soils of southern Chile. Lysimeters (0.60 m depth, 0.11 m2) were collected in April 2010 from permanent grassland sites with no grazing from the Osorno (Typic Hapludands, 17% SOM), Cudico (Typic Hapludults, 14% SOM) and Chonchi series (Acrudoxic Durudands, 24% SOM) (CIREN, 2003). All soils were transported to INIA Remehue (40º 35’ S 73º 12’ O) so that they were managed under similar temperature and rainfall conditions. All lysimeters received a basal application of P, K, S and Mg (66, 100, 40 and 17 kg ha-1, respectively). The fate of the added N was evaluated with the overcast application of smashed fertilizer, equivalent to 200 kg N ha-1, as 10 atom % 15N ammonium sulphate, with four replicates. During the experimental period, yield and 15N plant uptake, available N and 15N leaching losses and N2O emissions were measured. The pasture was harvested each time it reached 20 cm height leaving a 5 cm residue (n=7). Cut grass was oven-dried (60°C) for 24-48 h and analyzed for total N and 15N concentration. Total and 15N plant uptake was calculated as the result of yield and N concentration in the respective grass sample (g N m-2). Leachate samples were collected from the bottom of the lysimeters three times per week during the drainage period (May-October 2010) and the samples were analysed for total N, NH4+, NO3- and 15N. Total and 15N leaching losses were calculated from the cumulative of the individual losses at all sampling occasions estimated from the recorded volume of drainage and N concentration in the respective samples (kg N ha-1). Gas samples were taken periodically for up to 50 days (n=14) following N application at time 0 and time 45 mins with the use of hermetic lids that were used to cover the top of the lysimeters without disturbing the soil surface. Samples were analysed for N2O by gas chromatography. Total emissions were estimated as the sum of emissions per sampling period (g N ha-1 day-1). Rainfall was recorded with the use of an automatic weather station placed within 1 km distance of the experimental site.
Soil temperature (0-10 cm depth) was recorded manually at each sampling time with the use of a soil thermometer. ANOVA was used to analyze statistical differences between treatments, using Genstat 12.0.
3. Results & Discussion Soil organic matter contents varied between 14% (ultisoil) up to 24% (andisoils). During the experimental period rainfall reached up to 1008.4 mm, being 21% lower than the 33 year average value in the area. There was little difference in dry matter yield between the soils and fertilizer increased yield significantly (P0.05; Figure 1a). During the first experimental year, an average of 45% of N taken up by plants came from the fertilizer, while the difference was supplied by the soil
Figure 1. Nitrogen fate in volcanic ash soils with different soil organic matter content (a) yield (g DM m-2), (b) plant uptake (g N/15N m-2), (c) leaching losses (kg N-NO3 ha-1), (d) flux of N2O-N (g ha-1 d-1).