Showing papers by "Nicolas Tremblay published in 2010"

Nitrous oxide fluxes from corn fields: on-farm assessment of the amount and timing of nitrogen fertilizer

Abstract: Nitrogen fertilization is considered as an important source of atmospheric N 2 O emission. A seven site-year on-farm field experiment was conducted at Ottawa and Guelph, ON and Saint-Valentin, QC, Canada to characterize the affect of the amount and timing of N fertilizer on N 2 O emission in corn (Zea mays L.) production. Using the static chamber method, gas samples were collected for 28-days after preplant and 28-days after sidedress fertilization at the seven site-year, resulting in 14 monitoring periods. For both methods of fertilization, peak N 2 O flux and cumulative emission increased with the amount of N applied, with rates ranging from 30 to 900 μg N m ―2 h ―1 . Depending on N amount and time of application, cumulative emission varied from 0.05 to 2.42 kg N ha ―1 , equivalent to 0.03% to 1.45% of the N fertilizer applied. Differences in N 2 O emission peaks among fertilizer treatments were clearly separated in 13 out of 14 monitoring periods. Total N 2 O emissions may have been underestimated compared with annual monitoring in 10 out of the 49 cases because the monitoring period ended before N 2 O efflux returned to the baseline level. The flux of N 2 O was negligible when soil mineral N in the 0-15 cm layer was 15 °C was likely the driving force responsible for the higher levels of N 2 O found for sidedress than preplant application methods. However, caution must be taken when interpreting these later results as preplant fertilization may have continuously stimulated N 2 O emissions after the 28-days monitoring period, especially in situations where N 2 O effluxes have not fallen back to their baseline levels. Increasing fertilizer rates from 90 to 150 kg N ha ―1 resulted in slight increases in yields, but doubled cumulative N 2 O emissions.

N2O emissions from an irrigated and non‐irrigated organic soil in eastern Canada as influenced by N fertilizer addition

Abstract: Drainage and cultivation of organic soils often result in large nitrous oxide (N2O) emissions. The objective of this study was to assess the impacts of nitrogen (N) fertilizer on N2O emissions from a cultivated organic soil located south of Montreal, QC, Canada, drained in 1930 and used since then for vegetable production. Fluxes of N2O were measured weekly from May 2004 to November 2005 when snow cover was absent in irrigated and non-irrigated plots receiving 0, 100 or 150 kg N ha−1 as NH4NO3. Soil mineral N content, gas concentrations, temperature, water table height and water content were also measured to help explain variations in N2O emissions. Annual emissions during the experiment were large, ranging from 3.6 to 40.2 kg N2O-N ha−1 year−1. The N2O emissions were decreased by N fertilizer addition in the non-irrigated site but not in the irrigated site. The absence of a positive influence of soil mineral N content on N2O emissions was probably in part because up to 571 kg N ha−1 were mineralized during the snow-free season. Emissions of N2O were positively correlated to soil CO2 emissions and to variables associated with the extent of soil aeration such as soil oxygen concentration, precipitation and soil water table height, thereby indicating that soil moisture/aeration and carbon bioavailability were the main controls of N2O emission. The large N2O emissions observed in this study indicate that drained cultivated organic soils in eastern Canada have a potential for N2O-N losses similar to, or greater than, organic soils located in northern Europe.

Plant-Based Diagnostic Tools for Evaluating Wheat Nitrogen Status

Abstract: The nitrogen nutrition index (NNI), based on critical plant N dilution curves, was developed to determine the in-season N status of many species including wheat (Triticum aestivum L.). We assessed the relationship between wheat NNI and two simpler diagnostic tools; namely, leaf nitrogen (N L ) concentration and chloro- phyll meter (CM) readings. The study was con- ducted at six site-years (2004−2006) in Quebec, Canada, using four to eight N fertilizer rates (0−200 kg N ha −1 ). Leaf N concentrations and CM readings were determined from the upper- most collared leaf during the growing season along with NNI determinations. Generally, NNI, N L concentrations, and CM readings increased with increasing N rates. Leaf N concentrations and CM readings were signifi cantly related to NNI during the growing season. Normalization of the CM values, relative to high N plots (relative chlorophyll meter (RCM) readings), improved the relationship with NNI by reducing site-year differences. However, variation among sam- pling dates was observed in all relationships. By restricting the sampling dates to essentially the elongation stage, the relationship between NNI and N L (NNI = −0.43 + 0.035 N L ; R 2 = 0.52), CM (NNI = −0.64 + 0.039 CM; R 2 = 0.68), or RCM (NNI = −1.31 + 2.45 RCM; R 2 = 0.82) was gen- erally improved. Nitrogen concentration, CM reading, or RCM reading of the uppermost col- lared leaf, preferably at the elongation stage, can therefore be used to assess the nutritional status of spring wheat.

Development and validation of fuzzy logic inference to determine optimum rates of N for corn on the basis of field and crop features

Abstract: A fuzzy inference system (FIS) was developed to generate recommendations for spatially variable applications of N fertilizer. Key soil and plant properties were identified based on experiments with rates ranging from 0 to 250 kg N ha−1 conducted over three seasons (2005, 2006 and 2007) on fields with contrasting apparent soil electrical conductivity (ECa), elevation (ELE) and slope (SLP) features. Mid-season growth was assessed from remotely sensed imagery at 1-m2 resolution. Optimization of N rate by the FIS was defined against maximum corn growth in the weeks following in-season N application. The best mid-season growth was in areas of low ECa, high ELE and low SLP. Under favourable soil conditions, maximum mid-season growth was obtained with low in-season N. Responses to N fertilizer application were better where soil conditions were naturally unfavourable to growth. The N sufficiency index (NSI) was used to judge plant N status just prior to in-season N application. Expert knowledge was formalized as a set of rules involving ECa, ELE, SLP and NSI levels to deliver economically optimal N rates (EONRs). The resulting FIS was tested on an independent set of data (2008). A simulation revealed that using the FIS would have led to an average N saving of 41 kg N ha−1 compared to the recommended uniform rate of 170 kg N ha−1, without a loss of yield. The FIS therefore appears to be useful for incorporating expert knowledge into spatially variable N recommendations.

Influence of irrigation and nitrogen fertilization on broccoli polyphenolics concentration.

Abstract: Polyphenolics are phytochemical compounds that may be beneficial or toxic to humans. They are found in fruits and vegetables known for their health promoting characteristics. These carbon-based secondary metabolites have roles such as protection against ultraviolet radiation, free radicals, oxidative stress, herbivores and pathogens. Their synthesis in plant material is therefore linked to both biotic and abiotic stress sources. Under nitrogen stress, for instance, an increase in polyphenolics concentration has been reported. This behaviour has been exploited in the design and marketing of the Dualex, a new diagnostic instrument aimed at establishing the in-season requirements of crops for nitrogen (N) fertilizer. The Dualex can estimate leaf polyphenolics concentrations from the measurement of ultraviolet (UV, 375 nm) absorption of the leaf epidermis by the double excitation of chlorophyll fluorescence. The value of the UV absorbance is directly connected to the amount of leaf polyphenolics. The objective of this study was to determine if irrigation and nitrogen fertilization can influence broccoli polyphenolics concentrations. A broccoli experimental field was established in 2005 at the Agriculture and Agri-Food Canada experimental farm of L'Acadie (Quebec). The crop was fertilized with either 0, 105, 135, 165, 195 or 225 kg N/ha and provided or not with supplementary irrigation after crop establishment. Four Dualex measurement campaigns were made, from 26 to 47 days after planting, as well as one laboratory estimation of polyphenolics. The absence of irrigation increased significantly polyphenolics concentrations on the two last dates (by 36 and 35%, respectively). The increase in fertilizer N was related to a linear or curvilinear decrease in polyphenolics. At the last date, unfertilized plots had 86 and 16% higher polyphenolics than fully fertilized ones, in irrigated and non-irriguated plots, respectively. Yields of marketable heads increased in a curvilinear matter with N rate, with a tendency to plateau at high rates. The percent of hollow stem was increased at high N rates, only under the irrigated treatment. Plots placed under conditions to produce the highest possible polyphenolics content were however the least productive ones, from a fresh market standpoint. Since these stresses are impacting crop growth and development, there is a clear antagonism between the production of polyphenolics from broccoli, on one hand, and fresh market production, on the other hand. The Dualex has the potential to establish broccoli N requirements by its capacity of detecting polyphenolics concentration in leaves but irrigation may interfere in the diagnosis.

Evaluation of Nitrogen Sources and Application Methods for Nitrogen‐Rich Reference Plot Establishment in Corn

Abstract: Five different N sources were compared with null N treatment to evaluate their performance for N-rich reference plot establishment in corn (Zea mays L.). The sources, including calcium ammonium nitrate (CAN), urea ammonium nitrate (UAN), polymer-coated urea (PCU) and environmentally smart nitrogen (ESN) in 2007 and 2008, and urea (URE), were broadcast or in-soil banded at the rate of 225 kg N ha -1 . A greenhouse trial was also conducted with N applied as CAN, URE, and ESN. Net photosynthesis rate (P N ) and chlorophyll fluorescence parameters (Fv/Fm or Fv'/Fm') were measured to assess N sources effects on corn photosynthesis. Relative photosynthetic capacity (RPC) and relative chlorophyll fluorescence capacity (RCFC) were calculated to evaluate the performance ofN sources in N-rich reference plot establishment. There were no differences in the release pattern ofN from different sources that could lead to differences in RPC and RCFC during the period when N status diagnosis is normally performed. Hence, all sources were equally effective to establish N-rich reference plots in our experimental conditions. It was also found that growers have the flexibility to either broadcast N at sowing or to band N along the rows at a later time after corn emergence.

Ammonia volatilization: On-farm assessment of the amount and timing of nitrogen fertilizer application in corn production

Abstract: An on$farm field experiment was carried out for thr ee years at Ottawa, ON and two years at Guelph, ON and Saint$Valentin, QC, Canada. Our objectives were to (1) quantify the flux and the amount of NH 3 volatilization as affected by the rate and time of N fertilizer; (2) assess the impact of rainfall and soil temperatures on NH 3 volatilization; and (3) determine the threshold level of N fertilizer at which large NH 3 volatilization losses occur. Using the static chamber method, NH 3 volatilization was monitored after preplant or sidedress N application. Rate of NH 3 volatilization peaked at 3 to 7 d and then dropped sharply within the next 7 d before levelling off in the following weeks. The amount of NH 3 volatilization increased with increasing N levels applied preplant or sidedress at all site$yrs. Peak NH 3 volatilization ranged from 40 to 8000 g N/ha/d after preplant fertilization and from about 100 to 2100 g N/ha/d after sidedress, resulting in NH 3 losses of 0.1 to 47 kg N/ha and 0.6 to 20 kg N/ha, respectively. Our data clearly indicate that sidedress applications may reduce NH 3 volatilization losses simply due to lower total N rates.