Organic soils are an important resource for vegetable crops. However, these crops are very demanding in terms of pest control, fertilization and tillage. Combined with organic soil subsidence, current practices threaten the sustainability of this resource. In this study, we test the potential of Sunn hemp ( Crotalaria juncea) ) as a green manure to control populations of plant-parasitic nematodes and as a carbon input to the soil. Incorporating Sunn hemp resulted in a tenfold reduction in populations of the northern root-knot nematode ( Meloidogyne hapla) ) and a significant increase in carrot yields the following year. However, no significant effect was observed on the root-lesion nematode, Pratylenchus penetrans. .

Les sols organiques sont une ressource importante pour les cultures maraîchères. Par contre, ces cultures sont très exigeantes en termes de contrôle phytosanitaire, de fertilisation et de travail du sol. Combinées à la problématique d’affaissement des sols organiques, les pratiques actuelles menacent la pérennité de cette ressource. Dans cette étude, nous testons le potentiel de la crotalaire (Crotalaria juncea) comme engrais vert afin de contrôler les nématodes phytoparasites et comme apport de carbone. L’enfouissement de la crotalaire a permis de réduire de dix fois les populations du nématode cécidogène du Nord (Meloidogyne hapla) et d’augmenter significativement les rendements de carottes l’année subséquente. Aucun effet significatif n’a cependant été observé sur le nématode des lésions, Pratylenchus penetrans.

Caron, J., Rancourt, G. T., Bélec, C., Tremblay, N. and Parent, L.-É. 2014. Nitrogen budget for fertilized carrot cropping systems in a Quebec organic soil. Can. J. Soil Sci. 94: 139–148. After reclamation, organic soils tend to shift from net N immobilization to net N mineralization. The N amounts mineralized annually can be sufficient to cover the N needs of the crop, reducing the need for supplemental N fertilization. The objective of this study was to assess N budgets and to infer the apparent N mineralization in fertilized and unfertilized carrot (Daucus carota L.) crops in an organic soil in southwestern Quebec. Five pre-plant N fertilization treatments (0, 25, 50, 75, and a split 25+25 kg N ha−1) were applied over a 3-yr period to non-irrigated carrots. Crop yield and plant and soil N contents were measured. Apparent net N mineralization was an important source of N, averaging 117 kg N ha−1yr−1. Crop yield was not affected by the N fertilization rate, by splitting of the fertilizer application or by the previous year’s crop. Increasing the N fertilizer rate increased the soil nitrate content below the root zone (∼40 cm below the surface), enhancing the risk of nitrate leaching. Thus, because soil N mineralization was sufficient for the carrots’ requirements in this organic soil, supplemental N fertilization was found to be unnecessary and could exacerbate the environmental risk of nitrate leaching.

Information-based crop management, such as variable rate technology, allows for changing rates of fertilization according to local needs. Fertilizer prescription maps can be derived from crop growth status assessed through proximal canopy sensing technologies. Typically, a vegetation index, such as the NDVI, is used to estimate a Nitrogen Sufficiency Index (NSI=NDVI/NDVIN-rich). NSI is related to N intake in comparison to the measurements in N-rich reference areas created artificially with high N rates applied at planting. This approach requires N-rich areas representative of different field conditions, which is not always practical. To circumvent this limitation `naturally N-rich' reference areas linked to natural field characteristics can be identified. The goal of this present work was to show that the NSINLR estimated using less laborious Natural Local References (NLR) has a benefit comparable to the more traditional NSIN-rich from N-rich plots. Experiments were performed on corn fields located in the Montérégie area of Quebec. The NDVI values were measured using 5 tractor-mounted GreenSeeker sensors. The spatial variability of the soil was analyzed using maps of apparent electrical conductivity (ECa) obtained using a Veris 3100 system. The NSINLR, set at the 90th percentile of the NDVI values obtained around each sensed area, was compared to NSIN-rich. The NSI values estimated using both techniques were strongly correlated and demonstrated a high capacity to estimate the optimal N rate for corn.

Soil properties and weather conditions are known to affect soil N availability and plant N uptake; however, studies examining N response as affected by soil and weather sometimes give conflicting results. Meta-analysis is a statistical method for estimating treatment effects in a series of experiments to explain the sources of heterogeneity. In this study, the technique was used to examine the influence of soil and weather parameters on N response of corn (Zea mays L.) across 51 studies involving the same N rate treatments that were performed in a diversity of North American locations between 2006 and 2009. Results showed that corn response to added N was significantly greater in fine-textured soils than in medium-textured soils. Abundant and well-distributed rainfall and, to a lesser extent, accumulated corn heat units enhanced N response. Corn yields increased by a factor of 1.6 (over the unfertilized control) in medium-textured soils and 2.7 in fine-textured soils at high N rates. Subgroup analyses were performed on the fine-textured soil class based on weather parameters. Rainfall patterns had an important effect on N response in this soil texture class, with yields being increased 4.5-fold by in-season N fertilization under conditions of "abundant and well-distributed rainfall." These findings could be useful for developing N fertilization algorithms that would prescribe N application at optimal rates taking into account rainfall pattern and soil texture, which would lead to improved crop profitability and reduced environmental impacts.

Nitrogen (N) fertilizers are often applied to maize (Zea mays L.) in excess of economically optimal rates because of the uncertainty of dealing with seasonal and spatial variability. A better understanding of the relationships among field, apparent soil electrical conductivity (ECa), elevation, slope and seasonal characteristics is therefore essential for performing optimal variable-rate N applications. This study focused on responses during the exponential growth phase, when it is critical that N supply be not limited. Measurements at high spatial resolution allowed to understand the effects of the relationships among N, ECa, elevation, slope and season on future yield formation. The study was conducted over three years (2005–2007). Mid-season growth responses to applied N were greatest where ECa levels were high and elevation was low in 2005 and 2007, but not in 2006. Areas with slope ≥1 degree were also more responsive to N rates. Overall best mid-season growth was found in areas of low ECa, high Elevation and low Slope. However, the best responses to in-season N fertilization were found in areas with opposite properties (high ECa, low Elevation and high Slope). Indeed, relatively high rates of in-season N were needed to enhance crop growth in areas of high ECa, low Elevation and high Slope, which are characteristic of unfavourable growth conditions. In counterpart, lower N rates were sufficient for optimal growth in soils at low ECa high Elevation and low Slope. Also, despite the fact that conditions of high soil variability were specifically selected for the study, the effects and interactions reported for soil NO3–N content were small. The interaction of ECa with early seasonal precipitation is likely a key relationship to consider in variable-rate N application: low-lying areas with fine soil texture showed the greatest dependence on weather for optimal N rates. Indeed, the relationships among factors influencing the response to in-season N fertilization were stronger when seasonal conditions were particularly favourable to maize growth. These results are fundamental to the establishment of in-season application rules for spatially variable N algorithms.

A fuzzy Inference System (FIS) was developed to generate recommendations for spatially variable applications of nitrogen (N) fertilizer using soil, plant and precipitation information. Experiments were conducted over three seasons (2005-2007) to assess the effects of soil electrical conductivity (ECa), nitrogen sufficiency index (NSI), and precipitations received in the vicinity of N fertilizers application, on response to N measured at mid-season growth. Another experiment was conducted in 2010 to understand the effect of water supply (WS) on response to N, using a spatially variable irrigation set-up. Better responses to N were observed in the case of high ECa, low NSI and high WS. In the opposite cases (low ECa, high NSI or low WS), nitrogen fertilizer rates can be reduced. Using fuzzy logic, expert knowledge was formalized as a set of rules involving ECa, NSI and cumulative precipitations to estimate economically optimal N rates (EONR).

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.

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.

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 of N sources in N‐rich reference plot establishment. There were no differences in the release pattern of N 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.

Dualex and SPAD are devices developed for the purpose of testing crop nitrogen (N) status. These instruments were used in a wheat experiment in order to compare their respective performance in assessing leaf nitrogen (N) concentration, response to N topdressing application, soil nitrate (NO3)-N levels and in predicting grain yield. The experiment included different N rates in 2005 and 2006 in the Monteregie region of Quebec, Canada. Dualex readings correlated negatively with SPAD readings, leaf N concentration, soil NO3-N content and wheat grain yield. SPAD alone and the ratio of SPAD to Dualex measurements (Chl/Phen) were linearly related to N application rate but no effect of N application rate was found for individual Dualex parameters. However, both SPAD and Dualex readings were affected by year effects. The Dualex was also capable of indirect evaluation of in-season soil NO3-N accumulation and the prediction of wheat yield, but more so as Chl/Phen.

Commercial production of broccoli is highly dependent on nitrogen (N) fertilization. With high amounts of precipitation or irrigation, leaching of N below the root zone may constitute an environmental risk, especially when available soil N exceeds plant uptake, which is often the case early in the season. The recommendation in Quebec is a split application of 85 kg N/ha at transplanting and 50 kg/ha at sidedressing (four to five weeks later). The sidedressing application can be adjusted based on a prior test of N sufficiency. The aim of this study was to determine the effect of N rate and irrigation on the sensitivity of different tests, including the Dualex, a new instrument measuring the status of leaf polyphenolics (Phen). Experimental fields were established in 2005 and 2006 at the Agriculture and Agri-Food Canada experimental farm of L'Acadie (Quebec). The crop was fertilized with 0, 105, 135, 165, 195, or 225 kg N/ha and provided, or not, with supplementary irrigation after crop establishment. Sap NO3, leaf epidermis Phen, and chlorophyll contents (Chl) were determined periodically using the Nitrachek reflectometer, the Dualex, and the SPAD-502 chlorophyll meter (chlmeter) respectively. Yields of marketable heads increased in a curvilinear matter with N rate, with a tendency to plateau at high rates. There was low mineral N available in the soil at harvest, regardless of irrigation, but the level was linearly related to N rate. Dualex readings were generally not affected by irrigation and quick to react to N application, generally in a linear manner. They compared well to both the sap test and the SPAD meter. The ratio of chlorophyll meter to Dualex readings (Chl/Phen) was particularly sensitive to seasonal N requirements.

Nitrogen (N) fertilizer rates applied spatially according to crop requirements can improve the efficiency of N use. The study compares the performance of two commercial sensors, the Yara N-Sensor/FieldScan (Yara International ASA, Germany) and the GreenSeeker (NTech Industries Inc., Ukiah, California, USA), for assessing the status of N in spring wheat (Triticum aestivum L.) and corn (Zea mays L.). Four experiments were conducted at different locations in Quebec and Ontario, Canada. The normalized difference vegetation index (NDVI) was determined with the two sensors at specific growth stages. The NDVI values derived from Yara N-Sensor/FieldScan correlated with those from GreenSeeker, but only at the early growth stages, where the NDVI values varied from 0.2 to 0.6. Both sensors were capable of describing the N condition of the crop or variation in the stand, but each sensor had its own sensitivity characteristics. It follows that the algorithms developed with one sensor for variable-rate N application cannot be transferred directly to another sensor. The Yara N-Sensor/FieldScan views the crop at an oblique angle over the rows and detects more biomass per unit of soil surface compared to the GreenSeeker with its nadir (top-down) view of the crop. The Yara N-Sensor/FieldScan should be used before growth stage V5 for corn during the season if NDVI is used to derive crop N requirements. GreenSeeker performed well where NDVI values were > 0.5. However, unlike GreenSeeker, the Yara N-Sensor/FieldScan can also record spectral information from wavebands other than red and near infrared, and more vegetation indices can be derived that might relate better to N status than NDVI.

Field corn experiments were conducted over the years 2004 to 2006 inclusive in the Monteregie area of the province of Quebec, Canada. Terrain features were characterized and crop vegetation index were monitored. At mid-growth stage, V9-VT, a Duncantech multispectral digital camera with 0.25 m resolution was performed in 2004 and a hyperspectral CASI (Compact Airborne Spectrographic Imager) with I in resolution were flown in both 2005 and 2006 to record variations in crop characteristics. The normalized difference vegetation index (NDVI) was extracted from the above images and NDVIn, which quantified the mid-season corn growth, was calculated. The resulting maps were also used to sort out the relative importance of topography, apparent soil electrical conductivity (ECa) and plant status on responses to nitrogen (N) rates. The results of an ANOVA showed that the influence of N rate and spatially variable factors on corn mid-season growth were largely seasonal dependent. Reductions in fertilizer N as compared to grower practice without yield losses ranged from 7% to 49% depending on year. Residual N found after harvest in the soil was relatively low. It is concluded that the environmental risks related to N management in corn production are related to N losses early in the season, when crop uptake is low and N in the soil is susceptible to intense leaching episodes. Based on this study, a responsible decision-support system for crop N management is outlined around the use of remote sensing and geographic information system technologies.

The Dualex is a new leaf-clip instrument that can be used to monitor corn nitrogen (N) status. It is based on the measurement of polyphenolics (Phen), which are secondary metabolites affected by stress factors. The purpose of this study was to compare Dualex to SPAD (chlorophyll meter), the latter having been used for several years in monitoring crop N status. As well, the interest of combining Dualex and SPAD information in Chl/DUAD (ratio of SPAD to Dualex reading on adaxial side), Chl/DUAB (ratio of SPAD to Dualex reading on abaxial side), and Chl/Phen (ratio of SPAD to the sum of DUAD and DUAB) ratios were considered. Significantly positive and negative correlations with corn leaf N concentration were found for SPAD and Dualex, respectively. Successful N status diagnosis could be achieved with either Dualex or SPAD for corn within 21 days after topdressing while the Dualex lost sensitivity at later stages. Dualex measurements could be limited to leaves abaxial side or adaxial side, instead of adaxial + abaxial sides, with no inconvenience. Among all parameters considered, the combined ratios with SPAD (Chl) and Dualex readings, Chl/DUAD, Chl/DUAB, and Chl/Phen were strongly related to applied N dose at all samplings dates, and found the most sensitive and robust through the season.

Weather is the primary driver of both plant growth and soil conditions. As a consequence of unpredictable weather effects on crop requirements, more inputs are being applied as an insurance policy. Best management practices (BMPs) are therefore about using minimal input for maximal return in a context of unpredictable weather events. This paper proposes a set of complementary actions and tools as BMP for nitrogen (N) fertilization of vegetable crops: 1) planning from an N budget, 2) reference plot establishment, and 3) crop sensing prior to in-season N application based on a saturation index related to N requirement.

The effects of six control strategies involving calcitic lime, hydrated lime, calcitic limestone dust and a granular form of calcium cyanamide were evaluated on a cauliflower crop during a 2-year field study. Prior to the first growing season, fall applications of 5 and 25 t ha−1 of calcitic lime broadcast were made. In the first growing season, only pre-planting application of hydrated lime and calcium cyanamide successfully reduced disease indices and increased yields. Post-planting application of calcium cyanamide, and post-harvest application of calcitic lime the preceding year were ineffective. In the second growing season, the best clubroot control results were obtained with the finest lime materials (hydrated lime, calcitic limestone dust) and the preceding post-harvest intensive liming treatment. Successful treatments raised pH from 5.7 to 7.0 in the first season and from 6.7 to 7.4 in the second season. The high cost of using calcium cyanamide was reduced by means of band application along the transplant rows.

Clubroot of crucifers is a major problem worldwide. Liming has been used as a control measure since the early 19(th) century. Liming must be done so as to raise soil pH to a suitable level as quickly as possible. For this purpose, relatively massive applications may be used sometimes with faster acting lime types than agricultural lime. However, the single use of lime often falls short of a satisfactory control on the disease. This study compared the effects of six control strategies involving calcium cyanamid, a nitrogen fertilizer known as having disease control properties, together with lime treatments for a cauliflower crop. Application of calcitic I lime [CaCO3] was made in fall, just after ploughing. Two rates were applied (5 t.ha(-1) and 25 t.ha(-1)). In spring, calcium cyanamid (500 kg.ha(-1) preplant or post-planting) and hydrated lime [Ca(OH)(2)] (1.5 t.ha(-1) banded at planting) treatments were applied on top of the different calcitic lime treatments. Soil pH was monitored throughout the growing season. Even if the control plot received 5 t.ha(-1) of calcitic lime, the yield losses caused by clubroot were considerable with a marketable yield of only 1.2 t.ha(-1). The best control strategy, with a marketable yield of 18.8 t.ha(-1), was calcium cyanamid applied pre-plant on top of 25 t.ha(-1) of calcitic lime. Hydrated lime banded at planting in combination with 5 t.ha(-1) of calcitic lime also showed good results, with a marketable yield of 13.1 t.ha(-1). There was a synergetic effect among treatments. Calcitic lime application alone, even at 25 t.ha(-1), did not provide satisfactory clubroot control.

Areas with intensive animal production can now take advantage of industrial process that treat the raw manure and turn it into dried granular fertilizer material suitable for transportation over long distances. The objective of this study was to evaluate the agronomic potential as a nitrogen source for broccoli of a granulated organo-mineral fertilizer. The experiment was conducted on two different sites in Quebec. Supplemental nitrogen requirements at 5 wk after planting (sidedress) were assessed with the help of a diagnostic test measuring nitrate in petiole extracts.The Agrior product in combination with inorganic fertilizer gave as good yields as those obtained with conventional inorganic fertilizer N management. Yields obtained with either 1 or 2 t ha(-1) of the organo-mineral fertilizer were not different. The amount of N to applied at side dress was optimized using the analysis of nitrate in petiole extracts. Biological activity in the soil tended to increase with organo-mineral fertilizer rates. Evaluation of the over winter effect of the organo-mineral fertilizer has been done with the establishment in 2001 of a wheat crop on top of the former broccoli set-up. Wheat yields showed a significant overwinter positive effect of the organic material.

Vegetable crops, such as broccoli (Brassica oleracea L. spp. italica), are heavily fertilised with nitrogen, often to the detriment of water quality and at the risk of health effects from elevated nitrate levels in our food. Broccoli fertilisation can be made more efficient by diagnosing the nitrogen status of plants, and adjusting the fertiliser accordingly. In this study, two diagnostic tests were compared: a nitrate sap test and a chlorophyll meter. Broccoli plants were given 0, 50 or 100 kg N/ha at planting, and 0, 50, 100 or 150 kg N/ha five weeks post-transplant. Sap nitrate levels were read using the test strips and reflectometer, and non-destructive chlorophyll readings were taken, five and seven weeks post-transplant. Both methods gave values correlated with N application rate, but only the sap test demonstrated a site*treatment interaction. The sap test was more sensitive to changes in application rate than the chlorophyll meter, and is the better choice of diagnostic tool for fine-tuning the second dose of a split application of fertiliser at five weeks post-transplant.