Onion Response to Added N in Histosols of Contrasting C and N Contents

Adjusting the N fertilization to soil potentially mineralizable N in Histosols is required to secure high vegetable yields while mitigating nitrate contamination of surface waters. However, there is still no soil test N (STN) relating the response of Histosol-grown onion (Allium cepa L.) to added N. Compositional data analysis can integrate soil C and N composition into a STN index computed as Mahalanobis distance (M2) across isometric log ratios (ilr) of diagnosed and reference soil C and N compositions. Our objective was to calibrate onion response to added N against a compositional STN index for Histosols. Reference compositions were computed from high N-mineralizing Histosols reported in the literature. Soil analyses were total C and N, and a residual soil mass (Fv) was computed as 100%-%C-%N to close the compositional vector to 100%. The C, N, and Fv proportions were synthesized into two ilrs. We conducted thirteen onion N fertilization trials in Histosols of south-western Quebec showing contrasting C, N, and Fv proportions. Each crop received four N rates broadcast before seeding or split-applied. We derived two STN classes separating weakly to highly responsive crops about the M2 value of 5.5. Onion crops grown on soils showing M2 values >5.5 required more N and yielded less in control treatments compared with soils showing M2 values 5.5) soils responded significantly (P < 0.10) to 60 and 180 kg N ha-1, respectively. Using literature data and the results of this study, we elaborated a provisory N requirement model for Histosol-grown onions in Quebec.

Positioning Temperature Sensors for Frost Protection in Northern Cranberry Production

Frost can cause serious economic losses in cranberry fields, particularly in northern regions. When the air temperature reaches a low critical threshold, sprinklers are operated to protect vines, to insure crop production and profitability. To avoid frost injury, proper positioning of temperature sensors is critical. A field experiment was designed and conducted to determine the optimal installation height of sensors above soil surface. Temperature data was used to investigate the spatial temperature gradient in the section of a cranberry field. A computer simulation of the temperature profile was performed to simulate the effect of wind velocity on the prediction of air temperature. For optimal use, sensors should be installed at the height of the canopy and several meters away from a dike. On nights with low wind velocities, the canopy air temperature was 2.7°C below that of 500 cm above the ground. The sensors should be put at least five m away from a dike to avoid the transfer of heat from the dike to the sensor. Also, multiple sensors should be installed because of the large variations in air temperature that were measured across the experiment. The simulated temperature indicated that wind velocity strongly influenced the temperature estimation;the effect of the wind on temperatures gradients was greater when the wind velocity was low (<2.3 m/s).

Harvest of Short-Rotation Woody Crops in Plantations with a Biobaler

The biobaler is an alternative to the modified self-propelled forage harvester to cut and collect short rotation woody crops (SRWC). It is less capital intensive and more versatile, being able to harvest woody crops on plantations, on abandoned farmland, on brush land or within forest understory. The biobaler was evaluated specifically on five different plantations over 19 experimental units (546 bales harvested with an average mass of 427 kg and 49% moisture content). Average bale density was 266 kg wet mass (WM)/m3 or 139 kg dry mass (DM)/m3. Average harvest capacity was 35 bales/h (7.7 t dry matter/h), and ranged from 23 to 48 bales/h. Harvest in plantations with a 149 kW tractor cost on average CAN $175/h, $5/bale and $22.84/t DM. Non recovered biomass (field loss) averaged 11% at random locations in the field and 8% at the point of bale ejection as a result of chip abrasion. While the biobaler remains a versatile harvester for SRWC, its preferred utilization will be in environments of diverse woody crops with final application as a rough mulch or for combustion in furnaces requiring minimal processing or size reduction.