C. Karemangingo1, D. Savoie2 and H. Rees3
Partner: New Brunswick Potato Agency
Abstract: This project assessed the impact of the landscape position on the distribution of nutrients within a terraced potato field and an up-and-down slope-worked one. The two fields covered 21.6 ha and their slope varied from 2 to 10% steep and higher than 150 m long. In 2003, the terraced field was cropped to grains while the other field was cropped half to Raygrass and half to potatoes (100m x 450m each crop). The soils were sampled in the fall based on a 50 m x 50 m grid and tested for nutrient contents. Soil organic matter and soil particle size were tested from 50 m x 100 m grids. The analysis results were used for mapping soil physical and chemical properties and calculating semivariograms associated with their variability of these properties within the field. All the grid points were georeferenced. In the terraced field, soil pH, phosphorus, potassium, calcium, and magnesium contents varied from 5.5 to 6.4, 64 to 271 ppm, 83 to 179 ppm, 562 to 1716 ppm, and 63 to 159 ppm, respectively. Soil organic matter varied from 0.9 to 4.1% while sand, silt and clay contents varied from 22.2 to 46.1%, 39.4 to 54.2%, and 12.5 to 24.1%, respectively. The general soil texture was a loam. Similar ranges of soil properties were found in the up-and-down plowed field. Semivariograms of soil nutrient contents resulted in separation distances (ranges) varying from 200 to 225 m. Such ranges appeared consistent with the 5 ha field size currently recommended as a soil sampling unit. Ordinary kriging and mapping of soil nutrient contents did not show any landscape effects on the distribution of nutrients. The high grid size (5m x 50 m) might have masked the soil variability. Despite this, low levels of soil nutrients were measured over a 50 m width alongside the grassed waterway and at the bottom end of the field. In the up-and-down plowed field, the distribution of most nutrients was more a function of the crop (potatoes versus Raygrass) than that of the landscape position, except for soil phosphorus. Soil phosphorus was within-field distributed in such a way that the plateau section was richer than the sheds. In this case, cross slope working should make it possible specific potato P fertilization of different sections upon their landscape position. These preliminary results are to be validated across many fields.
1 NB Department of Agriculture, Fisheries and Aquaculture, Land Development Branch, PO Box 6000, Fredericton, NB, E3B 5H1
2 NB Department of Agriculture, Fisheries and Aquaculture, Agriculture Development Branch, PO Box 5001, Grand Falls, NB, E3Z 1G1
3 Agriculture and Agri-Food Canada, Potato Research Centre, PO Box 20280, Fredericton, NB, E3B 4Z7