Case Studies: Champ E
Champ E is located southeast of Montréal near St Jean sur Richelieu. As can be seen from the aerial photo (field outlined in pink), this field was originally two fields. The old ditch dividing the two fields can be seen as a dark line in the centre (running north south). The very dark area in the centre of the black and white photo corresponds to an area of high O.M. % (Figure 1 ) however it does not match the zone of highest soil moisture % (Figure 2 ) taken in August/99. The producer has done land leveling on this field to eliminate micro-topography. The rotation is grain corn, silage corn, small grain and hay. The main characteristic of the field is the high silt content in the southeastern portion and high sand content in the northwestern section. The sand is a very fine sand which grades into the silt size fraction.
The 8-ha field was sampled on a 40 x 40 m grid with approximately 8 samples per ha and a total of 68 samples. Figure 3 shows the relative elevation and grid-sampling pattern. There is a minor slope between the north and south half - a one-meter difference - most of the micro-topography has been eliminated. There are no previous yield maps available for this field and as the producer decided to harvest silage corn there was no yield map from the combine for 1999. Yield measurements were taken at each of the 68 sample points.
Phosphorus & Potassium
The spatial distribution of P is given in Figure 4 . The P levels ranged from 80 to 295 kg/ha with an average value of 147 kg/ha (P fertilizer recommendation 40 kg P2O5/ha for corn). In this field 52% of the area received the recommended P fertilizer level, 1% was under-fertilized and 39% was over-fertilized. The P distribution pattern runs north - south, while the soil texture change runs closer to east west. The P patterns were influenced by manure application, direction of equipment and crop planting (north south). Figure 5 shows the potassium levels in the field. The average K value was 224 kg/ha with a range of 55 to 655 kg/ha. Both the K and P patterns do not show any correlation with yield.
Crop Yield Patterns B Unaltered
The yield map based on hand sampling is given in Figure 6 . The average corn yield was 8.6 t/ha. The yield map has a high yielding zone running in a curve through the field. This curve approximates the transition zone or gradation from sand to silt. According to the soil textural triangle, the curve of high yield follows the "loam" soil textural class, north of the curve is a sandy loam and south of the curve is a silt loam. These textural differences can impact aeration, soil aggregation, water infiltration and nutrient movement in the soil. Sand, clay and silt distributions are given in Figures 7, 8 and 9 respectively. The soil textural class can be determined by entering the % sand and % clay into the triangle on the following site. A AX@ will mark the soil class. http://www.ncat.edu/~lik/wetland/images/Stt.html.
Crop Yield Patterns B Normalized
Figure 10 gives the normalized yield pattern where in 1999, 52% of the field was within 10% of the average yield. High yields were found in 27% of the area. The low yields were localized to the edges of the fields and near the ditches. The low yield could be caused by compaction or poor drainage.
Spatial, Temporal and Classified Management Maps
These management maps require several years of yield data that were unobtainable for this field.
Soil Physical and Nutrient Maps
The P saturation map (Figure 11 ) and the aluminum distribution (Figure 12 ) are strongly correlated. The high P saturation % is not because of a high application of manure in this area or reduced yields, which reduce P uptake and removal. The high levels of P saturation correspond to the zones where the Al concentration is very low. The reason for the wide range in Al levels is not clear. The calcium and magnesium distribution in the field (Figures 13 and 14 ) parallel the sand and clay patterns. The northern section of the field with the high sand level has relatively low Mg levels that could pose a problem to crop growth as corn has a high Mg demand. There is a large range in the Ca levels from 1000 to 10,500 kg/ha. As calcium is an essential plant nutrient the low zone could impact crop growth. Figure 15 gives the uniformly low ammonium-N levels in the field which were taken in the beginning of August/99. The nitrate-N distribution is given in Figure 16 and the higher values correspond to the old ditch that divided the field. The soil pH (Figure 17 ) is a good level for corn and there is little variation. The organic matter % (Figure 1 ) has its highest level in the zone of highest clay content, however it quite low in the sandy northern section. The bulk density (Figure 18 ) is relatively high which may reflect the land leveling performed on this field as well as the low organic matter content.
Conclusions & Recommendations
The spatial patterns on this field are mostly related to the soil texture, which is a soil property that cannot be altered. The identifiable zones correspond to the high sand or silt areas. These areas could be managed separately especially with regards to Ca and Mg application. As well the high sand area has a low organic matter % which should be increased. Effects of the old ditch should decrease over time.