Case Studies: Champ G
Champ G is located south of Montréal. The aerial photo shows evidence of the old management practices on this field. Champ G was originally four fields, and traces of the original ditches can be seen as white lines running northeast to southwest. The soil is a silty clay to a heavy clay and before subsurface drainage, management practices on heavy clays used a form of surface drainage that involved slightly raised beds of approximately 50-m in width. Small ditches formed the sides of these raised beds. A major ditch ran down the centre of the field. No visible traces of these ditches remain on the field. However, the raised beds are still slightly visible.
With the installation of sub-surface drains and the increase in machinery size, many of these smaller fields have been joined together into one field. However traces of the old management practice can be still be seen on the soil parameter maps. Figure 1 shows the soil pH and Figure 2 gives the organic matter content. The soil has higher pH values where the two small ditches were located (dark blue colour = pH > 7), as the subsoil had a higher pH value than the surface soil. However the central ditch has a lower pH but also has the highest organic matter level as this ditch was used the longest (the four fields were joined to make two fields, then joined into one field - Champ G). The organic matter decomposition and wetter soils keep the soil pH at a lower level in this old ditch area.
The 8-ha field was sampled at a density of 10 points per ha with a total of 81 sample points. The elevation map (Figure 3 ) shows a relatively flat field with an elevation change of less than 1 -m. The grid soil sampling pattern is given in Figure 3.
Phosphorus & Potassium
Figure 4 shows the phosphorus distribution pattern. The field has a relatively low average value of P, 83 kg/ha and a range of 16 to 144 kg P/ha. The recommended fertilizer rate of P for corn is 60 kg P2O5/ha for this soil test level of P. According to the P distribution patterns, 38% of the field received the recommended P fertilizer rate, while 18% was under-fertilized and 44% was over fertilized. The central portion of the field, running northeast to southwest shows much higher levels of P compared to either side. The reason for this is unclear. The potassium levels are high with an average value of 367-kg K/ha and a range of 294 to 556 kg/ha (Figure 5 ). High K values are common in high clay soils.
Crop Yield Patterns B Unaltered
Unfortunately due to a misunderstanding between the producer and the combine operator, a yield map for 1999 was not obtained and this field has no previous yield maps.
Crop Yield Patterns B Normalized
There were no yield maps
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 % (Figure 6 ) was low, and 95 % of the area was less than 5% saturation. This is good in case this field is required for manure application. The aluminum distribution pattern is given in Figure 7 but is not strongly correlated with the P saturation % as the Al level was relatively uniform and high throughout the entire field. The calcium (Figure 8 ) and magnesium (Figure 9 ) levels are very high but this is a reflection of the soil parent material. These Ca and Mg levels are normal for this clay soil. Correspondingly the soil pH (Figure 1 ) is high with 90% of the field greater than pH 6.6. These high levels should not cause a problem with crop growth. The organic matter content (Figure 2 ) is good for a clay soil with 50% of the field ranging between 4.8 to 6.8 %. The sand, silt and clay distribution patterns are given in Figures 10 , 11 and 12. The sand content is less than10% through the entire field while the silt content ranges between 35 to 50%
Conclusions & Recommendations
As there were no yield maps for this field, no relationships between soil factors and the yield can be discussed. However, it is important to note that the effects of management practices (old ditches, drainage measures etc) persist for a long time. Soils have a long memory.