Case Studies: Champ C
Champ C is located southeast of Montréal near St Jean sur Richelieu. The crop rotation was grain corn from 1995 to 1999 and in 2000 the producer grew soybeans. A low rate (unknown amount) of liquid cow manure was applied in the fall of 1998 and solid cow manure was applied in the spring of 1999. Over 75 % of the field has 50% sand while 1/3 of the field has approximately 75 % sand, which allows the field to be worked early in the spring but drought is often a problem. According to the producer there is no major problems with weeds. Lime was not applied in the previous five years. The fertilizer for corn was applied at seeding and at the seven leave stage, anhydrous ammonia was applied.
The field is 12 ha and was sampled on a 40 x 80-m grid, which gave 6 to 7 samples per ha, and a total of 81 soil samples. Figure 1 shows the relative elevation and the grid sampling points. There is a strong uniform slope that ends in the ditch paralleling the southeastern edge of the field. There are no previous yield maps for this field and the wet fall in 1999 prevented the hiring of a combine with GPS. Grain corn was hand-sampled for yield determination at each of the soil sample points. The aerial photo shows the section of the field under study (outlined in pink). The light coloured northwestern section corresponds to the zone of 75% sand (Figure 2 ).
Phosphorus & Potassium
Figure 3 shows the spatial distribution of P. The P ranged from 107 to 548 kg/ha with a field average of 216 kg/ha (fertilizer recommendation of 30 kg P2O5/ha for corn). In this field 57% of the area received the recommended rate of P, while 16% was under-fertilized and 28% of the area was over-fertilized with respect to P. The high levels of P correspond to the high % sand area, which also had a low yield (<90% of the average) in 1999 (Figure 6 ). The reduced crop growth due to drought also reduced crop uptake and removal of P. As well, movement of P to the roots is slowed by low soil moisture. The K distribution exhibited a wide range from 96 to 729 kg K/ha with an average value of 284 kg/ha. High levels of K (Figure 4 ) corresponded to the high P values. Again, this level of K may be due to reduced crop uptake and removal of K.
Crop Yield Patterns B Unaltered
There is only one year (1999) of crop yield data as in 2000 the producer grew soybean and did not use a combine with GPS for harvest. Figure 5 shows the grain corn yield in t/ha. The field average was 8.4 t/ha, with a range of 3 to 12 t/ha. This map is based on 81 sample points which is very low when compared to between 50,000 to 60,000 points that would be obtained from a combine harvester with GPS on a field this size. The area of the field with the high sand content shows reduced yields (drought). The central portion of the field had the highest yield but there is no clear relationship with any other variable.
Crop Yield Patterns B Normalized
The normalized yield map is given in Figure 6 and it can be seen that approximately 50% of the field had a medium yield (+/- 10% of the average yield). The high yield area corresponds to the centre of the field which had lower levels of P and K, though these levels may correspond to long term patterns of P and K uptake and removal (greater with higher yields). The soil moisture taken in July/99 in the high yielding area is low, around 12% moisture content (Figure 7 ).
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 clay and silt distributions are given in Figures 8 and 9 , respectively. The silt % increases in the southern portion of the field and during the sampling season, up-welling of groundwater could be seen in this area. The nitrate (Figure 10 ) and ammonium (Figure 11 ) are low and variable. The high sand content allows rapid mineralization of the organic N in the manure and rapid movement of nitrate through the soil profile. The P saturation % is given in Figure 12 and although the northern portion of the field has the highest levels in soil P, this area also has the highest level in soil aluminum (Figure 13 ) which lowers the P saturation level (P saturation = kg P/kg Al). The organic matter level (Figure 14 ) is low to average, most sand soils cannot maintain an O.M. % greater than 4 (rapid breakdown). The soil pH is low (Figure 15 ), although corn can tolerate low pH levels crops such as soybean and alfalfa will have a problem (optimum pH 6.5 to 7.5). The calcium (Figure 16 ) and magnesium (Figure 17 ) levels are low on approximately 75 % of the field.
Conclusions & Recommendations
As there is only one year of yield data, management zones are impossible to establish. It cannot be determined if the climate has a major impact on the crop yields (do the high, medium and low zones vary from year to year?). From the soil analysis, a lime application is recommended preferably one that contains both Ca and Mg. The soil pH is low (especially for almost all other crops than corn) and the levels of Ca and Mg, essential plant nutrients, are low as well. The low soil moisture content would slow movement of these nutrients to the roots and if the soil levels are low as well, there could be possible deficiencies.