Field History

Champ A is located north of Montréal near St Esprit. Table 1 gives the growing season (April to October) cumulative rainfall. Although the levels for 1998 and 1999 were higher than the 10-year average, the distribution pattern over the season is extremely important. In 1999 there was a very wet fall which made harvesting difficult.

Table 1 Growing season rainfall

Champ A was originally two fields that were joined in1996-1997. The aerial photo  shows the whole field outlined in red (the yield maps are of the whole field) and the half of the field which had grid soil sampling is outlined in green. Figure 1  is the topographic map of the soil-sampled section showing the grid pattern of the 85 soil samples. The total field size was 25 ha and the section soil sampled on a 80 x 40 m grid was 13 ha. The field is bisected by a steep ridge that runs across most of the field (7-m difference in height). The producer plows across the ridge so as to reduce soil erosion. It is visible on the aerial photo as light coloured band. According to the field history, solid chicken manure was applied once every four years, approximately 6 t/ha, however the application rate is not uniform over the entire field. The manure was concentrated on the ridge, which can be seen in the distribution of P and K in the field, Figures 2  and 3.  The highest concentrations of these nutrients occur either on the ridge or in the north headlands (field entrance).

There was an infestation of yellow nut sedge (Cyperus esculentus L.) in the headlands and on the north side of the ridge. This weed is often found in areas that have problems with drainage. The field is sub-surfaced drained, however compaction can slow down drainage. Other poorly drained areas exist in the field where the old drainage ditches were located. The crop rotation starting in 1996 was wheat, soya, grain corn, soya and grain corn in 2000.

Phosphorus & Potassium

The P levels ranged from a minimum of 34 kg/ha to a maximum of 640 kg/ha. Figure 2  shows the P distribution based on the CPVQ/CRAAQ fertilization tables. The field P average is 156 kg/ha, which gives a recommended P application rate of 30 kg/ha. Analysing the areas of P distribution gives 57% under-fertilised, 29% receiving the correct application rate and 14% over-fertilised. High levels of P were found on the ridge area, which received additional manure and at the entranceway to the field. Potassium levels ranged from 67-602 kg/ha and paralleled the P distribution with high levels found on the ridge and at the entrance (Figure 3 ). Crop yields were low on the ridge and in the headlands, thus the additional manure application containing P and K had little impact on crop yield as compaction and sandy stoney soils reduced the yields.

Crop Yield Patterns B Unaltered

Figures 4  to 7, show the crop yields in t/ha. Patterns on these maps were identified as to the possible causes of reduced or higher yields. In 1997 and 1998, reduced yields can be found where the old drainage ditch was located between the two fields (Figures 4  and 5 ). In most years, the two strips down the centre of each field indicate a dead furrow, or combine harvesting error. In all years low yields were found in the headlands (Figures 6  and 7 ) and on the ridge.Table 2 gives the average yield for the crop. Some years had spot drainage problems, which are indicated on the maps.

Table 2: Crop yield

Crop Yield Patterns B Normalised

In order to examine the yields independent of the individual crop, the yields were "normalised", that is the yield was calculated as a percent of the average yield and then divided into three levels relative to the average yield (equal to 100%): <90%, 90-110% and > 110%. Figures 8  to 11  show maps of the normalised yield. These maps were used to develop the three management maps for the following section. The dry year in 1997 caused a low average yield in the soybeans and field exhibited a large amount of variability in yield (Figure 8 ). In contrast, Figure 10  for soybeans in 1999 shows that the yield was almost uniformly average over the entire field (normal rainfall). The two years of corn show contrasting patterns of yield. In 2000 (Figure 11 ) the majority of the field yielded +/- 10% of the average yield, however the unaltered yield map (Figure 7 ) shows variability. In 1998 (Figure 9 ) the field had larger areas of different yield levels.

Spatial, Temporal and Classified Management Maps

The spatial map (Figure 12 ) is basically a summation of the normalised yield patterns (four years). It can be seen the majority of the field gave an average yield. The areas that were a problem regardless of the crop were the ridge and the headlands. The temporal map (Figure 13 )  is derived form the normalised yield maps and indicates whether the yield patterns consistently yield low, medium or high regardless of the crop or the weather. However it can be seen that 85% of the field is "unstable" in yield patterns. The classified management map (Figure 14 ) was derived from both the spatial and temporal maps. This map was used to determine if there were stable management zones in the field. It can be seen that a majority of the field varies its level of yield over time (that is, in one year the yield may be low and the next year the yield may be high).

Soil Physical and Nutrient Maps

The aluminum distribution is given in Figure 15  and the P saturation % in Figure 16 . The highest P saturation values are found on the ridge, which corresponds to the lowest Al levels. The additional manure put on the ridge causes this increase in P sat % levels. Organic matter levels and soil pH are found in Figures 17  and 18, respectively. Both nutrient levels are good and do not show any direct relationship to yield. Calcium and magnesium levels (Figures 19  and 20 )  are lower on the ridge but the levels are still adequate for crop growth. Nitrate (Figure 21 ) and ammonium (Figure 22 )  were determined in July/00. This field, compared to other fields in the study, had much higher levels of nitrate. However the nitrate patterns did not correspond to the yield patterns. The soil moisture from July/00 (Figure 23 ) has lower levels on the ridge. The sand (Figure 24 ) and clay (Figure 25 ) distribution vary throughout the field. However, the level of silt (Figure 26 ) appears to correspond to some of the areas of spot drainage problems. In the northern half of the field, the area of >55% silt corresponds to the spot drainage problems shown in Figures 9  and 11.

Conclusions & Recommendations

The factors that reduce and cause yield variability in Champ A are partially identifiable. The factors that reduce yield on the ridge are low moisture holding capacity, stoniness, difficulty in harvesting, erosion etc, however measures to improve yield in this area are difficult to implement. Additional manure, with corresponding high P and K levels, will not offset the effect of the other factors. Spot drainage problems associated with the higher silt % and as well, the yellow nut sedge infestation in these areas cause yield reduction but the installation of additional subsurface drains may or may not prove profitable. However, additional manure (containing P) could be applied to this field as the spatial distribution of P is highly variable and just over half the field is under fertilised with respect to P.