Field History

Field B is located north of Montréal near St Esprit. This region has a higher precipitation level and has cooler temperatures as compared to Montréal. The field varies both in topography and soil texture and is actually two fields divide by a narrow tree line. The aerial photo  clearly shows the location of the trees that partially surround the field. The producer said that there was land clearing done on the ridge in 1993 (see Figure 15  for the topography). The field was sub-surface drained, however two new drainpipes were installed in 2001, in the smaller, easternmost portion of the field which had severe spot drainage problems (visible on the yield maps). The crop rotation was corn- wheat B corn B corn - corn (2001). Solid poultry manure was applied at a rate of 7 t/ha in the previous fall before the corn. Additional poultry manure was applied to the newly cleared area on the ridge B the effects of which are clearly visible in the K and P maps (Figures 1 and 3 ). Liquid fertilizer containing N, P and K was used as a starter for corn and additional nitrogen was applied as a side-dress in June. The major weed problems were Lambsquarters (Chenopodium album L.) and Foxtail (Setaria viridis (L.) Beauv.).

The two fields, which are managed as one, have a combined area of 6 ha. The sampling grid was approximately 40 by 40-m and 58 soil sample points were geo-referenced. This gave a sampling density of 10 samples per ha.

Phosphorus & Potassium

The K distribution pattern derived from the 58 points is shown in Figure 1. Most of the field was in the "rich to excessively rich" zone for K for field crops. It is clear from the map that additional manure quantities had been applied to the ridge, as the K quantity was between 251 to 670 kg/ha. However there was an interaction between the soil texture and K retention in the soil. The western side of the ridge which has a higher clay content, 28% compared to 18 % (see Figure 21 ), had the higher K level. Clays retain a greater portion of the applied cations (K⁺, Ca²⁺, Mg²⁺) compared to the sands. The lower level of K on the eastern side of the ridge was caused either by leaching of K from the sandier soil or possibly by a greater uptake by the trees/forest that form the boundary of the eastern edge of the field (see Figures 5  and 6 ) . The producer stated that additional manure was applied to the area on the ridge that had been cleared of trees. Figure 3 , a map of P distribution in the field, shows extremely high P levels (251-830 kg/ha) on the ridge/cleared area. As P does not readily leach in the soil, the P applied from the manure has remained on the ridge.

The distribution patterns for K and P based on the commercial sampling grid of 1 per ha are given in Figures 2 and 4 . These sampling points missed the areas with extremely high levels of both P and K. The K pattern in Figure 2  does approximate the average level in the field, which is excessively rich (> 251 kg/ha). However, the P map (Figure 4 ) gives a misleading estimate of the true P levels in the field. From the 58 sample points shown in Figure 3 , it can be seen that approximately 2/3 of the field is rich to excessively rich in P (151- 250 and > 250 kg P/ha). However, from Figure 4 , which is derived from 6 sample points, the producer would assume that half of the field is only in the "medium to good" range (61 to 150 kg P/ha). It is extremely critical when grid sampling is done (and if the producer is going to pay for this service) that the maps are representative of the field.

Crop Yield Patterns B Unaltered

Figures 5, 6, 7, 8  and 9  show the yield patterns without any alteration. The yield data for all three crops has been filtered for unnaturally high or low values, but no interpolation or modification of the actual levels was done. The producer examined the yield maps and the explanations for the yield variation were noted on the Figures 5 , 6 and 7. Figures 8  and 9  are corn yield maps for 2000 and 2001. All years and crops (wheat and corn) showed effects from the trees B a yield reduction along the edges with trees B and are identified on the maps 1997-1999. There is a major weed infestation in the western corner of the field that appears to be a constant problem. However it may be related to drainage as well. All of the maps indicate some problems with the combine when turning in the headlands. The straight line down the centre of Figure 5  is either due to a dead furrow or due to the "last pass" on the combine taking less than 8 rows. The producer indicated that there were no old drainage ditches in this field. The spot drainage problem, which is strongly evident in years 1997, 1999 and 2000 and mildly visible in 1998, has been corrected in 2001 (installation of two new drainpipes). The corn yield in 2001 did not show any problems in this area. Table 1 gives the average yield from 1997 to 2001.

Crop Yield Patterns B Normalized

The crop yields in 1998 and 1999, which may have similar dry springs, show the strongest patterns (high and low yielding areas) in yield. There was an early frost in 1997 and the corn did not reach its full potential B as demonstrated by the fact that the maximum yield was only 38% greater than the field average, whereas in 1999 this difference was 45% (Figures 10  and 12 ).

The normalized yield maps (Figures 10 , 11, 12, 13  and 14)  show a reduction in yield due to the trees (shading, nutrient and water uptake), as both the northern and eastern sides of the field have trees. The weed problem in the western corner also has severely limited the yield potential for all of the crops. The northern side of the ridge exhibited lower yield for all years. However, it is difficult to speculate on what is causing the yield reduction. It is the zone with the highest P levels of up to 830 kg/ha (compare Figure 3  to Figures 10 , 11 and 12 ). The high P levels may be interacting with zinc, an essential micronutrient and reducing the zinc uptake by the crop. The soil was not analyzed for zinc and the producer did not indicate that there were deficiency symptoms visible on the crop. In 1999, the low elevation zone in the north section of the field had higher yields, this may be due to a greater moisture holding capacity of the soil B high levels of organic matter (see Figure 20  and Figure 23 )

Spatial, Temporal and Classified Management Maps

From Figure 16 , which shows the low to high yielding areas of the field (based on 1997-2001), it can be seen that most of the field was on average high yielding. The northern side of the ridge had a medium yield while those areas nearest the trees and the weed patch were low yielding. However, Figure 17 , which gives the stability of those areas over the five years, shows few large areas that are stable in yield. Approximately 3/4 of the field had unstable yields (that is, only a few areas are always high, medium or low yielding).

The Classified Management Map shown in Figure 18 , which is formed from the addition of the spatial and temporal yield maps (1997-2001), does not show many "management zones". There are high yielding areas, however they are too small to be managed differently from the rest of the field. At least 2 of the field have unstable areas, which means that the level of crop yield is not stable in time. Because of the instability in crop yield, it would be difficult to apply precision farming techniques to this field. However, it was through using the yield maps, and through onsite observation, that the producer decided to do some spot drainage A greater number of yield maps (more years) may show an improvement in the yield patterns, especially if the years were divided into wet and dry ones.

Soil Physical and Nutrient Maps

Figure 19  gives the K: Mg ratio for the field, but it does match any of the yield patterns for any of the years or crops. The most of the ratios are good (0.2-0.8), falling close to the target level of 0.5. Soil moisture levels (Figure 20 ) appear to be closely related to soil organic matter levels (Figure 23 ) and clay content (Figure 21 ). This area of high organic matter and high clay is also a high yielding area on the maps for years 1998 and 1999 (Figures 9 and 10).  These years had prolonged dry spells, which may have affected the crop growth. The low yielding area on the north side of the ridge had a high sand content (Figure 22 ), 29-48 %, which would also reduce the moisture holding capacity of the soil. The highest areas of silt were found in the northeastern portion of the field (area of poor drainage) and in the southwest (Figure 24 ). The soil pH level was good for both corn and wheat (Figure 25 ). The pH patterns were not related to the crop yields. The aluminum distribution is given in Figure 26  and the P saturation % in Figure 27 . 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. Calcium and magnesium levels (Figures 28  and 29 ) are high but the levels are still good for crop growth. Nitrate (Figure 30 ) and ammonium (Figure 31)  were determined in July/00. The ammonium levels were highest along the eastern tree line and nitrate-N levels were high over most of the field.

Conclusions & Recommendations

Field B, does not have the distinct management zones that Field D  does. However, there may be some basic improvements in management that can be done. The levels of P and K from the additional applied manure on the ridge should be reduced. It is possible that the excessively high P levels are impacting the crop yields causing a reduction. The drainage problems in the eastern part of the field have been corrected. The weed problem in the western corner was a source of weed seeds and may be affecting a greater area than is suspected. This has consistently low yields for all of the crops. The edge effect from the trees is difficult to manage. The woodlot is a mature sugar maple (Acer saccharum  Marsh) stand. Perhaps clearing the underbrush away from the field edges would reduce the impact of the trees/brush on nutrient and soil moisture levels.