North Dakota and the Canadian Prairies are dry-land agriculture, right? Evidently, not always. During the last six years rainfall has been higher than normal. In 1999, many acres were not seeded on time and a substantial number of fields in the region were not planted at all due to a exceptionally wet spring. What will be the affect of last years’ debacle and what affects will the wet weather have on year 2000 soil fertility?

Too much water affects nutrients in two ways. It directly affects nutrient movement and availability and it may alter soil microbial populations if the wet weather caused land to be fallowed.

In fields that have been flooded with water, for example land not farmed due to the extensive flooding in 1993 in the Missouri and Mississippi River valleys, there may be an entire season without vegetation of any kind growing on it. In those cases, as in a true fallow, microbial populations, especially symbiotic populations of mycorrhiza may be reduced. If these populations are reduced, some plants have a more difficult time taking up phosphorus and growth and yield are also reduced. However, in most fields not seeded in 1999 in the region, there was abundant weed growth before the fields were finally dry enough to till. Therefore, the "fallow syndrome" is not likely to happen in these fields in 2000. In fields that were devoid of any vegetation in 1999, application of high rates of P, preferably in a band at planting will help to alleviate the stress. Corn is particularly susceptible to fallow syndrome. Legumes should also be inoculated as a precaution.

It is relatively easy to predict what nutrient levels will be following a drought. Nitrogen levels are stable, not only on average, but over the landscape. Following wet weather, N levels are widely variable. Sandier soils may lose N through leaching. Heavier soils may lose N through denitrification. Higher water tables may result in new acres becoming saline, and may affect N levels in composite soil tests. The uptake of N by weeds and the mineralization of residues after tillage is also an issue.

Fields need to be soil tested. County averages or fertilization based on habit will not be good enough. At least a composite soil test should be taken. For fields with variable soil texture, separating the field into hilltops, slopes and depressions may sort out the effects of water on nutrient availability. There may be considerable variability within fields in N availability in variable soils.

Sulfur will be leached from sandier soils. Sulfur is nearly always applied for canola as a general practice, so canola management will not be affected. However, sulfur for other crops may not be easy to manage. Application of sulfur to entire fields for crops other than canola may not be profitable. However, if areas of fields known to be most at risk are treated, such as sandy hilltops and eroded slopes, then application stands a much better chance of profitability.

Wet soils seldom affect micronutrient availability. One exception to this is with iron. Iron availability is greatly affected by bicarbonate concentration and by soluble salt levels. Susceptible crops such as soybeans, flax and dry beans will be more affected by chlorosis when soils are wet than when they are dry. Last years’ wet weather will only be a factor in iron availability if this spring has normal rainfall or above. If soil is wet at critical stages of each of these crops, significant chlorosis should be expected.

Expect salt levels to be higher this year due to shallower water tables. Check with seed suppliers regarding salt tolerance. Try to plant varieties with high yield potential which are also tolerant to salt. Salt levels can also be checked in a soil test. The surface (0-6 inch depth) is most important, but with more sensitive crops, the 6-24 inch depth also has some affect.

Most farmers in the region would much rather deal with drought than too much water. However, reality is that growers must deal with wet conditions in a region not well suited to high moisture. Growers should watch N levels carefully. Consider variable application of sulfur if soils are variable. Soil test for N, and consider landscape based sampling. Be aware of soluble salt levels and plant varieties with some degree of tolerance. It is not business as usual.