ISSUE 8 JUNE 24, 1999
MID-SEASON PLANT NUTRITION NOTES
As mid-season approaches for many crops, the use of supplemental fertilizer may come to mind. The following is a summary of possible results of mid-season application of fertilizer.
Application of additional nutrients with the exception of N is not generally recommended or useful. In some situations on sandy soil where high levels of rain have fallen over the past 30 days, some areas may show S (sulfur) deficiency. These areas may be identified not so much by soil test or deficiency symptoms (although by the book they should have yellow upper leaves and green lower leaves, but this year the S deficiency could also be accompanied by low N, so general plant yellowing is more likely), but by a plant analysis. A relatively low S plant level associated with good to high N levels is a characteristic of a S deficient plant. Supplemental S application could be made with ammonium sulfate solutions or ammonium sulfate/urea solutions.
N deficient barley should be left alone, unless malting grade is not an issue. Although a little higher N level may be desirable, there is also a risk of over-fertilization resulting in too high protein for malting.
If low N levels in wheat and durum are seen, supplemental N before the 5-leaf stage will result in higher yields and may also result in higher protein if the N applied is greater than the yield potential. Supplemental N may be especially important to growers in NW-NC, and SW North Dakota whose planting was delayed over a month due to exceptionally wet weather. After the 5-leaf stage, whatever N is applied will be useful only in increasing protein levels, and modestly at that. Increasing potential protein levels more than 1% with a post-anthesis/water-ripe stage N application at a high rate of 30 lb N/acre is unlikely. If liquid applications of N are made, cut the rate with water 50/50. Even at the diluted rate, leaf burning is likely in some years, especially if the temperatures are greater than 80 degrees F.
Row crops, especially corn and sunflowers will respond to N even late into the season with supplemental N if levels are short. Plant analysis and sometimes soil testing is important in determining whether N is needed. If corn remains yellow even after temperature and soil moisture conditions improve, a shortage of N should be suspected and investigated. Side-dressing is relatively easy to do. Ammonia can be applied with a soil knife type applicator. Liquid or dry treatments can be applied with knife or cultivator treatments. Broadcast N applications however are not recommended, as severe burning will probably result. A better alternative to a broadcast treatment is the use of straight-stream orifices placed so that they will apply a narrow stream of fertilizer in between the rows without drift to the rows. A hose attachment can also be dragged along the ground after the orifice to make certain the no fertilizer reaches the corn/sunflower plants. This boom set-up is relatively easy to rig up and works very well if followed within 48 hours with a rain or cultivation.
Zinc is usually applied to dry beans unless the soil test is compelling enough to convince the producer that the levels are high enough. However, zinc should not be applied to soybeans. Zinc will not hurt soybeans, but it probably will not help them either. Dry beans and soybeans differ on their zinc requirements. A side-dress application of N is sometimes used in dry beans as a supplement for higher yields, although the level should be modest so that delays in maturity do not result. Dry beans which have good nodule coverage on their roots should not need a supplemental N application. Soybeans seldom respond to a mid-season N application if properly inoculated. Some work has been done in Kansas which shows that sometimes a side-dress application can result in greater yield, but this has most often been on high yield irrigated trials or an exceptionally high yielding dryland site. When yields are around average, no gain in yield was seen. A recent study at Iowa State showed that sometimes mid-season foliar treatments with N increase yield, but the researchers were at a loss, despite many locations being tested, of finding some common thread among responders. Their conclusion was that once in a while it may be successful, but not often enough and consistent enough to pay over many fields.
Most canola should now be flowering, or close to it. If by some chance canola is at bolting and sulfur/nitrogen deficiencies are detected, supplemental N or S can be applied to increase yield. Once canola reaches the 5-leaf stage and certainly near or at bolting, it is relatively resistant to leaf burning by ammonium thiosulfate (12-0-0-27S) or ammonium sulfate solutions (11-0-0-12). Elemental sulfur will not be useful as a post-treatment. Do not apply N or S during flowering. The petals may be burned and the seed pods made unfruitful. Supplemental S following flowering has not been effective in restoring yields.
Low N levels in potatoes can be detected through careful petiole testing. Under irrigation supplemental N is easy to apply. Once the potatoes begin to develop under dryland it is more difficult to supplement. If low N levels are detected before the last cultivation, a supplemental N application may be made at that time. If this timing is missed, then the grower may need to be more creative. Simply applying N in the middle of the rows may not be effective, since the rooting depth of potatoes is seldom more than 2 feet. However, if the application was timed before a rain, some of the N may spread into the hill.
Sugarbeets will reach to great depths for N, so the need for supplemental N for beets is not likely, especially in medium to coarse textured soils. With the high levels of rainfall in Traill and Grand Forks counties, some heavier soils may have experienced greater denitrification than can reasonably be expected to be made up with increased mineralization of N from the soil. Also, in heavy soils it is unlikely that high levels of N can be found deep, as may be the case in more aerated soils. If supplemental N is applied, the levels should be modest, since higher levels of N may result in lower sugar content if overdone. Dribbling N between the row with an orifice rigged boom and dragging a hose may be a good method. Avoid broadcast applications of either dry or liquid N. Liquid N could result in burning and dry N is easily caught in the crown of the leaves and may also burn the plants.
General notes on supplemental fertilizer-
Crops low in N may respond to supplemental N if applied early enough in the season to influence important yield components-tillers in small grains, ear size in corn, or protein enhancement. Crops that are subject of quality degradation due to excess N such as barley and sugarbeet should be carefully assessed before application. Crops that may suffer due to increased susceptibility to white mold or other diseases such as dry beans or soybeans should also be carefully assessed. The deep or shallow rooted nature of certain crops should be assessed along with the possible soil levels of N at depth to determine the likelihood of return from N fertilizer and the possible contribution of soil N. The use of plant analysis, soil testing and a knowledgeable crop consultant can help to determine these critical needs and possible solutions.
Dr. Dave Franzen
NDSU Extension Soil Specialist