C.A. Grant , L.D. Bailey

Agriculture Canada, Brandon Research Station

Kim Brown

University of Manitoba

David Rourke and Andrew Hargrave

Ag. Quest, Ltd.

Efficient fertilizer management is important, not only to improve the economics of crop production, but also to maintain soil quality and reduce the likelihood of damage to the environment. Fertilizer placement is one of the tools that a producer can use to improve the efficiency of fertilizer use.

Efficiency of both N and P fertilizer is normally increased when the fertilizer is placed in a concentrated band in the soil. For both N and P, minimizing the contact between the soil and the fertilizer slows the reactions of the fertilizer in the soil and reduces its loss, but the specifics differ for the two nutrients.

Phosphorus is a relatively immobile nutrient in the soil-it does not move readily through the soil system and so generally remains near the site of placement. Phosphorus will react with the calcium and magnesium present in the high pH soils of the prairies and northern Great Plains area to form sparingly soluble calcium and magnesium phosphate compounds, which are less available to the plant than the fertilizer and become increasingly less available over time. On low pH soils, similar reactions occur with iron and aluminum oxides. By banding the fertilizer, contact between the soil and fertilizer is reduced and the formation of these phosphate compounds is slowed so the fertilizer remains in a plant-available form for a longer period of time. Many plants are able to proliferate their roots when they contact a concentrated source of P, such as fertilizer band. This allows the plant to effectively "mine" the P from the band, increasing the P use efficiency. Also, as roots cannot take nutrients up from dry soil, placing the band in a position where the soil does not dry out early in the season avoids having the fertilizer "stranded" where it cannot be utilized by the plant.

Phosphorus will not move through the soil, therefore it must be in a position where it can be intercepted by plant roots. Placing the P in a band close to the root allows the root to contact and utilize the band. Therefore, fertilizer P is most efficiently used when seed-placed or placed in a band close to the seed. This is particularly important for crops such as flax, which have poorly developed root systems early in the growing season. When seed-placing P with small seeded crops such as flax or canola, seedling damage may occur at rates of P required for optimum yield. In that case, side-banding the fertilizer near the seed may be the best choice.

Placing the P near the seed-row is most important in soils with low P or under cool soil conditions. Low soil P supply and slow root growth combine to cause severe P stress early in the growing season when plant demand for P can outstrip the soil’s ability to supply the nutrient. In soils with a history of P fertilization, where the soil P levels are not extremely low, P fertilizer may be effectively applied in a deep-band, as a dual band with N. Dual banding with N is important, particularly in high pH prairie soils where the presence of N tends to reduce the pH in the fertilizer band. This increases the availability of P and the efficiency of P utilization by crops. Phosphorus fertilizer applied as a band more than 1.5 inches from the seed without N is not efficiently used by the crop and so is not a recommended practice.

As with P, efficiency of nitrogen fertilizer is generally increased by band placement. However, the reasons for the increase in efficiency are different for N as compared to P. Nitrogen fertilizer supplies N in the form of ammonium, nitrate, urea (which rapidly converted to ammonium in the soil), or as a blend of these ions. The ammonium ions will be converted by microorganism in the soil to form nitrate through nitrification, if the soil temperatures are warm enough for microbial activity. The rate of conversion will increase as soil temperature increases.

Ammonium sources are readily lost by volatilization when left on the soil surface, so banding ammonium or ammonium producing sources below the soil surface reduces volatilization losses. But, once in the soil, nitrogen is more readily lost from the nitrate form than the ammonium form. Both ammonium and nitrate can be incorporated into the organic component of the soil through immobilization by soil microorganisms, but nitrate is more mobile in the soil and can also be lost by leaching below the rooting zone. Nitrate is also subject to losses by denitrification, the conversion of nitrate to nitrogen oxides which lost to the atmosphere. Placing the fertilizer in a band reduces the contact between the fertilizer and the soil microorganisms, reducing immobilization. Banding also slows the conversion of urea to ammonium and of ammonium to nitrate. This can reduce losses by denitrification and leaching.

The benefits of banding vary with environmental conditions. Banding of N generally has the greatest benefits in areas of the prairies with the higher moisture levels and higher yield potentials. These are also the areas with the highest was of fertilizer N. On the Black, Dark Grey and Grey soil zones, banding of N has a large advantage over broadcast applications. Under drier conditions, such as in the Brown and Dark Brown soil zones, the method of N application is less important. The soil disturbance associated with banding may lead to loss of moisture and loss of seed-bed quality, which can lead to lower yield. Since the rate of N required to optimize yield under dry conditions may be relatively low, seed-placed fertilizer may be the best option in many of the drier areas of the prairies (Harapiak et al. 1993).

There are a wide variety of banding options for N fertilizer. Fertilizer can be banded in the fall, when surface soil temperatures have cooled below 5 to 10 C, so that reaction of the N in the soil will be reduced. Fertilizer can be pre-plant banded in the spring, side-banded during seeding, seed placed (which is also a form of banding), and injected or nested into the soil near the time of planting or later in the growing season. Surface dribble banding is another option, but it has the disadvantage of leaving the fertilizer on the soil surface.

Unlike P, with adequate moisture the N will move out from the band relatively quickly. This is why one rarely notices much "striping" from anhydrous ammonia bands, even when they are placed 16 inches apart. Due to the ability of the N to move through the soil, the precise location of the band is not as critical as it is with P and there is generally little to no advantage with precision side-placement of N as compared to deep-banding the fertilizer away from the seed row.

For efficiency of N use, the various in-soil banding methods are generally equally efficient. Therefore, seed-placed, side-banded or pre-plant banded N fertilizer will be equally effective, as long as the level of seed-placed fertilizer is not high enough to produce seedling damage. At 50% of the recommended rate, these placements produced similar yields. As the amount of fertilizer applied increased, the yield obtained with seed-placed urea decreased in comparison to that obtained with the pre-plant band or the side-band, until at 150% of the recommended rate, yield with the seedplaced urea was lower than with the 50% rate.

The amount of seed-placed fertilizer that can be safely applied depends on a number of factors including environmental conditions, crop grown, soil type, width of the seed/fertilizer source. Rate applied with the seed must be decreased on light textured soils, with low soil organic matter, cool growing conditions, low soil moisture, in the presence of salts or free lime, or with the use of wide row spacing. Small seeded crops such as flax or canola are more sensitive to seedling damage than crops such as wheat or barley. Urea tends to be more damaging than ammonium nitrate, while urea ammonium nitrate (UAN) tends to be intermediate, since it is a blend of urea and ammonium nitrate. The amount of damage from seed-placed fertilizer can vary greatly from year to year, depending on the specific conditions at seeding, so a rate which caused no problems one year may cause significant damage the next. A conservative approach to seed-placement may be most economic in the long run.

Correct fertilizer placement is likely to be more important under reduced tillage systems than under conventional tillage. Under zero tillage, moisture relations, distribution of nutrients in the profile and deposition patterns of organic matter differ from under conventional tillage. The soil tends to warm up more slowly in the spring, which may slow the rate of nutrient mineralization and reduce early root growth. Soils generally contain more water, due to increased snow trapping by standing stubble and reduced evaporative losses due to the trash cover maintained on the soil surface. Maintenance of the crop residue on the soil surface, where contact between the residue and the soil microorganisms is limited, may also slow the breakdown of the raw organic matter, reducing the rate of nutrient release. These factors may all serve to reduce the amount of nutrients available to the crop under a reduced tillage system as compared to a conventional tillage system, particularly during the first years under reduced tillage.

Broadcast applications of fertilizers may be relatively less available under a reduced tillage system as compared to a conventional tillage system, particularly when urea is used as the fertilizer source. Urea is subject to volatilization losses if surface applied without incorporation. Presence of crop residues may increase volatilization, since the residues contain the urease enzyme which breaks down urea and makes it subject to loss as ammonia gas.

The presence of a high concentration of raw matter on the soil surface may tie up broadcast nitrogen as the residue decomposes. Therefore, separation of the crop residue and the fertilizer by banding the fertilizer beneath the soil surface may be even more important under reduced tillage than conventional tillage systems. Studies in Alberta have indicated that zero tillage systems if the fertilizer was broadcast, but a yield advantage when the fertilizer was banded (Harapiak et al. 1993). Placement of the fertilizer below the surface crop residue improves the effectiveness of the fertilization program.

In spite of the potential for loss of surface applied nitrogen, use of ammonium nitrate or UAN dribble bands as post-seeding treatments, up to the 4^th leaf stage of the crop has produced good results in preliminary studies conducted by Ag. Quest in 1992 and 1993.

The problem with in-soil banding under reduced tillage systems relates to the fact that a banding operation tends to be a tillage operation, leading to soil disturbance. Seed-planted N is effective, but as mentioned previously, care has to be taken to avoid exceeding the levels that can be tolerated by the emerging seedling. A number of openers and seeders are on the market that have the ability to side band the fertilizer away from the seed. However, there have been some problems with achieving sufficient separation with some of the openers, leading to severe problems with crop emergence. Many of the newer seeders available do a good job of side-banding, but frequently a large price tag is attached to these machines. Also, there tends to be a large increase in draft requirement and often in seed-bed disturbance associated with a side-band operation.

Use of a two-pass system, with a pre-plant banding operation either in the fall or spring, followed by a separate seeding operation is a popular option and can be very effective in increasing fertilizer efficiency. A fall banding operation also allows for spreading of the workload, by shifting the fertilization operation to late in the fall, rather than during seeding in the spring. Fertilizer costs may also be lower in the fall as compared to the spring and for those producers concerned about taxes, there may be a benefit to purchasing fertilizer in the fall. The reduced cost of seeding equipment as compared to a seeder with side-banding capabilities must be compared to the increased cost of a second operation and the effect of the banding operation on soil moisture and seed-bed quality.

Fall banding performed very well under zero tillage in 1993 in studies evaluating source, placement and timing of N placement on two soils in southwestern Manitoba. Under zero tillage, the highest yields were consistently obtained with fall banded NH3. Fall banded UAN tended to be slightly less efficient under zero tillage, particularly on the fine sandy loam. The nitrate present in the UAN is subject to loss by denitrification and leaching, which may be more of a problem under zero tillage than under conventional tillage. When applied as a spring band, urea, NH3, and UAN were equally effective.

Broadcast and surface dribble applications were consistently lower yielding than the fall banded NH3 under zero tillage. However, surface dribble bands frequently produced yields comparable to those obtained with spring band application, under both zero and conventional tillage systems. There is a risk of poor performance with dribble banded fertilizer, as occurred with the durum on the clay loam soil under zero tillage, where yield was 4.5 bu per acre lower with surface dribble banded as compared to spring banded urea. Results from surface applications are likely to be more variable than in-soil band applications, particularly if urea is used, as losses from surface applications can be substantial, if conditions after fertilizer application encourage losses. Losses from surface applications will be higher pH soils and light textured soils low in organic matter. Losses will increase with high temperatures, high soil moisture, presence of surface crop residue, and a prolonged period without significant rainfall after fertilizer application. Nitrogen losses from surface applications can be reduced by using ammonium nitrate rather than urea.

The final decision on what fertilizer placement system is best depends on the particular farm. The effect of placement on fertilizer use efficiency varies considerably with soil type and environmental conditions and so when evaluating placement methods, one should be careful to look at information from sites with conditions similar to those on one’s own farm. But, fertilizer efficiency is only one factor to consider. Equipment and repair costs and availability, cost of operations, relative prices of various fertilizer sources, availability of labour in the fall and spring, effect of the fertilizer application system on timeliness of operations, safety and environmental consideration and the relative importance of seed-bed disturbance and moisture conservation as compared to fertilizer use efficiency must be considered. Fertilizer management is only one part of the entire management package and must be considered as part of the system than as an individual item. By balancing the efficiency of various placement methods against the various economic, logistical and personal considerations in the entire system, a management decision can be made that is right for your particular farm.