Beginning Direct Seeding - Fertilizer Placement Option

Adrian Johnston¹ and Tom Jensen²

1Potash and Phosphate Institute of Canada; ²Agrium Inc.

Summary

Direct-seeding systems are the most rapidly evolving tillage practices in western Canada, moving from 9% of seeded acreage in 1990, to 30% in 1998 for Saskatchewan. Because direct seeding encompasses a broad range of seeding and fertilization methods, questions have arisen regarding the relative efficiency of different approaches. Achieving minimum soil disturbance while applying the crops nutrient requirements has resulted in many farmers adopting a one-pass seeding and fertilization system. However, two-pass seeding systems, that involve application of a portion of the fertilizer independent of seeding, have been shown to be an effective method of reducing field operations and efficiently applying the required fertilizer. There are many examples of farmers who have successfully moved to direct seeding by modifying their existing equipment, and many who continue to succeed in the absence of new equipment purchases. By combining an understanding of how fertilizer nutrients are best managed to optimize fertilizer-use efficiency, with local soil and environmental conditions, most innovative farmers can capture the moisture conservation, erosion control and operational efficiency benefits of direct seeding.

Understanding Fertilizer Nutrients

Fertilizer nutrients that we commonly use can be categorized into mobile and non-mobile nutrients. Mobile nutrients include nitrate-N and sulphate-S, while non-mobile nutrients include phosphate and potassium. When we apply ammonium forming N sources (urea and anhydrous ammonia) the vast majority of the fertilizer N is rapidly converted to nitrate-N under the warming soil conditions characteristic of spring. The same applies for the 50% of Urea-ammonium nitrate (UAN) solution N that is urea N. Once in the nitrate-N forms the fertilizer nutrients move with soil water, and as a result diffuse away from the point of application. Fall application of ammonium forming N sources after soil temperatures drop below 10 °C results in most of the N staying in the ammonium form until the following spring, and preventing potential N losses. The sulphur in ammonium sulphate is mobile once it dissolves in the soil. Elemental S sources must be converted to sulphate by microbial oxidation, a process dependent on small particle size and surface broadcast application to allow breakdown. Solution ammonium thiosulphate (15-0-0-20) is a mixture of 50% sulphate and 50% finely dispersed elemental S that is converted to sulphate-S once in the soil. Because of their mobility in the soil, placement of nitrogen and sulphate-S become less critical than immobile nutrients. Band applications tend to slow the conversion of the N sources to nitrate-N, and as such can be effective with fall application and where N is applied long before the crop will use it. In areas of higher precipitation broadcast application can be effective, however, can also stimulate unwanted weed growth.

The most common sources of phosphorus fertilizer sold in western Canada are dry mono-ammonium phosphate (11-52-0; 12-51-0; 10-50-0) and solution ammonium polyphosphate (10-34-0). Once dissolved, a portion of the phosphate is taken up by the crop (10-30%), while the rest binds with other minerals to form stable phosphorus compounds that are released later in the season and to subsequent crops in rotation. Potassium (K) fertilizer is generally sold as dry potassium chloride (0-0-60; 0-0-62), with solution K fertilizers made from dissolving these dry products. Once the fertilizer dissolves in the soil it separates into K and chloride (Cl) ions, with the potassium binding to the mineral and organic matter particles in the soil. The Cl is mobile and moves with soil water similar to nitrate-N. The lack of movement of P and K in the soil means that when low rates of these two nutrients are applied they be placed as close to the seed as can be achieved without causing any damage to crop emergence. High rates of P and K can be broadcast or band applied to meet most crop requirements for an extended period of time.

1. One-Pass Seeding and Fertilizing Systems

Seeding and fertilizing a crop in one field operation is referred to as one-pass seeding. This is the approach which many of the machinery manufacturers have taken as they develop new equipment that is adaptable to direct seeding. This usually requires a double-shoot air system, where fertilizer is delivered through one system, independent of the seed delivery system. However, if you do not have one of these new air drills there are some options that can be easily and cheaply adapted to your current seeding system. They include applying the fertilizer with the seed, or fitting a solution fertilizer system to your seeding implement.

Seed Placement of Fertilizer

The ability to seed place high rates of fertilizer depends on a number of factors. These include the crop being grown, the fertilizer rates used, the fertilizer forms, the distribution of seed and fertilizer (often referred to as seed-bed utilization and influenced by opener and row spacing), the soil type, the landscape of the field, and the soil moisture conditions at, and immediately following, seeding. The first priority when considering seed row application of fertilizer is to ensure that the non-mobile nutrients are included in the blend, such as P and K. Given that the efficiency of low application rates of these two nutrients is highest when seed placed, makes this imperative to effectively overcoming any P or K deficiency that may exist. Sulphur is also often included in these starter fertilizer blends applied in the seed row of many crops, especially when oilseed crops are grown. While most seeding systems allow for the application of all the crop P and K requirements, the tolerance of most crops to seed placed P and K are described in the Sask. Agriculture and Food fertilizer guidelines (see:

http://www.agr.gov.sk.ca/Crops/Soil_Fertility_Fertilizers.asp?firstpick=Crops&secondpick=Soil%20Fertility_Fertilizers). The oilseed and pulse crops are the most sensitive to seed placed fertilizer and as a result may often require a separate operation if the higher fertilizer rates cannot be separated from the seed row.

Applying N in the seed row requires a good understanding, and lots of trial and error experience, on your soil conditions, with your equipment and across your landscape. Nowhere will you find anything but rough guidelines on tolerable limits for seed placed N, a reflection of the high risk this practice can be for many farmers. However, there are those producers on heavy clay soils, with lots of soil moisture, and a high (25-50%) seedbed utilization, that successfully apply high rates of N with the seed at seeding. In most cases they do this with cereal crops, an indication of their higher level of tolerance to seed row fertilizer. Using a wider opener, such as a 2 ½" spoon, or a 3-4" spreader tip, reduces the number of individual seeds that end up in direct contact with fertilizer granules. While ammonium nitrate (34-0-0) is less damaging to the germination of many crops than urea, it is impractical as a fertilizer used in blends given its reaction with the ammonium N in phosphorus and sulphur fertilizers. The ability to control the placement of solution fertilizer allows for it to be adapted to seed row application better than dry products. There are large numbers of farmers who direct a stream of solution fertilizer under their opener, and in most cases achieve minimal damage to seedling germination and emergence. This works particularly well when using a wider opener, such as a spoon or 3-4" spreader tip. Placement of solution N fertilizer with the seed in a narrow seed row will result in a high level of stand damage, similar to dry fertilizer products (Table 1).

Table 1. Crop emergence and grain yield response to dry and fluid fertilizer blend placement, Melfort and Brandon, 2000.

* Side dribble is fluid fertilizer applied next to the seedrow, over the seedrow with dry; Mini-sweep is a 4" sweep on 9" row spacing with fluid fertilizer dribbled behind shank and dry spread under sweep.

Research into coatings and inhibitors for urea fertilizer continues, however, there are few products that are commercially available. The urease inhibitor sold as Agrotain is used to treat urea fertilizer and slow its conversion to ammonia, which is toxic to germinating seedlings. The idea behind using the product with seed placed urea is that by the time the urea converts to ammonia the fertilizer has migrated away from the seed placement zone (urea is mobile) enough to minimize any toxic effect. Research conducted at the Brandon Research Station by Cynthia Grant showed that addition of Agrotain to urea reduced the damage to germinating seedlings and increased final grain yield in 4 of the 5 trials. In the study they used a ¾" opener on 8" spacing, and found the largest differences at the highest N rates (70 and 90 lb N/A rates). While research continues into the use of Agrotain, the marketing of the product into Canada is uncertain at this time. Coating urea granules to control the release of the fertilizer is also an area of ongoing research. Research conducted by Agrium of Calgary reported that when applied in the seed row, controlled release urea (CRU) was effective in reducing seedling stand damage of canola, wheat and barley, and also resulted in grain yield responses similar to side banding the urea (Table 2). The challenge associated with CRU is developing a price competitive product that when seed placed will prevent stand damage, and at the same time release the fertilizer so that it is available to the crop before too late in the plants growth. While CRU products are available at this time, they are currently price prohibitive for small grain and oilseed production systems. Progress to date is impressive and time and future innovations will determine the use of such a product in western Canadian cropping systems.

Table 2. Crop response to side banded urea, seed row applied urea and control release urea (CRU) at a variety of locations in Saskatchewan and Alberta in 1998 and 1999.

Solution Fertilizer Adaptations

The ability to fit solution fertilizer tubes to the side of openers allows for single shoot airseeders and seed drills to be easily adapted to deliver all fertilizer at seeding. Farmers have developed systems to deliver solution fertilizer N alone, as blends of N and S, or as complete blends of N, P, K and S. A number of research trials in Manitoba and Saskatchewan have evaluated the surface dribble band of solution fertilizer blends adjacent to the seed row at seeding. In all cases, the application of the solution band was found to be as effective as an in-soil band (Table 1 and 3). In particular, the crop uptake of P early in the growth of the seedling did not appear to be reduced where it was measured. The actual adaptations that have been developed for application of solution fertilizers at seeding are too numerous to mention, however, they do reflect the local soil conditions in most instances. That is, where we have heavy textured soils we tend to see openers adapted to work as shallow as possible, limiting the soil disturbance. In loam and sandy loam soils, the uniform flow of the soil around the opener allows for operation deeper in the soil with little negative impact on seed placement. In these cases farmers have developed solution delivery tubes that apply the fertilizer below the soils surface, or have purchased one of the "dimple or wart" openers, modified to allow the placement of the solution fertilizer band either adjacent to or below the seed.

Table 3. Spring wheat (cv. Katepwa) response to solution N (28-0-0) placement at Manitoba Zero Tillage Research Farm, 1996*.

* Similar results found in 1997 and 1998, however, data not reported.

2. Two-Pass Seeding and Fertilizing Systems

A two-pass seeding system involves application of some of the crops fertilizer requirements in an operation separate from seeding. This can involve pre-seeding application of N as a broadcast, band, coulter or spoke injection, or surface dribble band of solution fertilizer. Similarly, several of these treatments can also be used post-seeding prior to tillering. Early post-seeding application will prevent a nutrient deficiency early in the plants development when yield potential is being established. In most cases where a two-pass seeding system is used, best results can be expected when a starter fertilizer is seed placed. This starter will usually include the immobile nutrients such as P and K, but may also include the entire S and some of the crop N requirements. Having some N in the starter fertilizer blend takes some of the pressure off of getting post-seeding N applied. The amount of seed placed fertilizer will depend on the criteria discussed under seed placement of fertilizer above.

Pre-Plant Banding of Fertilizer

In-soil banding of fertilizer N, and in some cases N and S, are very common in areas where two-pass seeding systems are used. These banding operations may occur in either the late fall or in spring prior to seeding. While fall banding is likely more popular in the drier regions of the prairies, as well as much of the Parkland, there are farmers who like to do their banding in the spring to simply increase soil drying and warming with the banding operation. The narrow knife openers currently available result in minimal soil disturbance, and when used in the fall are likely to have little effect on stimulating spring weed growth. A research trial at Brandon, Melfort and Beaverlodge evaluated spring and fall banding relative to side banding fertilizer N (Figure 1 and 2). While large differences were recorded in crop emergence between treatments, fall and spring banding was as good as side banding. There are a number of farmers who have opted to seed with coulter openers, and many of them use their coulter openers in the fall of the year to band their fertilizer. Where P is added to the pre-plant band it is important to also add some starter P to the seed row at seeding. This will ensure that early season P deficiencies, common to cold soils, will not restrict early season plant development.

Pre- and Post-Plant Fertilization Options

There are farmers who broadcast dry fertilizer in the spring as a means of meeting their N, and in some cases N and S, requirements. Given that almost all the N broadcast is urea, a farmer needs to be aware of those factors that can result in some loss of the urea N. Surface applied urea is subject to N loss by volatilization under conditions of warm air temperatures and a moist soil surface. As a result, those farmers that broadcast often do so early in the spring when air temperatures are low, and the chance of precipitation (rain or snow) is high. The broadcast fertilizer is moved into the soil by the precipitation and available for the crop after it is seeded. If fertilizer is broadcast post-seeding, the potential for N loss by volatilization become even greater. As a result, post-seeding broadcast applications are very dependent on precipitation to move the fertilizer into the soil and minimize N losses. An alternative option for post-seeding application is to use ammonium nitrate instead of urea, which is not subject to volatilization losses. Where conditions for N losses are high, the price premium paid for ammonium nitrate relative to urea can be justified when there are superior crop responses. Fall broadcast fertilizer application is likely the least efficient method of application. If it is used, it should be carried out late in the fall, and should not be used in areas with rolling topography, where runoff of the fertilizer is common.

Solution fertilizer offers a wide range of options when it comes to pre- and post-seeding application. Solution fertilizer can be applied either before or after seeding with a low disturbance coulter applicator, with spoke injection, or using a dribble band onto the soil surface. A research project at Brandon evaluated the time, form and method of N application on no-till canola and durum wheat (Table 4). While the results vary between the two crops and soil types, post-seeding dribble band application of N was a relatively effective method. It is interesting to note that in this study there were few of the treatments that were superior to pre-plant bands of N.

Table 4. No-till canola and durum yield response to fertilizer N form and placement. Average response for period 1992-1995 at Brandon, MB.

When in-soil bands or injection is used, all fertilizer nutrients could be applied that are not included with the starter fertilizer in the seed row. Timing the coulter application so as to minimize excessive disturbance of the seedbed is likely of greater importance than when the spoke injection is used. In addition, if P is to be applied with the coulter or spoke injection, early application becomes more critical. When surface dribble banding, sticking with the mobile nutrients N and S is likely the best option. Nozzles for sprayers are also available which deliver the solution fertilizer in two or three stream bands on the 20 inch centers common to field sprayers. Application of the dribble fertilizer onto emerged crop is likely to result in some leaf burning. However, if done early enough this leaf damage will have little effect on final grain yield formation. Likely the most common mistake made by farmers using post-seeding application is delaying the time when the fertilizer is applied, especially when little or no N was applied with the starter fertilizer blend.