Western Canada Director, Potash & Phosphate Institute

Suite 704, CN Tower, Saskatoon, SK S7K 1J5

Manitoba-North Dakota Zero-Tillage Workshop, Brandon, Manitoba, Jan. 23-25, 1995.

Many aspects of fertilizer management in conventional and zero till systems are similar. However, special challenges exist in zero till systems because many surface soil properties are modified (Carter 1982, Gauer et al. 1982, Lafond et al. 1992, Blevins and Frye 1993, Grant and Lafond 1993,1994). When tillage is reduced surface crop residues increase. This results in improved water conservation, soil compaction, accumulations of soil organic matter, improved soil tilth and aggregation, higher water infiltration rates, lower soil temperatures in the spring and warmer soil temperatures in the fall, and nutrient stratification. In addition, microbiological activity is increased which affects organic matter breakdown and immobilization (tie-up) of applied nutrients. These changes affect plant growth early in the growing season and influence use efficiency of soil and applied nutrients.

FERTILIZER EFFICIENCY

Fertilizer use efficiency refers to the proportion of applied nutrient recovered by the crop. It is commonly expressed as a percentage of fertilizer used by the crop or alternatively in terms of crop yield per unit of fertilizer (e.g. bushels per pound of applied nutrient). Fertilizer use efficiencies vary widely and decrease as fertilizer rates increase. Nitrogen (N) efficiency, based on grain yield, rarely exceeds 50 to 60% and can be as low as 20% (Rennie et al. 1993). First year fertilizer efficiencies are normally 10 to 30% for phosphorus (P) and 20 to 60% for potassium (K), although efficiencies can be greater over the long-term because of the residual properties of these nutrients.

Higher efficiencies are difficult because above ground plant growth must compete with soil organic matter, microbes, and roots for applied nutrients. In addition, P and K become less available as they interact with other soil minerals and N may be lost from the field through leaching, volatilization, and denitrification. All nutrients may be lost through erosion. Because of these unavoidable transfers and potential losses it is impossible for fertilizers to be 100% efficient. However, through good management it is possible to increase fertilizer use efficiency.

FERTILIZER EFFICIENCY - WATER EFFECTS

Nitrogen and water are the two most limiting nutrients in dryland crop production in the prairies. The efficient use of both are dependent on each other and a shortage of either will reduce the efficiency of the other. This relationship is illustrated with wheat data from a Saskatchewan zero till study in Figure 1. More bushels per pound of soil and fertilizer N are produced as available water increases, and at a given moisture level, more bushels are produced as N fertility increases. The exception being when N levels are too high for the available water. Similar positive interactions between water and other nutrients would be expected although the response would not be as great unless those nutrients were more limiting than N.

Figure 1. Soil water positively influences applied N in a Saskatchewan zero till study (Adapted from Campbell et al. 1993).

This suggests that fertilizer efficiency will be optimized with improved water conservation, a condition inherent in zero till systems. However, zero tillage alone does not ensure optimum water conservation, particularly in drier regions. Cereal stubble needs to be managed to maximize snow trapping and water recharge.

In the Prairies, even under the most favorable conditions at least 3.5 in. of water are needed before any grain yield is produced (de Jong 1990). However, if rainfall is poorly distributed as much as 8 in. may be required before any grain can be harvested. Water use above that minimum can increase yields from 2.5 to 7 bu/in. of available water depending on the crop and local environment. North Dakota researchers have concluded that on average every inch of stubble height over 5 in. increased available soil water by 0.1 in. (Bauer and Tanaka 1986). An 8-yr study (1982-1989) in southern Saskatchewan with zero till spring wheat, found tall cereal trap strips (18-24 in.) conserved an average of 0.4 in. more water than short stubble (6-8 in.) and in years of severest moisture stress (1984 and 1985), the tall stubble conserved an additional 1.1 in. of soil water (Campbell et al. 1992).Figure 1. Soil water positively influences applied N in a Saskatchewan zero till study (Adapted from Campbell et al. 1993).

FERTILIZER EFFICIENCY - TIME AND PLACEMENT EFFECTS

After water conservation is optimized, fertilizer placement and time of application are the two most common methods of manipulating fertilizer efficiency. However, placement options are limited as tillage is reduced. Nitrogen presents the biggest challenge in zero till systems, largely due the demand and the rates required. However, that does not mean P and K are not important. About 77% of the soils in Manitoba and 66 % of the soils in North Dakota test medium or less in available P, and require fertilization (PPI 1994). For K, 16% of Manitoba soils and 14% of North Dakota soils test medium or less.Figure 1. Soil water positively influences applied N in a Saskatchewan zero till study (Adapted from Campbell et al. 1993).

NITROGEN

Lower cereal yields are often experienced in the initial transition from conventional to zero tillage. This is partially due to inefficient use of fertilizer N when traditional application methods are employed. Broadcast application is the most common and practical means of applying N in zero till cropping systems. It allows large amounts of N to be applied without danger of injuring the plant and provides flexibility in time of application. However, large amounts of broadcast-applied N can be immobilized by surface crop residues or lost through volatilization. To maximize crop recovery of fertilizer N requires placement below the residues. The data in Table 1 illustrate increased N response and increased N efficiency when N is subsurface applied compared to surface broadcast.

Table 1. Application method influences barley yield and N efficiency under zero tillage in central Alberta (6 yr trial).
Method	Yield (bu/A)	N Efficiency (bu/b N)
Broadcast	45	0.76
Side Band	52	0.86
Below Seed	51	0.85
Check Yield: 23 bu/A; N Rate: 60 lb/A urea (Maihi and Nyborg 1993)

Urea is the most dominant granular prairie fertilizer, but when surface-applied it can have substantial N losses through volatilization. Table 2 compares N use efficiency in zero till barley for several broadcast N sources. Urea was the least effective. However, if washed into the soil by rain soon after application or banded, urea efficiency is increased greatly (Table 3). Note the high efficiency of the potassium nitrate (Table 2). Balancing N application with needed P and K will increase N efficiency.

Table 2. Broadcast fertilizer influences N efficiency in zero till barley at two locations in central Alberta.
	N recovery (% in grain)
Urea	27.8
Ammonium Sulfate	32.2
Ammonium Nitrate	39.1
Potassium Nitrate	50.0
N rate: 45 lb/A (Maihi et al. 1994)

Table 3. Rainfall influences urea N efficiency in zero till barley at two locations in central Alberta.
	N recovery (% in grain)
Broadcast	22.8
Broadcast + 0.4 inch simulated rain	31.9
Side Band	36.9
Deep Band	38.4
N rate: 45 lb/A (Malhi et al. 1994)

Other options for fertilizer placement in zero till cropping Systems include nesting and point-injection. Nesting places the fertilizer at regular intervals below the soil surface in clusters of granules or as large "super" granules. This approach has proven effective in increasing N efficiency in zero till Systems (Malhi and Nyborg 1993), but its practical application has not been developed.

Point-injection is a more promising approach to N placement in zero till cropping systems. Like band applications, point-injection can improve N efficiency by placing the fertilizer below the soil surface, but unlike banding, point-injection does not disrupt the soil making it more compatible with reduced tillage systems. And, the spokes do little damage to the roots of growing crops, making point-injection ideal for top dressed N applications. Alberta research has shown point-injection to have comparable efficiency to conventional band and broadcast applications (Table 4). However, point-injection requires only a fraction of the horsepower that banding does to apply the same amount of nutrient.

Table 4. Point-injection produces comparable yields and N efficiency in zero tilled spring wheat in southern Alberta.
	Carmangay		Pincher Creek
	Yield	N Efficiency	Yield	N Efficiency
	bu/A	bu/lb N	bu/A	bu/lb N
	Seeding Application
Broadcast	15	0.42	40	1.11
Band	18	0.50	43	1.19
Point-injection	18	0.50	40	1.11
	Top-dress Application
Broadcast	12	0.33	35	0.97
Point-injection	14	0.39	38	1.06
N rate: 36 lb/A as 34-0-0 or 28-0-0 (Roberts et al. 1992) Top-dress application: average of several post-emergent treatments.

Spring banding is usually the most effective N application method; fall broadcast is the least (Table 5). Fall banding can be as good as a spring banding if the soil isn't saturated for an extended period in the spring and may be more effective if spring seedbed moisture conditions are poor. However, fall banding (excluding point-injection) may not be an option if soil disturbance is to be kept at a minimum.

Table 5. Application time influences yield and N use efficiency in zero till barley in central Alberta.
Time	Yield	N Efficiency
	bu/A	bu/lb N
Fall Broadcast	46	0.34
Fall Band	53	0.50
Spring Broadcast	50	0.44
Spring Band	52	0.48
N rate: 45 lb/A urea (Malhi and Nyborg 1993)

Surface banding is another alternative to fall banding. North Dakota researchers found N solution dribble banded on the soil surface produced comparable yields to N solution banded below the surface in zero till spring wheat (Table 6). They concluded that under the cool temperatures and the adequate precipitation of late fall, surface dribble would be as effective as band placement.

Table 6. Surface banding is comparable to deep banding in North Dakota zero till spring wheat.
	Yield	N Efficiency
	bu/A	bu/lb N
Surface dribble band	36	0.60
Deep band	39	0.65
N Rate: 60 lb/A urea ammonium nitrate (Deibert et al. 1985)

Other than broadcast or some type of band application, seed-placement is rapidly becoming the method of choice among many zero till producers. With air seeders gaining in popularity, and many of them ideally suited for direct seeding of crops into standing stubble, farmers want to apply all their fertilizer with the seed in a one-pass operation. The question is, how much fertilizer can safely be applied with the seed?

Increasing rates of seedrow fertilizer can cause severe germination damage, poor stands, delayed emergence, delayed maturity and yield loss (Fig.2). Nitrogen is of particular concern, although K can also be injurious to germinating seedlings. To limit seedling damage recommendations for small grains in western Canada suggest that seedrow N plus K20 should not exceed 40 lb/A, and that no more than 25 lb/A of urea N should be applied with the seed. These general recommendations are suitable for press and hoe type seeding implements that place seed and fertilizer in close contact, but are too restrictive for newer seeding implements which can scatter the seed and fertilizer over greater distances.

Figure 2. Urea placement and rate influences germination, maturity and yield of barley in an Albert study (Solberg et al. 1994).

Current research is showing that seedbed utilization (i.e. the seed/fertilizer scatter) is critical to the amount of N that can be safely applied with the seed. Figure 3 shows how yields and N use efficiency increase at high N rates when the seed and fertilizer are scattered over a greater proportion of the seedbed.

Figure 3. Influence of seedbed utilization on barley yield and N use efficiency in an Alberta study (Solberg et al. 1994).

Soil moisture and texture are also important. Higher fertilizer rates can safely be applied with the seed when the seedbed is moist or if the seedbed utilization is greater (Fig. 4). Rainfall immediately after seeding will move fertilizer N away from the seed and reduce germination damage. Germination can also be delayed as the seedbed becomes drier even if no fertilizer is applied.

Texture influences the amount of fertilizer that can safely be applied with the seed in two ways. It determines: (1) the amount of water the soil can hold, and (2) the soils cation exchange capacity. The latter influences the soils ability to adsorb ammonium ions and prevent the buildup of free ammonia released from N fertilizers. Ammonia toxicity is a major cause of germination and seedling damage when urea is the N source. Heavier textured soils tolerate more seed-placed fertilizer than lighter textured soils because they have a higher water holding capacity and a higher cation exchange capacity. Figure 3. Influence of seedbed utilization on barley yield and N use efficiency in an Alberta study (Solberg et al. 1994)

Figure 4. Influence of soil moisture and seedbed utilization on germination in response to 60 lb N/A of seed-placed urea (Solberg et al. 1994)

PHOSPHORUS AND POTASSIUM

A significant concern in the management of P and K in zero till Systems is nutrient stratification. These immobile nutrients accumulate near the soil surface at the depth of application. This is illustrated with the Manitoba data in Figure 5. Soil samples were taken at the end of a 4 yr study where P was banded (50 lb P205/A) and K was broadcast (120 lb K20/A). The lack of soil mixing during the 4 yr period caused both P and K to accumulate where they were originally placed.

Figure 5. Influence of tillage system on P and K distribution in a silty clay Manitoba soil (Grant and Bailey 1994).

When soil conditions are dry, nutrients near the surface may be positionally unavailable for plant uptake. This can be a common problem in the prairies where precipitation is limited and soils are naturally low in P. However, it can easily be corrected, with maximum fertilizer efficiency, by use of starter fertilizers with the seed.

Figure 6 illustrates the effectiveness of starter P over a 24 yr period in southern Saskatchewan in a fallow-wheat-wheat rotation. Phosphorus application (13 lb/A P205) produced about 3 bu/A more grain for wheat grown on fallow and 2 bu/A more grain for wheat grown on stubble. The yield variability over the 24 yr period was closely related to spring weather conditions. Greatest P response occurred when the soils were cool and moist. Low soil temperatures slow root growth, hinder P movement in the soil and uptake, and slow translocation in the plant. Although the above study was with conventional tillage, the effects of starter P under zero tillage would be as large or larger.

Figure 6. Starter P application in a Saskatchewan fallw-wheat-rotation (Zentner et al. 1992).

Figure 6. N rate influcence P efficiency in dual N-P bands in barley (Harapiak and Beaton 1986)

Although all the P requirements for annual small grain production can be safely applied in the seedrow, other crops, like ouseeds and pulses, will not tolerate more than 1 5 to 20 lb/A of P205. Additional nutrients can be broadcast on the soil surface or banded away from the seed during planting, but some efficiency may be sacrificed. The efficiency of the latter can be improved by including some N in the band.

Dual N-P banding is advantageous because ammonium N enhances P fertilizer efficiency (Harapiak and Beaton 1985). The added N increases root proliferation in the fertilizer zone and reduces the pH which results in greater P availability and uptake. However, too much N in the N-P band can interfere with P uptake, unless the bands are allowed to ìageî (Fig.6). This Alberta data shows that 90 lb/A of urea-N reduced the efficiency of 50 lb/A P205 when dual banded at seeding in a 12 in. row spacing. Allowing the bands to incubate in the soil for a period of three weeks improved efficiency substantially. If the band spacing were reduced to 8 in. the N rate could increase to 1 35 lb N/A before the interference would begin. That's because the fertilizer becomes more concentrated as row spacing increases. If higher rates of P are needed, placement of some starter P in the seedrow would offset the potential short-term delay in P uptake from dual N-P bands.

SUMMARY

Maximum fertilizer efficiency is a challenge in all tillage systems. Careful attention must be paid to fertilizer source, time and method of placement. Subsurface N application is usually more effective than surface application. With P and K, starter applications applied with the seed are usually the most effective. However, building soil P and K levels prior to starting a reduced tillage system will offset the potential problems associated with nutrient stratification. Aside from fertilizer management, any practice which will help optimize yields will increase fertilizer efficiency.

REFERENCES

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