Ohio State University Extension
Department of Horticulture and Crop Science
2021 Coffey Road, Columbus, Ohio 43210-1044

Best Management Practices: Managing Fertility in No-Till

AGF-209-95

Introduction

No-till crop production is becoming quite popular in Ohio. There are several valid reasons for this shift.

• Possible reductions in labor and energy.
• Savings in fuel and energy.
• Conservation compliance rules.
• Possible yield advantages, especially on doughty soils.
• Belief many farmers have that the land must be protected and preserved.
• Many Soil Conservation Service plans require decreased tillage.

No-till farming requires a new set of producer skills, especially in the area of crop fertility, weed control, equipment, and pest control. Fertilizing and liming no-tillage fields can be complicated by two factors: (1) the lack of incorporation of applied materials by tillage, and (2) the accumulation of organic matter and crop residues on the soil surface. These factors affect the methods of lime and fertilizer application. Planting and fertilization systems in no-tillage production generally require more management than conventional systesm, but are certainly not beyond the capabilities of today's farmers. This fact sheet will deal with the adjustments needed to manage fertilization of no-till corn.

Soil Tests - The Benchmark

Agronomists all agree that routine soil tests are a must for efficient fertility management. This is especially true in no- tillage production. Sampling patterns should take into account soil variability in a field. There are currently two approaches to soil testing procedures. Grid sampling is gaining popularity in some areas. Systematic grids of approximately 2.5 acres are established and sampled to check the variability of a total field. As sophisticated fertilizer application equipment becomes more commonplace, the grid system will have more application.

Each of Ohio's counties have soil survey maps which differentiate soil types within fields. These maps are available at Extension offices or Soil Conservation Service offices. Composite samples within a particular soil type should adequately check the variability of soil test levels of Ohio's soils. This will allow the grower to efficiently apply fertilizers only where needed.

Research indicates that phosphorus (P) and potassium (K) layer or concentrate near the soil surface in no-tillage and reduced tillage systems. This is especially a concern after several years of continuous no-till operations in a given field (see Table 1).

Because of this stratification of nutrients, split sampling can be used to see if corrective action is necessary. Merely split the 8" core sample into a top 4" sample and a bottom 4" sample.

TABLE 1. P and K Soil Test Levels Found at Various Depths in the Soil. Cruz, 1982.

Phosphorus Requirements

Phosphorus accumulates in soils because it tends to be chemically bound to soil particles. Therefore, most plant-available phosphorus in soils is adsorbed (attached) to soil particles and is not removed in large quantities by leaching with water. The results are that phosphorus pollution of ground water (water held in the subsurface soil profile) is exceedingly rare.

However, when soil particles move, the soil-bound phosphorus moves with them. The vast majority of phosphorus lost from fields is lost through soil erosion. Most of the phosphorus entering Ohio's lakes and streams does so during periods of maximum runoff and erosion. Pollution can occur when eroding soil enriched with phosphorus enters a waterway and becomes 'sediment.'

Many studies have shown that one important characteristic of no- tillage systems is an accumulation of phosphorus near the soil surface. This happens because broadcast applications are normally applied in no-till and phosphorous is slow to move down through the soil horizon. In addition, natural cycling of nutrients due to plant uptake can lead to surface stratification of phosphorus. This usually results in lower levels of phosphorus in the lower portions of the original tillage zone.

Ohio research indicates that producers involved with no-till systems should definitely consider somewhat higher levels ofsoil test phosphorus and the phosphorus fertilizer material should be subsurface banded. See Table 2.

Table 1 shows that there is a significant enrichment of the surface layer even on this unfertilized plot. This indicates that phosphorus taken up by roots from deeper in the soil profile is deposited near the soil surface.

Subsurface banding will have a yield advantage in addition to a positive impact on water quality by reducing surface accumulations of phosphorus. This is especially true of soils with low or moderate levels of phosphorus.

TABLE 2. Levels of Phosphorus Soil Tests Required in Conventional Broadcast vs. No-Till Broadcast and Subsurface Banded Applications to Achieve 100% Relative Yields.

Potassium Requirements

It is important that producers build up recommended potassium levels prior to starting a continuous no-till system. This can best be accomplished by practicing periodic deep tillage, which would allow incorporation of potassium throughout the top soil profile. See Table 1.

Potassium rates should be based on soil tests and comparisons should be made between samples taken at the 0-4 inch depth and the 4-8 inch depth. Using large quantities of potassium in starter fertilizer is not a valid alternative to providing adequate fertility throughout the top soil layer, since only a very small portion of the root system would be in contact with the band. This would restrict plant uptake. Producers may have to use occasional tillage to increase the fertility level of the nutrient uptake problems.

Starters in No-Till

Banded nutrients near the crop now are critical whenever environmental conditions cause plant demand to be high relative to the root system's capacity for uptake. Conditions leading to high nutrient demand include:

• Cold Soils. Root uptake power is decreased, nutrient translocation to shoots is slowed, carbohydrate translocation to roots is reduced, and nutrient transport to root surfaces is slowed.

• Root Growth Restrictions. Anything that reduces total root surface area or length, reduces the root system's ability to take up nutrients. Such factors include compaction, high acidity, and herbicide carryover.

Starters are a very efficient method of providing plant nutrients, especially in no-till situations. See Table 3. Subsurface banded starters will provide the early needs of the young plant as well as assist in reducing stratification of nutrients.

TABLE 3. Nutrients Responsible for Starter Response. Indiana.

No-Till Nitrogen

The biggest changes in no-tillage fertilization methods should be in nitrogen management. The protective cover of crop residue causes several changes to occur in soil which also affects nitrogen fertilizer efficiency. The surface cover reduces runoff, increases infiltration, and reduces evaporation. In addition, there seems to be lower soil temperatures as the surface cover increases. These factors lead to higher soil moisture contents in no-till systems which can lead to greater leaching losses of nitrogen. This can result in less plant growth.

Another important fact is that nitrogen losses in no-till can be quite significant when nitrogen materials are broadcast on the surface of residue. Applying urea or urea based products such as urea-ammonium nitrate solutions (UAN) to the surface of residue covered soil can result in severe losses. As much as a third of surface applied urea has been shown to be lost in a no-till corn field. Losses from surface applied UAN, such as 28% N, have been found to be about one sixth of the applied nitrogen. See Table 4.

TABLE 4. Effect of N Source and Placement on No-Till Corn Yield and Ear Leaf N in Seven Experiments Conducted from 1978 through 1980. Indiana.

Urea can be broken down to ammonium carbonate by the enzyme urease, which is present in crop residue and then escape into the atmosphere as ammonia gas. Adding nitrogen to a soil surface that has a high mulch content greatly increases the chances of denitrification losses. This is due to prolonged moisture conditions and the increase in carbon sources (mulch) which promotes biological activity.

Anhydrous ammonia is the preferred source of nitrogen in no-till systems if the surface has enough cover and the slope is low enough to prevent the knife opening from causing erosion. Since anhydrous ammonia is injected into the soil, it does not interact with surface residue and no problems associated with tillage or residue are normally anticipated. It may be necessary to mount coulters in front of knives to cut through heavy residue. Subsurface nitrogen application has little effect on surface pH, making it easier to maintain a favorable pH for weed control. However, deep bands of nitrogen may increase subsurface acidity. Lime may need to be tilled into the soil every 3-5 years. Just as in conventional tillage systems, 25-50 lb of nitrogen per acre should be applied with the planter to promote early root growth when anhydrous ammonia is the primary nitrogen source.

Nitrogen solutions (28-32% N) contain significant amounts of urea, which can be lost if applied on the surface residue. Solutions should be injected or at least banded to reduce losses. The best time to apply solutions is just prior to a rain. Nitrogen losses can be quite severe when applying solutions to standing residue such as a cover crop. See Table 4.

Ammonium nitrate is available in some areas of the state, but material handling problems have limited its widespread adoption. This material contains no urea and is a safe material for surface application.

Recommended N Fertilizers for No-Till:

	First Choice	Anhydrous Ammonia
	Second Choice	Ammonium Nitrate
	Third Choice	Nitrogen Solutions
	Fourth Choice	Urea

Surface applied nitrogen fertilizers will greatly depress surface soil pH in no-till fields. Proper soil sampling and liming procedures should be followed to ensure effective weed control when using triazine herbicides.

Summary

Most of the problems associated with no-till fertilizer efficiency can be overcome by good fertilizer management. A top notch soil testing program is necessary in no-tillage systems. Producers have to realize that stratification of crop nutrients is possible in no-till. It is quite probable that surface pH problems will be an important factor. This can lead to lower yields and poor response from herbicides.

It is recommended that producers consider injecting anhydrous ammonia or UAN solutions in order to avoid the interaction with surface crop residue. Nitrogen management is probably the key to a successful fertilizer program in no-till systems.

Starter fertilizer responses have been shown to be more common in reduced tillage situations. Subsurface banding of starters gets the nutrients down close to the plant root development and helps prevent surface stratification of nutrients.

It may be advisable to build soil test levels to high levels before going into continuous no-till programs. An alternative might be to chisel every 3 or 4 years in order to mix lime and fertilizer throughout the topsoil layer.

With the development of new equipment, efficient no-till fertilization can now be a reality.

Prepared by:
BMP Team:
Dr. Jay Johnson, Extension Agronomist
Dr. Mark Loux, Extension Agronomist
George Ropp, Agricultural Consultant
James Adams, Agricultural Consultant