Spring-Banded Potash Increases Conservation-till Corn Yield
By Tony Vyn, Ken Janovicek and Dragan Galic, Department of Plant Agriculture, University of Guelph

Effective nutrient management for no-till corn production is not only dependent on knowing the quantity of nutrient required, but also on where required nutrients should be placed. A 1996 survey of 54 long-term no-till fields in Ontario indicated that immobile nutrients such as phosphorous (P) and potassium (K) have become stratified. Soil K concentrations were relatively high within the surface two inches and were relatively low below four inches. Stratification of K can result in inadequate K availability for both corn and soybeans, even when standard soil tests indicate that sufficient K should be available. (Refer to February issue of Ontario Corn Producer for details.)

Adequate K availability is especially crucial for corn plants between the 10-leaf stage (knee high) and silking, when up to 80 per cent of the total K uptake will occur. Dry soil conditions at this time can reduce K uptake. Stratified no-till fields are especially vulnerable to poor K uptake during prolonged drought conditions because of limited root function close to the soil surface where K levels are the highest.

Until recently, corn farmers had just two placement options for potash. They could either broadcast or apply in a starter band at planting. Sometimes they did both, in part because they were limited in the amount of potash they could apply close to the seed, especially when relatively large amounts of N were applied close to the row at planting as well. Recent availability of air delivery systems for dry fertilizers has now made possible a third application option of deep banding in the row area. Deep banding is usually combined with pre-planting zone-tillage with coulters and/or shanks in the fall or spring.

This article summarizes some of the on-farm research conducted from 1996 to 1998 evaluating the effectiveness of various potash placement options for corn planted in long-term no-till fields with significant K stratification.

Fall versus Spring Banding
Five experiments which evaluated fall and spring (starter-band) potash application options in three tillage systems were conducted on fields which were in continuous no-till for a minimum of seven years near Kirkton (Perth County) and Belmont (Elgin County). The degree of K stratification at the 1998 Kirkton site (Figure 1) is typical of the K stratification observed at the other no-till fields in this study. Potash was fall applied at a rate of 90 lb K2O/ac by surface broadcasting in the no-till system, surface broadcasting and plowing under in the fall moldboard system, and deep-banding six inches deep in the zone-till system. Fall applied potash in the zone-till system was applied in conjunction with fall zone-tillage operations. Two rates of starter potash were applied (0 or 45 lb K2O/ac) in a two-inch by two-inch starter-band at planting. Actual nitrogen (N) and P was applied at rates of 27 lb/ac each in the starter band for both fall K rates in all tillage systems.

Average yields for Kirkton shown in Table 1 are representative of starter potash responses observed at both Belmont and Kirkton when soil exchangeable K tests were in the medium range (70-100 ppm). When the no-till system was continued, corn yields increased 13 bu/ac with starter potash alone, compared to just seven bu/ac with broadcasting double the potash rate. Starter banding potash was also more beneficial to corn yields than deep banding alone in zone-till, and than broadcast application before plowing in the moldboard treatment.

When soil K test levels were very high (i.e. above 160 ppm) there was no corn yield benefit to potash application by any method, even though stratification was significant after years of no-till (Belmont 1997, data not shown).

Plowing After No-Till?
Some agronomists suggest periodic plowing of no-till fields is an effective method of increasing availability of stratified K. Fall moldboard plowing at Kirkton did increase corn yield; however, the size of the yield increase was the same where potash was not applied and where the highest rate of potash was applied (90 lb K2O/ac fall broadcast plus 45 lb K2O/ac starter band). It is interesting to note that when only starter potash was applied, moldboard and no-till yields were similar. This suggests yield response to tillage on soils with medium levels of exchangeable K may be affected by K fertility and/or by both rate and method of K application.

Comparison of Spring Application Options
We also compared three spring potash application methods in three tillage systems on a loam soil that has been in continuous no-till for 11 years near Paris (Brant County). The potash application methods were surface broadcast, half surface broadcast plus half applied in a two-inch by two-inch planter band, and deep (six-inch) in-row band. The tillage systems were no-till, spring zone-till (six- to seven-inches deep) and spring mulch-till with a field cultivator. Potash was applied at a total rate of 115 lb K2O/ac and any broadcasting occurred before tillage.

Deep-banded potash in a spring zone-till system produced the highest corn yield on this drought-susceptible loam soil (Table 2). Surface broadcast potash also increased no-till and zone-till yields, but not to the same levels obtained when potash was deep banded in the zone-till system. No-till and zone-till yields were often higher than mulch-till when potash was applied, so using tillage to incorporate K was not helpful at this site.

Conclusions and Recommendations
Shallow-banded potash in two-inch by two-inch planter starter bands is available to corn in no-till and zone-till systems. In fact, some of the largest no-till and zone-till yield responses to potash were observed (on soils with a medium exchangeable K rating only) when significant amounts of potash (45 lb K2O/ac) were included in the starter fertilizer blend.

The availability of shallow-placed potash in this study may, in part, be due to the fact that corn was planted in rotation with wheat, where the high surface residue cover and improved soil structure conditions may stimulate more root growth close to the soil surface. Whether the same response to potash applied in a starter band will occur when corn is planted no-till following soybeans needs more investigation.

We recommend that no-till and zone-till corn producers with fields testing in the low-to-medium range consider applying significant amounts of potash (e.g., 30-50 lb K2O/ac) in a two-inch by two-inch band at planting. Relying solely on broadcast applications of K will not be adequate if these fields continue in no-till or some form of zone-till. However, on soils with an exchangeable K rating less than 80 ppm, potash should be bulk applied in addition to the starter-band application. Growers attempting to produce corn on drought-susceptible, K-deficient soils may want to consider deep applying potash in a zone-till system since this resulted in substantial yield increases.

We realize there has been a move away from two-inch by two-inch dry-starter fertilizer band application, primarily because of the time and equipment costs. However, recent advancements in air application technology (see photo) reduces the costs and time involved with applying dry starter fertilizers at planting. Besides being easily mounted on coulter carts, these units can also be readily mounted directly onto the planter. Also, many no-till producers stopped banding because they could not get dry fertilizer coulters to band starter fertilizer at a constant depth. Recently, new no-till dry fertilizer coulters which are designed to more consistently apply fertilizer bands at a constant depth have become available.

Finally, although in the ideal world farmers would not begin continuous no-till until their soils tested over 120 ppm exchangeable K, intensive tillage operations are not essential after several years of no-till if the sole purpose is to incorporate potash on medium testing K soils. Proper banding is all that's necessary, making sure that total band applied N plus K in starter does not exceed 80 lb/ac (for 30-inch rows). There are good alternatives now to keep erosion loss low, input costs low and corn yields high.

We wish to recognize the financial support provided by the Ontario Corn Producers Association, Potash and Phosphate Institute of Canada, Pioneer Hi-Bred International Ltd. and the Grow Ontario Investment Program. We also wish to acknowledge Becker Farm Equipment for supplying the Trans-till and Till-Tech Systems Ltd. for providing the potash application equipment. Cooperating farmers were Bill Denham (Kirkton), Bill Erickson (Belmont) and Clinton Potruff (Paris).

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