Many wheat fields in Kansas have soil pH lower than 5.5, often caused by long-term use of ammonium-based fertilizers and crop removal of base cations.

At soil pH levels below 5.5, toxic aluminum becomes more soluble in the soil, which has detrimental effects on wheat growth. The main effect of available aluminum in soil solution is decreased root growth, which reduces the capacity of roots to explore the soil for water and nutrients.

As a consequence, wheat becomes stunted, resulting in reduced forage production and grain yield. Early-season wheat growth and forage production is generally more affected by low soil pH and aluminum toxicity than grain yields, so the penalty for low soil pH is often greater for dual-purpose or forage-only wheat farmers than for grain-only producers.

The recommended practice to correct low soil pH is to apply agricultural lime based on soil test recommendations. An article in the August 14, 2015 issue of the Agronomy eUpdate gives me details on liming acid soils for optimum wheat production.

However, changing soil pH is not always a rapid process. It can sometimes take a year or more to fully realize the effects of agricultural lime, so the economics of broadcasting lime on rented ground can be greatly influenced by the lease duration.

Banding of phosphorus (P) fertilizer in-furrow at planting is an alternative strategy often implemented by farmers to reduce the negative effects of low soil pH. In-furrow P fertilizer may be a suitable alternative for rented ground as it can result in increased wheat growth and forage production in low pH soils by reducing aluminum toxicity and increasing the amount of readily available P to the crop.

Table 1. Soil pH measured at wheat harvest as affected by liming or phosphorus treatments on an acid soil near Waukomis, Okla.

Likewise, some producers have considered banding 200 or 400 lbs/acre/year of pelletized lime at sowing as a low-cost alternative to broadcast applications, similar to in-furrow P application.

Pelletized lime contains finely ground limestone compressed into granules. This allows for even and accurate distribution of the material in the field and avoids dust problems. Although pelletized lime is frequently marketed as a low-use-rate, quick fix for low soil pH; research has shown that broadcast pelletized lime is not more efficient than broadcasted regular agricultural lime when applied at similar effective rates. When used at recommended rates, pelletized lime is cost prohibitive because it is 4 to 5 times more expensive than regular agricultural lime. Thus, pelletized lime has been proposed as a maintenance product to be applied annually at 300 to 400 lbs/acre/year.

A recent study on acid soils in north central Oklahoma has shown that this practice is not effective in ameliorating acid soils. Adding 200 or 400 lbs/acre/year in-furrow pelletized lime or 25 or 50 lbs/acre/year triple super phosphate (TSP) at time of sowing did not increase soil pH when compared to the control treatment in most cases (Table 1). On the other hand, application of broadcast incorporated agricultural lime at 2,000 or 4,000 lbs/acre significantly increased soil pH when compared to any of the other treatments.

Additionally, volume of soil in which pelletized lime effectively increased soil pH was very limited. This was evaluated by slicing vertical trenches perpendicular to wheat rows after wheat harvest and taking pH measurements at regular intervals from the application band. The vertical trenches opened at the plots where pelletized lime was applied at 400 lbs/acre/year following wheat harvest from two growing seasons is shown in Figure 1.

Figure 1. Trenches opened in (A) June 2011 and (B) June 2012 showing little or no diffusion of the pelletized lime across the soil profile. Pellets were visible and practically unmodified approximately 220 days after pelletized lime banding. Photo by Romulo Lollato, K-State Research and Extension.

The pellets of lime applied in-furrow remained intact even after several months from their application and were still visible to the naked eye both years. This indicates that the lime pellets have very little or no dissociation within the winter wheat growing season, and consequently will induce limited changes in soil pH.

Measurements of soil pH taken in the trenches opened after wheat harvest indicates that pelletized lime at 200 and 400 lbs/acre/year raised soil pH to values higher than 5.0 only at and around the pellet (Figure 2). In the 400 lbs/acre/year pelletized lime treatment, soil pH ranged between 5.3 and 6.0 in an area within about a 0.5-inch radius surrounding the pellet.

The pH averaged 4.5 deeper in the profile. Broadcast-incorporated lime led to a greater increase in soil pH — as high as 6.5 — than that produced by the pelletized lime. In addition, broadcast incorporated lime increased soil pH throughout the incorporated depth with a much wider change in soil pH across the soil profile.

 With such a limited soil area affected by banded pelletized lime, very little contribution could be expected from pelletized lime to wheat aboveground growth or grain yield. Indeed, early spring wheat biomass production was not increased due to the application of in-furrow pelletized lime at 200 or 400 lbs/ac/yr when compared to the control plots (Figure 3).

Figure 3. Poor stand establishment, tillering, and biomass production of the wheat crop in the 200 lb/ac in-furrow pelletized lime treatment in an acid soil at Waukomis, OK. Although soil pH was not increased by the triple super phosphate (0-46-0) treatments, wheat growth was similar to that observed on the plots that received 4,000 lbs/ac of broadcast agricultural lime due to the positive effects of readily available P to the crop.

 

Figure 2. Distribution of pH measured following wheat harvest in June 2011 across the soil profile (depth and distance from furrow) as a function of acidity correction strategy at Waukomis, Okla. Notice the difference in scales between the two upper panels and the lower panel. Broadcast ECCE ag-lime resulted in a greater increase in soil pH than did 400 lb/acre pelletized lime or the control.