Potassium Bioavailability in a Tropical Kaolinitic Soil

Marcelo Raphael Volf,Michael L Thompson,Antônio Carlos De Azevedo,John L Kovar,Ciro Antonio Rosolem,Carlos Alexandre Costa Crusciol

doi:10.3390/agronomy11102016

Abstract

Some plant species are able to acquire non-exchangeable forms of K, which improve K availability and cycling in cropping systems, and which may explain the lack of response to K. However, this would not be expected in soils dominated by kaolinite. The aim of this study was to assess non-exchangeable K (Kne) use by three selected plant species grown in a tropical Haplic Plinthosol with low exchangeable K (Ke). A greenhouse experiment was conducted with soybean (Glycine max L., Merr.), maize (Zea mays L.), and ruzigrass (Urochloa ruziziensis) with or without K fertilization for three growing cycles. The crop treatments were compared with a control without plants. In the absence of K fertilization, all the tested plants were able to use non-exchangeable K and non-exchangeable K contributed more than 80% of the K demand of the plants in the first growing cycle, even in this kaolinitic soil. In the first growing cycle, soybean and maize took up more non-exchangeable K than ruzigrass, concomitant with higher dry matter yields. Over the three crop cycles, as both biomass yield and K uptake decreased in the unfertilized systems, the dependence of plants on non-exchangeable K decreased. Unfertilized ruzigrass showed a strong ability to acquire non-exchangeable K from the soil. Over the course of three growing cycles, K application decreased the absolute uptake of non-exchangeable K as well as its fractional contribution to total K uptake by the crops.

Highlights

The uptake of nutrient Potassium (K) is the second most, only behind nitrogen, and between the essential nutrients required by plants
When K fertilizer was applied, potassium uptake was less in the third crop cycle than in the first for soybean and ruzigrass but not for maize
Despite plant uptake of K from fractions that are less soluble than exchangeable K, uptake and removal of soil K over successive crop cycles can eventually lead to a decrease in K and dry matter production [43,44,45]

Summary

Introduction

The uptake of nutrient Potassium (K) is the second most, only behind nitrogen, and between the essential nutrients required by plants. K is transported to roots primarily by diffusion in the soil solution; under some conditions, mass flow may be an important transport mechanism [2,3]. The K concentration in soil solution is primarily buffered by K ions adsorbed electrostatically at the surfaces of soil minerals and organic colloids. When these ions move into the soil solution and are taken up by plants, it is commonly assumed that they can be slowly replenished by K from interlayer sites in secondary layer silicates and possibly by structural K in primary minerals (micas and feldspars), where most soil K typically occurs [4,5,6,7,8,9]. Structural K in the minerals of silt and sand fractions of soils is usually discounted as a significant source of plantavailable K during a growing season because of the slow K release and low surface area of these particles

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