Does Ferralsol Clay Mineralogy Maintain Potassium Long-Term Supply to Plants?

Abstract

Ferralsols (Latossolos) should contain few or no 2:1 clay minerals and have low potassium (K) contents, and consequently low levels of non-exchangeable K forms are expected. The aim of this study was to evaluate how the clay mineralogy of a Ferralsol affects the soil K dynamics in response to K fertilization during cropping and whether the clay mineralogy was altered due to successive crops and K fertilization. A tropical Brazilian Ferralsol under field conditions was sampled (0.00-0.20 m) in contrasting K fertilization plots: no K application (control plot) and 3,200 kg ha-1 applied K 2 O fertilizer. These two treatments were submitted at eight different crop cycles, performed in pots under greenhouse conditions, and fertilized with 0, 30, and 90 mg kg-1 K 2 O before each crop cycle. The biomass K, exchangeable K, non-exchangeable K, and structural K contents were determined after each crop cycle. At the end of the experiment, the presence of 2:1 clay minerals with hydroxy-aluminum interlayered in the soil clay fraction was verified, which ensured K adsorption in a form available to plants when K fertilizer was added. Cropping without K fertilization resulted in limited crop yields and exhausted the exchangeable and non-exchangeable K soil reserves. The previous K fertilization history influenced the soil K reserve and its availability to plants in the Ferralsol studied. The crops without K addition decreased the proportion of 2:1 hydroxy-Al interlayer minerals in the soil in relation to the kaolinite clay minerals.

Distribuição das formas de potássio no solo em decorrência da aplicação de calcário

“…Entretanto, outro estudo em um Argissolo cultivado no Rio Grande do Sul concluiu que, apesar do grau de intemperismo, existia grande reserva de K estrutural, com efeito significativo na disponibilidade para as plantas (MOTERLE et al 2016), demonstrando a variabilidade entre solos de mesma classe de acordo com a região, material de origem e cultivo. É importante ainda considerar que em solos intemperizados e com alto teor de argila, como os Latossolos, as pequenas quantidades de minerais 2:1 encontradas nessa fração podem controlar a disponibilidade de K, garantindo o poder tampão (MOTERLE et al 2019).…”

“…Embora a caulinita e os hidróxidos de Fe e Al presentes na fração argila não sofram alteração pela ausência de adição de K nos sistemas de cultivo, os filossilicatos 2:1 podem ter sua ordem estrutural alterada, diminuindo a sua cristalinidade, bem como a estabilidade dos argilominerais com hidróxi-Al nas entrecamadas, conforme descrito por FIRMANO et al (2020) em um Latossolo no Paraná. Esse resultado corrobora com o observado em um Latossolo do Rio Grande do Sul, onde foi constatada a redução da proporção de argilominerais 2:1 em relação à caulinita (MOTERLE et al 2019). Em outro estudo com Argissolo, no mesmo estado, concluiu-se que os baixos teores de K disponíveis levaram à completa transformação da ilita em vermiculita (MOTERLE et al 2016).…”

Exchangeable potassium reserve in a Brazilian savanna Oxisol after nine years under different cotton production systems

“…As the Oxisol is typically well drained and the experiment was installed in a field almost flat, greater importance of leaching can be expected in the potential K losses. According to Moterle et al (2019), when K fertilization generates a positive balance that exceeds the soil buffering capacity, the presence of higher exchangeable K levels increases leaching. Thus, once a sufficiency level for a given soil type is established, fertilizer recommendations closer to the crop needs are desirable, in amounts equivalent to K export in the harvested products, which minimizes translocation down the profile and eventual K losses outside the root zone (Kaminski et al, 2010).…”

“…Therefore, in addition to making the soil prone to lose K through erosive processes, the frequent tillage limits SOM accumulation, favoring a disruption in the K storage capacity in the topsoil. There is a weak K retention strength in highly weathered soils, such the Cerrado Oxisols, as result of the low frequency of 2:1 clay minerals to generate negative charges and adsorb cations, besides the competition with Ca and Mg derived from liming on adsorption to colloids (Moterle et al, 2019;Rosolem et al, 2019). These conditions make the K surplus from fertilization more susceptible to leaching.…”

Potassium buffering capacity and corrective potassium fertilizer recommendations in soils from Southern Brazil

“…It is possible that soils with lower CEC pH7.0 , due to their low capacity to perform chemical adsorption, are making K available in the system (native K of the soil). On the other hand, adsorption processes (K retention in 2:1 minerals, for example), may make part of the applied K unavailable (or simply undetectable by traditional routine methods) (Moterle et al, 2019). A similar phenomenon occurs with P, where the extraction power of the method depends on the clay content (Mumbach et al, 2020).…”