Potassium Dynamics in Ruzigrass Rhizosphere

Abstract

Ruzigrass (Urochola ruziziensis) has a large capacity to take up K from the soil, including non-exchangeable forms, and can play an important role in nutrient cycling in integrated production systems. However, K transport to roots of brachiarias is not well known, nor the nutrient dynamics in the rhizosphere, where a concentration gradient may be established towards the non-rhizospheric soil, creating a favorable environment for the release of non-exchangeable K. This study aimed to evaluate the effect of ruzigrass on K dynamics in the rhizosphere and on non-exchangeable K release. Ruzigrass was grown in pots filled with a Latossolo Vermelho Amarelo (Typic Hapludox) that was collected at 0.00-0.20 and 0.20-0.60 m layer from a cultivated area and fertilized with 0, 30, and 60 mg kg -1 of K, plus a treatment with forest soil, used as control. Thirty days after plant emergence, soil samples were taken at the following distances from the roots: 0.5, 1.0, 1.5, 3.0, 5.0, and 10.0 mm. For the highest exchangeable K rate (60 mg dm -3 ), the exchangeable K level was higher from 0 to 0.5 mm of the roots for both soils (0.00-0.20 and 0.20-0.60 m). Therefore, more K was transported to the rhizosphere than the plant could take up. A depletion of exchangeable K observed in the rhizosphere resulted in the release of K from non-exchangeable forms, as observed in the soils from 0.00-0.20 (60 mg dm -3 ) and 0.20-0.60 m (without application of K). Ruzigrass grown on low K soils without fertilizer application results in a larger exchangeable K depletion zone than in soils that were fertilized or originally high in exchangeable K, showing a high potential for K cycling in the system.

Potassium application to the cover crop prior to cotton planting as a fertilization strategy in sandy soils

“…A dry spell was observed when cotton grow rate was supposed to experience a sharp increase, and so K uptake 19 . Considering that soil K transport to the root surface occurs by diffusion and mass flow 2,5 , it depends on soil water. It is hypothesized that the lower leaf K concentration was caused by the poor rainfall during flowering (for both early-45-60 DAE-and late stages-60-75 DAE) in the 2016/17 season.…”

“…Apparently, the K fertilizer use efficiency was decreased by ruzigrass ( Fig. 4), but it is important to consider that this grass has a high ability to take up soil K, and it is considered non-exchangeable 5 , and can accumulate as much as 400 kg ha −1 of K in stems and leaves 25 . As K is not metabolized and binds weakly with organic molecules 9 it is available to be washed out of the straw after cover crops are terminated, which depends on the rainfall 10 .…”

Exploring the synergism between surface liming and nitrogen fertilization in no‐till system

“…Reducing AS along the soil profile by liming is an efficient management practice to ensure greater crop root growth (Bossolani, Crusciol, Portugal, et al., 2021; Da Costa et al., 2018). Moreover, organic compounds exuded by roots can convert non‐exchangeable K into exchangeable K (Hinsinger & Jaillard, 1993; Volf et al., 2018), increasing soil K + content and, indirectly, the efficiency of liming through biocycling. Consistent with these effects, we observed an increase in K content in the soil as the lime rate increased from 0 (no lime) to 6,000 kg ha –1 .…”

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

“…When compared to annual crops in general, Urochloa species develop a root system that penetrates deeper into the soil, with a large volume of roots, enabling high K absorption (Rosolem et al, 2019), including the non-exchangeable forms (Volf et al, 2018). According to Römheld and Kirkby (2010), K is transported mainly by diffusion from the soil to the root surface and the presence of hairs is crucial in absorption, as it increases the surface area of the root cylinder and the concentration gradient that triggers the K influx.…”