Potassium Dynamics in Ruzigrass Rhizosphere

Volf, Marcelo Raphael; Guimarães, Tiara Moraes; Scudeletti, Daniele; Cruz, Igor Vilela; Rosolem, Ciro Antonio

doi:10.1590/18069657rbcs20170370

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Division – Soil Use and Management, Commission – Soil Fertility and Plant Nutrition • Rev. Bras. Ciênc. Solo 42 • 2018 • https://doi.org/10.1590/18069657rbcs20170370 copy

Potassium Dynamics in Ruzigrass Rhizosphere

Authorship SCIMAGO INSTITUTIONS RANKINGS

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.

Keywords:
Urochloa ruziziensis; non-exchangeable K; exchangeable K; rhizospheric soil

Soils	pH(CaCl₂)⁽¹⁾ (1) pH in CaCl2 at a ratio of 1:2.5 v/v.	P⁽²⁾ (2 and 3) extracted with resin.	ExcK⁽³⁾ (2 and 3) extracted with resin.	Non-excK⁽⁴⁾ (4) extracted with boiling HNO3.	Ca²⁺⁽⁵⁾ (5) Chemical analyses were determinated according to Raij et al. (2001).	Mg²⁺⁽⁵⁾ (5) Chemical analyses were determinated according to Raij et al. (2001).	OM⁽⁵⁾ (5) Chemical analyses were determinated according to Raij et al. (2001).	Clay⁽⁶⁾ (6) Clay, silt, and sand were determinated according Claessen (1997).	Silt⁽⁶⁾ (6) Clay, silt, and sand were determinated according Claessen (1997).	Sand⁽⁶⁾ (6) Clay, silt, and sand were determinated according Claessen (1997).
		mg dm⁻³ ___________________	mmol_c dm⁻³_____________				g dm⁻³_________________	g kg⁻¹_________________
0.00-0.20 m	5.2	20	0.65	3.83	22.2	11.7	17.0	205	112	682
0.20-0.60 m	4.0	5	0.45	4.75	4.5	3.1	6.0	280	100	620
Forest	3.8	6	1.34	5.89	4.1	3.5	12.0	275	175	550

Source of variation	Forest	0.00-0.20 m			0.20-0.60 m
Source of variation	Forest	no K	30 mg kg⁻¹ K	60 mg kg⁻¹ K	no K	30 mg kg⁻¹ K	60 mg kg⁻¹ K
	pH(CaCl₂)
Distancefrom roots	0.072	0.180	0.950	0.475	0.625	0.480	0.041
Block	0.000	0.001	0.001	0.470	0.545	0.055	0.006
LSD		0.19	0.12	0.63	0.60	0.12	0.07
	Exchangeable K
Distancefrom roots	0.029	0.029	0.163	0.004	0.035	0.692	0.122
Block	0.004	0.003	0.619	0.019	0.796	0.797	0.028
LSD	0.12	0.08	0.32	0.18	0.22	0.17	0.19
	Non-exchangeable K
Distancefrom roots	0.000	0.682	0.001	0.249	0.923	0.004	0.001
Block	0.089	0.012	0.776	0.030	0.997	0.234	0.792
LSD	0.31	0.70	0.50	1.09	1.02	0.45	0.34

Source of variation	Distance from the rhizosphere (mm)
Source of variation	0.5	1	1.5	3	5	10
	pH(CaCl₂)
Treatment	0.000	0.000	0.000	0.000	0.000	0.000
Block	0.622	0.152	0.142	0.347	0.845	0.871
LSD	0.59	0.52	0.17	0.15	0.18	0.14
	Exchangeable K
Treatment	0.000	0.000	0.000	0.000	0.000	0.000
Block	0.969	0.483	0.356	0.32	0.724	0.604
LSD	0.23	0.24	0.14	0.16	0.19	0.30
	Non-exchangeable K
Treatment	0.000**	0.000**	0.000**	0.006**	0.002**	0.005**
Block	0.527	0.69	0.195	0.926	0.389	0.272
LSD	0.73	0.75	0.64	0.94	0.80	0.89

TreatmentSoil/K rate	Distance from the rhizosphere						Average
TreatmentSoil/K rate	0.5 mm	1.0 mm	1.5 mm	3.0 mm	5.0 mm	10.0 mm	Average
Forest	1.13 bc	1.09 ab	1.04 b	1.15 ab	1.28 a	1.13 ab	1.13
0.00-0.20 m – no K	0.58 e	0.47 d	0.45 e	0.46 e	0.51 c	0.56 c	0.50
0.00-0.20 m – 30 mg kg⁻¹ K	1.06 bc	0.84 c	0.83 c	0.89 c	1.04 b	1.2 ab	0.96
0.00-0.20 m – 60 mg kg⁻¹ K	1.26 ab	0.82 c	1.04 b	1.00 bc	0.96 b	0.96 ab	0.10
0.20-0.60 m - no K	0.76 de	0.37 d	0.65 d	0.71 d	0.61 c	0.57 c	0.63
0.20-0.60 m – 30 mg kg⁻¹ K	0.92 cd	0.85 bc	0.84 c	0.95 c	0.90 b	0.93 b	0.91
0.20-0.60 m – 60 mg kg⁻¹ K	1.47 a	1.25 a	1.18 a	1.27 a	1.28 a	1.28 a	1.28
LSD	0.23	0.24	0.14	0.16	0.19	0.3

Treatment	Distance from the rhizosphere						Average
Treatment	0.5 mm	1.0 mm	1.5 mm	3.0 mm	5.0 mm	10.0 mm	Average
Forest	6.37 a	5.74 a	5.48 a	6.04 a	5.45 ab	5.35 ab	5.61
0.00-0.20 m - no K	4.23 d	4.00 d	3.68 c	3.84 c	3.97 e	3.84 c	3.90
0.00-0.20 m – 30 mg kg⁻¹ K	4.92 cd	3.80 d	3.93 c	4.44 bc	4.48 de	3.80 c	4.20
0.00-0.20 m – 60 mg kg⁻¹ K	6.05 ab	4.98 bc	5.11 a	5.09 b	5.88 a	5.43 a	5.27
0.20-0.60 m - no K	5.14 c	4.78 bc	4.93 ab	4.95 b	4.63 cde	4.76 ab	4.85
0.20-0.60 m – 30 mg kg⁻¹ K	4.92 cd	4.24 cd	4.31 bc	5.00 b	5.03 bcd	4.48 bc	4.70
0.20-0.60 m – 60 mg kg⁻¹ K	5.45 bc	5.26 ab	5.11 a	4.95 b	5.40 abc	4.57 abc	5.18
LSD	0.73	0.75	0.64	0.94	0.8	0.89

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[1] *Corresponding author: E-mail: ciro.rosolem@unesp.br