AS K SOURCE FOR CROPS IN TROPICAL

Volf M*, Benites M. V2, Rosolem A. C1, Crusciol A. C1, Moraes F. M3, Menezes F. J4, Silva C. A5 1. Marcelo R. Volf Department of Crop Science,, São Paulo State University – UNESP [email protected]. 2. Brazilian agricultural research company- EMBRAPA. 3. Federal University of Mato Grosso – UFMT. 4. Rio Verde University/Agronomy College – UniRV 6. Dalcin Laboratory of and Plant.

INTRODUCTION Results and Conclusions Mato Grosso state is the Brazil’s largest producer of grain crops, and the Vale do Araguaia region, in the The soils in the Vale do Araguaia region presented high levels of non-exchangeable K, in some cases the state’s northeast, is an agricultural frontier region that accounts for more than 16% of the state’s soybean concentration of non-exchangeable K was up to 2.39 times more than that of exchangeable K in the top layer, and output (IMEA, 2015). Few studies have been conducted to investigate the influence of production system or up to 5.52 times more in the 20-40 cm layer. silt content in the soil on the potassium nutrition of crops, especially in soils with high concentrations of non- The ratio between non-exchangeable K and exchangeable K in relation to the levels of silt. It can be seen that the exchangeable K, characteristic of this region of Mato Grosso state. levels or silt are correlated with higher levels of non-exchangeable K in these samples. The objective of this study was to assess the forms of exchangeable and non-exchangeable K in soils under different management systems and uses. MATERIAL AND METHODS

600 200 Silte_20-40 = 43,723+0,2652*x 18 88 Studied region was the Vale do Araguaia (Araguaia Valley - Figure 1), which basically contains four soil K_HNO3 20-40 = -3,1407+2,0403*x 180 500 R2 = 0,6007; r = 0,7750; p = 00,0000; y = -3,1407 + 2,0403*x 160 41 39 ) 3

) 140 21 classes: Dark-Red (Oxisoil); Red-Yellow Latosol (); and Plinthosol (Plinthaquox) and Red- -1 400 Fonte: Isabella A. Brito 120 02 43 Yellow Argisol (). The predominant minerals are kaolinite, hematite, goethite and gibbsite, except 42 64 18 300 100 41 32 66 64 80 in the Plinthosol, where hematite is absent (Ker, 1997; Galvão et al., 2007). Soil samples were collected 66 32 200 42 62

20-40 cm (mg. dm (mg. 20-40 cm 24 60 24

3 43

from 91 sites. Soil samples were collected in areas cultivated with soybeans, in a line transversal to the Kg (g. cm 20-40 Silt 0861 40 100 09 rows, at depths of 0-20 cm and 20-40 cm. Soil samples were also collected in areas of pasture and native HNO K 25 20 (B) vegetation (Cerrado or forest). Cropped areas were chosen for contrast regarding the use before planting 0 (A) 0 soybeans: corn, millet, Urochloa (Brachiaria) or fallow . -100 -100 0 100 200 300 400 -20 0 20 40 60 80 100 120 140 160 180 200 K non-exchangeable 20-40 cm (mg. dm-3) K exchengeable 20-40 cm (mg. dm3)

200 88 Silte_20-40 = 39,2492+13,2997*x 180

160 39 41

) 140

-1 21 02 120 18 43 100 16 66 64 42 80 32 71 60 24 10

Silt 20-40 cm (g. Kg Silt 40 53 20 (C) (D) 0

0 1 2 3 4 5 6 Ration of K non-exchangeable of the K exchangeable (Knt/Kt)

Relation of levels of exchangeable K and K extracted in nitric acid (HNO3) (A) and non-exchangeable K and silt in the 20-40 cm (B), Ratio between levels of non-exchangeable K and exchangeable K in relation

to silt levels in the 20-40 cm (C).Multiple regression of K extracted in nitric acid (HNO3), (D)

Table 1. Simple pairwise linear correlation coefficients between the levels of exchangeable K, non-exchangeable K and silt in the two soil layers (0-20 cm and 20-40 cm).

Figure 1. Map indicating the region where the soil samples were collected.

ACKNOWLEDGMENTS

Conclusions The levels of silt were directly correlated with the levels of non-exchangeable K and based on the values of

exchangeable K and the silt concentration, the levels of non-exchangeable K (extractable in HNO3) can be estimated. Forage species used as cover between crops or as pasture in silt-rich soils absorb exchangeable K and non- exchangeable K from the , recycling K to the arable layer with mineralization of residues.