Soils from the X Region

The surface samples (0-20 cm) collected from ten representative volcanic ash soils of the X Region were classified according to the Soil Taxonomy [8], as shown in Table VIII.

168

TABLE IV. CHARACTERIZATION OF SOILS FROM REGION IX IN CHILE

The soils were sampled following a line east-west direction and from 1082 masl to 160 masl, starting with

a Vitrandic Udorthent with a very low profile development with clear stratification of volcanic materials.

The Huilma Soil Series was sampled under three different soil management conditions, which included Huilma forest vegetation, wheat crop and fallow systems.

The maximum accumulation of OC (Table IX) was found in the Alerce soil (Duric Placaquand) and the minimum OC accumulation in Antillanca soil (Vitrandic Udorthent).

The Ultisols (Fresia and Huilma fallow) under the same land use showed similar amounts of OC. It should be mentioned that the wheat monoculture in Huilma soil produced a decline in the soil OC. Under Pinus radiata, by the effect of the permanent vegetal cover and limited erosion, an effective accumulation of OC is observed at least in the surface horizon.

The lowest accumulation of OC was found in the soils with high volcanic glass content (Antillanca and Ralún). Both vitric soils are coarse textured (mostly sandy and gravelly) with a high leaching potential and low water retention. The reaction is strongly acid (pH 5.0) (Table VIII) and P retention (Blakemore) is relatively low due to the small amounts of short-range order minerals. The available P (Olsen) is lowand the OC is low.

169 TABLE V. CHARACTERIZATION OF SOILS FROM REGION IX IN CHILE

Soil Depth CEC Na K Ca Mg Exch bases

Although Corte Alto soil series is considered an Andisol, it seems that the volcanic materials have undergonea more intense weathering to such extent that the mineralogy exhibit the presence of halloysite as a common mineral [9].

The Olsen P gave very low values (Table X), which are normal for Andisols. According to the results, Pinus radiata vegetation cover does not produce an important alteration in the soil parameters of pH, Olsen P, P retention (Blackmore), total N, OC and C/N.

The retention index is less than 0.2. The inverse relation of the index retention (r₁/R) is very high [4].

This result indicates the great difficulty in increasing the available P in these soíls, even when high rates of phosphate fertilizers are applied. The principal P limiting factor in both regions is the intensity factor (Table XI).

The Cp values are very low (Table XI) and agree with the index retention. The immediately available pool of P was slightly higher in the Huilma soil under fallow than in the other two management systems (Table XII). The A, B and C pools showed a relatively homogeneous distribution. An increase inthe pool D that represents the P inmobilized from former applications was observed.

In the Huilma soil under pines the unique source of P for plants comes from pool D, which will decrease gradually as it is absorbed by plants. In the Huilma soil with wheat, the major part of P is ound inthe pool A coming from the recent application of fertilizers [4].

170

TABLE VI. ISOTOPIC PARAMETERS OF SOILS FROM REGION IX OF CHILE

Soil Depth Cp E₁ E₁/Cp R₁/R Km Tm Fm

cm mgP/L mgP/kg L/kg L/min min mgP/kg min Quiripio

HAPLUDAND

H-A1 0- 13 0.0120 4 339 0.030 6.9E+03 1.4E-04 7.7E+02 H-A2 13- 28 0.0109 7 654 0.015 3.1E+04 3.3E-05 3.2E+03 H-B1 28- 48 0.0064 28 4287 0.002 9.8E+09 1.0E-10 5.7E+08 H-B2 48-170 0.0109 57 5167 0.002 3.3E+06 3.0E-07 4.0E+05

Metrenco PALEUDULT

H-A1 0- 9 0.0186 7 360 0.028 7.6E+03 1.3E-04 1.4E+03 H-A2 9- 24 0.0213 9 429 0.023 9.6E+04 1.0E-05 2.1E+04 H-B1 24- 52 0.0103 40 3907 0.003 1.1E+16 8.9E-17 1.2E+15 H-B2 52- 73 0.0131 131 7106 0.001 1.2E+09 8.1E-10 1.6E+08 H-B2T 73-180 0.0124 62 6260 0.002 1.1E+11 9.3E-12 1.3E+10

Pto. Dominguez

FULVUDAND

H-A1 0 - 5 0.0193 14 728 0.014 - - - H-A2 5 - 11 0.0127 10 766 0.013 2.4E+03 4.2E-04 3.0E+02 H-A3 11- 24 0.0109 32 2920 0.003 4.9E+03 2.1E-04 5.3E+02 H-B1 24- 37 0.0150 55 5144 0.002 1.1E+04 9.4E-05 1.1E+03 H-B2 37- 69 0.0081 34 4154 0.002 3.0E+03 3.3E-04 2.4E+02 H-B3 69-110 0.0102 51 5993 0.002 7.4E+03 1.4E-04 7.5E+02

Los Prados

MELANUDAND

H-A 0- 45 0.0011 1 918 0.011 9.8E+02 1.0E-03 1.1E+01 H-B1 45-106 0.0022 5 2413 0.004 8.5E+02 1.2E-03 1.9E+01 H-B2 106-120 0.0048 27 5666 0.002 1.1E+05 9.1E-06 5.4E+03

171 TABLE VII. ISOTOPIC PARAMETERS OF SOILS FROM REGION IX

OF CHILE (CONT)

TABLE VIII. SOIL CLASSIFICATION (KEYS TO SOIL TAXONOMY, 1996) AND CHEMICAL CHARACTERISTICS OF SOIL FROM REGION X OF CHILE

Series Classification pH Al+1/2Fe

Depth 0- 20cm H₂O %

Alerce Medial isomésica Duric Placaquand 4.6 3.3 Frutillar Medial isomésica Typic Placaquand 4.7 4.8 Antillanca Ashy frígida Vitrandic Udorthent 5.0 0.7

Chanleufu Medial Humic Udivitrand 4.7 0.9

Ralún Udivitrand 5.1 1.1

Corte Alto Medial isomésico Typic Hapludand 4.8 3.3 Puerto Fonk Medial isomésico Pachic Melanudand 5.0 4.6 Puyehue Medial isomésico Acrudoxic Hapludand 4.8 2.1

Huilma Fallow Typic Paleudult 5.1 1.6

Huilma Pine Typic Paleudult 5.0 1.5

Huilma Wheat Typic Paleudult 5.1 1.4

Fresia Typic Hapludult 4.7 2.0

172

TABLE IX. CHARACTERIZATION OF SOILS FROM REGION X OF CHILE

Soil OM OC Total N C/N Biomas-N Biomas-C C/N

TABLE X. CHARACTERIZATION OF SOILS FROM REGION X OF CHILE Soil Olsen P Carolina P P Retention Total P

TABLE XI. ISOTOPIC PARAMETERS OF SOILS FROM REGION X OF CHILE

173 TABLE XII. ISOTOPIC PARAMETERS OF SOILS FROM REGION X

OF CHILE (CONT.)

This work was conducted under research contract CHI-7499 in the frame of the FAO/IAEA Coordinated Research Project “The use of nuclear and related techniques for evaluating the agronomic effectiveness of phosphate fertilizer, in particular rock phosphate”, for which we are very grateful.

REFERENCES

[1] SADZAWKA, M.A., Métodos de análisis de suelos. Instituto de Investigaciones Agropecuarias (Chile) Est. Exp. La Platina (Santiago). Serie La Platina N° 16. (1990), 130 p.

[2] BROOKES P.C., LANDMAN A., PRUDEN G., JENKINSON D.S., Chloroform Fumigation and the Release of Soil Nitrogen: A Rapid Direct Extraction Method To Measure Microbial Biomass Nitrogen in Soil. Soil Biol. Biol.Biochem. Vol.17, N°6, (1985) 837-842.

[3] FARDEAU, J.C., GUIRAUD, G., MAROL, C., Bioavailable soil P as a key to sustainable agriculture. In: Proceedings of a symposium “Nuclear techniques in soil-plant studies for sustainable agriculture and environmental preservation” IAEA. STI/PUB/947(1995),131-144.

[4] FARDEAU, J.C., P-32 isotopic exchange kinetics. Experimental procedure, interpretation of results. Application to the prediction of the efficiency of P fertilizers. Working paper presented at the Third Research Coordination Meeting of the FAO/IAEA Coordinated Research Project

“The use of nuclear and related techniques for evaluating the Agronomic Efectiveness of Phosphatic fertilizers, in particular Rock Phosphate” (1997). Report D1-RC-542.3.

[5] FARDEAU, J.C., Dynamics of phosphate in soils. An isotopic outlook. Fertilizer Research 45 (1996), 91-100.

[6] NOVOZAMSKY, I., VAN DIJK, D., LEE, J.J., HOUBA, V.J.G., Automated determination of trace amounts of phosphate in soil extracts using malachite green. Commun. Soil Sci. Plant Anal. 24 (9&10) (1993) 1065-1077.

[7] FARDEAU, J.C., Le phosphore assimilable des sols: sa representation par un modele fonctionnel a plusiers compartiments. Agronomie 13 (1993), 317-331.

[8] SOIL SURVEY STAFF, Keys to Soil Taxonomy. 7^th edition. Natural Resources Conservation Service. USDA. (1996). 644 p.

[9] BEINROTH, F H., LUZIO, W., MALDONADO, F., ESWARAN, H., Proceeding of the Sixth International Soil Classification Workshop, Chile and Ecuador. Part II. (1985), 236.

174

STUDIES ON P AVAILABILITY OF VOLCANIC ASH SOILS FROM CHILE AMENDED