CATEN A V01,11,197,200 Bmunscweig 1984

SOIL STRUCTURE UNDER DIFFERENT LAND USES

P.IC Sharma, Manila, and G.C. Aggarwal, Ludhiana

SUMMARY

Structural status of soils under different land uses, viz. aerable, native grass land, tea planting and native forest, was studied using different structural indices. Land use showed a significant influence on soil structure. Water-stable aggregates ( > 0.25 mm dia), mean weight diameter and total porosity were significantly higher, whereas bulk density was signi- ficantly lower in tea than in aerable soils. In general, tea soils showed better structural status than other soil groups. It was observed that use of one index alone is not a satisfactory approach to soil structure evaluation.

ZUSAMMENFASSUNG

Untersucht wurde die Beeinflussung der Bodenstruktur durch unterschiedliche Land- nutzung. Ausgew~ihlt wurden Ackerbau-, natiJrliche Grasland, Tee- und Waldstandorte in der feucht-warmen Bergregion des Kangra Distrikts (H.P.) in Indien. Fiir die Bestimmung der Bodenstruktur wurden folgende Faktoren zugrunde gelegt: Aggregatstabilitiit, durchschnittliche Aggregatgr613e (mean weight diameter), Bodendichte und Gesamtporen- volumen. Unterschiedliche Landnutzung zeigte einen signifikanten EinfluB aufdie Boden- struktur. So waren die Aggregatstabilit/it verbessert, die durchschnittliche Aggregatgr613e und das Porenvolumen erh~Sht und die Bodendichte geringer. Die Untersuchung zeigte, dab zur Evaluation der Bodenstruktur ein Strukturmerkmal allein nicht ausreicht.

1. INTRODUCTION

Soil structure is a dynamic soil property, altered by any stress on soil, natural or artificial. Extensive data are available in literature showing the influence of manures, fertilizers, tillage, cropping systems and natural forest vegetation on soil structure (WILLIAMS & COOKE 1961, LOW 1972, BHUSHAN et al. 1973, SHARMA & BISWAS 1974, YADAV & SINGH 1976, VISWANATH & PILLA11978, GRIEVE 1980, HEWlTF & DEXTER 1980). But most of these data do not provide any understanding about the influence of land use on soil struc- ture under similar environmental conditions. These informations are essential to protect lands, especially marginal ones, from degradation of their productivity by putting them under appropriate land use pattern.

This report compares the structural status of soils under four land uses - soils under cul- tivation of mainly cereals (aerable soils), natural grasses (grass land), tea planting (tea soils) and native forest vegetation (forest soils).

ACG WAL

warm and wet mountainous zone of Kangra district (H.P., India), were selected for this stu- dy. This area lies between the latitude 32 ° to 32°15'N and longitude 76o20 ' to 77°20'E. Soils, mostly Alfisols and Ultisols, owe their origin to igneous and metamorphic parent rocks, con- sisting mainly of granites and gneisses. Annual rainfall is about 200 cm.

Sixty surface soil samples (0-15 cm), fifteen from each of the four land uses, varying in texture from loamy sand to silty clay loam, were collected to determine water-stable aggregates > 0.25 m m dia. (YODER 1936), mean weight diameter (VAN BAVEL 1950), bulk density (PRIHAR & HUNDAL 1971), total porosity and organic carbon (titration method of WALKLEY & BLACK). Total porosity was computed from bulk density using actual values of particle density of soils. All determinations were made immediately after the collection of soil samples.

Tab. 1: MEAN VALUES OF WATER STABLE AGGREGATES (W.S.A. >0.25 mm), MEAN WEIGHT DIAMETER (M.W.D.), BULK DENSITY, TOTAL POROSITY, AND ORGANIC CARBON AND THEIR CORRELATION COEFFICIENTS WITH ORGANIC CARBON IN SOILS UNDER DIFFERENT LAND USES.

Land use

Structural indices C.D. Aerable Grassland Tea Forest (P = 0.05)

W.S.A. >0.25 mm (%)41.09 + 9.75 a 68.67 -t- 14.52 b 70.29 + 13.08 b 69.52 + 14.23 b 9.44 r = 0.89** r = 0.76** r ~ 0.76** r = 0.75**

M.W.D. (mm) 2.44 + 0.51 a 3.62 + 0.55 b 4.12 + 0.80 c 3.92 + 0.66 b,c 0.46 r = 0.56* r = 0.70* r = 0.90** r = 0.63**

Bulk density (g/cm 3) 1.54 + 0.08b 1.52 + 0.12b 1.35 + 0.15a 1.41 + 0.16a 0.10 r = -0.63* r = -0.79** r = -0.74** r ~ -0.74**

Total porosity (%) 38.81 + 3.81 a 39.74 + 2.82 a 46.43 + 5.45 b 43.66 + 6.27 b 3.45 r = 0.65** r = 0.83** r = 0.67** r = 0.62*

Organic carbon(%) 0.87 + 0.25a 1.11 -t- 0.39a, b 1.52 + 0.44c 1.34 + 0.65 b,c 0.33

In a row, mean values followed by a common letter are not significantly different at 5% level. * Significant at 50/0 level (r = 0.514) ** Significant at 1% level (r = 0.641)

3. RESULTS AND DISCUSSION

Data in Table 1 reveal significant differences in the mean values of all the structural indices of soil under different land uses. The variation in structural indices was significantly correlated with the organic carbon content o f soils. It accords well with most of the published studies which exhibit significant dependence of soil structure, especially aggregation, on or- ganic carbon levels (BOEKEL 1963, YADAV & S I N G H 1976, GRIEVE 1980). According to GREENLAND (1971) and HAMBLIN & GREENLAND (1977), the type of organic matter is as important as the amount in determining the structural stability of soils. Bulk density is n,~,~,,~.t-;~,,~h, .-.,'-.,,',r'ol.~t,arl ~',,,;tk * h a r~rn-,-.ni,"...,~r4~nr', [ (~T TI~r'I"T~ ~ D C ' t ~ T 1Q~A ~. AI?"d l 1 0 [ ~ ,

SOIL STRUCTURE, DIFFERENT LAND USE 199

our results do not show any difference in the bulk density ofaerable and grass land soft. The reason could be the collction of soft clods for bulk density determination just after the cul- tivation of land. The determination of bulk density from core samples collected from cul- tivated soils after the crop harvest may show significant differences from those of grass land soils.

The data in Table 1 further show that the structural status of soft is dependent on the structural index used for its evaluation. For instance, on the basis of water-stable aggregates and MWD, grass lands, tea, and forest soils had the same st~ctural status, which was signifi- cantly better than those of aerable softs. But on the basis of bulk density and total porosity, only tea and forest soils had the best structure. BOEKEL (1963) and LOW (1972) also observed that in heavy clay soils total porosity was better structural index than the amount of water-stable aggregates obtained by wet-sieving. BRYAN (1971), while working on some English and Canadian soils, concluded that the efficiency of structural indices varied with the soft type. Hence, it is essential to use various indices simultaneously for the satisfactory evaluation of soil structure. In our study, on the basis of four indices the soft structure under different land uses follows the following trend:

Tea = Forest > Grassland > Aerable softs

4. CONCLUSION

These results clearly demonstrate the significant dependence of soil structure on land use. The land use which provides a continuous soil cover and avoids frequent soil manipu- lations, offers better opportunities for structural development. It is suggested to extend such studies to different agroclimatic zones in order to develop relation between soil structure and land use based upon different soil structural indices.

REFERENCES

BHUSHAN, L.S., VARADE, S.B. & GUPTA, C.P. (1973): Influence oftiUage practices on clod size, porosity and water retention. Indian Journal of Agricultural Sciences 43, 466-471.

BOEKEL, P. (1963): The effect of organic matter on the structure of clay soils. Netherlands Journal of Agricultural Sciences 11,250-263.

BRYAN, R.B. (1971): The efficiency of aggregation indices in the comparison of some English and Canadian Soils. Journal of Soil Science 22, 166-178.

CURTIS, R.O. & POST, B.W. (1964): Estimating bulk density from organic matter content in some forest soils. Soil Science Society America Proceedings 28, 285-286.

GREENLAND, D.J. (1971): Changes in nitrogen status and physical conditions of soils under pastures. Soils and Fertilizers 34, 237-251.

GRIEVE, I.C. (1980): The magnitude and significance of soil structural stability declines under cereal cropping. CATENA 7, 79-85.

HAMBLIN, A.P. & GREENLAND, D.J. (1977): Effect of organic constituents and complexing metal ions on aggregate stability of some East Anglian soils. Joumal of Soil Science 28, 410-416.

HEWlTr, J.S. & DEXTER, A.K (1980): Effects of tillage and stubble management on the structure of a swelling soil. Journal of Soil Science 31,203-215.

LOW, A.J. ( 1972): The effect of cultivation on the structure and other physical characteristics of grassland and aerable soils. Journal of Soil Science 23, 363-380.

PRIHAR, S.S. & HUNDAL, S.S. (1971): Determination of bulk density of soil clod by saturation. Geoderma 5, 283-286.

SAINI, G.K (1966): Organic matter as a measure of bulk density of soil. Nature 210, 1295-1296. SHARMA, J.S. & BISWAS, T.D. (1974): Role of different forms of phosphates in the mechanism of

soil aggregation. Journal of Indian Society of Soil Science 22, 6-12.

200 51-tARMA & AGGARWAL

VAN BAVEL, C.H.M. (1950): Mean weight diameter of soil aggregates as a statistical index of aggrega- tion. Soil Science Society of America Proceedings 14, 20-23.

VISWANATH, G.IC & PILLAI, S.C. (1978): Influence of superphosphate on the formation of water- stable aggregates. Journal oflndian Institute of Sciences 60, 1-8.

WILLIAMS, R.J.B. & COOKE, G.W. (1961): Some effects of farmyard manure and of grass residues on soil structure. Soil Science 92, 30-39.

YADAV, J.S.P. & SINGH, IC (1976): Effect of forest plantations on water-stable aggregates of soil. Journal of Indian Society of Soil Science 24, 363-368.

YODER, IL E. (1936): A direct method of aggregate analysis and a study of the physical nature of erosion losses. Journal of American Society of Agronomy 28, 337-351.

Addresses of authors: P.tC Sharma, Department of Agronomy, IRRI, P.O. Box 933 Manila, Philippines G.C. Aggarwal, Department of Soils, Punjab Agricultural University Ludhiana - 141004 (Pb.), India