Biocalcification: the biological accumulation of CaCO3 in rice soils

Lowland rice cultivation can enhance the proliferation of snails resulting in the accumulation of calcium carbonate (CaCO3) in the topsoil. Frank Moormann and Nico Van Breemen, well-known Dutch pedologists, first observed this phenomenon in Central Luzon, Philippines, while visiting the experimental sites of the International Rice Research Institute in the 1970s. H.U. Neue, head of the Soils Department of IRRI at the time, encouraged this writer to investigate the phenomenon. Our research revealed that such biological accumulation of CaCO3 which we named biocalcification, occurs in several rainfed and irrigated rice-growing areas in the Philippines (Asio, 1987; Asio and Badayos, 1998).

The figure below shows the proposed generalized model of biocalcification in rice fields. It consists of two stages. Stage 1 is on the proliferation of snails which is generally dependent upon the calcium content of the soil or irrigation water. Moormann et al. (1976) suggested that calcium, of which some is present in the irrigation water as Ca(HCO3)2, is taken up by the snails and transformed into shells which in turn form the source of the free CaCO3 present in the soil surface. Thus, calcium-rich irrigation waters favor snail proliferation in soils regardless of calcium content and origin. On the other hand, calicum-poor irrigation waters would only promote snail abundance if the soils are rich in calcium like those formed from basic parent materials. In rainfed areas,bunding soils rich in calcium could also enhance snails proilferation or from direct transport of shells from irrigation ditches.

Stage II starts with the accumulation of shells. Dissolution of shells in water normally takes years (CaCO3 is slowly soluble in pure water) particularly in non-acid soils. But in rice soils chemical dissolution of the shells is enahnced by the carbonic acid formed by the reaction between carbon dioxide coming from organic matter decomposition, and water. Moreover, the physical disintegration of the shells is hastened by alternate dry and wet condition which commonly occurs in rice fields, and by field operations particularly puddling. The end result is the accumulation of free CaCO3 and the rise of pH in the soil surface. This condition in turn promotes the proliferation of snails.

Among the soil fertility effects of biocalcification include an increase in the availability of calcium and magnesium but a decrease in the availability of phosphorus and zinc to the rice plant.

References

Asio VB. 1987. Biocalcification and siltation in paddy soils. MSc thesis, UP Los Banos/International Rice Research Institute, Laguna.

Asio VB and Badayos RB. 1998. Biological accumulation of calcium carbonate in some lowland rice soils in the Philippines. The Philippine Agriculturist 81: 176-181.

Moormann FR, Tinsley RL and Van Breemen N. 1976. Notes on a visit to multiple cropping project in Pangasinan. Mimeographed papers (unpublished), IRRI, Laguna, 4pp.

Native tree species affect changes in chemical properties of a highly weathered soil

Contributed by Juvia P. Sueta, University of Göttingen, Germany

There is growing interest in the use of indigenous tree species in reforestation programs at present. Thought to be well adapted to their native areas, indigenous tree species are able to survive well and strongly influence the soil. However, the lack of published data on their performance often limits their full use and casts uncertainties on whether they have beneficial or negative impacts on the soil. To better understand the role of trees in improving soil quality, an understanding of how nutrient availability changes with time is important (Kelly and Mays, 1999).

In this study which we conducted at the VSU-GTZ reforestation project site (see photo) in Mt. Pangasugan, Leyte, Philippines, we looked at the influence of two native tree species- Parashorea plicata and Dipterocarpus warburgii- on the nature and rate of changes on the chemical properties of a highly weathered soil following a change in land use from Imperata grassland to plantation of indigenous tree species. Monthly sampling of carefully selected plots in two sites (dominated by native or indigenous species) was carried out to evaluate temporal as well as spatial variations in important soil chemical properties. In addition, rates of litter decomposition of the two species were also investigated on the sites.

We found significant monthly variations of soil pH, organic matter content, total N and available P. Significant differences between sites were also observed for organic matter, total N as well as Ca and Mg contents suggesting individual tree species effects. For most of the soil properties evaluated, irregular fluctuations at certain times of the year characterized by periods of high and low availability. This suggests a highly dynamic nutrient cycling within the system.

The influence of these native tree species could be attributed to its litter contribution to the soil. In both sites, some centimeters thick of organic layer could be observed on the soil surface throughout the year. An evaluation of decomposition revealed high rates for both species. This result suggests that aside from being dynamic, the cycling of nutrients also tends to be efficient. This efficient cycling of nutrient may also help explain why these native tree species appeared to grow well despite the inherently low levels of nutrients in this old, highly weathered soil.

References

Kelly JM and PA Mays. 1999. Nutrient supply changes within a growing season in two deciduous forest soils. Soil Sci Soc Am J 63: 226-232.

Sueta JP, VB Asio and AB Tulin. 2007. Chemical dynamics of a highly weathered soil under indigenous tree species in Mt. Pangasugan. Annals of Tropical Research 29: 73-89.