THE ROLE OF MACROPORES IN THE CULTIVATION OF BELL PEPPER IN SALINIZEDSOIL

The hypothesis tested in this paper is that, because the freshest wate r occurs in the largest soil pores (macropores), plants of low to mode rate transpiration rate can survive in salinized soil because they pre ferentially extract water from macropores. The hypothesis predicts tha t a plant growing in a macroporous soil should have greater growth und er a given salinity treatment than a similar plant growing in a soil w ith the same mineralogy but without macropores. This hypothesis was te sted by growing bell pepper (Capsicum annuum) in the greenhouse in pot s filled with either a commercial fritted clay (a highly macroporous s oil) or the same clay ground to a finer texture and sieved to remove m acropores and produce a microporous soil. The pots sat in pans filled with salt water. Half of the pots were irrigated once a day with fresh water and the other half received no fresh water. Plants growing in t he macroporous soil had greater growth for a given salinity treatment than the plants growing in the microporous soil under both the irrigat ed and non-irrigated conditions. Under the irrigated condition for the highest salinity treatment, the non-reproductive fresh weight per pla nt, total dry weight per plant and fruit fresh weight per plant was 11 4 g, 12 g and 50 g, respectively, for the macroporous soil and 47 g, 4 .5 g and 5 g, respectively, for the microporous soil. The results of t his study provide evidence to suggest that a better understanding of w hat constitutes a 'good' structure in a saline soil may aid us in our efforts to improve the management of saline soils. We suggest that it may be possible to increase the agricultural production on salinized l and by no-tillage agriculture which preserves macroporosity. Possible obstacles could be the tendency of field saline-sodic soils to swell a nd the unavailability of relatively fresh irrigation water in areas wi th saline soils.