02168naa a2200169 a 450000100080000000500110000800800410001910000210006024501680008126000090024952016270025865000160188565000130190165000140191470000170192877300530194512795832025-01-27       1990    bl uuuu     u00u1 u    #d1 aMCGONIGLE, T. P.  aEffect of degree of soil disturbance of mycorrhizal colonization and phosphorus absorption by maize in growth chamber and field experiments.h[electronic resource]  c1990  aPrior studies have established that phosphorus absorption by maize from undisturbed soil is greater than from soilwhich has been disturbed since the previous period of growth. Those experiments were conducted undercontrolled conditions and with only two disturbance treatments, namely disturbance of the soil by hand sufficientthat it will pass a 5 mm sieve, and no disturbance at all. We present here two experiments in which additionaltreatments of intermediate degrees of disturbance are included.In a growth chamber experiment, cutting the soil into 1, 2 or 4 cm cubes reduced the phosphorus absorptionand shoot dry matter, but the reduction was not as great as that after hand disturbance of the soil. In a fieldexperiment, the phosphorus absorption and shoot dry matter found in a conventional tillage and no-till treatmentswere less than in hand-planted no-till plots, but greater than with severe soil disturbance. In both experimentsincreases in shoot dry mass and shoot phosphorus concentration in the less disturbed treatments were notaccompanied by an increase in mycorrhizal colonization. This is inconsistent with earlier studies in whichcolonization was greater in undisturbed soil.Since it has now been demonstrated that increased colonization is not a necessary component in the processwhereby lack of disturbance results in improved plant performance, the role of mycorrhizas in this effect shouldbe reconsidered. If mycorrhizas are important in this respect then this can only be by means of changes in theexternal mycelium. However, without experimental confirmation this interpretation is speculative.  aFertilidade  aFósforo  aMicorriza1 aEVANS, D. G.  tNew Phytologistgv. 116, n. 4, p. 629-636, 1990.