Soil Moisture Effects on Root Growth and Phosphorus Uptake by Corn1

Abstract

AbstractWhile the effects of soil moisture and P level on corn (Zea maysL.) root growth and P uptake have been measured, the extent each of the mechanisms involved in P uptake is affected by soil moisture has not been determined. The objective of this study was to investigate the effect of soil moisture on each of the parameters used in a mechanistic mathematical model to predict P uptake by corn. The effect of volumetric soil moisture, 0.22 (M0), 0.27 (M1), and 0.32(M2), the water held at potentials of −7.5, −33, and −170 kPa, respectively, and three soils (S0and S1, Raub, fine‐silty, mixed, mesic Aquic Argiudolls and S2, Chalmers, fine‐silty, mixed, mesic Typic Haplaquolls, silt loams) obtained from plots having different longtime P histories, on root growth and P uptake by corn was investigated in a series of pot experiments in a controlled climate chamber. As soil moisture was raised from M0to M1, total plant weight increased by 13 to 43%, total P uptake by corn increased by 55 to 70%, and corn root length increased 41 to 52% with the three soils for measurements made at 28 days. Raising soil moisture content further from M1to M2, in contrast, decreased total plant weight by an average of 13%, total P uptake by an average of 15%, and root length by an average of 16% at 21 days. Root surface area and mean P influx, which both increased as soil P increased, were correlated with P uptake. These correlations suggest that increasing soil P increases P uptake, both by increasing P influx and root growth. Raising soil moisture from M0to M1increased P uptake by increasing root growth. Soil moisture did not significantly (P<0.05) affect P influx. Using data for three moisture levels on three soils, predicted P uptake (y) in µmol pot−1calculated with the simulation model for corn grown for 7, 14, and 21 days agreed with observed P uptake (x) (y= 0.78x+ 10.93; r= 0.975**, significant at the 0.01 level).