Relation of Cotton Growth and Yield to Minimum Leaf Water Potential1

Field studies were conducted over a 3 year period in the San Joaquin Valley of California to define the associations between minimum or midday leaf water potential (ψ 1 )and cotton ( Gossypium hirsutum L.) growth parameters, mainstem elongation and fiber growth, and to evaluate the suitability of using minimum ψ 1 as an index for irrigation scheduling. Locations on two soils, differing widely in water retention and transmission properties, were maintained for two of the test years. Mainstem elongation (E L ) was greatest after stress was alleviated by irrigation. E L (cm/day) was reduced linearly as minimum ψ 1 (bars) declined; the function E L = 5.08 + 0.200ψ 1 was derived from available observations. Mainstem elongation essentially stopped when minimum ψ 1 dropped to −24 bars. Fiber growth (elongation and weight increase) proceeded unchecked until ψ 1 reached ‐27 to ‐28 bars, when the growth rate decreased markedly, indicating that fiber growth is probably a preferred sink at high stress levels. Minimum ψ 1 declined linearly with time following irrigation. High yields were obtained when minimum ψ 1 was allowed to decline to about ‐19 bars before irrigating. Any response resulting from differential conditioning, from prior water stress, was not sufficient to detract from the usefulness of minimum ψ 1 as an index for scheduling irrigation.