Effects of root zone volume and plant density on the vegetative and reproductive development of cotton

Abstract Vegetative and reproductive development of cotton ( Gossypium hirsutum L.) was affected by both planting density and root zone volume. Shoot and root growth per plant were considerably reduced by either increasing plant density from 6 to 10 per m 2 , or by decreasing root zone volume in pots, from 10 to 2 l. Growth was reduced to a greater extent by a decrease in root zone volume than by an increase in planting density. Water tension in the pots was maintained in the range of 0.0–0.15 MPa by frequent irrigation pulses. Restriction of roots to 2 l resulted in development of compact plants characterized by short branches and high boll density. In spite of the reduced shoot growth of plants in smaller pots their flowering rate, over a period of 60–100 days from sowing, was similar to that of plants in larger pots. Earliness of flowering and boll opening was observed in plants grown in the smaller root zone volume. Increased plant density reduced the average yield (seed cotton) per plant but increased yield per unit soil area in both root zone volumes. At both plant densities, the proportion of the total assimilate production allocated to the bolls was greater with the smaller root zone volume and vegetative growth was more restricted. It is concluded that restriction of root zone volume may be used to accelerate flowering and harvest. It may also affect the internal distribution of assimilates between the vegetative and reproductive organs resulting in a preferential translocation of assimilates to the bolls.