Gutstein, Y.

The type of relationship between yield of seed-cotton and plant populations ranging from 1 to 21 plants per m2, was investigated in several cultivars of the Gossypium hirsutum L. and G. barbadense L. species, under irrigated and dryland conditions over several seasons, localities and dates of sowing The simple and quadratic equations and the simplified exponential reciprocal expression, as proposed by Holliday and by Bleasdale, respectively, similarly and very adequately described the investigated relationship at the plant level over the whole range of populations tested. The θ{symbol}-constant of Bleasdale's equation exhibited a high degree of cultivar specificity. In the dryland experiments its intercultivar values were linearly positively correlated with estimated maximum yields of seed-cotton per unit area. At the unit area level the estimated relationship was of two types: asymptotic and parabolic. It actually was dynamic in type and assumed transient forms throughout the boll-opening period, generally being parabolic at first and asymptotic at later stages. The ultimate response type exhibited a great intercultivar variability and cultivar constancy, being asymptotic in Acala 4-42 and Acala 1517 C and parabolic in Coker 100 W and in two Pima-type cultivars. Environmental growth factors enhancing prolific vegetative growth during the reproductive phase deviated from a specific asymptotic response pattern to a parabolic type. The estimated optimum plant density of the parabolic response types ranged between 4.0 and 5.7 plants per m2. This range was extended by an average of 0.7 plants per m2 when 5% of the maximum yield, estimated for asymptotic types, was discounted. The top estimated maximum yields were 1940 and 4600 kg seed-cotton per ha in the dryland and irrigated environments, respectively. © 1973 Dr. W. Junk B.V. - Publishers.