Effects of time and duration of competition between rice (Oryza sativa L.) and Heteranthera reniformis Ruiz et Pavon
1996
Vescovi, F.D. | Tano, F. | Sparacino, R. | Ferro, R. | Riva, N. (Universita degli Studi di Milano (Italy). Istituto di Agronomia)
An experimental trial has been carried out in small basins in order to study the effects of the duration and period of competition, in rice weeded with Heteranthera reniformis. Extending the duration of the competition between rice and Heteranthera reniformis from the seeding time (DCT), rice grain yield per basin decreased following a logistic model (equation Y=a(1-bx/(1+bx/c))). Yield reductions increased till 45 days after rice emergence. Longer duration of Heteranthera reniformis competition did not substantially lead to any further grain yield loss. Also grain yield per panicle and number of kernels per panicle were described by the same logistic model. Extending the weed-free period (WFP) from seeding to harvest, grain yield and the other yield components increased following a hyperbolic model (equation Y=a/(1+b (e exp. cx))). Grain yield/basin did not significantly improve any more for longer weed-free periods after the first 15 days. A critical period (CP) in which weeding should take place to restrict losses to below an economically acceptable level can be suggested. The curves can also be used to give a prediction of the likely financial loss per unit of time caused by a delay in weeding
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