Investigating interaction effect of different tillage methods, soil initial moisture level and trifluralin herbicide application time on weed control and cotton yield (Gossypium hirsutum L.)

This study was set up as a factorial split block design in RCBD layout with 4 replications at a research farm in south east of Ali Abad Katool district in 2013 to investigate different tillage methods (T), soil initial moisture (M) and trifluralin application (W) effects on weed control and cotton lint yield. The main factors were two tillage methods (disk plow (T1) and moldboard plow (T2)) in a factorial combination with two soil moisture levels at 24 cm soil depth (12-14% (M1) and 17-19% (M2)). The sub-factor consisted of six trifluralin herbicide application times (hand hoeing (W1), PPI application of trifluralin at 1.5 lit/ha rate at the time of the first irrigation plus the herbicide application rate of 1 lit/ha with irrigation (herbigation) six weeks after planting (W2), PPI trifluralin application at 1.5 lit/ha and the application at 1 lit/ha with soil incorporation by cultivator six weeks after planting (W3), trifluralin application at 2.5 lit/ha after planting and prior to irrigation (W4) PPI application of trifluralin at 2.5 lit/ha with soil incorporation(W5) and check treatment where no weed control was undertaken (W6)). The data from the experiment were subjected to variance analysis using SAS statistical software and means were compared with least significant difference (LSD) test at the 5% probability level.The results indicated significant differences amongst the main effects of treatments and their interaction for many of the measured traits in cotton. Slicing of interactions of soil initial moisture in each tillage level indicated that majority of difference between soil initial moisture levels was related to their response to tillage type and M2 in comparison to M1 was significantly superior in secondary mean weight diameter of soil aggregate, weed control efficiency (WCE) at the 4th and 8th week after planting as well as boll numbers per plant under disk plow. Dheyab (2017) reported that with increasing soil moisture and reducing the size of soil aggregates up to 30 cm depth, the effectiveness of chemicals in weed control increased significantly. Meanwhile it must be noted the existence of more soil moisture content in moldboard plows plots creates a wet and homogeneous substrate with high seed contact with soil that allows seeds to quickly germinate, leading to the uniform emergence of cotton seedlings. Under different M levels, W5 treatment resulted in the highest WCE and total lint yield in the 4th week since planting as compared to W2 and W3. The most significant and positive correlation coefficients among the studied traits was found between total lint yield and WCE at the 4th week after platning (R2=0.88**) and WCE at the 8th week after platning (R2=0.85**). The highest total lint yield was produced by W5 in different trifluralin application levels. In current study, among the different treatments, T2M2W5 with 3730 kg/ha gave the highest lint yield, which had no significant difference with treatments involving hand hoeing under different tillage types and soil initial moisture levels.