Effects of Reduced Doses of Bromoxynil + 2, 4-D and Nitrogen Fertilizer on Wheat (Triticum aestivum L.) Yield in Competition with Common Mallow (Malva neglecta Wallr.)

Modeling fertilizer-herbicide relationship is helpful to minimize the competition of weeds with crops. The goal of present study was to develop the empirical models for predicting crop yield, number and weight of common mallow seed using integrated dose-response curves of herbicide and fertilizer application.

An experiment was conducted in split plot design based on randomized complete block design with three replications in Agricultural Sciences and Natural Resources University of Khuzestan in 2017 growing season. Experimental factors were N-fertilizer as main plot at 5 levels (0, 75, 150, 225 and 300 kg ha-1 of urea) and dose of bromoxynil+2, 4-D as sub plot at 5 levels (0, 0.25, 0.50, 0.75 and 100% rate of recommended dose (1.5 L ha-1)). Common mallow density (50 plant m-2) was fixed in all plots and wheat sowing density was 350 plant m-2. The wheat cultivar was Chamran 2. Spraying was carried out using a 20-liter rechargeable Matabi back Sprayer equipped with a nozzle (11003) and a pressure of 2 bar (calibrated based on 200 to 300 liters of water per hectare) in the post-emergence stage at the middle of the wheat tillering stage (6-4 The leaf of the common mallow). Half of the nitrogen fertilizer was applied at sowing stage and the other half was distributed in the middle of the wheat tillage stage. The plants were then cut at surface and dried in oven (75 °C) and weighted. The four parameters sigmoid model was used to assess wheat and common mallow yield response to herbicide reduced dose and N fertilizer. The three parameters power model was also applied to explain the change of mallow number and weight in response to reduced herbicide dose and different levels of N-fertilizer application.

Wheat grain yield increased in response to increasing herbicide dose and reducing the competitive ability of common mallow in different levels of urea fertilizer application. The grain yield was equal to 202, 277, 329, 408, 443 and 450 g m-2, when 300 kg of urea fertilizer ha-1 with 0.375, 0.60, 0.75, 1.05, 1.35 and 1.50 L ha-1 of the recommended dose of herbicide was employed, respectively. Moreover, the dose required to reduce 50% of the weed competition effects on wheat grain yield was decreasing in urea fertilizer levels. The results showed that the higher levels of urea fertilizer decreased wheat grain yield, but increased the number and weight of the common mallow seeds. The number of common mallow seeds was maximum for the higher levels of urea fertilizer and lesser doses of bromoxynil+2, 4-D, was minimum under low urea fertilizer consumption and the higher levels of bromoxynil+2, 4-D. The density of common mallow seeds under no-herbicide conditions ranged from 4.78 to 35.87 g m-2 for each urea fertilizer level. The number of common mallow seeds produced under no-herbicide application varied between 1915.95 and 16540.76 seeds per m-2 for each fertilizer level. However, in the case of higher doses of bromoxynil+2, 4-D, weight and seed number of common mallow showed a decreasing trend. Thus, under no-herbicide condition, common mallow produced much more seeds when higher N-fertilizer rates were applied. Application of 300 kg of urea ha-1 without herbicide application led to the highest common mallow seed number and weight and the lowest wheat yield. The greatest wheat yield (i.e. 515.40 g m-2) was obtained by consuming 225 kg of urea ha-1 along with 1 L ha-1 bromoxynil+2,4-D. In addition, the higher urea fertilizer levels reduced wheat grain yield, but increased the common mallow seed number and weight.

Increasing the competitive ability of weeds, application of high N-fertilizer rate results in a larger yield loss. However, herbicide application with the application of high N-fertilizer is highly likely to control weed, causing an increase in wheat yield. The combined model helps to lessen the herbicide and fertilizer application.