Combining Effect of Lower Rate of Trifluralin Herbicide and Sunflower residues on mycorrhizal association with cowpea and soil nitrification

Abstract

Field and laboratory experiments were conducted during the course of study to
test if the sunflower residues along or with 50% full rate of trifluralin herbicide has
any impact on mycorrhizal association and soil nitrification which are important
processes for improving growth and productivity of crops. Results revealed that
incorporation of sunflower residues significantly increased spores number at 2, 4
and 6 weeks of residue decomposition compared to control treatment. However,
when the residues applied in combination with reduced rate of trifluralin herbicide,
sporulation was appreciably decreased by sunflower residues at 3 t ha-1 but it
remains almost the same at 6 t ha-1 rate of residues. Field soil amended with label
rate of trifluralin showed lower sporulation during the first six weeks from
beginning of the experiment. Colonization rate was appreciably increased by
application of sunflower residues at 6 t ha-1 and decreased by label rate of herbicide
and weed free treatments. The highest colonization intensity (83.4) was recorded by
application of sunflower residues at 6 t ha-1, followed by treatment of sunflower
residues at 3 t ha-1 (72.2). Label rate of herbicide recorded the least colonization
intensity (54.4). Incorporation of sunflower residues at 3 and 6 t ha-1 significantly
reduced nitrification rate at all incubation periods in comparison to control.
However, when the residues was applied along with the reduced rate of herbicide,
nitrification rate was significantly increased over the sole application of sunflower
residues at all incubation periods except 4 and 8 days incubation periods but it
remains below control. Soil sterilization treatment showed the least nitrification rate
at all incubation periods. In all bioassay experiments, the amounts of NH4
+
converted
in the incubated soil was significantly correlated with the amount of NO3
- produced
over the periods of incubation suggesting that soil incubation is efficient method that
can be used for measuring nitrification process.It can conclude Sunflower residues
amended in field soil was found to provide a good medium for growing Glomus
mosseae fungus and best way to inhibited nitrification rate and thus may contribute
in alleviating losses of NO3 used by plants and reducing the environmental
pollution.