Abstract
ABSTRACT The residue of imidazolinone herbicides in soil can be detrimental to soybean cultivation in rotation with Clearfield® rice. Thus, this research aimed to evaluate the ryegrass phytoremediation capacity on the imazapyr+imazapic residue in the soil in two soil moisture conditions in the off-season, and the effect on soybean growth in the next growing season. Two experiments were conducted between 2016 and 2017 in Santa Maria, Rio Grande do Sul state, Brazil. It was used the randomized block design in a 3 × 2 factorial. The first factor being the residue in the soil of 0, 210 and 420 g c.p.·ha–1 of the formulated mixture of the herbicides imazapyr+imazapic(525 + 175 g a.i.·kg–1) applied to rice in the 2015/2016 growing season, and the second factor being the presence or absence of ryegrass in the off-season. One experiment was conducted under soil moisture above 70% of field capacity in the off-season, and the other under ambient condition of soil moisture. The soil residue of the application of 420 g c.p.·ha–1 of the imazapyr+imazapic herbicides performed129 days before planting caused phytotoxicity and reduced dry matter of ryegrass under high soil moisture condition in the off-season in irrigated rice areas. Soybean, when planted 359 days after application, has its initial root and shoot growth affected by the residue of 210 and 420 g c.p.·ha–1 rates in high soil moisture condition in the off-season, regardless of ryegrass cultivation during the same period. However, grain yield is not affected.
Highlights
The Clearfield® system has been widely used in irrigated rice fields to control weeds such as weedy rice and barnyardgrass (Sudianto et al 2013; Kraehmer et al 2016)
The first factor being the residue in the soil of 0, 210 and 420 g c.p.·ha–1 of the formulated mixture of the herbicides imazapyr+imazapic (525 + 175 g a.i.·kg–1) applied to rice in the 2015/2016 growing season, and the second factor being the presence or absence of ryegrass in the off-season
Soybean, when planted 359 days after application, has its initial root and shoot growth affected by the residue of 210 and 420 g c.p.·ha–1 rates in high soil moisture condition in the offseason, regardless of ryegrass cultivation during the same period
Summary
The Clearfield® system has been widely used in irrigated rice fields to control weeds such as weedy rice and barnyardgrass (Sudianto et al 2013; Kraehmer et al 2016). The introduction of soybean into areas traditionally cultivated with irrigated rice from the Clearfield® system is an alternative to reduce damage from the occurrence of resistant weeds in these growing areas. Imidazolinones have high persistence in the soil, which may compromise the success of crop introduction in rotation to the tolerant rice (Pinto et al 2009a; Souza et al 2016). The persistence of these herbicides is regulated by their sorption, which in turn is influenced by temperature and moisture, solution pH, organic matter content and soil texture (Kraemer et al 2009b). Imazaquin and imazethapyr, the field half-life is 25-142, 60 and 60-90 days, respectively (Shaner 2014)
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