Alegría Cabrera

Influence of biochar amendments on the sorption-desorption of aminocyclopyrachlor, bentazone and pyraclostrobin pesticides to an agricultural soil.

The many advantageous properties of biochar have led to the recent interest in the use of this carbonaceous material as a soil amendment. However, there are limited studies dealing with the effect of biochar on the behavior of pesticides applied to crops. The objective of this work was to determine the effect of various biochars on the sorption-desorption of the herbicides aminocyclopyrachlor (6-amino-5-chloro-2-cyclopropyl-4-pyrimidinacarboxylic acid) and bentazone (3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide) and the fungicide pyraclostrobin (methyl 2-[1-(4-chlorophenyl) pyrazol-3-yloxymethil]-N-methoxycarbanilate) to a silt loam soil. Aminocyclopyrachlor and bentazone were almost completely sorbed by the soils amended with the biochars produced from wood pellets. However, lower sorption of the herbicides was observed in the soils amended with the biochar made from macadamia nut shells as compared to the unamended soil, which was attributed to the competition between dissolved organic carbon (DOC) from the biochar and the herbicides for sorption sites. Our results showed that pyraclostrobin is highly sorbed to soil, and the addition of biochars to soil did not further increase its sorption. Thus, addition of biochars to increase the retention of low mobility pesticides in soil appears to not be necessary. On the other hand, biochars with high surface areas and low DOC contents can increase the sorption of highly mobile pesticides in soil.

Availability of Triazine Herbicides in Aged Soils Amended with Olive Oil Mill Waste

Amendments are frequently added to agricultural soils to increase organic matter content. In this study, we examined the influence of alperujo, an olive oil mill waste, on the availability of two triazine herbicides, terbuthylazine and atrazine, in two different sandy soils, one from Sevilla, Spain, and the other from Minnesota. The effect of aging on herbicide sorption and bioavailability was also studied. Soils were amended with alperujo at a rate of 3-5% (w:w) in laboratory studies. Apparent sorption coefficients for the triazine herbicides were calculated as the ratio of the concentrations of each herbicide sequentially extracted with water, followed by aqueous methanol, at each sampling time. These data showed greater sorption of terbuthylazine and atrazine in amended soils as compared to nonamended soils, and an increase in the amount of herbicide sorbed with increasing aging time in nonamended soils. The triazine-mineralizing bacterium Pseudomonas sp. strain ADP was used to characterize triazine bioavailability. Less mineralization of the herbicides by Pseudomonas sp. strain ADP was observed in soils amended with alperujo, as compared to the unamended soils, and, despite the increase in sorption with aging in unamended soils, herbicide mineralization also increased in this case. This has been attributed to Pseudomonas sp. strain ADP first using alperujo as a more readily available source of N as compared to the parent triazines. In summary, addition of alperujo to the soils studied was shown to increase triazine herbicides sorption and hence to reduce its availability and potential to leach.

Terbuthylazine persistence in an organic amended soil

The aim of this work was to study the effect of the application of a solid waste from olive oil production (alperujo) on the movement and persistence of the herbicide terbuthylazine (N2-tert-butyl-6-chloro-N4-ethyl-1,3,5-triazine-2,4-diamine). An experimental olive grove was divided in two plots: (i) Plot without organic amendment (blank) and (ii) Plot treated with alperujo during 3 years at a rate of 17920 kg of alperujo ha− 1. Terbuthylazine was applied to both plots at a rate of 2 kg ha− 1 a.i. Triplicates from each plot were sampled at 3 depths (0–10, 10–20 and 20–30 cm), air-dried, remains of olive leaves, grass roots, and stones removed and sieved through a 5 mm mesh sieve. Terbuthylazine was extracted with methanol 1:2 weight:volume ratio, the extracts were evaporated to dryness, resuspended in 2 mL of methanol, filtered and anylized by high performance liquid chromatography (HPLC). Higher amounts of terbuthylazine were detected at each sampling depth in plots treated with alperujo. The increase in soil organic matter content upon amendment with alperujo slightly increased sorption, suggesting that other factors beside sorption affect terbuthylazine degradation rate in organic amended soils.

Imazamox-clay complexes with chitosan- and iron(III)-modified smectites and their use in nanoformulations.

BACKGROUND Imazamox is an ionisable herbicide, weakly retained and with high soil vertical mobility, that is used for the control of the root-parasitic plants Orobanche spp. A natural smectite (SW) modified with the biopolymer chitosan (Ch) or with Fe(3+) cation was assayed as adsorbent or carrier for imazamox controlled-release formulations (CRFs). RESULTS The greatest adsorption (74%) was observed for SWFe at high initial concentration (500 µM) and low pH (4.3). The interaction mechanism of imazamox on SWFe implies interlayer polar adsorption, followed by protonation of the imidazolinone ring, whereas ionic, polar and hydrophobic interactions seemed to occur in imazamox adsorption on SWCh. The herbicide release into water was inversely related to the strength of the imazamox-clay interactions and ranged in the first 10 min for imazamox-SWFe and imazamox-SWCh complexes from 27 to 75%, whereas commercial imazamox released 86%. The imazamox-SWCh weak complex (SWCh6 WC) showed similar herbicidal activity to the commercial formulation but produced a reduction of 15% in the total soil leaching losses and a reduction of 40% in the peak maximum concentration in soil column leachates. CONCLUSION The imazamox-clay weak complex (WC) of SWFe and SWCh and the strong complex (SC) with SWCh showed appropriate behaviour as nanopesticides or smart delivery systems to be incorporated in CRFs.

Effect of Carbonaceous Soil Amendments on Potential Mobility of Weak Acid Herbicides in Soil

Use of carbonaceous amendments in soil has been proposed to decrease potential off-site transport of weak acid herbicides and metabolites by increasing their sorption to soil. The effects of organic olive mill waste, biochars from different feed stocks, and humic acid bound to clay on sorption of 4-chloro-2-methylphenoxyacetic acid (MCPA), aminocyclopyrachlor, or indaziflam acid metabolite to soils with varying physical and chemical properties were determined. At natural agricultural pH soil levels, these chemicals are anionic and weakly sorbed to soils; sorption of the three weak acids on soil was in the order MCPA (K f = 0.1) 10,000×. While generalizations have been made that soil sorption of nonpolar, neutral, or weakly basic chemicals increases by the addition of different carbonaceous amendments, no such generalizations can be made for weak acids. More work on properties of these amendments, biochars in particular, and how they affect weak acid sorption is required.