Initial Storm Effects on Macropore Transport of Surface‐Applied Chemicals in No‐Till Soil

Abstract

Previous research has established that macropores can rapidly transmit water through soil. This observation has raised concern that macropores may also promote rapid movement of agricultural chemicals to groundwater. This is a particular concern for no‐till fields where lack of disruption by tillage can lead to the development of extensive macropore systems. In order to investigate the effect of initial rainfall on chemical transport, strontium bromide hexahydrate (SrBr2·6H2O) and atrazine (2‐chloro‐4‐ethylamino‐6‐isopro‐pylamino ‐s‐triazine) were surface‐applied to six 30 by 30 by 30 cm blocks of undisturbed soil obtained from a 25‐yr‐old, no‐till corn (Zea mays L.) field with evidence of well‐defined macropores attributable to earthworm activity. Half of the blocks then received a 1‐h 5‐mm simulated rain, which did not produce percolate. Two days later, the blocks received a 0.5‐h 30‐mm simulated rain, followed by another 0.5‐h 30‐mm rain 1 wk later. The remaining blocks received only the two 30‐mm events. An average of 12% of the applied water passed through all the blocks during and shortly after the first 30‐mm rain. Bromide, Sr, and atrazine losses in this percolate were 7, 10, and 2 times less, respectively, from blocks that received the 5‐mm rain than from blocks not receiving this initial, light rain. The second 30‐mm rain on the blocks not receiving the initial 5 mm produced 1.6× more percolate than the first 30‐mm rain. Yet, transport and flow‐weighted average concentrations of Br, Sr, and atrazine were all reduced. These results indicated that the first storm after application can move solutes into the soil matrix, thereby reducing the potential for transport in macropores during subsequent rainfall events.

Statistical screening for descriptive parameters for pesticide occurrence in a shallow groundwater catchment

“…-Whilst a prerequisite for estimation of overall contamination potential, in more detail, relatively more precipitation both before and after pesticide application may serve to decrease resultant groundwater concentrations and thus likelihood for detection. Dilution, increased run-off, decreased soil matrix retainment (Shipitalo et al, 1990) and decreased top-soil cracking (Brown et al, 1995) are potential explanations. More and higher-resolution studies of the effects of precipitation on pesticide contamination potential of groundwater in different environments and in relation to actual pesticide use are needed in order to be able to better and more accurately account for the resultant effects in terms of risk assessment of pesticide contamination of groundwater on different scales.…”

“…Other studies who have reported relatively less pesticide transport from wet than from dry soils have further suggested increased soil matrix incorporation and retainment in relatively wetter soils (Shipitalo et al, 1990), and increased top-soil cracking allowing for increased downward flow of water and associated solutes during relatively drier periods of time (Brown et al, 1995) as plausible explanations. It could also be the case that increased run-off in relation to greater precipitation amounts could result in decreased groundwater contamination potential.…”

“…Tiktak et al, 2004). However, on a more detailed note, it might be that dilution and run-off in relation to relatively larger amounts of precipitation, enhanced soil matrix incorporation and retainment in relatively wetter soils (Shipitalo et al, 1990), as well as increased top-soil cracking allowing for increased downward transport of water and associated solutes during relatively drier periods of time (Brown et al, 1995) need to be considered in terms of contamination potential.…”

Effects of soil moisture and treatment volume on bentazon mobility in soil

“…The opposite was observed when studying mobile herbicides' (isoproturon and mecocrop) transfer through a loamy clay soil (Brown et al, 1995a). In a soil column experiment, Shipitalo et al (1990) pointed out the effect on solute (bromide, strontium and atrazine) availability to transfer of slight precipitation occurring prior to heavy rainfall. Laboratory studies have also displayed the variability of pesticide movement depending on the humidity level of the soil (Geissbuhler et al, 1963;Green et al, 1968).…”

Agricultura irrigada e o licenciamento ambiental

“…Esse uso intensivo, embora proporcione uma otimização econômica de uso do capital investido pelo produtor, acarreta algumas conseqüências que terminam por causar seqüelas ao meio ambiente, quais sejam: (i) maior quantidade de agro-químicos por hectare ano (ALBUS; KNIGHTON, 1998;NOLDIN et al, 2002), (ii) maior compactação de solo, pelo maior tráfego de máquinas e pelo impacto da gota de irrigação (AHUJA; LEHMAN, 1983;SHIPITALO et al, 1990) com conseqüente aumento no escorrimento superficial e do processo erosivo, (iii) maior incidência de pragas e doenças e seleção de populações de pragas resistentes aos pesticidas, o que aumenta a intensidade de uso dos mesmos, em um ciclo vicioso.…”