Variations in concentrations of N and P forms in leachates from dried soils rewetted at different rates

Abstract

The rate at which dried soils are rewetted can affect the quantities and forms of nutrients in leachates. Both dried and moist replicated (n03) samples of two contrasting grassland soil types (clayey vs brown earth) were irrigated during laboratory experiments with identical total amounts of water, but at different rates, ranging from 0 h, increasing by 30-min increments up to 4 h, and additionally a 24-h rewetting rate. Total P concentrations in leachates from dried samples of both soils generally decreased as rewetting rate increased, ranging from 2,923±589 μg P L −1 (0.5 h rewetting rate) to 731± 46.0 μg P L −1 (24 h, clayey soil) and 1,588±45.1 μg P L −1 (0.5 h) to 439±25.5 μg P L −1 (24 h brown earth). Similar patterns in concentrations occurred for molybdate reactive P (MRP), although concentrations were generally an order of magnitude lower, indicating that the majority of the leached P was probably organic. The moist brown earth leached relatively high concentrations of MRP (maximum 232±10.6 μg P L −1 , 0.5 h), unlike the moist clayey soil (maximum 20.4±10.0 μg P L −1 , 0 h). The total oxidised N concentrations in leachates were less affected by rewetting rate, although longer rewetting rates resulted in decreased concentrations in leachates from the dried samples of both soils. The difference in responses to rewetting rates of the two soils is probably due to differences in the fate of the microbial biomass and adsorption properties in the soils. Results show that soil moisture could be an important factor in regulating nutrient losses and availability, especially under changing patterns of rainfall predicted by future climate change scenarios.

Responses of carbon, nitrogen and phosphorus to two consecutive drying–rewetting cycles in soils

“…More specifically, the reduction in moisture in the DRW treatment resulted in an increase in mineral N, both of and TON forms. The increase in after 7 might be due to the mineralization of SOM or also to the release of from the lysis of microbial cells after rewetting ( e.g ., Blackwell et al., ). Likely, the increase of was due to the disruption of soil aggregates and loss of physical protection of SOM ( Adu and Oades , ).…”

“…Immediately after sampling, the soil was prepared as described by Blackwell et al. (), Sun et al. (), Iovieno and Bååth (), who tested the variations of nutrients, microbial community composition, and bacterial growth, respectively, in dried and rewetted soils.…”

“…Blackwell et al. (), investigating the effect of the rate of rewetting dried soils on nutrient concentrations in leachate, reported a little effect of 0‐ and 4‐h treatments on the total oxidized N concentrations in leachates from dried soils, whereas in the 24‐h rewetting rate resulted in a significant decrease. Moreover, Blackwell et al.…”

“…Moreover, Blackwell et al. () reported a decrease in the concentrations of P compounds in leachates from dried soil with a more rapid rewetting rate, possibly as a result of increased microbial activity over time and changing soil physical properties. Moreover, Nguyen and Marschner () found that drying and rewetting events resulted in a rapid increase in both MBP and labile organic P, and these effects were exacerbated in soils with high organic matter content.…”

Phosphate stable oxygen isotope variability within a temperate agricultural soil

“…Given the negligible contribution of bedrock apatite PO 4 it is assumed that the bulk of the HCl PO 4 is comprised of PO 4 adsorbed to soil particles and microbial PO 4 . The soils in this region have been shown to have a high microbial biomass P content, which in turn has been shown to be released upon drying and rewetting through cell lysis (Blackwell et al, 2013). The amounts of HCl PO 4 measured are very similar to the levels of microbial P reported by Blackwell et al (2013) and therefore we assume that HCl PO 4 in these soils represents, in large part, adsorbed soil PO 4 and intracellular microbial PO 4 , the latter normally exceeding the former (Blackwell et al, 2010).…”