Rupngam Thidarat, Messiga Aimé J, Karam Antoine
Agassiz Research and Development Centre, Agriculture and Agri-Food Canada, 6947 Highway 7, P.O. Box 1000, Agassiz, BC V0M 1A0, Canada.
Soils and Agri-Food Engineering Department, Laval University, 2425 Rue de l'Université, Québec, QC G1V 0A6, Canada.
Heliyon. 2023 Feb 7;9(2):e13502. doi: 10.1016/j.heliyon.2023.e13502. eCollection 2023 Feb.
Understanding how extended excess soil moisture exacerbated by extreme weather events affects changes in iron (Fe) chemistry is crucial for assessing environmental risk associated with soil phosphorus (P) in high P soils. The objective of our study was to assess the effects of three soil moisture regimes (field capacity, water saturation, and waterlogging), two Fe nitrate level (Fe nitrate addition and no Fe nitrate addition), and the duration of incubation (0, 3, 7, 14, 21, 28, 35, 49, 63, 90, and 120 days) on the (i) reduction of ferric (Fe) to ferrous (Fe) iron, (ii) solubility of soil P, and (iii) soil microbial biomass and greenhouse gas emissions. Surface soils (0-20 cm) were collected from a maize silage field located in the Fraser Valley (British Columbia, Canada). Decreased redox potential (Eh) of 155 mV in waterlogged soils coincided with the reduction of Fe to Fe of about 1190 mg kg and an increase in soil pH of 0.8 unit compared to field capacity regime at 120 days after pre-incubation ( < 0.001). The increase of pH is due to the microbially-mediated reduction of metal cations which consumes H cations. Water-extractable P (Pw) concentrations increased with increasing soil moisture regimes from 1.47 to 2.27, and 2.58 mg kg under field capacity, water saturation, and waterlogged regime respectively. Mehlich-3 extractable P concentrations significantly decreased from 196 to 184 and 172 mg kg under water saturation, field capacity, and waterlogged regime respectively. Concomitant to Pw concentrations, microbial biomass carbon and nitrogen as well as DOC, CO and NO emissions increased with increasing soil moisture regimes. The Fe nitrate addition had an inhibitory effect on Fe reduction, Pw concentration at the first 35 days, and DOC but a stimulating effect on NO emission. A high NO emission at the first 63 days, CO emission after 35 days, and a non-remarkable concentration of Fe at the first 63 days with Fe nitrate addition under waterlogged soil suggests that NO is more preferable than Fe as an electron acceptor. Our results showed that soils maintained under extended anoxic conditions could increase the soluble and available P and subsequent risk of P transport to surface and drainage waters, whereas Fe nitrate addition could minimize or delay this effect.
了解极端天气事件加剧的长期土壤水分过剩如何影响铁（Fe）化学变化，对于评估高磷土壤中与土壤磷（P）相关的环境风险至关重要。我们研究的目的是评估三种土壤水分状况（田间持水量、水饱和及涝渍）、两种硝酸铁水平（添加硝酸铁和不添加硝酸铁）以及培养持续时间（0、3、7、14、21、28、35、49、63、90和120天）对（i）三价铁（Fe）还原为二价铁（Fe）、（ii）土壤磷的溶解度以及（iii）土壤微生物生物量和温室气体排放的影响。表层土壤（0 - 20厘米）取自加拿大不列颠哥伦比亚省弗雷泽谷的一个玉米青贮田。与预培养120天后的田间持水量状况相比，涝渍土壤中氧化还原电位（Eh）降低155毫伏，同时铁还原为亚铁约1190毫克/千克，土壤pH值升高0.8个单位（P < 0.001）。pH值升高是由于微生物介导的金属阳离子还原消耗了氢离子。水溶态磷（Pw）浓度随着土壤水分状况的增加而升高，在田间持水量、水饱和及涝渍状况下分别为1.47、2.27和2.58毫克/千克。Mehlich - 3可提取磷浓度在水饱和、田间持水量及涝渍状况下分别从196显著降至184和172毫克/千克。与Pw浓度相伴，微生物生物量碳和氮以及溶解有机碳、一氧化碳和一氧化氮排放随着土壤水分状况的增加而增加。添加硝酸铁对铁还原、前35天的Pw浓度和溶解有机碳有抑制作用，但对一氧化氮排放有促进作用。在涝渍土壤中添加硝酸铁时，前63天一氧化氮高排放、35天后一氧化碳排放以及前63天铁浓度无显著变化，这表明一氧化氮比铁更适合作为电子受体。我们的结果表明，长期处于缺氧条件下的土壤会增加可溶性磷和有效磷以及随后磷向地表水和排水水体迁移的风险，而添加硝酸铁可以最小化或延迟这种影响。
