Facilitated transport of ferrihydrite with phosphate under saturated flow conditions.

With increasing phosphate (P) entering the environment during agricultural application, the subsurface flow of particular P has been recently discussed as a vital P transport pathway. Iron (oxyhydr)oxide colloid-facilitated P transport is critical for iron and P biogeochemical processes in the subsurface. This study investigated the ferrihydrite colloid-facilitated P transport through adsorption and column experiments under different P concentrations and three pH conditions. Increased P loading on ferrihydrite colloids decreased the transport of ferrihydrite colloids (< 8.0%) under acid conditions through pore straining and irreversible attachment. Under neutral and alkaline conditions, ferrihydrite colloids exhibited more negative surfaces and smaller diameters with increasing P, which further enhanced ferrihydrite colloid transport (maximum to 95.6%). Ferrihydrite colloid-facilitated P transport was limited under acid conditions, and it was 10% - 57% enhancement under neutral and alkaline conditions with increasing P adsorption. Under neutral conditions, ferrihydrite colloid-facilitated P transport was strongest (maximum to 68.84%) because of its stronger ferrihydrite colloid transport than under acid conditions and larger P adsorption capacity than under alkaline conditions. Our findings indicate that the facilitated transport of ferrihydrite colloids in the presence of P may be appreciable in iron and phosphate-rich soil and subsurface systems, which is essential for evaluating the fate of iron and iron-facilitated P and potential environmental risks of P transport in the subsurface.

Processed animal manure improves morpho-physiological and biochemical characteristics of Brassica napus L. under nickel and salinity stress.

Soil contamination with readily soluble salts and heavy metals is a major challenge concerning sustainable crop production. The use of organic wastes in agriculture not only helps in waste reduction but also acts as a soil conditioner and bio-stimulant for enhancing crop growth. In this regard, a pot experiment was conducted to investigate the effect of raw and processed animal manure (AM) on the growth, yield, and physicochemical parameters of Brassica napus L. developed under salinity and Ni stress. The experiment comprised two salinity levels (1.05 and 8 dS m-1), two Ni levels (0 and 50 mg kg-1), and two types of AMs (raw and processed at a rate of 2% w/w). A control treatment without AM incorporation was also included. In results, the application of AM markedly increased the growth and yield of B. napus under Ni and salinity stress; at the same time, it improved the physiological and chemical parameters of the said crop. Similarly, incorporation of processed AM significantly improved nutrient uptake and decreased Na/K ratios in the shoot and grain under the different stress conditions, as compared to the control. Likewise, Ni uptake in the grain, shoot, and root samples was also significantly reduced under the AM treatment. Also, the application of AM significantly reduced the daily intake of metal (DIM) index and the health risk index (HRI) values under the different stress conditions, as compared to the control. In conclusion, the application of processed AM constitutes an effective agricultural strategy to alleviate the adverse effects of Ni and salinity stress on growth, physiology, and yield of B. napus, thus resulting in enhanced productivity, as well as reduced risks associated with human health.

Evaluating the Contribution of Growth, Physiological, and Ionic Components Towards Salinity and Drought Stress Tolerance in Jatropha curcas.

Salinity and drought stress, singly or in combination, are major environmental menaces. Jatropha curcas L. is a biodiesel plant that can tolerate long periods of drought. However, the growth performance and stress tolerance based on physical, chemical, and physiological attributes of this plant have not yet been studied. To address this question, J. curcas seedlings were grown in a completely randomized design in plastic pots filled with soil to evaluate the effects of salinity and drought stresses on growth, ionic composition, and physiological attributes. The experiment consisted of six treatments: control (without salinity and drought stress), salinity alone (7.5 dS m-1, 15 dS m-1), drought, and a combination of salinity and drought (7.5 dS m-1+ Drought, 15 dS m-1+Drought). Our results revealed that, compared with the control, both plant height (PH) and stem diameter (SD) were reduced by (83%, 80%, and 77%) and (69%, 56%, and 55%) under salinity and drought combination (15 dS m-1+Drought) after three, six, and nine months, respectively. There was 93% more leaf Na+ found in plants treated with 15 dS m-1+Drought compared with the control. The highest significant average membrane stability index (MSI) and relative water content (RWC) values (81% and 85%, respectively) were found in the control. The MSI and RWC were not influenced by 7.5 dS m-1 and drought treatments and mostly contributed towards stress tolerance. Our findings imply that J. curcas is moderately tolerant to salinity and drought. The Na+ toxicity and disturbance in K+: Na+ ratio were the main contributing factors for limited growth and physiological attributes in this plant.

Variations in the profile distribution and protection mechanisms of organic carbon under long-term fertilization in a Chinese Mollisol.

Long term fertilization may have a significant effect on soil organic carbon (SOC) fractions and profile distribution. However, previous research mostly explored the SOC in the topsoil and provided little or no information about its distribution in deeper layers and various protection mechanisms particularly under long-term fertilization. The present study investigated the contents and profile distribution (0-100 cm) of distinct SOC protection mechanisms in the Mollisol (black soil) of Northeast China after 35 years of mineral and manure application. The initial Organic Matter content of the topsoil (0-20 cm) ranged from 26.4 to 27.0 g kg-1 soil, and ploughing depth was up to 20 cm. A combination of physical-chemical fractionation methods was employed to study various SOC fractions. There were significant variations throughout the profile among the various fractions and protection mechanisms. In topsoil (to 40 cm), mineral plus manure fertilization (MNPK) increased the total SOC content and accounted for 16.15% in the 0-20 cm and 12.34% in the 20-40 cm layer, while the manure alone (M) increased the total SOC by 56.14%, 48.73% and 27.73% in the subsoil (40-60, 60-80 and 80-100 cm, respectively). Moreover, MNPK and M in the topsoil and subsoil, respectively increased the unprotected coarse particulate organic carbon (cPOC) (48% and 26%, respectively), physically protected micro-aggregate (µagg) (20% and 18%, respectively) and occluded particulate organic carbon (iPOC) contents (279% and 93%, respectively) compared with the control (CK). A positive linear correlation was observed between total SOC and the cPOC, iPOC, physico-biochemically protected NH-µSilt and physico-chemically protected H-µSilt (p < 0.01) across the whole profile. Overall, physical, physico-biochemical and physico-chemical protection were the predominant mechanisms to sequester carbon in the whole profile, whereas the biochemical protection mechanisms were only relevant in the topsoil, thus demonstrating the differential mechanistic sensitivity of fractions for organic carbon cycling across the profile.