The potential of durum wheat-chickpea intercropping to improve the soil available phosphorus status and biomass production in a subtropical climate.

The intercropping system is a promising approach to augmenting the soil nutrient status and promoting sustainable crop production. However, it is not known whether intercropping improves the soil phosphorus (P) status in alluvial soils with low P under subtropical climates. Over two growing seasons--2019-2020 and 2020-2021--two experimental fields were employed to explore the effect of durum wheat (Dw) and chickpea (Cp) cropping systems on the soil available P. A randomized complete block design was used in this experiment, with three blocks each divided into three plots. Each plot was used for one of the following three treatments with three replications: Dw monocrop (Dw-MC), Cp monocrop (Cp-MC), and Dw + Cp intercrop (CpDw-InC), with bulk soil (BS) used as a control. A reduction in the rhizosphere soil pH (-0.44 and -0.11 unit) was observed in the (Cp-MC) and (CpDw-InC) treatments over BS, occurring concomitantly with a significant increase in available P in the rhizosphere soil of around 28.45% for CpDw-InC and 24.9% for Cp-MC over BS. Conversely, the rhizosphere soil pH was significantly higher (+0.12 units) in the Dw-MC treatments. In addition, intercropping enhanced the soil microbial biomass P, with strong positive correlations observed between the biomass P and available P in the Cp-MC treatment, whereas this correlation was negative in the CpDw-InC and Dw-MC treatments. These findings suggested that Cp intercropped with Dw could be a viable approach in enhancing the available P through improved pH variation and biomass P when cultivated on alluvial soil under a subtropical climate.

Adsorption of phosphorus by alkaline Tunisian soil in a fixed bed column.

The present study evaluates the phosphorus (P) adsorption by alkaline soil in fixed bed column mode operation. The effects of flow rate, bed height, and initial P concentration on breakthrough curves were evaluated. Data confirmed that both the breakthrough and exhaustion time increased in parallel with the rise in bed height and the decline in flow rate and initial P concentration. The adsorption capacity was observed to increase with decreasing flow rate and bed height and increasing initial concentration. Moreover, continuous adsorption experiments were conducted using three salts (NaCl, KCl and CaCl2) with the same concentration (0.01 M) to investigate the P adsorption behavior in saline conditions. The results showed that all three salts improve the P adsorption in the soil column. Consequently, the bed performance was significantly enhanced with salts addition. The maximum adsorption capacity of 13.47 mg g-1 for P, 16.13 mg g-1 for P-NaCl, 22.10 mg g-1 for P-KCl, 30.05 mg g-1 for P-CaCl2 was attained at an initial influent concentration of 300 mg g-1, bed height of 22 cm, and flow rate of 10 mL min-1. TheCaCl2 addition was therefore the most effective in increasing P adsorption. Thomas, Yoon-Nelson and Clark models were applied to experimental results to forecast the breakthrough curves by nonlinear regression analysis. Meanwhile, the bed depth service time model was employed to examine the effective model parameters in scaling up the process using linear regression analysis. The values of correlation coefficient (R2) and the sum of squared error evidenced that the Thomas model is the most appropriate model to fit the experimental data. The reusability experiment showed that the adsorbent material still had high P adsorption capacity, and tolerable desorption efficiency.