Durum Wheat–Chickpea Intercropping Improves Soil Phosphorus Status and Biomass Production Under Small Soil Inputs

To understand how the intercropping system alleviates stressful conditions, this study was aimed at elucidating the effects of legume–cereal intercropping in enhancing phosphorus (P) availability in P-deficient soil under the semi-arid climate of southern Tunisia. During the two growing seasons––2018–2019 and 2019–2020––two experimental fields were employed to explore the effect of soil P availability on the growth of durum wheat and chickpea under different cropping systems. 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 four cropping systems with three replications: (i) monocrop chickpea (Ck-M); (ii) monocrop durum wheat (DW-M); (iii) durum wheat–chickpea intercrop (DWCk-IC); and (iv) vacant soil without plants as a control. Compared to the vacant soil, we found a significant increase in the Olsen P concentration in the soil rhizosphere by about 16%, 48%, and 36% for the DW-M, Ck-M, and DWCk-IC, respectively. Also, the increase in soil P availability was associated with a pH decrease of −0.73 and −0.37 units for Ck-M and DWCk-IC, respectively. In addition, the soil microbial biomass P increased significantly (P < 0.05), by about 27%, 22%, and 18% for the Ck-M, DWCk-IC, and DW-M, respectively, compared to the vacant soil. The increased soil P availability improved the P contents in the durum wheat and chickpea roots and shoots, although it mostly enhanced the intercropped dry weight. These findings demonstrate that durum wheat–chickpea intercropping could be a practical cropping system for improving the soil P availability through enhanced activity in the microbial community and soil acidification.