Mulched drip irrigation and maize straw biochar increase peanut yield by regulating soil nitrogen, photosynthesis and root in arid regions

Biochar has been increasingly recognized as a valuable soil conditioner, which is beneficial to peanut yield improvement. We conducted a three-year field experiment to investigate the effect of biochar applied at three rates (0 t ha−1 (B0), 24 t ha−1 (B1), and 48 t ha−1 (B2), which were 0%, 1%, 2% of the soil mass) on diurnal variation of net photosynthetic rate, soil available nitrogen (N), root characteristics, and peanut yield under two irrigation methods: CK (drip irrigation) and MDI (mulched drip irrigation). A biochar application rate of 24 t ha−1 (B1) increased soil available N, net photosynthetic rate of leaves, and relative chlorophyll values (SPAD) compared to B0. B1 increased total root length, root surface area, root volume and root bleeding sap (RBS) by 8.5∼29.9%, 13.5∼18.5%, 0.8∼12.1%, and 27.6–45.9%, respectively, compared to B0. Significant correlations between grain yield, SPAD, and RBS indicated that biochar enhanced grain yield by improving photosynthesis and root activity. For the irrigation treatments, MDI significantly increased peanut yield, net photosynthetic rate, and RBS, but had no significant effect on soil available N. High biochar application under MDI (IMDIB2) reduced peanut yield in 2020. Moderate biochar application under MDI (IMDIB1) had the highest peanut yield in three years. These results showed that 24 t ha−1 biochar combined with MDI achieved the highest soil available N, root development, and net photosynthetic rate thus which resulted in the highest grain yield, and this could be a management strategy to increase peanut yield.