Green manure incorporation enhanced soil labile phosphorus and fruit tree growth.

INTRODUCTION

The incorporation of green manures substantially enhances the conversion of external phosphorus (P) fertilizers and soil-reserved P into forms readily available to plants. The study aims to evaluate the influence of green manure additions on soil phosphorus dynamics and citrus growth, considering different green manure species and initial soil phosphorus levels. Additionally, the research seeks to elucidate the microbiological mechanisms underlying the observed effects.

METHODS

A citrus pot experiment was conducted under both P-surplus (1.50 g·P·kg) and P-deficient (0.17 g·P·kg) soils with incorporating legume (Leg), non-legume (Non-Leg) or no green manure residues (CK), and O-P labeled KHPO (0.5 g, containing 80‰ δO) was additionally introduced to trace the turnover characteristics of chemical P fertilizer mediated by soil microorganisms.

RESULTS AND DISCUSSION

In P-surplus soil, compared with the CK treatment, the Leg treatment significantly increased soil HO-P (13.6%), NaHCO-P (8.9%), NaOH-P (9.5%) and NaOH-P (30.0%) content. It also promoted rapid turnover of P sources into HO-P and NaHCO-P pools by enhancing the (576.6%) gene abundance. In contrast, the Non-Leg treatment significantly augmented soil HO-P (9.2%) and NaHCO-P (8.5%) content, facilitating the turnover of P sources into NaHCO-P pools. Under P-deficient soil conditions, compared with the CK treatment, the Leg treatment notably raised soil HO-P (150.0%), NaHCO-P (66.3%), NaHCO-P (34.8%) and NaOH-P (59.0%) content, contributing to the transfer of P sources into NaHCO-P and NaOH-P pools. This effect was achieved through elevated ALP (33.8%) and ACP (12.9%) activities and increased (48.1%), (42.9%), (21.7%), and (27.4%) gene abundances. The Non-Leg treatment, on the other hand, led to significant increases in soil NaHCO-P (299.0%) and NaHCO-P (132.6%) content, thereby facilitating the turnover of P sources into NaHCO-P and NaOH-P pools, except for the gene abundance. Both Leg and Non-Leg treatments significantly improved citrus growth (7.3-20.0%) and P uptake (15.4-42.1%) in P-deficient soil but yielded no substantial effects in P-surplus soil. In summary, introducing green manure crops, particularly legume green manure, emerges as a valuable approach to enhance soil P availability and foster fruit tree growth in orchard production.