Abstract: 【Objective】The aim of this study was to assess the effects of lime on soil acidity and barley seedling growth in an acidic soil (pH 3.9), and to determine the suitable dosage of lime and thus providing scientific proof for acidic soil improvement and reasonable application rate. 【Method】 The trial was conducted at the experimental base of Huazhong Agricultural University. Soil incubation and pot experiments were used. The Ca(OH)₂ titration method was employed to estimate the lime requirement, and six treatments were designed: no lime, 0.3 g·kg^-1, 0.9 g·kg^-1, 1.8 g·kg^-1, 2.4 g·kg^-1 and 4.8 g·kg^-1 lime application rates. Samples were collected on 10, 20, 30, 40, 50, 60, 70 and 90 days after incubation to monitor the dynamic changes of soil pH, soil exchangeable acidity, exchangeable H⁺ and exchangeable Al³⁺. Barley was sowed on the 90th day and harvested after 2 weeks to assess the effects of liming rates on barley biomass, morphological parameters, and root activity. 【Result】 Soil incubation results demonstrated that lime application significantly improved soil pH, however the content of exchangeable acidity and exchangeable Al³⁺ were decreased significantly during the first 30 days. The content of potential acid decreased gradually with the increasing dosage of lime, therefore the content of soil exchangeable acid, exchangeable H⁺ and exchangeable Al³⁺ were zero in the treatment of 4.8 g·kg^-1. From then on, due to the influences of soil buffer, low lime dosages (< 1.8 g·kg^-1) showed no obvious effects on improving soil pH but significantly reduced soil potential acidity. The results of pot experiment showed that application of lime significantly enhanced barley growth through improving plant height, biomass and root development. Barely seedlings plant height, dry mass, total root length and surface area, and root activity improved with the lime application rate from 0 to 1.8 g·kg^-1. Whereas, lime input decreased root average diameter. Barley growth was inhibited significantly when lime application rate was above 1.8 g·kg^-1. The root activity in the treatment of 4.8 g·kg^-1 was lower than that of 0.9 g·kg^-1, the excess of lime application retarded the root growth. Thus, the optimum liming rate was 1.8 g·kg^-1, which agreed with the lime requirement calculated using the Ca(OH)₂ titration method. 【Conclusion】 Lime application is capable of neutralizing soil acidity and promoting barley seedling growth. Under the conditions of this study (soil pH 3.9), the appropriate liming rate was 1.8 g·kg^-1 (4 t·hm^-2). This rate was consistent with that from the Ca (OH)₂ titration method, confirming that the approach adopted in this study is appropriate for determining the lime application rate.

Key words: lime application rate, soil acidity, barley seedling, root morphological index parameters