Responses of Phaseolus calcaltus to lime and biochar application in an acid soil.

Rice bean (Phaseolus calcaltus), as an annual summer legume, is always subjected to acid soils in tropical to subtropical regions, limiting its growth and nodulation. However, little is known about its responses to lime and biochar addition, the two in improving soil fertility in acid soils.

In the current study, a pot experiment was conducted using rice bean on a sandy yellow soil (Orthic Acrisol) with a pH of 5.5. The experiment included three lime rates (0, 0.75 and 1.5 g kg^-1) and three biochar rates (0, 5 and 10 g kg^-1). The biochar was produced from aboveground parts of Solanum tuberosum using a home-made device with temperature of pyrolysis about 500 °C.

The results indicated that both lime and biochar could reduce soil exchange Al concentration, increase soil pH and the contents of soil microbial biomass carbon and microbial biomass nitrogen, and enhance urease and dehydrogenase activities, benefiting P. calcaltus growth and nodulation in acid soils. Lime application did decrease the concentrations of soil available phosphorus (AP) and alkali dispelled nitrogen (AN), whereas biochar application increased the concentrations of soil AP, AN and available potassium (AK). However, sole biochar application could not achieve as much yield increase as lime application did. High lime rate (1.5 g lime kg^-1) incorporated with low biochar rate (5 g biochar kg^-1) could obtain higher shoot biomass, nutrient uptake, and nodule number when compared with high lime rate and high biochar rate.

Lime incorporated with biochar application could achieve optimum improvement for P. calcaltus growing in acid soils when compared with sole lime or biochar addition.