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The investigation in three groups of pomelo trees (good, average, bad) was conducted. Each group included 15 orchards. The number of soil samples collected for analysis is 15 samples × 2 depths (0–15 cm and 15–30 cm) × 3 groups of plants = 90 soil samples. The results indicated that the soil texture of the good pomelo orchard group and the average pomelo orchard group is silty clay loam, and the bad pomelo orchard group has a silty clay. The average pH value in the bad pomelo orchard group is lower than the average pomelo orchard group and the good pomelo orchard group at both soil depths of 0–15 cm and 15–30 cm. The soil EC of the three groups of pomelo orchards is not different at depths of 0–15 cm and 15–30 cm and does not affect the plants. The average organic matter content at both soil depths 0–15 cm and 15–30 cm of the good pomelo orchard group shows the highest organic matter value. Soil bulk density in the group of bad pomelo orchards had the highest value at both depths of 0–15 cm and 15–30 cm. The porosity of the good pomelo orchard group has the highest value at two depths, 0–15 cm and 15–30 cm. Field capacity of good pomelo orchards have the highest values at both depths of 0–15 cm and 15–30 cm. The K sat at a depth of 0–15 cm of the good pomelo orchard group is quite slow, while the average pomelo orchard group and the bad pomelo orchard group are at a slow level. The bad physical and chemical properties had negative effects on pomelo growth.

Given that rice husk biochar has been shown to modulate salinity in salt-affected acid soils, the objective of this study was to investigate the effects of organic amendment of salinized acid soils on P fractions, enzyme activities, and associated rice yield. Four treatments, viz. Rice–Rice–Rice, [RRR]; Fallow–Rice–Rice, [FRR]; Fallow–Rice–Rice + 3 Mg ha−1 of compost [FRR + Comp]; and Fallow–Rice–Rice + 10 Mg ha−1 of biochar [FRR + BC] were established at Ben Tre and Kien Giang sites, Viet Nam, over six consecutive crops. Soil properties at harvest of the sixth crop showed that there were diverse patterns of fractionation between P forms with respect to treatment. Overarchingly, biochar increased labile and moderately labile inorganic P and organic P by 30% to 70%, respectively, whilst compost had a relatively modest effect on these pools. Soil phosphatase activities at crop tillering increased following the FRR + Comp and FRR + BC treatments compared with those in RRR, except for acid phosphatase at Ben Tre. At harvest, there were no significant differences between the enzyme activities among the treatments. Rice yield was positively correlated with the more labile forms of P, soil C, and acid phosphatase activity. In the absence of organic amendments, there was no effect of triple versus double rice crops being grown in one-year cycle. Repeated application of biochar (10 Mg ha−1 × 5 times) showed potential to increase grain yields and total soil C in salt-affected acid soils, via modulation of P transformations to more plant-available forms. [ABSTRACT FROM AUTHOR]