Influence of Rice Husk Biochar and Compost Amendments on Salt Contents and Hydraulic Properties of Soil and Rice Yield in Salt-Affected Fields

Nguyen Thi Kim Phuong,Dang Duy Minh,Tran Ba Linh,Nguyen Van Sinh,Thi Tu Linh,Koki Toyota,Tran Anh Duc,Karl Ritz,Chau Minh Khoi

doi:10.3390/agronomy10081101

Abstract

Soil salinity may damage crop production. Besides proper management of irrigation water, salinity reduction can be achieved through soil amendment. The objectives of this study were to evaluate the effects of rice husk biochar and compost amendments on alleviation of salinity and rice growth. Field experiments were conducted at two salt-affected paddy rice fields located in distinct sites for five continuous crops. Treatments, with four replicates, consisted of continuous three rice crops per year (RRR), two rice crops rotated with fallow in spring–summer crop (FRR), FRR plus compost at 3 Mg ha−1 crop−1 (FRR + Comp), and biochar at 10 Mg ha−1 crop−1 (FRR + BC). Salt contents and hydraulic properties of soils, plant biomass, and plant uptake of cations were investigated. Soil bulk density (BD), exchangeable sodium (Na+), and exchangeable sodium percentage (ESP) were reduced remarkably by biochar application. Biochar application significantly increased other soil properties including total porosity, saturated hydraulic conductivity (Ksat), soluble and exchangeable potassium (K+), K+/Na+ ratio, available P, and total C. Compost application also improved BD, total porosity, and available P, but not exchangeable Na+ and ESP. Total aboveground biomass of rice showed a trend of FRR + BC > FRR + Comp > FRR > RRR. Relatively higher K+ uptake and lower Na+ uptake in rice straw in FRR + BC resulted in a significant two times higher K+/Na+ ratio over other treatments. Our results highlight that biochar amendment is a beneficial option for reducing ESP and providing available K+ and P under salinity-affected P-deficient conditions, hence improving straw biomass.

Highlights

Soil salinity is a major global issue threating agricultural productivity and sustainability.Salt-affected soil is a general term used for soils containing either high exchangeable sodium percentage (ESP) or soluble salts [1]
At Kien Giang province (KG), the soil pH was not affected by biochar, but was significantly affected by compost, with an increase of average 0.2 units
At Ben Tre province (BT), averaged across the 5 sampling times, the electrical conductivity (EC) values were greater in fallow in spring–summer crop (FRR) + Comp than in rice crops per year (RRR) and FRR, with an increase of 18% (p < 0.05)

Summary

Introduction

Salt-affected soil is a general term used for soils containing either high exchangeable sodium percentage (ESP) or soluble salts [1]. Most salt-affected soils occur in semi-arid and arid regions of Asia, Australia, and South America [2], but are found in some sub-humid to humid climate areas and along coastal areas [3]. Salt-affected soils are spreading globally in at least 75 countries [4], and occupy 20–30% of Agronomy 2020, 10, 1101; doi:10.3390/agronomy10081101 www.mdpi.com/journal/agronomy. Salt-affected soils are projected to increase in coastal areas due to a rise in sea level caused by future climate changes [6]. The electrical conductivity of saturated soil paste extract (ECe) of salt-affected soils is < 4 mS cm−1 [1]. ESP is an important indicator for salt-affected soils. According to Raine and Loch [7], ESP < 6 is defined for “non-sodic”

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Conclusion