Hardpan and maize root distribution under conservation and conventional tillage in agro-ecological zone IIa, Zambia

K.B Esser

doi:10.4314/acsj.v24i3.5

Abstract

Hardpans (plough/hoe pans) are commonly believed to restrict plant root growth and crop yields under conventional small-scale agriculture in sub-Saharan Africa. This study questions the notion of widespread hardpans in Zambia and their remedy under conservation tillage. Soil penetration resistance was measured in 8x12 grids, covering 80 cm wide and 60 cm deep profiles in 32 soil pits. Large and fine maize roots were counted in 8x6 grids. Soil samples from mid-rows were analysed for pH, exchangeable H+, exchangeable Al3+, cation exchange capacity, total N and extractable P (Bray 1) at six depths from 0-10 to 50-60 cm. Cultivation-induced hardpans were not detected. Soils under conservation tillage were more compact at 5 cm depth than soils under conventional tillage. No differences in root distributions between conservation and conventional tillage were found. Maize ( Zea mays L.) roots were largely confined to a relatively small soil volume of about 30 cm x 30 cm x 30 cm. Root growth appeared to be restricted by a combination of low concentrations of N and P. Soil acidity and Al saturation appeared to play a minor role in root distribution. L-shaped taproots in soils under manual tillage reported earlier were not necessarily due to hardpans, but may rather be caused by temporarily dry, impenetrable subsoils early in the rain season. There is no scientific basis for the recommendation given to farmers by agricultural extension workers to “break the hardpan ” in fields under manual or animal tillage in the study areas. Key Words: Soil acidity, Zea mays

Highlights

Negative effects of hardpans on crop yield under conventional oxplough and hand-hoe cultivation are commonly referred to by agricultural project documents and extension manuals for sub-Saharan Africa
No cultivation-induced hardpans capable of restricting root growth existed in the studied soils in the Central, Southern and Eastern Provinces of Zambia
Soils under conservation tillage are more compact at 5 cm depth than soils under conventional tillage

Summary

Introduction

Negative effects of hardpans (plough pans and hoe pans) on crop yield under conventional oxplough and hand-hoe cultivation are commonly referred to by agricultural project documents and extension manuals for sub-Saharan Africa. Such pans are regarded as significant obstacles to root development and water infiltration to the subsoil, resulting in constrained crop yield (Baudron et al, 2007; ICRAF, 2009; FAO, 2009; SUSTAINET EA, 2010; IFAD, 2011). Douglas et al (1999) concluded on the basis of shapes and distributions of crop roots in Malawi that cultivation-induced hoe pans reduce crop yields significantly. Baudron et al (2007) stated that “taproot bent within 20 cm of soil depth is evidence of plough pan”

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