Seasonal Dynamics of Soil Organic Matter and Total Nitrogen in soils under different land uses in Owerri Southeastern Nigeria

Ge Osuji,Sk Osuaku,Lc Agim,Eu Onweremadu,Bn Ndukwu

doi:10.4314/as.v11i1.7

Abstract

The study investigated seasonal dynamics of soil organic matter and total nitrogen in soils affected by different land use types in Owerri, Southeastern Nigeria. A total of 72 soil samples were randomly collected at two monthly intervals in the dry season (October/November, December/January and February/March) and rainy season (April/May, June/July and August/September) at 0-20 cm depth in all the studied land uses, namely soils under continuous cassava cultivation (CCS), pineapple orchard soil (POS), bush fallow (FS) and bare fallow (BF.) . Collected soil samples were air dried, passed through 2mm sieve and were analysed using standard methods. The experiment was factorially arranged in randomized complete block design (RCBD), with three factors namely, season, month and landuse. The treatments were replicated three times. Generated soil data were analysed using analysis of variance (ANOVA) and significant means were separated using least significant difference (LSD) at 5% probability. Results showed that soil organic matter and total nitrogen were significantly higher (P<0.05) in the dry season especially between January and April compared to the rainy season where the least was found around June/July in all the studied land uses, although in all cases, their variability was minimal, ranging from 30.49% in (CCS) to 47.68% in bare fallow. Significant positive correlation (P < 0.05) was found between soil organic matter (SOM) and total nitrogen (r2= 0.966 CCS; 0.935 FS, 0.626 POS, and 0.796 BF), and negative correlation with CN ratio (r2=0.917 CCS; 0.729 FS, 0.3 POS; 0.347 BF), respectively, bulk density (r2 = 0.63) only in FS. Similarly significant negative correlations (P< 0.05) were also found between TN and CN ratio (r2 =0.865 CCS, 0.716 FS, 0.796 POS and 0.328 BF).Keywords. Tropical soil, seasonal variability, total nitrogen, organic matter, land use, Southeasthern Nigeria.

Highlights

Soil organic matter is a product of plant and animal materials that have undergone decomposition process (Bot and Benites, 2005); and is one of the major earth’s carbon reservoirs, storing around 1.5 1018 g of carbon (Xiao, 1999), which is slightly more than twice the amount of carbon present in the atmosphere as CO2 (Jackson, 2000)
Clay and silt range from 125.73 in pineapple orchard soil (POS) to 248.52 g/kg in fallow soil (FS) and 45.50 g/kg in FS to 157.60 g/kg in cassava cultivated soil (CCS) repectivedy. Sandiness of these soils is due to a combination of sandy parent material (Coastal Plain Sands), tropical climate and land use (Onweremadu, 2007), and high precipitation in the area resulting to clay lessivage (UnambaOpara et al, 1987; Eshett et al, 1990; Chukwuma et al, 2010)
Bulk density was significantly higher (P

Summary

Introduction

Soil organic matter is a product of plant and animal materials that have undergone decomposition process (Bot and Benites, 2005); and is one of the major earth’s carbon reservoirs, storing around 1.5 1018 g of carbon (Xiao, 1999), which is slightly more than twice the amount of carbon present in the atmosphere as CO2 (Jackson, 2000). Seasonal dynamics of soil organic matter and nitrogen are directly linked with temperature changes, soil moisture availability, soil organism, carbon nitrogen ratio of the decomposing material, oxygen content of soil, type of material added to the soil and stage of decay (Singer and Munns 1999; Brady and Weil 1999). Soil organic matter is readily available in the soil when the soil is not near saturation such that aerobic condition that favours soil organisms prevails (Bot and Benites, 2005)

Objectives

Methods

Results