Manurial amendments and source of water for supplemental irrigation of sawah-rice system influenced soil quality and rice yield

Adaobi L Nnadi ,C A Igwe ,Sunday E Obalum ,J N Nwite ,Vivian Ukamaka Ugwu ,Toshiyuki Wakatsuki

doi:10.4314/as.v20i1.15

Abstract

Soil and water management research on adapting the promising sawah ecotechnology for lowland rice farming in West Africa has largely focused on the abundant inland valleys; floodplains which too represent a huge agricultural resource in the region have not been so involved. Sawah refers to a bunded, puddled and leveled basin for rice, with water inlets and outlets for irrigation and drainage, respectively. In conventional sawah, soil fertility is augmented using mineral fertilizers, with an option to harness lowland water resources for use in small-scale irrigation to create the so-called sawah typologies. In this study, we evaluated the effects of three manurial amendments (rice husk, rice-husk ash and poultry droppings, each at 10 t ha–1) and NPK 20:10:10 at 400 kg ha–1 interacting with source of water (spring or pond) used for supplemental irrigation of three sawah typologies in a floodplain in southeastern Nigeria. Plots amended with poultry droppings and supplemented with spring water recorded the overall best performance of the sawah-rice system; the control being the unamended non-supplemented (solely rainfed) plots recorded the worst. Rice-husk ash and rice husk enhanced soil pH and soil organic carbon, respectively. The three sawah typologies showed a consistent trend thus spring-supplemented ≥ pond-supplemented ≥ non-supplemented sawah. Rice grain yield was influenced by soil total nitrogen and the sum of the three plant-nutrient basic cations (K+ , Ca2+ and Mg2+), with the influence of K+ alone being the greatest. To enhance rice performance including grain yields in floodplain sawah, farmers should utilise poultry droppings as soil manure and spring water for supplemental irrigation.

Highlights

The African adaptive lowland sawah† system remains a highly promising platform for not just increasing rice (Oryza sativa) production and attaining rice self-sufficiency in tropical Africa in a sustainable manner
During the preparation of Rice-husk ash (RHA) in the present study, the proportion of rice husk that was not converted into RHA but merely steamed was probably very small; so, applying the RHA to the soil resulted in its liming value dominating over the effect of decomposition of the steamed RH
The overall best results for soil fertility parameters as well as for rice growth and grain yield were from plots with Poultry droppings (PD) as manurial amendment and spring as source of water for the supplemental irrigation

Summary

Introduction

The African adaptive lowland sawah† system remains a highly promising platform for not just increasing rice (Oryza sativa) production and attaining rice self-sufficiency in tropical Africa in a sustainable manner. Sawah-based rice farming is increasingly popular in especially West Africa where the relative abundance of such categories of lowland as inland valleys and floodplains is an advantage. Floodplain soils show higher clay content and fertility status than inland-valley soils in West Africa (Abe et al, 2006); the reverse is true for topo-features that make for ease of water control. Sawah has numerous agronomic and ecological benefits It promotes the efficiency of soil and water management; conserves the fertility of lowland soils (nutrient-rich fine particles in the saturated puddled soils, alluvial flows and geo- and topo-accumulated water settle and build-up in the topsoil) and makes for proper harnessing of water and nutrients in the lowlands (Asubonteng et al, 2001; Wakatsuki and Masunaga, 2005). For non-sawah fields (with uncontrolled flooding), these sediments elude the topsoil with the attendant hampering of rice growth and yield

Methods

Results

Conclusion