Abstract

Abstract. The present study attempts to employ potassium (K) release parameters to identify soil-quality degradation due to changed land use patterns in sweet potato (Ipomoea batatas (L.) Lam) farms of the highlands of Papua New Guinea. Rapid population increase in the region increased pressure on the land to intensify subsistence production mainly by reducing fallow periods. Such continuous cropping practice coupled with lack of K fertilization practices could lead to a rapid loss of soil fertility and soil-resource degradation. The study aims to evaluate the effects of crop intensification on the K-release pattern and identify soil groups vulnerable to K depletion. Soils with widely differing exchangeable and non-exchangeable K contents were sequentially extracted for periods between 1 and 569 h in 0.01 M CaCl2, and K-release data were fitted to four mathematical models: first order, power, parabolic diffusion and Elovich equations. Results showed two distinct parts in the K-release curves, and 58–80% of total K was released to solution phase within 76 h (first five extractions) with 20–42% K released in the later parts (after 76 h). Soils from older farms that were subjected to intensive and prolonged land use showed significantly (P < 0.05) lower cumulative K-release potential than the farms recently brought to cultivation (new farms). Among the four equations, first-order and power equations best described the K-release pattern; the constant b, an index of K-release rates, ranged from 0.005 to 0.008 mg kg−1 h−1 in the first-order model and was between 0.14 and 0.83 mg kg−1 h−1 in the power model for the soils. In the non-volcanic soils, model constant b values were significantly (P < 0.05) higher than the volcanic soils, thus indicating the vulnerability of volcanic soils to K deficiency. The volcanic soils cropped for several crop cycles need immediate management interventions either through improved fallow management or through mineral fertilizers plus animal manures to sustain productivity.

Highlights

  • Sweet potato (Ipomoea batatas (L.) Lam) is the major staple food crop in highlands of Papua New Guinea (PNG) with production and consumption of tubers well over 1.5 million tonnes (Bourke, 2005)

  • In PNG, much of the sweet potato production is through subsistence agriculture with hardly any input of mineral fertilizers and little or no manure use

  • A range of soil samples used by Walter et al (2011) from the four highland provinces (Western Highlands, Eastern Highlands, Simbu and Enga) of PNG, with widely differing K fractions were selected for the present study (Table 1)

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Summary

Introduction

Sweet potato (Ipomoea batatas (L.) Lam) is the major staple food crop in highlands of Papua New Guinea (PNG) with production and consumption of tubers well over 1.5 million tonnes (Bourke, 2005). In PNG, much of the sweet potato production is through subsistence agriculture with hardly any input of mineral fertilizers and little or no manure use. Over several years of continuous farming and in the absence of any mineral nutrient inputs, fertility of old farms generally decreases and farmers abandon such farm areas for fallow. The population of the highlands region, has been increasing by ∼ 3 % each year, placing increasing pressure on the land resources to produce extra food for the growing populace, as observed in other parts of the world (Abu Hammad and Tumeizi, 2012). Pressure on land resources has increased dramatically because of the population growth; fallow periods between cropping cycles have

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