Figure 2 - uploaded by Gunnar Kirchhof
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Monilochaetes infuscans-sweetpotato scurf; left: affected storage roots in a Papua New Guinea (PNG) market (photo courtesy of J. Lovatt, Department of Primary Industries, Bundaberg, Queensland); right: discolouration caused by scurf in a farmer's field, Western Highlands province, PNG, 2007.
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The authors wish to make the following correction to this paper [...]
We use co-integration and error-correction techniques under a single equation functional form, with quarterly data spanning 1994 to 2006.
Our results suggest that a long-run equilibrium relationship
exists for total exports and for the two subsectors of exports:
farming, forestry and fisheries, and minerals and petroleum.
The results also sugges...
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... Current production is more than 3 million tons per annum and is worth an estimated $A700 million. Consequent to soil fertility decline and shortening of fallow periods in the highlands region of PNG, a decline in productivity of 1997;Hartemink et al., 2000;Kirchhof, 2009). Follow-up studies by Bailey et al. (2009) through an extensive survey in all the four highlands provinces, established widespread deficiencies of phosphorous (P), potassium (K) and sulfur (S) in the highlands region. ...
Soils from eight sites in the highlands of Papua New Guinea were evaluated for the vegetative growth response of sweetpotato vines at three rates of sulfur (S) 4, 10 and 20 mg S kg-1 soil (corresponding to
12.5, 25 and 50 kg S ha-1, respectively), and a control (0 kg S ha-1) in a pot experiment. There was significant (P < 0.05) increase in sweetpotato growth (vine length, leaf area, fresh weight and dry weights of the tops) with the application rates of S, in soils from five sites. Cate-Nelson‟s plot of
0.15% CaCl2 extractable soil S, against percent relative dry weight of sweetpotato tops revealed a critical concentration of 6.5 mg S kg-1 soil, for these soils. Calcium chloride soil test for the available S appeared to have good correlation with plant response, although two data points did not allow statistically significant models to be fitted.
... Declining crop productivity, however, appears to be threatening the sustainability of sweetpotato-based farming systems within the region, a probable cause being the exhaustion of soil nutrient reserves in continuously cultivated sweetpotato gardens. To assess the extent of the problem, an ACIAR funded survey of sweetpotato gardens (SMCN/2005/043) was conducted across four highlands provinces and information on soil and crop variables was obtained for old gardens (cultivated over many seasons) and new gardens (newly brought into cultivation) on soils of volcanic and non-volcanic origin (Kirchhof 2009). Crop leaf nutrient data collected in the survey suggested that K deficiency was the primary cause of poor crop production in almost a third of sweetpotato gardens. ...
Declining soil fertility is threatening the productivity of sweetpotato in the highlands of Papua New Guinea (PNG). A survey of sweetpotato gardens (SMCN/2005/043) identified K, S and P deficiencies as the main nutritional limitations on tuber production in the region. A pot experiment was conducted to evaluate how sweetpotato vines, propagated on three important soil types (Humult, Aquept and Aqoll), are affected by sequentially omitting 13 nutrients (N, P, K, Ca, Mg, S, Fe, Bo, Zn, Mn, Cu, Mo, Ni) from fertiliser applications. On the Humult, only the minus Mo treatment produced significantly less shoot yield than the all nutrient control (ALL), but symptoms of S deficiency were also present in plants on the minus S treatment. On the Aquept, the minus N, P, Ca, S, B and Mn treatments had significantly less shoot yields than the control, but the minus S and N treatments were lowest yielding, and the S deficiency being clearly manifest. On the Aqoll, the minus N, P, S, Mn, Zn, Mo and Ni treatments had significantly lower shoot yields than the control, and again the minus S treatment produced the lowest yield. On all three soils, vine yields in the minus K treatments were not significantly less than those in the ALL, even though the concentrations of K in soil were very low (0.02 meq/100g). It was concluded that the early stage of vine propagation is probably less K-demanding than the tuber production stage in mature crops. Introduction Sweetpotato (Ipomoea batatas) is the staple food crop in the PNG highlands. Declining crop productivity, however, appears to be threatening the sustainability of sweetpotato-based farming systems within the region, a probable cause being the exhaustion of soil nutrient reserves in continuously cultivated sweetpotato gardens. To assess the extent of the problem, an ACIAR funded survey of sweetpotato gardens (SMCN/2005/043) was conducted across four highlands provinces and information on soil and crop variables was obtained for old gardens (cultivated over many seasons) and new gardens (newly brought into cultivation) on soils of volcanic and non-volcanic origin (Kirchhof 2009). Crop leaf nutrient data collected in the survey suggested that K deficiency was the primary cause of poor crop production in almost a third of sweetpotato gardens. Phosphorus deficiency was also a problem on volcanic soils, and S deficiency on non-volcanic soils (Bailey et al. 2009). A follow-up study was planned to acquire more detailed information on nutrient dynamic processes in sweetpotato cultivation systems, and to use this information to develop optimal nutrient management regimes capable of sustaining sweetpotato production on three key soil types. The preliminary phase of the follow-up study involved nutrient omission trials. These were used to evaluate how the growth of sweetpotato vines, propagated on three important soil types were affected by sequentially omitting a range of macro and micronutrients from fertiliser applications. Methods Soils Soils were collected from the A horizon at three sites: (1) Aiyura, (2) Kondiu, and (3) Tambul. The locations of these sites are denoted by stars in Figure 1. The soil types were classified according the 1975 USDA scheme of soil taxonomy as: (1) Humult, (2), Aquept, and (3) Aqoll.
Sweetpotato has been the subject of little research worldwide compared with other major crop staples, and this is especially so for less developed countries where sweetpotato is critical for food security. This review synthesises information on plant protection issues that affect smallholder sweetpotato farmers in less developed countries to identify major issues and suggest research priorities. Though the pests and diseases of sweetpotato in less developed countries are largely common to industrialised systems, their relative importance differs and losses tend to be more severe as a result of differing agronomic practices and relative unavailability of management options and technical support that are important in developed countries. Smallholders are heavily reliant on cultural practices such as traditional forms of biological control using ants and livestock, fallowing and composting (sometimes with plant materials having biocidal properties). Crop protection methods that have been developed for use in sweetpotato production in developed countries, such as pathogen-tested planting material, early maturing varieties, pheromone trapping and pesticides are less accessible to, and relevant for, smallholders. Smallholders also typically harvest a given crop progressively which extends the period over which storage roots are potentially vulnerable to attack but reduces the risk of post-harvest losses. Human population growth in developing countries is leading to an increase in cropping intensity with shorter fallow periods and more years of continuous crops. This has the dual effect of depleting soil nutrients and increasing the potential for pest and pathogen build-up. Associated with this, the adoption of strategies to manage crop nutrition, such as not burning crop residues, promote carryover of pests and pathogen inocula. As a consequence of these factors, sweetpotato yield losses from diseases, especially viruses, and pests, particularly weevils, can be high. Climate change is likely to result in more frequent drought and this will increase losses caused by sweetpotato weevils that are favoured by dry conditions. This review of sweetpotato pests and their management options concludes with suggestions for some future research priorities including the combination of traditional practices that have pest management outcomes with relevant practices from industrial production that are able to be transferred or modified for use in smallholder production. Increased technical support for decision making and diagnostics, including molecular approaches that have scope for field use, will be important in reducing the burden imposed by biotic threats to this important global crop.
Ralstonia solanacearum, which consists of five races/biovars, is considered a “species-complex” and is an important phytopathogen that causes wilt disease in more than 200 plant species. R. solanacearum race 1 biovar 4 (R1bv4) has caused yield losses of 30–80 % in the vegetable sweet potato (VSP) in the last decade in Taiwan. To identify the source of the initial inoculum of R1bv4 in VSP fields, soil and cuttings from these fields were examined from 2009 to 2010. The results of the investigation indicated that the population of R1bv4 was generally distributed throughout the natural soil of VSP fields at a density ranging from 1.3 × 102 to 9.5 × 105 cfu/g soil; however, the incidence of bacterial wilt was not significantly associated with the density of the R1bv4 population in soils (R2 = 0.084). In contrast, densities of R1bv4 ranging from 2.3 × 103 to 5.9 × 105 cfu/g tissue were detected in the vine tissue of asymptomatic plants in the fields. Additional experiments demonstrated that R1bv4-free VSP cuttings without visible symptoms planted in infested soils in the greenhouse setting could carry approximately 3.1 × 105 R1bv4 cfu/g tissue, which suggests the existence of a latent period for R1bv4 in VSP plants. The results of a BIO-PCR analysis showed that R1bv4 was detected in 2.0 to 98.0 % of the VSP cuttings used for propagation in fields; in addition, the percentage of VSP cuttings carrying R1bv4 and the incidence of bacterial wilt in fields were positively correlated (R2 = 0.909). The inoculation experiments conducted in greenhouses and in fields showed that the cutting inoculum (CI) contributed more to the incidence of bacterial wilt in VSP plants than the soil inoculum (SI). In the field experiments conducted in 2010, an incidence of disease of 27.1 to 38.5 % was detected in healthy field cuttings 8 months after transplantation; in contrast, the incidence of disease in field cuttings carrying R1bv4 was 49.0 to 68.8 %. The incidence of disease was significantly lower in healthy cuttings than in cuttings carrying R1bv4 (p = 0.05).
