Dry matter accumulation, nutrient uptake and nutrient use efficiency of two improved cultivars of taro (Colocasia esculenta) under screen house conditions in Samoa

Taro (Colocasia esculenta (L.) Schott) is a staple crop of many of the South Pacific nations with an ever increasing export demand. In recent years, yields of taro have in creased dramatically through breeding and selection. However, selections of improved lines are often entirely based on final yield. There are many physiological pathways by which increased potential yield may be achieved. Factors such as the accumulation of dry matter and nutrient use efficiency, merit investigation. Two improved (blight resistant) taro cultivars were planted and harvested for biomass measurements on a monthly basis for a total of eight months (30-240 days after planting) through destructive sampling. At each harvest, plants were separated into various plant parts and their dry matter accumulation and nutrient content were determined. Comparatively, cultivar Samoa 2 showed significantly higher uptake of N (25%), P (37.5%), K (33%), Mg (36.4%), Mn (22.7%) and Zn (48.3%) than cultivar Samoa 1. Even though maximum levels of total plant uptake of nutrients by the two cultivars did not differ between the cultivars, cultivar Samoa 1 plants absorbed 17% less N,26% less P and 20% less K than those of cultivar Samoa 2 with the uptake uniformly distributed over the entire life cycle of the crop. Although cultivar Samoa 2 resulted in higher total plant (19.6%) and corm dry matter (10.4%) productions, cultivar Samoa 1 had a higher nutrient use efficiency, (kg of edible dry matter produced per kg of nutrient taken up), for N, P, K, Mg, Mn and Cu over cultivar Samoa 2. However, for Ca, Fe and Zn. Cultivar Samoa 2 had a higher nutrient use efficiency over cultivar Samoa 1. Based on nutrient use efficiency of the cultivars, Samoa 1 is recommended for marginal to rich soils while Samoa 2 for good to rich soils

Nutrient use efficiency of two improved cultivars of Taro (Colocasia esculenta) under screen house conditions in Samoa

Taro (Colocasia esculenta (L.) Schott) is a staple crop of many of the South Pacific nations with an ever increasing export demand. In recent years, yields of taro have increased dramatically through breeding and selection. However, selections of improved lines are often entirely based on final yield. There are many physiological pathways by which increased potential yield may be achieved. Factors such as the accumulation of dry matter and nutrient use efficiency, merit investigation. Two improved (blight resistant) taro cultivars were planted and harvested for biomass measurements on a monthly basis for a total of eight months (30-240 days after planting) through destructive sampling. At each harvest, plants were separated into various plant parts and their dry matter accumulation and nutrient content were determined. Comparatively, cultivar Samoa 2 showed significantly higher uptake of N (25%), P (37.5%), K (33%), Mg (36.4%), Mn (22.7%) and Zn (48.3%) than cultivar Samoa 1. Even though maximum levels of total plant uptake of nutrients by the two cultivars did not differ between the cultivars, cultivar Samoa 1 plants absorbed 17% less N, 26% less P and 20% less K than those of cultivar Samoa 2 with the uptake uniformly distributed over the entire life cycle of the crop. Although cultivar Samoa 2 resulted in higher total plant (19.6%) and corm dry matter (10.4%) productions, cultivar Samoa 1 had a higher nutrient use efficiency, (kg of edible dry matter produced per kg of nutrient taken up), for N, P, K, Mg, Mn and Cu over cultivar Samoa 2. However, for Ca, Fe and Zn. Cultivar Samoa 2 had a higher nutrient use efficiency over cultivar Samoa 1. Based on nutrient use efficiency of the cultivars, Samoa 1 is recommended for marginal to rich soils while Samoa 2 for good to rich soils

Organic amendments increased sweetpotato (Ipomoea batatas L.) yield in a calcareous sandy soil of Samoa

A five-month field experiment was conducted to investigate the effects of organic amendments on yields of two sweetpotato cultivars in a calcareous sandy soil of Samoa. The treatments consisted of three organic amendments; gliricidia, gliricidia + biochar, poultry litter, and a control, and two improved sweetpotato cultivars (IB/PH/03 and IB/PR/13). All amendments were applied at equivalent rate of 100 kg N ha-1 while biochar at 5 t ha-1. Plots were arranged in a RCB design with four replicates. Results showed that all organic amendments significantly increased total storage root and marketable storage root yields, compared to yields of the control. Total marketable root yield was increased by 134, 118, and 294% over control in response to gliricidia, poultry litter, and gliricidia + biochar treatments, respectively. The highest yield, yield attributing parameters and nutrient uptake by storage root were recorded in gliricidia + biochar treatment, which appears to synergistically influence crop yield relative to organic amendments applied singly; a potential amendment for improving sweetpotato productivity in sandy calcareous soil. Cultivar IB/PH/03 performed better than IB/PR/13 on all measured crop parameters except for fresh weight of nonmarketable root and percent dry matter content showing better potentiality for promotion under similar agroenvironmental condition

Performance of improved sweetpotato (Ipomoea batatas L.) cultivars under different soil types of Samoa

There is need to diversify crop production in Samoa which currently depends mainly on taro crop, that has proved to be susceptible to fungus and other diseases, to as safeguard against risks of crop failures and adapt to climatic changes. The potential of introducing sweetpotato as a second staple food in Samoa is explored in this study. The study analyses the suitability of sweetpotato cultivars in Samoan agro-environment and major soil types. For this purpose a twenty week pot experiment was conducted to investigate the performance of three improved sweetpotato cultivars (IB/PR/12, IB/PR/13 and IB/PH/03) on four different types of soils in Samoa (Savaia calcareous sandy loam, Matafa’a red acidic, Faleula silty clay and Saleimoa silty clay) in a factorial arrangement of treatments in randomised complete block design with three replications. Results revealed that soil type had a significant effect on vine growth, and storage root yield with the best yield obtained in the silty clay soils having high K content. Retarded plant growth observed under the acidic soil having low K content resulted in lowest storage root yield. A significant varietal difference was recorded in sweetpotato growth and yield. IB/PH/03 was inferior in vine length, but produced comparatively highest number of vines per plant, and storage root yield attesting its adaptability in all the four tested soil types of Samoa and has potentiality to be promoted for wider adoption. A follow-up field study is needed to verify our preliminary results under pot culture on different soil types of Samoa

An investigation into the process of dealumination in soils of the Auckland, Bay of Plenty and Waikato regions of New Zealand

Dealumination is a term used to describe an increase in the concentration of acid extractable Al as a result of accelerated weathering or chemical attack of primary crystalline and short-range order aluminosilicates. Two specific mechanisms have been proposed: (1) partial dissolution of clay minerals by local areas of high acidity associated with fertiliser granules; (2) surface complexation and extraction by the fluoride and residual hydrofluoric acid present in phosphate fertilisers. This process has been observed in State of the Environment data from the Waikato region, New Zealand, for farmed soils (which receive substantial inputs of phosphate fertilisers) but not for background soils (which are unfertilised). Additional data, including results from XRF analysis for total Al on the original Waikato region samples, acid extractable Al from two neighbouring regions, Auckland and Bay of Plenty, and trends in the data at sites resampled 5 years apart are reported in this work. Retrospective analysis of the Waikato samples by XRF for total Al showed that there was no significant difference between farmed and background soils (whereas the increase in acid extractable Al was significant, p<0.0001), indicating total Al concentrations were not increasing in farmed soils but the form of it was changing. In farmed soils, proportionately more Al is becoming acid extractable over time. Acid extractable Al results were consistent with dealumination occurring in all 3 regions (p<0.015 to <0.0001) and significant (p<0.0001) increases were seen in farmed soils compared to background ones over 5 years, with a mean increase in acid extractable Al of about 1000 mg/kg/year. The actual mechanisms of dealumination and associated soil processes need to be verified, and the relative importance of possible causative factors delineated (two possible causes are high localised acidity around fertiliser granules, and high annual loadings of F). Whatever the causes, the effects of this process on soil properties and implications to soil management need to be ascertained