Fresh Tuber Yield Research Articles

Evaluation of a Rapid Field Test Method for Assessing Nitrogen Status in Potato Plant Tissue in Rural Communities in the Bolivian Andean Highlands

The relatively poor accessibility, high costs, long turnaround time for analysis, and lack of information about soil and plant testing in the Andean highland region (Altiplano) of Bolivia has hampered informed and timely nutrient management decisions for potato (Solanum tuberosum L.) crops. The objective of this study was to determine if the Cardy nitrate meter (Horiba Ltd., Kyoto, Japan), a low-cost, portable, and rapid field test method, could be used to improve nitrogen (N) fertility management among isolated rural indigenous communities at different elevations in this rugged semi-arid environment. Fully matured leaf petioles were sampled at blooming time from potato trials established in three communities during the 2006–2007 and 2007–2008 growing seasons. Those trials were composed of 12 fertility treatments (i.e., an unfertilized control and different combinations of sheep and cow manure, inorganic fertilizer, commercial household/urban compost, and a commercial microbial activator soil amendment) arranged in a randomized complete block design with four replications. In general, in both growing seasons and in all communities, nitrate measured in the sap of leaf petioles by the Cardy meter had relatively low but significant correlations with leaf petiole total N (ranging from r2 = 0.07 to r2 = 0.60 across seasons and communities) and with total fresh tuber yield (ranging from r2 = 0.11 to r2 = 0.50 across seasons and communities). However, some problems were encountered with being able to consistently calibrate the meter with supplied standards prior to each use of the meter. These results indicate that the Cardy ion meter might be an effective tool for potato growers or agricultural professionals working in the Altiplano of Bolivia if further research can be conducted to determine if the meter is consistent for diverse sites in the Altiplano and is practical for the cultural, economic, and environmental conditions of the region.

Effects of Plastic Film Mulching Cultivation on Young Roots Growth Development, Tuber Formation and Tuber Yield of Sweet Potato

A two-year trial and a one-year pot experiment were performed to investigate growth and development and absorbing ability of young roots, endogenous hormones content of differentiated roots at early growing stage using variety Jixu 23 with two types of plastic film mulching cultivation, and no plastic as control(CK). The tuberous root fresh weight per plant at 50 days after planting was determined, and its relationship with tuberous root yield at harvest time was analyzed. The results showed that, at 10 and 20 days after planting, the number, total length, fresh weight, and volume of young roots significantly increased compared with control, and the differences in activity, total absorption area and active absorption area of young roots between two plastic film mulching treatments were significant(P0.05), showing the black plastic film mulching(BF) superior to the transparent film mulching(TF). Besides, zeatin riboside(ZR) content of differentiated roots(at 10 and 20 days after planting) was significant improved, which was in favor of procambium activity and tuberous roots formation. On the other hand, at early expansion period of tuberous roots, plastic film mulching cultivation increased abscisic acid(ABA) content and decreased gibberellin(GA) content in differentiated roots, as well as improved the secondary cambium activity, starch accumulation and differentiated root expansion. Meanwhile, abscisic acid(ABA) content and gibberellin(GA) content under the black film mulching significantly changed. Film mulching cultivation increased the number and fresh weight of tuberous roots per plant at 50 days after planting, which contrib-uted to higher fresh yield of tuberous root at harvest time. In the two year experiment, two treatments significantly enhanced the valid tuber number and fresh tuber yield compared with CK. The average increments were 10.71% and 5.76% in 2011, and 12.99% and 7.45% in 2012, respectively.

Fresh Tuber Yield Stability Analysis of Fifteen Cassava Genotypes Across Five Environments in East Java (Indonesia) Using GGE Biplot

The research aimed is to determine the yield stability of 15 cassava genotypes using GGE biplot. The study was conducted at five locations starting in November 2010 to August 2011.The results showed that environment, genotype, and genotype-by- environment interactions significantly affect the yield. Environment gives the most effect (64.69%), followed by genotype-by- environment interaction effect (6.53%), and genotype effect (4.94%). CMM 03038-7 has the highest yield among other clones, and higher than the controls clones (UJ5, Malang 6, and Adira 4), but not significantly different from Malang 4. GGE biplot identified that CMM 03038-7 is the most stable clones with high yield.

Effects of dynamic and static deficit and partial root zone drying irrigation strategies on yield, tuber sizes distribution, and water productivity of two field grown potato cultivars

New strategies of partial root-zone drying (PRD) and deficit irrigations (DI) were studied on potatoes in a semi-arid area of Iran. A factorial experiment was conducted as a complete randomized design in three replications. The potato cultivar treatments were Agria and Ramos. The whole growth period of both cultivars was divided into three stages based on the BBCH scale. There were five furrow irrigation treatments. The full irrigation treatment (FI) received 100% of potential evapotranspiration (ET); static deficit irrigation (SDI) received 75% of ET during the growth period; dynamic deficit irrigation (DDI) received 90% of ET in the first one-third of growth period, 75% of ET in the second one-third of growth period, and 50% of ET in the last one-third of growth period; static partial root zone drying irrigation (SPRD) received 75% of ET during the growth period; dynamic partial root zone drying irrigation (DPRD) received 90% of ET in the first one-third of growth period, 75% of ET in the second one-third of growth period, and 50% of ET in the last one-third of growth period. Analysis showed that there were significant differences between irrigation strategies as DI did outperform PRD in tuber production. The SDI, DDI, SPRD, and DPRD irrigation treatments decreased the potato tuber yield by 4%, 7%, 56%, and 52% compared to FI, respectively. SPRD and DPRD decreased potato tuber yield by 54% and 48% compared to SDI and DDI, respectively. Results also showed that there were no significant differences between cultivars. Interaction between irrigation strategies and cultivars was not significant. Furthermore, water productivities (WP) were significant among irrigation strategies. Compared to FI, the SDI and DDI increased WP by 28% and 34%, respectively, but SPRD and DPRD decreased WP by 40% and 31%, respectively. In general, the DI strategy (SDI, DDI) is recommended in the study area due to the slight fresh tuber yield reduction (4%, 7%) and considerable increase (28%, 34%) in WP relative to FI. Furthermore, the dynamic irrigation strategies led to higher WP than the static ones. It was also found that Agria outperformed the Ramos because of higher fresh tuber yield under water-saving irrigation strategies. Under non-limiting water conditions, Ramos produced higher fresh tuber yield. Furthermore, it is required to decrease the duration of wet/dry cycle under PRD strategy to guarantee efficient PRD and cope with extra water stress and hot weather in the region.

Worldwide Sustainability Hotspots in Potato Cultivation. 1. Identification and Mapping

Potato and its derivatives increasingly become globally traded products. Commercial companies more and more want to quantify the environmental footprints such as the efficiency of the use of land and water, greenhouse gas emissions, and the risks of eutrophication and contamination of the environment with pesticides. From various sources, global maps with grid cells of circa 8,600 ha (near the equator) were drawn representing potato-harvested area, potato fresh tuber yield (land use efficiency), slopes (risks of erosion), precipitation deficit (risks of depletion of fresh water resources through irrigation), and average daily maximum temperature throughout the season (risks of occurrence of pest epidemics and emission of pesticides). Hotspots for erosion are the slopes of the mountains in the Andes, African Rift, Southern China and volcanic areas in southern China, and the island countries in Southeast Asia. Fresh water availability may become limited in the East of North America, northern India, and China. Risks of insects are increased in continental hot summer climates and short spring crops with high temperatures towards harvest. Late blight is a threat in all humid areas such as maritime Europe, equatorial tropical highlands, and the humid western Pacific Ring. The examples discussed in this paper can be elaborated for more soil and weather-related factors such as acidity and salinity and heat waves or torrential rains. Sustainable long-term and long-range sourcing is deliberated as well as repercussions of trends such as globalization and climate change; the latter being relative favorable for the root and tuber crop potato compared to grain crops.

Farming systems affect potato (Solanum tuberosum L.) tuber and soil quality

In organic farming, nutrient cycling is based mainly on a farm level with external inputs only when organic fertilisers are not cycled and produced, and conventional systems largely depend on external inputs. Therefore, crop rotations are important tools for maintaining soil fertility and for increasing crop yields and qualities not only in organic farming systems but also in conventional systems. Moreover, proper nutrient management is a key element for sustainable farming. To identify the farming systems that would be sustainable for a longer period, a field experiment was conducted. The aim of this study was to investigate how different farming systems influenced tuber yields and quality (N, NO3−, P, K, Ca, Mg, dry matter and starch concentrations) of potato as well as how potato cultivation within a crop rotation under different farming systems affects soil quality (pH, Ntot, Corg, plant available P, K, Ca and Mg concentrations). Potato (Solanum tuberosum L.) was part of a five crop rotation experiment in which red clover (Trifolium pratense L.), winter wheat (Triticum aestivum L.), peas (Pisum sativum L.), potato and barley (Hordeum vulgare L.) followed each other simultaneously on a same field. Data presented in this paper concerned the first 3 years of the rotation during 2009–2011. The experiment was performed with six different farming systems as follows: two organic and four conventional. In both organic farming systems, catch crops (Organic CC) were used to provide organic green manure. In the second organic system, fully composted cattle manure (Organic CC+M) at a rate of 40tha−1 was also added as a fertiliser. The four conventional farming systems differed in the amounts of mineral fertilisers used as follows: N0P0K0 (control), N50P25K95 (low), N100P25K95 (average), or N150P25K95 (high). The average yield as well as tuber N, NO3−and Mg concentrations were significantly influenced by farming systems, year and their interaction. Fresh tuber yields were significantly higher under conventional systems in which nitrogen fertilisers were used. The use of average and high amounts of mineral nitrogen fertilisers increased tuber nitrogen and nitrate concentrations. The use of nitrogen fertilisers slightly decreased tuber Mg concentrations. There were no significant differences among farming systems in average tuber K, Ca, dry matter and starch concentrations. Only the year and its interaction with farming systems had a significant influence on these indicators. Different farming systems had different effects on some soil quality parameters. The Organic CC system significantly decreased the average soil K concentration after potato cultivation. The other organic system, Organic CC+M, significantly increased the average soil Corg and P concentrations after potato cultivation. The conventional control system significantly decreased the average soil Ntot, K and Mg concentrations and increased the P concentration. The conventional system that received 50kgNha−1 significantly decreased the average soil Ntot concentration after potato cultivation. The farming system that received an average amount of mineral nitrogen fertilisers significantly increased the average soil Corg and P concentrations and decreased the soil pH and K after potato cultivation. The conventional system that received 150kgNha−1 significantly decreased the average soil Corg, K and Mg concentrations. The average plant available Ca concentrations before and after potato crops did not have statistically significant differences among systems.

Genetic Diversity of Cassava (Manihot esculenta Crantz) Genotypes in Ethiopia

The experiment was conducted at Jimma Agricultural Research Centre . The objective of the experiment was to evaluate the genetic diversity of cassava using agronomic traits so as to characterize and cluster with in collected cassava genotypes. Thirty five cassava genotypes were sampled from the collection. Relatively high broad sense heritability was observed for plant height (42.08) and root diameter (31.88) indicating the existence of possibility for selection of genotypes for high fresh tuber weight. The clustering of genotypes based on 11 quantitative traits revealed the existence of five distinct groups. The maximum inter cluster distance was observed between genotypes under cluster II and V and I and V, hence, the genotypes grouped in these clusters could be used for crossing if high fresh tuber yield genotypes are planned in breeding program.

Potato Crop Response to Genotype and Environment in a Subtropical Highland Agro-ecology

Potato response to environment, planting date and genotype was studied for different agro-ecological zones in Lesotho. Field experiments were conducted at four different sites with altitudes ranging from 1,655 to 2,250 m above sea level during the 2010/2011 and 2011/2012 summer growing seasons. Treatments consisted of three cultivars that varied in maturity type, two planting dates and four sites differing in altitude and weather patterns. Various plant parts were measured periodically. To understand and quantify the influence of abiotic factors that determine and limit yields, the LINTUL crop growth model was employed which simulated potential yields for the different agro-ecological zones using weather data collected per site during the study period. Observed actual crop yields were compared with model simulations to determine the yield gap. Model simulations helped to improve our understanding of yield limitations to further expand potato production in subtropical highlands, with emphasis on increasing production through increased yields rather than increased area. Substantial variation in yield between planting date, cultivar and site were observed. Average tuber dry matter (DM) yields for the highest yielding season were above 7.5 t DM ha−1 or over 37.5 t ha−1 fresh tuber yield. The lowest yield obtained was 2.39 t DM ha−1 or 12 t ha−1 fresh tuber yield for cultivar Vanderplank in the 2011/2012 growing season at the site with the lowest altitude. Modelled potential tuber yields were 9–14 t DM ha−1 or 45–70 t ha−1 fresh yield. Drought stress frequently resulted in lower radiation use efficiencies and to a lesser degree harvest indices, which reduced tuber yield. The site with the lowest altitude and highest temperatures had the lowest yields, while the site with the highest altitude had the highest yields. Later maturing cultivars yielded more than earlier maturing ones at all sites. It is concluded that the risk of low yields in rain-fed subtropical highlands can be minimised by planting late cultivars at the highest areas possible as early as the risks of late frosts permit.

토양염농도에 따른 감자 품종들의 생장특성

This study was conducted to examine the basis for the information to select the suitable potato varieties grown in new reclaimed land. The potatoes of five varieties were planted in the port with 4 different electrical conductivities of saturated extracts of soil taken the Saemangeum reclamation area, which was made of non-treatment salt and three concentrations of salt treatment, 1.6 dS , 3.2 dS , 4.8 dS , respectively. All of the potato varieties were uniformly emerged without missing plant in all treatment groups, even 4.8 dS treatment group. According to the salt concentration of soil, required date to the emergence of the potato comparing to non-treatment salt was delayed 3-4 days in 1.6 dS , 6-10 days in 3.2 dS , 7-13 days in 4.8 dS , respectively, and the number of its branch decreased by 14-58% comparing to non-treatment salt depending on varieties. Since the increase of the salt concentration of the soil was more serious the decrease of the number of its branch, but plant height tended to increase when branch number per plant was small, which was depending on more number of its branch than salt concentration. Fresh tuber yield of potato comparing to non-treatment salt were decrease 33.7% in 1.6 dS , 59.5% in 3.2 dS , 79.3% 7-13 days in 4.8 dS , respectively. The threshold EC starting the growth inhibition of fresh weight decreased was 1.2 dS for Chudong, 1.8 for Chubeak, 1.9 for Chugang and Chuyeong, and 2.0 for Sumi, and EC which decreased 50% of dry weight index was 2.4 dS for Chubaek, 2.45 dS for Chudong, 2.81 dS for Chugang, 3.03 dS for Chuyeong, and 3.29 dS for Sumi. The present results suggest that Sumi is considered to the suitable potato variety grown on saline soils.

Analyzing potato response to irrigation and nitrogen regimes in a sub-tropical environment using SUBSTOR-Potato model

Increasing water scarcity and rising fertilizer cost warrant their judicious use in the world agriculture. It implies that management interventions should synchronize crop needs with soil supplies of these resources in the root zone to reduce probability of water and nutrient stresses and yield loss. This study examines the applicability of SUBSTOR-Potato model in analyzing potato response to irrigation and nitrogen regimes in a semi-arid sub-tropical environment of Punjab. In order to evaluate the model, database was generated by establishing a field experiment on potato (cv. Kufri Badshah) planted in mid-October on a sandy loam soil. Combinations of three irrigation regimes viz., irrigation water (IW) to pan evaporation (Ep) ratios of 0.8, 1.4 and 2.0 and four N rates viz., 0, 135, 180 and 225kgha−1 were randomized in a split-plot design with three replications. Half dose of N for a given rate was applied at planting and the rest half with a common irrigation 4 weeks after planting. The crop was managed for pest control by adopting local recommendations and harvested in end-January.Irrigation and fertilizer N had significant effects on tuber fresh yield, water use and N uptake. Performance of the SUBSTOR-Potato model was reasonable as indicated by close agreement of simulated crop phenology, biomass, water use, tuber yield and N uptake with the measured data. The normalized root mean square of deviations (RMSD) between simulated and measured values for harvest-time dry biomass and fresh tuber yield was 7.3 and 12.6%, while normalized RSMD for seasonal water use (ET+drainage) and total (tuber+haulm)N uptake was 12.4 and 19%. Simulation of tuber yield for independent data (2008–2009) was as good as for calibration data (2010–2011) giving confidence in the model. Scenario analysis based on historical weather data showed that mean potential tuber yield was 50.8tha−1 for October 1 planting that reduced to 41.8 and 37.8tha−1 for later (October 16 and October 31) plantings. The analysis also demonstrated that yield and ET-based water productivity (WPET) were greater on a sandy loam than a loamy sand soil for comparable irrigation and N regime. Interaction effects of irrigation and N on yield and ET indicated that irrigation response was greater in the presence of N. Greater initial soil water status reduced irrigation and N needs than with lower initial soil water for comparable tuber yield. Initial soil mineral-N also affected N and irrigation regime to achieve a given yield.

해발고도별 반하 종구 무게가 생육 및 수량에 미치는 영향

The plant growth and yield of Pinellia lernata (Thunb.) Breit. were studied by altitude and tuber weight. The emergence rates in low land area were not different by tuber weights, but it showed earlier emergence date in heavier weight of seed-tuber and low land area. The higher aerial growth such as plant height and number of leaves per plant was the heavier tuber weight in a planting year, but the growth was not different by the weight of tuber at second year after planting. The distribution pattern of tuber size perm` was not influenced by different seed-tuber weight. The number of harvested tuber was highest at more than 1 g of tuber weight, and followed I-2g and less than 2g. The distribution pattern of fresh tuber yield was not influenced by different altitude and seed-tuber weight. The marketable tuber, 2 g or more, tends to produced with more than 0.6 g seed-tuber. As the results above-mentioned, it was thought that the high yield was supposed to use seed-tuber over 0.6 g in the fertile soil.

VARIATION, HERITABILITY AND SELECTION RESPONSE OF SEVERAL CHARACTERS IN WHITE YAM (dioscorea rotundata poir)

Phenotypic and genotypic coefficients of variation, heritability, expected genetic gain and selection response were estimated for several agronomic characters among 40 selected clones of white yam. Three hybrid varieties (89-02565, H-2665, 89-2677) were included in the study as checks. Significant mean squares were observed in days to emergence, vine length, spininess, number of vines, and number of tubers, tuber length, tuber girth, tuber yield per hill, fresh tuber yield, and dry tuber yield among the selected 40 clones. Among the selected clones, fresh tuber yield varied from a minimum of 1.5 t/ha to a maximum of 25.5 t/ha. On the contrary, the fresh tuber yield of hybrid checks varied from a minimum of 6.0 t/ha to a maximum of 13.5 t/ha. The magnitude of phenotypic variance and phenotypic coefficient of variation were higher than genetic variance and genotypic coefficient of variation for all characters respectively. High heritability along with high genetic gain and high response to selection were observed for days to emergence, vine length, number of leaves, leaf area, number of vines, number of tubers, tuber per vine, tuber yield per hill, fresh tuber yield, and dry tuber yield. The study revealed that under more suitable environment, single plant selections followed by vegetative propagation should improve selection progress for higher tuber yield.

Diversity of Aerial Yam /Dioscorea bulbifera (L.)/ Accessions in Ethiopia Based on Agronomic Traits

The experiment was conducted at Jimma Agricultural Research Centre during 2007 cropping season. The objectives of the study were to evaluate the genetic diversity of aerial yam using agronomic traits so as to characterize and cluster with in collected aerial yam genotypes. Forty-seven aerial yam genotypes were sampled from the collection. Relatively high broad sense heritability was observed for Vine dry weight (53.14), tuber diameter (42.54), tuber length (42.04) and vine length (39.69) indicating the existence of possibility for selection of genotypes for high fresh tuber yield. The clustering of genotypes based on 11 quantitative traits revealed the existence of five distinct groups. The maximum inter cluster distance was observed between genotypes under cluster II and V and I (D2 =1844) IV and V (D2 =1702) hence, the genotypes grouped in these clusters could be used for crossing if high fresh tuber yield genotypes are planned in breeding program.

Morpho−Agronomical Characterization of Taro (Colocasia esculenta) Accessions in Ethiopia

One hundred accessions of taro (Colocasia esculenta) were tested at Jimma Agricultural Research Center dur-ing the 2011 growing season by using 10 x10 simple lattice design with two replications. The objectives of the study were to assess the nature and extent of diversity with in collected accessions based on key morphological descriptors and evaluate the accessions based on yield and yield related traits. Data on 17 qualitative and 13 quantitative traits were measured. Both sets of data collected were subjected to multivariate analysis using principal component (PCA), cluster analysis and of analysis of variance to determine the variability among accessions. The results of PCA based on qualitative traits reveled that characters have large contribution to the variability. The two-dimensional plot of the first two PCs showed a separation between accessions of big sized. Cluster analysis based on qualitative characters indicated the formation of seven clusters and existence of variability, based on their foliar and subterranean traits. Shannon-Weaver diversity index (H=0.27) showed that low levels of diversity existed among 100 C. esculenta based on the frequency of phenotypic characters that were considered. The analysis of variance for quantitative traits showed that number of active leaves/plant, petiole length and maximum horizontal distance highly significance differences exists for majority of characters studied and also path coefficient analysis at genotypic level showed that there are a number of characters exerting a maximum direct positive effect on fresh tuber yield suggesting that these characters are good contribution to the fresh root yield in taro. Overall, this study indicated that taro accessions collected from south and southwestern Ethiopia have an enormous wealth of traits variation for qualitative and quantitative characters, indicating huge potential for its genetic improvements through selection and hybridization. Therefore, selections based on these characters are efficient to maximize the fresh root yield and the genetic improvement of the crop.

Seasonal light interception, radiation use efficiency, growth and tuber production of the tuber crop Plectranthus edulis

Plectranthus edulis (Vatke) Agnew (Lamiaceae) is an ancient Ethiopian crop that produces below-ground, edible tubers on stolons. It is grown from seed tuber pieces. There is thus far little quantitative information on dry matter production of this crop and parameters determining growth and yield. The objective of this study was to understand and quantify the growth of P. edulis, and identify the processes determining and limiting yield. Two similar experiments were carried out at two sites (Awassa and Wondogenet in southern Ethiopia) in a split-plot design with five blocks and cultivar (Lofuwa and Chankua) as main factor and sampling date [20 2-weekly sampling dates from 14 to 280 days after planting (DAP)] as split factor. The crop was unknown at the start and showed an unusual growth pattern, for which reasons growth was analysed at a basic level.Maximum tuber weights were achieved 238 DAP in both cultivars and at both sites, and we consider the period up to 238 DAP as the growth period and the remaining time until the last sampling as the period of in situ storage, as is common farmers’ practice. Tuber dry weights at 238 DAP were c. 900–1000gm−2 and tuber dry matter concentrations 19–21%, corresponding to c. 4.5–4.9kgm−2 fresh tuber yield. Two processes limited the dry matter production: radiation interception by the crop and the conversion of the intercepted radiation into dry matter.Only about one third of the incident radiation was intercepted by the green leaves due to late emergence (c. 4 weeks), a slow development of the canopy after emergence until full ground cover was attained (c. 20 weeks), a short period during which ground cover was complete (c. 2 weeks) and a long period of declining ground cover starting 8 weeks before the end of the growing period.The radiation use efficiency (RUE) was established for the crops in Wondogenet and was only 1.59gMJ−1 PAR, on average across sampling dates. RUE varied across the growing period, increasing after emergence until early after tuber formation to about 2.7gMJ−1 PAR, then again decreasing because of a temporary stagnation (cv. Chankua in Awassa) or decrease (all other cultivar×site combinations) in total crop dry weight, starting 168 DAP in Awassa and 182 DAP in Wondogenet and lasting several weeks. During this period crop biomass decreased because the loss in canopy dry matter – especially stem dry matter – was not yet compensated for by an increase in tuber dry matter. Later, tuber production more than outweighed the decrease in canopy dry weight, and total dry weight and RUE increased again. During this last period the green stems might have significantly contributed to crop photosynthesis. The relative allocation of the total dry matter produced to the tuber varied between 81 and 99% at 238 DAP. Keeping the tubers in the soil after 238 DAP reduced tuber dry weights by 37–54% in 6 weeks.

Root distribution patterns of white yam (Dioscorea rotundata Poir.): a field study

The productivity of white yam (Dioscorea rotundata Poir) must increase to sustainably meet the demand of the increasing populations in the developing world where this is a staple crop. Although this could be achieved through the use of mineral fertilizers, reports indicate limited effects of these inputs on tuber yield. We hypothesized (i) that D. rotundata has a small and shallow root system and (ii) that this root system does not respond to mineral fertilizer application. Two field experiments were conducted in Côte d'Ivoire in year 1 and in year 2 to test these hypotheses. In the first field experiment we measured biomass production, as well as root density during plant growth in fertilized and unfertilized plots while in the second experiment, we analysed the distribution pattern of roots in horizontal and vertical root profiles in fertilized plots. The root system of D. rotundata consisted of seminal, adventitious and tubercular roots. Only the adventitious roots remained alive until the end of the growth cycle. The root length density was very low with a maximum of 0.25 cm cm−3. No roots were observed in the 15–30 cm horizon at 50 cm from the plant's crown. The horizontal and vertical root maps revealed that roots were mostly distributed in clumps, and there was a good correlation between the two methods of root sampling for this species. Fertilizer application had no significant effect on plant biomass, fresh tuber yield or on root growth. However, thinner and longer roots and higher tuber yields were observed in year 1 than in year 2. The different weather conditions and more specifically the higher soil temperature might explain the results obtained in year 1. Therefore, it could be recommended to farmers not to fertilize D. rotundata.

Variations in morphological and agronomic traits among Jerusalem artichoke (Helianthus tuberosus L.) accessions

Jerusalem artichoke is a diversely-utilized crop. Selection for high yield, inulin content and other economically important traits are useful for improving this crop. The objectives of the present study were to evaluate genetic variability for qualitative and quantitative traits among Jerusalem artichoke accessions and to identify different groups of accessions using morphological and agronomic traits. Seventy-nine accessions were evaluated in a randomized complete block design with two replications in the late rainy season 2008, the early rainy season 2009 and the late rainy season 2009 at Khon Kaen University agronomy farm, Thailand. Morphological and agronomic characteristics were evaluated for genetic variations. High variations were found among Jerusalem artichoke accessions for qualitative and quantitative characters, and selection for these characters is possible. High variations were observed for tuber width, number of tubers/plant, biomass, fresh tuber yield and tuber size. Correlation coefficient between fresh tuber yield and tuber size was positive and significant (0.58, P ≤ 0.01). Improvement of tuber size is a means to improve yield and tuber quality. Based on morphological and agronomic characteristics, Jerusalem artichoke accessions were clustered into four distinct groups (R2 = 0.88). These groups may be used as parental material to generate progenies for further improvement of this crop. This information will enable breeders to make informed decisions about possible heterotic groups for their breeding programs and germplasm conservation.

Differential response of potatoes (Solanum tuberosum L.) to salinity in an arid environment and field performance of the seed tubers grown with fresh water in the following season

Ten potato varieties, commonly grown in the Mediterranean region, were grown on sandy soil in an arid desert area of Israel. The potatoes were drip-irrigated with three water sources: fresh water (control – ENV1), saline water from a local well (intermediate salinity – ENV2) and the local well water enriched with NaCl (high salinity – ENV3). The average salinity levels expressed as the electrical conductivity (EC) measured in the soil extracts from the root zone were 2.35, 5.1 and 8.5dSm−1 for the ENV1, ENV2 and ENV3 treatments, respectively. Salinity stress decreased fresh tuber yields, increased tuber dry matter and soluble solids, increased tuber electrolyte content and lowered osmotic potential (OP) of the tuber sap in all varieties. ANOVA and Fisher's LSD pair-comparisons revealed highly significant differences among the varieties in all traits. Correlation analyses showed negative associations between tuber yield and tuber traits (dry matter, DM; total soluble solids, TSS, EC and OP). Positive associations were found between tuber DM and TSS, EC and OP. There was no positive association between early maturation or yielding capacity and tolerance to salinity. Vivaldi, a high-yielding variety and Almera, a low-yielding variety were found significantly less susceptible to salinity than Mondial, a late-maturing and high-yielding variety, and Charlotte, an early-maturing and low-yielding variety. The significant differences in the response to salinity stress indicated genotypic variation in the response to salinity and support the potential of breeding for tolerance to salinity in potatoes.When seed tubers of the three irrigation treatments were grown with fresh water irrigation during the following season, there were no significant differences in plant growth or tuber yields from the three seed sources in most varieties indicating the possibility of using saline water for the production of potato seed tubers.

Evaluation of Yield and Yield Attributes of Five Sweet Potato (<i>Ipomoea batata</i> (L)Lam) Varieties in Owerri - Imo State

Five sweet potato varieties (Ex –igbariam local, TIS 86/0356, TIS 8441, TIS 87/0087, and TIS 2532.OP.1.13) were evaluated for yield and agronomic performance in Imo State University Farm, Owerri. The experiment was laid out in a randomised complete block design with three replications. The planting density was 33,000 plants/ha and NPK (15:15:15) fertilizer was applied blanket at the rate of 100kg/ha. Significant (p= 0.05) differences were obtained in the performance of the varieties in fresh tuber yields, vigor at six weeks after planting, leaf area/plant, fresh biomass, tuber dry matter and biomass dry matter yields. Variety TIS 86/0356 gave significantly (p= 0.05) the highest mean fresh tuber yield of 7.38 t/ha and a significantly (p=0.05) high mean biomass dry weight of 3.08 t/ha, whereas the variety TIS 8441 gave the lowest mean fresh tuber and biomass dry matter yields of 1.28t/ha and 1.29t/ha, respectively. Variety TIS 86/0356 was therefore recommended for sweet potato growers in the region.Key words: Sweet potato, varieties, yield evaluation.

Soil Quality Changes and Quality Status: A Case Study of the Subtropical China Region Ultisol

Aims: To provide a soil quality assessment frame work and threshold limits for assessing soil quality in Ultisol of subtropical China region. Study Design: Selected minimum data set for soil quality assessment and threshold limits for the study were total carbon, nitrogen, soil pH and phosphorus, biomass carbon, nitrogen and phosphorus, maize grain and fresh potato tuber yields. Soil data (2000-2010), maize grain and fresh potato yield data (2000-2009) from a long term experiment under the Institute of subtropical Agriculture, China were analyzed using the SAS statistical package and means were graphically compared to determine threshold limits for selected data set and fitted into a soil quality model. Place and Duration of Study: The key Laboratory for Agro-ecological Processes in Subtropical Regions, Chinese Academy of Sciences; Institute of Subtropical Agriculture, Changsha, Hunan China long-term experimental site in Taoyuan county, conducted from the year 2000 to 2010. Methodology: Soils samples at the experimental fields were obtained from depths 0-20 cm using an auger at each replicate in triplicates and homogenized to obtain a composite sub sample, air-dried, sieved through 2.0 mm to obtain samples for analysis in the Laboratory. Parameters analyzed for were organic carbon concentration, measured by the combustion method using an automated C/N analyzer (Vario MAX CN, Elemental Co., Germany) while total nitrogen was by the Kjeldahl method of ISSCAS (1978). Microbial carbon, nitrogen and phosphorus levels were determined using the chloroform-fumigationextraction method (Jenkinson and Powlson, 1976; Vance et al., 1987; Brookes et al., Case Study