East African highland bananas (Musa spp. AAA-EA) 'worry' more about potassium deficiency than drought stress
Taulya, G. - \ 2013
Field Crops Research 151 (2013). - ISSN 0378-4290 - p. 45 - 55.
foliar nutrient status - biomass allocation - osmotic adjustment - plant-growth - root ratio - soil-water - nitrogen - shoot - fertilizer - weevil
Drought stress, potassium (K) and nitrogen (N) deficiencies are major constraints to rain-fed East African highland banana (EAHB) production in Uganda. It was hypothesised that the reduction in fresh bunch mass and increase in dry matter (DM) allocation to corms with drought stress, K and N deficiency is additive. Individual plant measurements at harvest from two field trials in central and south western Uganda were analyzed to evaluate effects of cumulative rainfall (CRF) received 365 days from sucker emergence, mineral K and N inputs on EAHB bunch yields. Dry matter content in aerial shoot (leaves and pseudostems) relative to that in the subterranean corm was also analyzed to evaluate DM allocation plasticity due to drought stress, K and N deficiency. This was verified with allometric analysis using pre-harvest stage plants from farms of known K and N nutritional status and plants from a screen house drought stress pot trial in Uganda. Dry matter production and yields were mainly driven by K interacting with CRF. Within 12 months, K input (250-600 kg K ha(-1) yr(-1)) increased bunch yield from 8 to 15 Mg ha(-1) yr(-1) irrespective of whether dry (CRF <1100 mm) or wet (CRF >= 1100 mm) conditions prevailed, possibly due to K-mediated osmotic adjustment under dry conditions. Without K input, wet conditions increased bunch yield from 6 to 8 Mg ha(-1) yr(-1) while dry conditions decreased it from 6 to 4 Mg ha(-1) yr(-1) within 12 months. Total DM and its distribution between the biomass structures followed similar trends. Nitrogen input (150-400 kg N ha(-1) yr(-1)) neither affected bunch yield nor DM allocation at harvest stage. At pre-harvest stage, reduction in DM allocation to the corm per unit increase in total DM was 14-22% significantly lower with N and/or K deficiency compared with that under sufficient K and N. Drought stress per se had no effect on DM allocation but enhanced DM allocation shifts due to K deficiency. Drought-stressed EAHB thus increase DM allocation to subterranean structures only if K-deficient, unlike responses reported for other plant species. Potassium nutrition is perhaps a more viable entry point for mitigation of drought stress in EAHB cropping systems than irrigation but this requires further agronomic and economic evaluation. It may be important to account for carbon allocated to osmotic adjustment for realistic simulation of water- and K-limited growth in EAHB. (c) 2013 Elsevier B.V. All rights reserved.
Biological control of invasive plant species: A stochastic analysis
Chalak, S.M. ; Ruijs, A.J.W. ; Ierland, E.C. van - \ 2011
Weed Biology and Management 11 (2011)3. - ISSN 1444-6162 - p. 137 - 151.
integrated weed management - cirsium-arvense - sclerotinia-sclerotiorum - pest-management - new-zealand - resistance - dynamics - weevil - information - populations
Biological control agents are regarded as a relatively safe method to control weeds. However, their impact on weeds can be relatively low and unpredictable. The aims of this article were to: (i) assess whether or not a weevil (Apion onopordi) and a mycoherbicide (Sclerotinia sclerotiorum) are desirable as biological agents for the control of Californian thistle (Cirsium arvense) in New Zealand despite their uncertain effectiveness; (ii) identify the combination of control options that is optimal to control the thistle; (iii) analyze the economic consequences of excluding chemicals from the weed control strategy; and (iv) assess the feasibility of the eradication of this weed. Two optimization models were developed and compared: one deterministic model and one stochastic model. The results showed that taking into account the stochastic effectiveness of biological agents can change the optimal integrated strategy, particularly if the biological control agent is relatively expensive. However, for a cheaper biological agent, the stochastic efficacy is less likely to change the optimal control strategy. On the basis of the modeling results, the authors argue that, in the context of the agri-environmental setting of this article's case study, chemicals can be replaced by more environmentally friendly control options at a relatively low cost. The authors also show that the eradication of the thistle is unlikely, at least given the efficacy of the existing control methods.
Mineral fertilizer response and nutrient use efficiencies of East African highland banana (Musa spp., AAA-EAHB, cv. Kisansa)
Nyombi, K. ; Asten, P.J.A. van; Corbeels, M. ; Taulya, G. ; Leffelaar, P.A. ; Giller, K.E. - \ 2010
Field Crops Research 117 (2010)1. - ISSN 0378-4290 - p. 38 - 50.
irrigated lowland rice - farming systems - soil fertility - uganda - yield - management - nitrogen - weevil - quefts - plant
Poor yields of East African highland bananas (Musa spp., AAA-EAHB) on smallholder farms have often been attributed to problems of poor soil fertility. We measured the effects of mineral fertilizers on crop performance at two sites over two to three crop cycles; Kawanda in central Uganda and Ntungamo in southwest Uganda. Fertilizers were applied at rates of 0N-50P-600K, 150N-50P-600K, 400N-0P-600K, 400N-50P-0K, 400N-50P-250K and 400N-50P-600K kg ha_1 yr_1. In addition 60Mg-6Zn-0.5Mo- 1B kg ha_1 yr_1 was applied to all treatments, with the exception of the control plots which received no fertilizer. Fresh bunchmass and yield increased with successive cycles. Yield increases above the control ranged from 3.1 to 6.2 kg bunch_1 (average bunch weight for all treatments 11.5 kg bunch_1) and 2.2- 11.2Mg ha_1 yr_1 (average yield for all treatments 15.8 Mg ha_1 yr_1) at Kawanda, compared with 12.4- 16.0 kg bunch_1 (average bunch weight for all treatments 14.7 kg bunch_1) and 7.0-29.5 Mg ha_1 yr_1 (average yield for all treatments 17.9 Mg ha_1 yr_1) at Ntungamo. The limiting nutrients at both sites were in the orderK > P > N. Potassium,Nand P foliar nutrient mass fractions were below previously established Diagnosis and Recommendation Integrated System (DRIS) norms, with the smallest K mass fractions observed in the best yielding plots at Ntungamo. Total nutrient uptakes (K > N > P) were higher at Ntungamo as compared with Kawanda, probably due to better soil moisture availability and root exploration of the soil. AverageN, P andKconversion efficiencies for twocrop cycles at both sitesamounted to 49.2 kg finger DM kg_1 N, 587 kg finger DM kg_1 P and 10.8 kg finger DM kg_1 K. Calibration results of the model QUEFTS using data fromNtungamo were reasonable (R2 = 0.57, RMSE = 648 kg ha_1). Using the measured soil chemical properties and yield data froman experiment atMbarara in southwest Uganda, the calibrated QUEFTSmodel predicted yields well (R2 = 0.68, RMSE = 562 kg ha_1). We conclude that banana yields can be increased by use of mineral fertilizers, but fertilizer recovery efficiencies need to improve substantially before promoting wide-scale adoption
Piecemeal versus one-time harvesting of sweet potato in north-east Uganda with special reference to pest damage
Ebregt, E. ; Struik, P.C. ; Odongo, B. ; Abidin, P.E. - \ 2007
NJAS Wageningen Journal of Life Sciences 55 (2007)1. - ISSN 1573-5214 - p. 75 - 92.
zoete aardappelen - gewasbescherming - cylas - ipomoea batatas - nematoda - curculionidae - uganda - sweet potatoes - plant protection - cylas - ipomoea batatas - nematoda - curculionidae - uganda - cylas-formicarius fab - millipede infestation - farmers information - cultural-practices - weevil - coleoptera - yield
In north-eastern Uganda, the sweet potato crop of small subsistence farmers is severely affected by many pests, including (rough) sweet potato weevils, nematodes and millipedes. Field experiments with sweet potato (Ipomoea batatas (L.) Lam.) were conducted at Arapai Station in Soroti District, north-eastern Uganda in three consecutive seasons to study the differences between the indigenous practice of harvesting piecemeal in combination with storage `in-ground on plants¿ and one-time harvesting after crop senescence, with special reference to damage caused by sweet potato weevils (Cylas spp.), rough sweet potato weevils (Blosyrus spp.), millipedes (Diplopoda) and nematodes. The area has two rainy seasons per calendar year, the first one with long, reliable rains and the second one with short, unreliable rains. Severe sweet potato weevil damage in the vines was responsible for the mortality of 46% of the plants in Experiment 1, which was carried out during the first rainy season. Starting 3 months after planting (MAP), sizable storage roots could be harvested, although their number and weight declined after 4 MAP with piecemeal harvesting. The highest storage-root yield (17.8 Mg ha¿1) was found in Experiment 2 (second rainy season) at the final harvest. The yield of storage roots stored `in-ground on plants¿ during the prolonged dry season (Experiment 3) was very low compared with the yields of Experiment 1 (first rainy season) and Experiment 2 (second rainy season). Sweet potato weevil damage of the storage roots was significantly less with piecemeal harvesting than with one-time harvesting, and piecemeal harvesting also increased the quality of the storage roots for human consumption and commercial purposes. However, with piecemeal harvesting the rough sweet potato weevil (Blosyrus spp.) caused more storage root damage than with one-time harvesting. No statistically significant differences between the two types of harvesting were found for damage caused by nematodes or millipedes. It was concluded that piecemeal harvesting of sweet potato storage roots contributes to the control of sweet potato weevil in both vines and storage roots and hence improves the quality of the harvested roots. As rainfall distribution affects the population dynamics of this weevil this method can only be used during a limited period of the year.