Kampala, Uganda
Kampala, Uganda

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Nyombi K.,Wageningen University | Nyombi K.,Makerere University | van Asten P.J.A.,International Institute Of Tropical Agriculture | Corbeels M.,TSBF CIAT | And 4 more authors.
Field Crops Research | Year: 2010

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 bunch mass 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 2.2-11.2 Mg 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 order K > P > N. Potassium, N and 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. Average N, P and K conversion efficiencies for two crop cycles at both sites amounted 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 from Ntungamo were reasonable (R2 = 0.57, RMSE = 648 kg ha-1). Using the measured soil chemical properties and yield data from an experiment at Mbarara in southwest Uganda, the calibrated QUEFTS model 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. © 2010 Elsevier B.V. All rights reserved.

Gentile R.,University of California at Davis | Vanlauwe B.,TSBF CIAT | Kavoo A.,TSBF CIAT | Chivenge P.,University of California at Davis | Six J.,University of California at Davis
Nutrient Cycling in Agroecosystems | Year: 2010

To address soil fertility decline, additions of organic resources and mineral fertilizers are often integrated in sub-Saharan African agroecosystems. Possible benefits to long-term C and N stabilization from this input management practice are, however, largely unknown. Our objectives were (1) to evaluate the effect of residue quality and mineral N on soil C and N stabilization, (2) to determine how input management and root growth interact to control this stabilization, and (3) to assess how these relationships vary with soil texture. We sampled two field trials in Kenya located at Embu, on a clayey soil, and at Machanga, on a loamy sand soil. The trials were initiated in 2002 with residue inputs of different quality (no input, high quality Tithonia diversifolia, medium quality Calliandra calothyrsus, and low quality Zea mays (maize) stover), incorporated at a rate of 4 Mg C ha-1 year-1 alone and in combination with 120 kg N ha-1 season-1 mineral fertilizer. Maize was grown in the plots each season, and a section of the plots was left uncropped. All aboveground maize residues were removed from the plots. Soil samples (0-15 cm) were collected in March 2005 to assess aggregation and C and N stabilization. The fine-textured soil at Embu was more responsive to inputs than the coarse-textured soil at Machanga. Residue additions increased macroaggregation at Embu, and cropping increased aggregation at Machanga. At Embu adding organic residue, regardless of the quality, and cropping significantly increased total soil C and N. This increase was also observed in the macroaggregate and microaggregate-within-macroaggregate fractions. Input treatments had little effect on C and N contents of the whole soil or specific fractions at Machanga. Nitrogen fertilizer additions did not significantly alter C or N content of the whole soil or specific fractions at either site. We conclude that residue quality does not affect the stabilization of soil organic C and N. Inputs of C and soil stabilization capacity are more important controls on stabilization of soil organic matter. © 2008 Springer Science+Business Media B.V.

Chivenge P.,University of California at Davis | Vanlauwe B.,Tsbf Ciat | Gentile R.,University of California at Davis | Gentile R.,Agresearch Ltd. | Six J.,University of California at Davis
Soil Biology and Biochemistry | Year: 2011

Organic C inputs and their rate of stabilization influence C sequestration and nutrient cycling in soils. This study was undertaken to explore the influence of the combined application of different quality organic resources (ORs) with N fertilizers on the link between aggregate dynamics and soil organic C (SOC) and soil N. A mesocosm experiment was conducted in Embu, central Kenya where 4 Mg C ha-1 of Tithonia diversifolia (high quality), Calliandra calothyrsus (intermediate quality) and Zea mays (maize; low quality) were applied to soil compared to a no-input control. Each treatment was fertilized with 120 kg N ha-1 as urea [(NH2)2CO] or not fertilized. The soils used in the mesocosms were obtained from a three-year old-field experiment in which the same treatments as in the mesocosm were applied annually. No crops were grown in both the mesocosms and the thee-year field experiment. Soil samples were collected at zero, two, five and eight months after installation of the mesocosms and separated into four aggregate size fractions by wet sieving. Macroaggregates were further fractionated to isolate the microaggregates-within-macroaggregates; all soils and fractions were analyzed for SOC and N. The addition of ORs increased soil aggregation and whole SOC and soil N compared to the control and sole N fertilizer treatments. There were no differences among different OR qualities for whole SOC or soil N, but maize alone resulted in greater mean weight diameter (MWD), macroaggregate SOC and N than sole added Calliandra. The addition of N fertilizer only influenced SOC and soil N dynamics in combination with maize where SOC, soil N and aggregation were lower with the addition of N fertilizer, indicating an increased decomposition and loss of SOC and soil N due to a faster aggregate turnover after addition of N fertilizer. In conclusion, compared to high quality ORs, low quality ORs result in greater aggregate stability and a short-term accumulation of macroaggregate SOC and N. However, the addition of N fertilizers negates these effects of low quality ORs. © 2010 Elsevier Ltd.

Gentile R.,Agresearch Ltd. | Gentile R.,University of California at Davis | Vanlauwe B.,TSBF CIAT | Chivenge P.,University of California at Davis | Six J.,University of California at Davis
Plant and Soil | Year: 2011

The decline of soil organic matter (SOM) and its associated fertility is one of the most important constraints to enhanced crop productivity in sub-Saharan Africa. Integrated soil fertility management recognizes the potential benefits of the combined use of organic residue and mineral fertilizer inputs for improved crop yield and SOM build up. However, these benefits may be controlled by residue quality. We examined the short- to long-term C and N dynamics following application of different quality residues with and without N fertilizer in a series of experiments comprising different timescales of measurement in a Kenyan Humic Nitisol. The combined results of these studies indicate that residue quality and fertilizer additions alter short-term C and N mineralization. Combining low quality residue and fertilizer inputs immobilized a greater amount of fertilizer-N than high quality residue. Under field conditions, this reduction in available N induced by the combination of low quality residue and fertilizer reduced environmental N losses and created a positive interactive effect on crop N uptake. While input management manipulated short-term nutrient dynamics, it did not influence long-term SOM stabilization. The input of residue, regardless of quality, contributed to long-term soil fertility improvement. In conclusion, organic residue quality can be manipulated to optimize short-term nutrient dynamics while still conferring the same benefits to long-term SOM contents. © 2010 The Author(s).

Chivenge P.,University of California at Davis | Vanlauwe B.,Tsbf Ciat | Gentile R.,Agresearch Ltd. | Six J.,University of California at Davis
Agriculture, Ecosystems and Environment | Year: 2011

Aggregation and stabilization of soil organic C (SOC) and N are highly dependent on soil texture and addition of organic resources (ORs). While OR quality may influence SOC and N stabilization within aggregates, the simultaneous addition of N-fertilizers may enhance OR decomposition resulting in loss of SOC. A mesocosm study was conducted on a clayey soil at Embu and a sandy soil at Machanga in central Kenya to determine the influence of soil texture, OR quality and N-fertilizer on aggregation, SOC and N. Tithonia diversifolia (high quality), Calliandra calothyrsus (medium quality) and Zea mays (maize; low quality) residues, natural abundance or labeled with 15N, were applied to soil at an equivalent rate of 4MgCha-1 compared to no input control. Each treatment was fertilized with 120kg 14N or 15Nha-1 as (NH2)2CO, or not fertilized. Soil samples were collected at installation of the mesocosms (start), and 8 months after installation (end). Soils were separated into different aggregate size fractions by wet sieving and macroaggregates were further fractionated to isolate microaggregates-within-macroaggregates. Total soil and aggregate fractions were analyzed for SOC and N. On average, 20% and 70% of SOC and N was in the macroaggregates in the sandy and clayey soils, respectively. There were no differences among OR quality in both soils but in the clayey soil all ORs resulted in greater SOC and N than in the control. However, proportions of OR-derived N in the macroaggregates, mostly in the microaggregates-within-macroaggregates were greater with sole applied maize in the clayey soil. The addition of N-fertilizer together with maize stover reduced soil N, macroaggregate N, and OR-derived N in the microaggregate and silt and clay fractions within macroaggregates compared to when maize was applied alone. In the sandy soil, Calliandra resulted in greater OR-derived N than Tithonia in the coarse particulate organic matter (cPOM; i.e., 5% compared to 2% of N applied). Thus, the greater polyphenol concentration in Calliandra likely slowed its decomposition compared to that of Tithonia. In addition, greater proportions of N and residue-derived N in the macroaggregates were observed in the coarse POM in the sandy soil whereas in the clayey soil it was in the microaggregates-within-macroaggregates. We conclude that the preservation of OR-derived N is affected by the chemical recalcitrance of the residues in sandy soils, whereas macroaggregate protection, and not OR quality, is the major factor in clayey soils. © 2010 Elsevier B.V.

Chivenge P.,University of California at Davis | Vanlauwe B.,TSBF CIAT | Six J.,University of California at Davis
Plant and Soil | Year: 2011

The combined application of organic resources (ORs) and mineral fertilizers is increasingly gaining recognition as a viable approach to address soil fertility decline in sub-Saharan Africa (SSA). We conducted a meta-analysis to provide a comprehensive and quantitative synthesis of conditions under which ORs, N fertilizers, and combined ORs with N fertilizers positively or negatively influence Zea mays (maize) yields, agronomic N use efficiency and soil organic C (SOC) in SSA. Four OR quality classes were assessed; classes I (high quality) and II (intermediate quality) had >2.5% N while classes III (intermediate quality) and IV (low quality) had <2.5% N and classes I and III had <4% polyphenol and <15% lignin. On the average, yield responses over the control were 60%, 84% and 114% following the addition of ORs, N fertilizers and ORs + N fertilizers, respectively. There was a general increase in yield responses with increasing OR quality and OR-N quantity, both when ORs were added alone or with N fertilizers. Surprisingly, greater OR residual effects were observed with high quality ORs and declined with decreasing OR quality. The greater yield responses with ORs + N fertilizers than either resource alone were mostly due to extra N added and not improved N utilization efficiency because negative interactive effects were, most often, observed when combining ORs with N fertilizers. Additionally, their agronomic N use efficiency was not different from sole added ORs but lower than N fertilizers added alone. Nevertheless, positive interactive effects were observed in sandy soils with low quality ORs whereas agronomic use efficiency was greater when smaller quantities of N were added in all soils. Compared to sole added ORs, yield responses for the combined treatment increased with decreasing OR quality and greater yield increases were observed in sandy (68%) than clayey soils (25%). While ORs and ORs + N fertilizer additions increased SOC by at least 12% compared to the control, N fertilizer additions were not different from control suggesting that ORs are needed to increase SOC. Thus, the addition of ORs will likely improve nutrient storage while crop yields are increased and more so for high quality ORs. Furthermore, interactive effects are seldom occurring, but agronomic N use efficiency of ORs + N fertilizers were greater with low quantities of N added, offering potential for increasing crop productivity. © The Author(s) 2010.

Gatere L.,Cornell University | Lehmann J.,Cornell University | DeGloria S.,Cornell University | Hobbs P.,Cornell University | And 2 more authors.
Agriculture, Ecosystems and Environment | Year: 2013

Conservation agriculture practices have been successfully applied to improve crop yields in South America, but questions arose whether these practices can be successfully implemented in Africa. Here we show that a specific set of soil conservation practices called conservation farming (CF) using planting basins and hand hoes disseminated on 280 farms in Zambia on average failed to increase maize yields compared to traditional farming (TF). Average grain yield was low with 1.2tha-1, but variation between farms was large with a variance of 32% for CF, ranging in individual farms from 0.02 to 2.8tha-1. Yields on farms that declared to practice CF were more constrained by inappropriate management (P<0.001 of multiple stepwise regression; 13% of total variability) such as lack of early planting and insufficient weeding (25% of total variability explained by management) than by site or climatic conditions. In contrast, yields under TF varied the most (26%) based on the amount and types of inputs. CF practices increased maize yields at rainfall below 1000mmyr-1, and in valley bottoms possibly due to the water-collecting properties of the planting basins, but decreased yields in lower slope and valley positions of higher rainfall regions above 1000mmyr-1 likely due to waterlogging. Observed management constraints in comparison to site or soil conditions highlight the critical importance of training needed to make complex interventions such as CF successful in areas where means and infrastructure are insufficient to provide farmers with external inputs. © 2013 Elsevier B.V.

Odhiambo J.A.,Egerton University | Vanlauwe B.,TSBF CIAT | Tabu I.M.,Egerton University | Kanampiu F.,CIMMYT | Khan Z.,ICIPE
Archives of Phytopathology and Plant Protection | Year: 2011

Striga hermonthica a major biotic constraint to cereal production can be controlled by trap crops. Soybean cultivars vary in ability to stimulate suicidal germination of the weed. An experiment was conducted to select soybean (Glycine max) varieties with the ability to stimulate germination of S. hermonthica seeds. Experiments were conducted with strigol Nijmegen 11 (GR 24), a synthetic stimulant, as a check. In the pot and field experiments, maize (variety WH507) was intercropped with soybeans. Variation occurred among soybean varieties in inducing germination of S. hermonthica. The relative germination induction by soybean varieties ranged from 8% to 66% compared to 70% for synthetic stimulant check. Varieties TGX1448-2E, Tgm 1576, TGX1876-4E and Tgm 1039 had the highest relative germination. Soybean varieties TGX 1831-32E, Tgm944, Tgm 1419 and Namsoy4m had high stimulation but low attachment. Intercropping maize with soybeans in the field led to a low S. hermonthica count and high maize yield. © 2011 Taylor & Francis.

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