Browsing by Subject "Soil physics"

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    Relationship between soil physical properties and crop yields in different cropping systems in southern Cameroon
    (2014) Tueche, Jacques Roberto; Cadisch, Georg
    Crop yields in sub-Saharan Africa (SSA) has been more or less stagnant since 1961. This can be connected to the traditional slash-and-burn agricultural based system. A growing population has forced most farmers to cultivate the same fields repeatedly. The resulting rapidly declining crop yields led eventually to an accelerated conversion of forest land into agricultural land to cope with food demand. However, the integration of leguminous species, the use of fertilizer and tillage have been proven to increase yield especially in intensive cropping systems. Although, depending on its frequency and kind, tillage can destroy soil aggregates resulting in degradation of soil organic matter. Else, it is known that improved crop varieties can be higher-yielding and more yield responsive to increased fertilizer application than traditional crop varieties. Information is scarce on the effects of soil physical properties on plantain, maize and tomato yield formation and on their changes during their cropping phase. This study aimed at understanding the relationships between soil physical parameters and crop yields in different cropping systems in southern Cameroon with the goal to identify improved management strategies. This led to the setup of 4 experiments: In a first experiment, the effects of soil physical properties on plantain yield were determined in a factorial trial in three southern Cameroonian villages comparing four cropping systems comprising two planted legumes (1) Flemingia macrophylla, (2) Pueraria phaseoloides, as well as (3) a crop, i.e. hot pepper, and (4) natural regrowth, all planted with plantain, established after conversion of old forest versus young bush fallow. Between 2002 and 2006, clay and silt content, MWD, GMD and the proportion of macroaggregates increased, whereas relative sand content, bulk density, the proportions of mesoaggregates and microaggregates decreased (not absolute decreased for sand content) in all villages, fallows and cropping systems. Changes of aggregate MWD and GMD were larger in the F. macrophylla and natural regrowth systems than in Pueraria systems. Plantain fresh bunch yield was 107 unaffected by village, fallow, and cropping systems. Plantain cultivation did not lead to a degradation of the determined soil physical properties. In a follow up second trial at Mfou, it was evaluated, if maize cropped immediately after plantain was affected by the previous plantain systems and if tillage or N fertilizer would affect maize growth and grain yield and soil physical properties. In 2006, all plantain plots were cleared and split into 4 subplots, to assess the response of maize to tillage versus no–till, and of 60 kg ha-1 of N as urea compared to no N in a 2 x 2 factorial design. Freshly cleared eight years old bush fallow served as control. Maize grain yield was highest in the previously not cropped bush control and lowest in the previous Flemingia system. Grain yield in the previous Pueraria and natural regrowth systems were not different from the control. Maize grain yield was highest, when tillage was combined with fertilizer application, being significantly higher than in individual tillage or fertilizer application treatments. Soil physical properties were affected by tillage but did not remain different until the end of the maize growing phase. In a third experiment the response of different tomato cultivars to different cultivation practices in an on-farm factorial trial was tested at Essong Mintsang in the central region of Cameroon on a Rhodic Kandiudult. Treatments were: current farmer practice of manual tillage yet not destumped, with either reduced input (no tillage, not destumped) or increased input (no tillage yet destumped, manual tillage and destumped, mechanical tillage and destumped). Yields of three tomato varieties were determined to assess, if changes in intensity of land preparation can improve soil physical properties and thus yields. At harvest, across land preparations the cv. Rossol produced higher yields (8.12 Mg ha-1) than cv. Roma (6.05 Mg ha-1) and cv. Rio Grande (4.46 Mg ha-1). Tomato total and marketable yields were significantly higher on the destumped tractor till, destumped manual till and stumps-retained manual till treatments than in the stumps retained no-till treatment. Total fresh yields of cvs. Roma and Rossol increased, when the soil was tilled, while cv. Rio Grande had no response to land preparation. Soil aggregates were least stable in the destumped, tractor till treatment, with significantly lower MWD (p=0.02) and higher mesoaggregate proportions (p=0.05) than in the other treatments. Across tomato cultivars and treatments, the marketable fruit yield could be predicted by clay, macroaggregates and bulk density. Early flowering and fruit production combined with nematode resistance were probably the main contributing factors to the high yields of cv. Rossol. 108 In a fourth experiment, the residual effects of the previous land preparation methods on maize growth and yield as well as impacts on soil physical properties were assessed. Land preparation methods had been applied to the preceding tomato crop. At harvest, maize fresh cob yield was significantly (P<0.05) lowest in the stump retained no till treatment. The equivalent maize dry grain yields varied from 2.35 Mg ha-1 in the stump retained no-till treatment to 4.16 and 4.33 Mg ha-1 in the manual till stump retained and destumped treatments, respectively. Soil aggregates were the least stable in the destumped tractor till treatment, with significantly lower (P=0.10) GMD than in the destumped manual till treatment. Maize fresh cob yield showed a strong correlation (R2~0.50, P=0.037) with soil aggregation and cone resistance to soil penetration. In summary, the transition from shifting to permanent cultivation with acceptable yields is possible if an appropriate combination of crops (cultivar), use of leguminous species, tillage and fertilizers is implemented. Soil physical properties can control crop yield and hence can be manipulated to maximise yield. Tillage can contribute to yield increase if there is an adequate SOM content and a suitable crop cultivar is chosen. Yet, tillage is labour intensive and degrades soil physical properties. Therefore, it is crucial to identify a minimum tillage frequency for low labour demand and minimal soil degradation, but with improved yields in conjunction with optimised fertilization and the development of improved crop cultivars adapted to a wide range of soil conditions.