Sokoine University of Agriculture

Environmental performance of smallholder organic and conventional cotton production systems in Meatu, Tanzania

Show simple item record Bwana, T. N. 2020-10-06T05:38:28Z 2020-10-06T05:38:28Z 2019
dc.description PhD Thesis en_US
dc.description.abstract Cotton (Gossypium hirsutum L.) is among the most important export crops in Tanzania, contributing directly to peoples‘ livelihood and economic development. Cotton is grown under both conventional and organic farming systems and both farming systems are characterised by low cotton yield. Low fertilizer input use and low fertility contributes to such low yields. A quick solution to address the low cotton yield seems to be enhanced use of fertilizer and pesticide, which is also challenging on how to simultaneously sustain natural resources conservation and the supply of cotton fibre. Inappropriate use of fertilizer is linked to increased greenhouse gases (GHG) emissions. One of these gases is nitrous oxide (N 2 O), and nearly 2/3 of the anthropogenic N 2 O emission originates from agricultural activities. However, there are limited studies involving in-situ measurement of N 2 O in smllhoder farming systems in Sub-Saharan Africa. The use of organic and synthetic fertilizers and pesticides can also change the soil environment and hence microbial activity and soil quality. To address the problem of low cotton productivity, adequate information on the soil status and its suitability for cotton production is important. However, availability and acquisition of such information related to soil qualities in the study area is limited. This study was undertaken for two growing seasons in semi arid cotton growing areas in Meatu, Simiyu region, Tanzania. This study aimed to generate soil information, characterise and evaluate suitability of soils in these areas in terms of their qualities for cotton cultivation; compare yield and economic performance of cotton in response to different soil fertility and pest management practices under low input small holder conventional and organic production systems; compare microbial activity as a proxy for soil quality and quantifying N 2 O emission from soil under different smallholder organic and conventional cotton production practices. To characterise the soils, four pedons were characterized namely Biore-P1 in Mwamishali village, Ng'ho-P1 in Nghoboko village, IT-P1 in Sanga Itinje village and MWAB-P1 in Mwabagalu village. Soil samples from the pedons' horizons were analyzed for physico- chemical properties and were classified according to the USDA Soil Taxonomy and the World Reference Base for Soil Resources. The soil suitability for cotton production was evaluated by using most limiting criteria approach. A field experiment was set to test performance indicators (yield, economic benefit microbial activity and GHG emission) for fertility and pest management practice in organic and conventional farming systems. For fertility management, the recommended and current farming practices (30 kg N ha -1 and 3 Mg farm yard manura (FYM) ha -1 ) were tested against high input scenario (60 kg N ha -1 and 5 Mg FYM ha -1 ) and alternative practices (30 kg N ha -1 + 3 Mg ha -1 FMY and 3 Mg ha -1 FMY + legume intercrop) for conventional and organic cotton production, respectively. For pest management in conventional and organic treatments, respectively, the current practice (3 sprays of synthetic pesticide and pyrthrum spray as needed after scouting), higher rate (6 sprays of synthetic pesticide and pyrethrum spray as needed after scouting) and alternative practice (3 sprays neem + cow urine and spray of Neem + cow urine as needed after scouting) were tested. Seed cotton yield, cost, revenue and gross margin for each treatment was measured to estimate yield and economic performance. For GHG emission, in-situ measurement of N 2 O emission from soil was done using static chambers technique and gas analysis by gas chromatography (GC). For microbial activity, enzyme activity (arylsalfatase), potential nitrification, basal respiration and birch effect for plots under current practice, recommended practice, high input scenario and alternative practices were tested against a no fertilizer and no pesticide control treatment. The results on soil site suitability show that soil moisture and temperature regimes in all study areas were ustic and isohyperthermic respectively. Except for Mwabagalu, which had very deep pedon (> 150 cm), all the other pedons had moderate deep and well drained soils. For Mwamishali and Ng'hoboko CaCO 3 concretions were observed, which is a characteristic of calcic horizon in subsoil. Soil texture was sandy clay throughout all pedons with top soil pH ranging from neutral to strongly alkaline (pH 7.05 - 9.54). In all areas pH increased with depth from topsoil to subsoil. The organic carbon content was low to medium while total N concentrations were very low; CEC and exchangeable bases ranged from low (19 and 10.1 cmol (+) kg -1 ) to medium (37 and 38.4 cmol (+) kg -1 ) repectively. According to the USDA Soil Taxonomy the soils at Mwamishali and Ng'hoboko were classified as Pachic Calciustolls, while that of Sanga-Itinje and Mwabagalu were Typic Rhodustalfs and Sodic Haplusterts, respectively. All the soils were rated as marginally suitable for cotton production due to soil fertility limitations and therfore, sustainable cotton production in these areas would need interventions for soil fertility and soil moisture conservation improvement. The results on yield and economic performance showed that, for the current farming practice, organic and conventional farming practice had no significant difference in yield. The seed cotton yield in current organic practice was 1.4 and 0.64 Mg ha -1 compared to the conventional practice with yield of 1.3 and 0.37 Mg ha -1 for season 1 and 2 respectively. The current organic farming practice had higher gross margin of USD 527 and 137 ha -1 compared to the conventional practice with gross margin of USD 321.2 and -74.9 ha -1 for season 1 and 2 respectively. However, at higher input rate (fertilizer and pesticide) conventional cotton had significantly higher yield of 1.8 and 0.51 Mg ha -1 ) than organic practice with seed cotton yield of 1.4 and 0.39 Mg ha -1 for season 1 and 2, respectively. The high input conventional cotton had relatively lower gross margin of USD 463 and - 85.9 ha -1 compared to the organic practice with gross margin of USD 477 and -81.3 ha -1 for season 1 and 2, respectively. For organic cotton practice the alternative practices (intercropping cotton with green gram) had lower cotton yield of 1.3 Mg ha -1 in season 1 than the alternative conventional (1.7 Mg ha -1 ) but had higher gross margin (USD 616.2 ha -1 ) than conventional (USD 476 ha -1 ) as a result of additional revenue from green gram. For conventional cotton the alternative practice of combining inorganic fertilizer and manure outperformed the current practice by having both better yield and gross margin. In the season with less rainfall (season 2) the control outperformed all other treatments in terms of economic return indicating the rationale for farmers reluctance in investing on inputs under such conditions. The results on N 2 O emission show that the current organic and conventional cotton farming practices had similar (p < 0.05) cumulative area-scaled N 2 O emission. However, yield-scaled emissions were significantly higher in conventional than organic farming systems. For the high input scenario conventional cotton had higher area-scaled and yield- scaled N 2 O emission than organic cotton in season 1 which received higher rainfall (759 mm) but not in season 2 which had less rainfall (522 mm). A combination of manure and inorganic fertilizer as alternative practice reduced yield-scale N 2 O emission by 17% from inorganic fertilizer. In season 1, intercropping cotton with legumes reduced area-scaled emission by 27%. The emission factor for both conventional and organic systems were < 1% of applied total N. Although the cummulative N 2 O emission varied between season 1 (0.24 and 0.31 kg N 2 O-N ha -1 ) and season 2 (0.52 and 0.60 kg N 2 O-N ha -1 ), results show that the current smallholder organic and conventional cotton farming practices had similar soil N 2 O emission, which is very low compared to reported emissions from cotton fields in high input farming system (0.78 - 10.6 kg N 2 O-N ha -1 ). The results also revealed no significant (P<0.05) difference in microbial activity between organic and conventional cotton production practices using the current levels of fertilizer and pesticide. However, increasing N level as synthetic fertilizer or manure increased microbial activity. Manure fertilizer combination as an integrated practice increased arylsulfatase activity and potential nitrification but relatively reduced basal respiration in conventional farming in both seasons. Intercropping green gram increased microbial activity (arylsulfatase) but reduced potential nitrification and basal respiration and hence had no clear trend on improving soil microbial activity. Pest management had no effect in microbial activity in both organic and conventional farming practice and there was no significant difference between organic and conventional. The major conclusions drawn from this study are that, all the soils were rated as marginally suitable for cotton production due to soil fertility limitations and hence sustainable cotton production in these areas would need interventions for soil fertility improvement. For the existing smallholder farming system in Meatu, Tanzania, organic and conventional cotton system have similar agronomic and economic perfromance. Increasing input level in conventional cotton would have higher yield with low economic return than organic. Combining manure and inorganic fertilizer as well as intercropping cotton with grain legumes has potential for increasing yields while reducing the risk of increased N 2 O emission from cotton fields and improving microbial activity and hence soil quality. Under the prevailing semi-arid conditions, smallholder farmers are rational on limited use of fertilizer and pesticide Based on these conclusions it is recommended that alternative practice of cotton-legume intercrop, fertilizer-manure combination and pest control by neem and cow urine mixture are viable farming practices for smallholder cotton farmers. Further studies on the effect of cotton-legume intercrop on soil microbial activity that include other legume species are recommended. Further studies that include higher input levels and higher sampling frequencies for GHG are also recommended. en_US
dc.language.iso en en_US
dc.publisher Sokoine University of Agriculture en_US
dc.subject Smallholder en_US
dc.subject Cotton production en_US
dc.subject Meatu en_US
dc.subject Tanzania en_US
dc.subject Environmental performance en_US
dc.subject Smallholder farmers en_US
dc.subject Organic cotton en_US
dc.subject Conventional cotton en_US
dc.title Environmental performance of smallholder organic and conventional cotton production systems in Meatu, Tanzania en_US
dc.type Thesis en_US

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