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Improving crop production by field management strategies using crop water productivity modeling: Case study of tef (Eragrostis tef (Zucc.) Trotter) production in Tigray, Ethiopia.
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Increasing food production to feed the fast growing world population particularly in developing countries relies on two options: either increase the arable land or improve the productivity of the existing cultivated land. This research focuses on the highly populated highlands ofTigray (northern Ethiopia), where improving the productivity of land isthe only option for sustainable food production. In the drought-prone and highly degraded highlands of Tigray, rainfed cereal production is restricted by low and highly variable rainfall with common occurrence of dry spells during the cropping season on the one hand, and low levels of soil fertility on the other hand. Water saving techniques and applying inorganic fertilizers to intensify the staple food production are essential to maximize the productivity of the land. Elaborated strategies developed by crop growth models can be used for designing and better understanding the impact of the aforementioned strategies. </>
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</>In this study the water productivity model AquaCrop developed by FAO was used as a tool to test different field management strategies for improving productivity of tef</> under the local environmental conditions in the highlands of Tigray. The model estimates yield by relating crop transpiration with biomass and yield production and allows the users to simulate yield under various conditions. </>
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</>Tef (Eragrostis tef </>(Zucc.)</> Trotter) is an endemic cereal crop and staple dietin Ethiopia. It is highly preferred by the farmers not only in view of its adaptability to a wide range of environmental conditions but also for its high market value of both grain and crop residue (straw). However,low productivity is often reported mainly due to water and fertility stress. </>
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Considering this context, a research project was designed with field experiments in Randomized Complete Block Design (RCBD) with split plot arrangement, conducted in 2008, 2009 and 2010 at two sites located in the south-east and east of Tigray in two soiltypes. Five levels of nitrogen (N) and phosphorus (P) fertilizers (no input, 50%, 75%, 100% and 150% of the recommended doses) were applied to both rainfed and irrigated plots. The objectives of the study were: </>
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a) </></></>to gain insight in the response of tef to water and soil fertility stress;</>
b) </></></>to obtain the necessary field data to calibrate and validate the AquaCrop model for the local crop tef, considering both water and fertility stress; </>
c) </></></>to investigate the effect of inorganic fertilizer application (N and P) on yield and yield components of the crop; </>
d) </></></>to evaluate the impact of supplementary irrigation (SI, a practice of applying a limited amount of water to essentially rainfed crops when the rainfall failsto provide sufficient moisture for normal growth) in mitigating the impact of dry spells during the growing season and to improve the productivity of tef;</>
e) </></></>to assess the nutrient use efficiency of tef in different conditions of nutrient availability and </>supplementary irrigation; and </>
f) </></></>to test different field management strategies to improve the productivity of tef in Tigray.</>
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The field experiments,complemented with a mini-lysimeter experiment conducted in 2008 and 2009, were used to gain insight in the response of tef to water and soil fertility stress and to calibrate and validate the AquaCrop model for tef under water and fertility stress conditions. Additionally, data collected during field experiments conducted in 2006 and 2007 in the frame of master research were also used as additional inputs for the calibration process. </>
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The results of the crop response revealed that the water sensitive stage for tef is at or around flowering. Supplementary irrigation (SI) during this growth stage produced a surplus of 98 to 111% in yield (Y), 52 to 54% in water use efficiency (WUE) and 41 to 88% in dry aboveground biomass (B) compared to rainfed crops. SI also improved the uptake of nutrients, thereby increasing the quality of the grain and also advancing the recovery capacity and agronomic efficiency of the crop. Similarly, the effect of various nutrient levels (N andP) showed a significant impact on Y, WUE and B. Y, WUE and B were significantly lower in plots without fertilizer (control), started to increase strongly if a small amount of the fertilizer (50% less than the recommended application dose) was applied and continued to increase until it reached the optimal rate (100% recommended dose). The optimal fertilizer application dose resulted in a significant increase in Y (43 to 69%), WUE (86 to 90%), B (55 to 63%) and total uptake of both nutrients. However, the crops efficiency to convert the applied nutrients into marketableyield was higher in the lowest nutrient application (50% less than the recommended). This study demonstrates</> </>that application of inorganic fertilizers more than the recommended dose is not advised as this did not resulted in an additional output, both in limited and unlimited water conditions. </>
</>
</>
The simulation analysis with AquaCrop revealed that the model was adequately able to simulate the yieldof tef in response to water and fertility stress under various environmental conditions in Tigray. This was confirmed by accurate estimation ofthe soil water balance and canopy development that determine the crop transpiration and the biomass and yield production. With the calibrated and validated model, three management strategies were evaluated in four locations and on three soil types in the region, including soil fertilitymanagement, early sowing and applying a small irrigation dose (deficit irrigation, DI) around flowering. </>
</>
</>
The effect of soil fertility management was assessed by simulating the production of tef according to the farmers practice sown at the end of July or beginning of August for six predetermined soil fertility categories. The high soil fertility levels (0 to 40% soil fertility stress) in locations with relatively good rainfall and on soils with a relatively high available water level (clay loam) resulted in low failure years (0-13%). However, high yield production was limited due to frequently occurring episodesof water stress during critical growth stages like flowering. This finding confirmed that a balanced rainfall distribution is more important than the total amount of rainfall, and urges for planning of optimal sowing time and / or DI if fertility levels are sufficiently high. In areas with relatively less rainfall, the estimated risk of failure years was 29%. Yet, on sandy loam and silty clay soils with poor and very poor soil fertility levels (60 to 75% soil fertility stress), the failure years reached 60-100% in areas with relatively low rainfall.</>
</>
</>
The production of tef according to the farmers sowing practice </>is strongly limited by water stress as maturity is far from reached atthe end of the rainy season. Planning for optimal sowing time is therefore crucial. For this purpose, the DEPTH criterion (Raes et al</>., 2004) that considers a cumulative rainfall depth of 40 mm during a maximum of four successive days was used to determine </>the onset of the growingperiod. </>The model simulations suggested 16</> to 20 July (2-3 weeks earlier than the normal practice) as </>optimal sowing time </>for </>tef. </>For this period, the risk of failure years was considerably reduced while the proportion of moderate and high yield production was increased. </>
</>
</>
Additional water supply combined with early sowing was found to further improve tef yield as the water demand of the crop exceeds the rainfall supply in the region. Given the possibility to collect, by surface runoff, a small amount of excess rainfall in field ponds during the short rainy season, the research was focused on DI.In DI strategy, one irrigation was applied at the critical growth stageat or around flowering. This strategy was beneficial both in areas withrelatively low rainfall and with relatively good rainfall and stablizedyield at a relatively high level. In the more rainy locations, the yields shifted not only from moderate to high but also the average high yield increased. Nevertheless, the crops benefited more in low rainfall areas since DI highly reduced the proportion of low yield and increased the possibility to produce high and moderate yields. </>
</>
</>
Improving water productivity is the greatest potential to increase food production in rainfed agriculture to feed the fast growing population. DI can help to mitigate the effect of dry spells during the growing season (where rainwater harvesting techniques in ponds or micro-dams can be used as a source). Careful planning of sowing dates for effective useof the available rainfall combined with DI and optimal application of inorganic fertilizers can be an important strategy for sustainable food production in drought-prone areas like Tigray as demonstrated in this study.</>
Increasing food production to feed the fast growing world population particularly in developing countries relies on two options: either increase the arable land or improve the productivity of the existing cultivated land. This research focuses on the highly populated highlands ofTigray (northern Ethiopia), where improving the productivity of land isthe only option for sustainable food production. In the drought-prone and highly degraded highlands of Tigray, rainfed cereal production is restricted by low and highly variable rainfall with common occurrence of dry spells during the cropping season on the one hand, and low levels of soil fertility on the other hand. Water saving techniques and applying inorganic fertilizers to intensify the staple food production are essential to maximize the productivity of the land. Elaborated strategies developed by crop growth models can be used for designing and better understanding the impact of the aforementioned strategies. </>
</>
</>In this study the water productivity model AquaCrop developed by FAO was used as a tool to test different field management strategies for improving productivity of tef</> under the local environmental conditions in the highlands of Tigray. The model estimates yield by relating crop transpiration with biomass and yield production and allows the users to simulate yield under various conditions. </>
</>
</>Tef (Eragrostis tef </>(Zucc.)</> Trotter) is an endemic cereal crop and staple dietin Ethiopia. It is highly preferred by the farmers not only in view of its adaptability to a wide range of environmental conditions but also for its high market value of both grain and crop residue (straw). However,low productivity is often reported mainly due to water and fertility stress. </>
</>
</>
Considering this context, a research project was designed with field experiments in Randomized Complete Block Design (RCBD) with split plot arrangement, conducted in 2008, 2009 and 2010 at two sites located in the south-east and east of Tigray in two soiltypes. Five levels of nitrogen (N) and phosphorus (P) fertilizers (no input, 50%, 75%, 100% and 150% of the recommended doses) were applied to both rainfed and irrigated plots. The objectives of the study were: </>
</>
</></>
a) </></></>to gain insight in the response of tef to water and soil fertility stress;</>
b) </></></>to obtain the necessary field data to calibrate and validate the AquaCrop model for the local crop tef, considering both water and fertility stress; </>
c) </></></>to investigate the effect of inorganic fertilizer application (N and P) on yield and yield components of the crop; </>
d) </></></>to evaluate the impact of supplementary irrigation (SI, a practice of applying a limited amount of water to essentially rainfed crops when the rainfall failsto provide sufficient moisture for normal growth) in mitigating the impact of dry spells during the growing season and to improve the productivity of tef;</>
e) </></></>to assess the nutrient use efficiency of tef in different conditions of nutrient availability and </>supplementary irrigation; and </>
f) </></></>to test different field management strategies to improve the productivity of tef in Tigray.</>
</>
</>
The field experiments,complemented with a mini-lysimeter experiment conducted in 2008 and 2009, were used to gain insight in the response of tef to water and soil fertility stress and to calibrate and validate the AquaCrop model for tef under water and fertility stress conditions. Additionally, data collected during field experiments conducted in 2006 and 2007 in the frame of master research were also used as additional inputs for the calibration process. </>
</>
</>
The results of the crop response revealed that the water sensitive stage for tef is at or around flowering. Supplementary irrigation (SI) during this growth stage produced a surplus of 98 to 111% in yield (Y), 52 to 54% in water use efficiency (WUE) and 41 to 88% in dry aboveground biomass (B) compared to rainfed crops. SI also improved the uptake of nutrients, thereby increasing the quality of the grain and also advancing the recovery capacity and agronomic efficiency of the crop. Similarly, the effect of various nutrient levels (N andP) showed a significant impact on Y, WUE and B. Y, WUE and B were significantly lower in plots without fertilizer (control), started to increase strongly if a small amount of the fertilizer (50% less than the recommended application dose) was applied and continued to increase until it reached the optimal rate (100% recommended dose). The optimal fertilizer application dose resulted in a significant increase in Y (43 to 69%), WUE (86 to 90%), B (55 to 63%) and total uptake of both nutrients. However, the crops efficiency to convert the applied nutrients into marketableyield was higher in the lowest nutrient application (50% less than the recommended). This study demonstrates</> </>that application of inorganic fertilizers more than the recommended dose is not advised as this did not resulted in an additional output, both in limited and unlimited water conditions. </>
</>
</>
The simulation analysis with AquaCrop revealed that the model was adequately able to simulate the yieldof tef in response to water and fertility stress under various environmental conditions in Tigray. This was confirmed by accurate estimation ofthe soil water balance and canopy development that determine the crop transpiration and the biomass and yield production. With the calibrated and validated model, three management strategies were evaluated in four locations and on three soil types in the region, including soil fertilitymanagement, early sowing and applying a small irrigation dose (deficit irrigation, DI) around flowering. </>
</>
</>
The effect of soil fertility management was assessed by simulating the production of tef according to the farmers practice sown at the end of July or beginning of August for six predetermined soil fertility categories. The high soil fertility levels (0 to 40% soil fertility stress) in locations with relatively good rainfall and on soils with a relatively high available water level (clay loam) resulted in low failure years (0-13%). However, high yield production was limited due to frequently occurring episodesof water stress during critical growth stages like flowering. This finding confirmed that a balanced rainfall distribution is more important than the total amount of rainfall, and urges for planning of optimal sowing time and / or DI if fertility levels are sufficiently high. In areas with relatively less rainfall, the estimated risk of failure years was 29%. Yet, on sandy loam and silty clay soils with poor and very poor soil fertility levels (60 to 75% soil fertility stress), the failure years reached 60-100% in areas with relatively low rainfall.</>
</>
</>
The production of tef according to the farmers sowing practice </>is strongly limited by water stress as maturity is far from reached atthe end of the rainy season. Planning for optimal sowing time is therefore crucial. For this purpose, the DEPTH criterion (Raes et al</>., 2004) that considers a cumulative rainfall depth of 40 mm during a maximum of four successive days was used to determine </>the onset of the growingperiod. </>The model simulations suggested 16</> to 20 July (2-3 weeks earlier than the normal practice) as </>optimal sowing time </>for </>tef. </>For this period, the risk of failure years was considerably reduced while the proportion of moderate and high yield production was increased. </>
</>
</>
Additional water supply combined with early sowing was found to further improve tef yield as the water demand of the crop exceeds the rainfall supply in the region. Given the possibility to collect, by surface runoff, a small amount of excess rainfall in field ponds during the short rainy season, the research was focused on DI.In DI strategy, one irrigation was applied at the critical growth stageat or around flowering. This strategy was beneficial both in areas withrelatively low rainfall and with relatively good rainfall and stablizedyield at a relatively high level. In the more rainy locations, the yields shifted not only from moderate to high but also the average high yield increased. Nevertheless, the crops benefited more in low rainfall areas since DI highly reduced the proportion of low yield and increased the possibility to produce high and moderate yields. </>
</>
</>
Improving water productivity is the greatest potential to increase food production in rainfed agriculture to feed the fast growing population. DI can help to mitigate the effect of dry spells during the growing season (where rainwater harvesting techniques in ponds or micro-dams can be used as a source). Careful planning of sowing dates for effective useof the available rainfall combined with DI and optimal application of inorganic fertilizers can be an important strategy for sustainable food production in drought-prone areas like Tigray as demonstrated in this study.</>
Date:18 Feb 2008 → 29 Jun 2012
Keywords:nutrients, drought stress, crop water productivity, modeling, barley, teff, maize
Disciplines:Soil sciences, challenges and pollution, Agriculture, land and farm management
Project type:PhD project