Koffi Djaman

Soil Water Extraction Patterns and Crop, Irrigation, and Evapotranspiration Water Use Efficiency of Maize under Full and Limited Irrigation and Rainfed Settings

The effects of full and limited irrigation and rainfed maize production practices on soil water extraction and water use efficiencies were investigated in 2009 and 2010 under center-pivot irrigation near Clay Center, Nebraska. Four irrigation regimes (fully irrigated treatment (FIT), 75% FIT, 60% FIT, and 50% FIT) and a rainfed treatment were implemented. The crop water use efficiency (CWUE, or crop water productivity), irrigation water use efficiency (IWUE), and evapotranspiration water use efficiency (ETWUE) were used to evaluate the water productivity performance of each treatment. The seasonal rainfall amounts in 2009 and 2010, respectively, were 426 mm (18% below normal) and 563 mm (9% above normal). Irrigation regime impacted soil water extraction pattern, which increased with irrigation amounts. In general, the soil water extraction decreased with soil depth, and the water extraction from the top soil (0-0.30 m) accounted for the largest portion of the seasonal total water extraction as 39%, 42%, 48%, 48%, and 51% of the total extraction under rainfed, 50% FIT, 60% FIT, 75% FIT, and FIT, respectively. The rainfed treatment extracted more water from the 0.60-0.90 m and 0.90-1.2 m layers (19% and 17% of the total, respectively) than all other treatments. In general, the deepest soil layer (1.5-1.8 m) contributed about 5% to 8% to the seasonal total water extraction. The efficiency values for the same treatments varied between the years due to their dependency on the seasonal water supply, water supply impact on water extraction, climatic conditions, and their impact on yield. The CWUE increased with irrigation from 1.89 kg m-3 for the rainfed treatment to 2.58 kg m-3 for the 60% FIT in 2009 and from 2.03 kg m-3 for the rainfed treatment to 2.44 kg m-3 for the FIT in 2010. The CWUE was strongly correlated to actual crop evapotranspiration (ETa) (R2 = 0.99 in both years), irrigation amounts (R2 = 0.97 in both years), and grain yield (R2 = 0.95 in 2009 and R2 = 0.99 in 2010). The IWUE and ETWUE decreased with ETa and the irrigation amounts in 2009, while they showed the opposite trend in 2010. The IWUE ranged between 3.63 kg m-3 for FIT and 5.9 kg m-3 for 50% FIT in 2009 and between 2.52 kg m-3 for 50% FIT and 3.24 kg m-3 for 75% FIT in 2010. On average, 60% FIT resulted in the largest IWUE of 4.33 kg m-3. The measured ETWUE varied from 4.65 kg m-3 for FIT to 6.09 kg m-3 for 50% FIT in 2009 and from 5.94 kg m-3 for 50% FIT to 6.73 kg m-3 for FIT in 2010. The 60% FIT and 75% FIT had similar or greater CWUE and ETWUE than the FIT in both years. The ETWUE was usually greatest when the ETa was about 580 mm in 2009 and 634 mm in 2010, indicating that in these experimental, climate, and management conditions, the maximum ETWUE and crop water productivity can be obtained at ETa values smaller than those for the fully irrigated treatment. The 60% and 75% FIT treatments were very comparable to the fully irrigated treatment in terms of productivity performance and are viable supplemental irrigation strategies for increasing crop water productivity of maize while using (withdrawal) 40% or 25% less irrigation water under these experimental, soil and crop management, and climatic conditions.

Economic Return versus Crop Water Productivity of Maize for Various Nitrogen Rates under Full Irrigation, Limited Irrigation, and Rainfed Settings in South Central Nebraska

AbstractField research was conducted at the University of Nebraska-Lincoln South Central Agricultural Laboratory (SCAL) located near Clay Center, NE, in the growing seasons of 2011 to 2014. A partial economic analysis was conducted for maize (Zea mays L.) at nitrogen (N) fertilizer treatments of 0, 84, 140, 196, and 252  kg ha−1 under full irrigation (FIT), limited irrigation (75% FIT), and rainfed settings for all growing seasons and then compared to crop water productivity (CWP) measured as crop water use efficiency (CWUE) and irrigation water use efficiency (IWUE). Nitrogen fertilizer increased CWUE and IWUE in all growing seasons. The CWUE values ranged from 0.90 to 2.81  kg m−3 and the IWUE values ranged from −1.01 to 3.24  kg m−3. Operational costs and net income varied among treatments and across years. Irrigation and N fertilizer rate had an interacting effect (P0.05<0.05) on both gross and net income in 2011, 2012, and 2013. Net income was maximized under rainfed settings with a N fertilizer rate...

Daily Reference Evapotranspiration Estimation under Limited Data in Eastern Africa

AbstractThe objective of this study was to evaluate the FAO-56 Penman-Monteith (FAO-PM) reference evapotranspiration (ETo) equation and two Valiantzas equations for estimating daily reference evapo...

Soil-Water Dynamics, Evapotranspiration, and Crop Coefficients of Cover-Crop Mixtures in Seed Maize Cover-Crop Rotation Fields. I: Soil-Water Dynamics and Evapotranspiration

AbstractCover crops are incorporated into row crop production systems as rotational crops because of their potential contributions to soil and water conservation. However, extremely limited data an...

Validation of Valiantzas Reference Evapotranspiration Equation under Different Climatic Conditions

Numerous daily reference evapotranspiration (ETo) equations were developed for different climatic conditions with different performance even within the same climatic region. Their calibration and validation to the local climate usually increase their performance. The objective of this study was to evaluate Valiantzas’ daily grass ETo equation with comparison to Penman-Monteith equation at 61 weather stations across 10 countries in Africa for the period of 1980-2012. The results showed good performance of Valiantzas’ ETo equation with very low RMSE varying from 0.03 to 0.27 mm/day, low percent error PE from 0.87 to 5.46%, MBE from -0.09 to 0.23 mm/day and MAE from 0.03 to 0.23 mm/day. For the pooled data set, RMSE averaged 0.10 mm/day, mean PE was 1.95%, mean MBE was 0.02 mm/day and the mean MAE was 0.08 mm/day. These indexes indicated the very high performance of the Valiantzas’ ETo equation compared to the Penman-Monteith equation and its adaptation to very broad conditions from humid to semiarid climates. *

Sum of Hourly vs . Daily Penman-Monteith Grass-Reference Evapotranspiration under Semiarid and Arid Climate

Under changing climate and the global warming, accurate estimation of crop evapotranspiration might help improving water management and maintaining or improving water productivity. The objective of this study was to compare the sum of hourly ETo with the daily average ETo using the standardized ASCE Penman-Monteith equation under semiarid dry climate. Pair comparison was performed between the sum of hourly reference evapotranspiration (ETo) and the daily average ETo based on the data from four automated weather stations in the State of New Mexico (USA) for the period of 2009-2017. The results showed good agreement between the sum of hourly ETo and daily average ETo with the regression slopes varying from 1.00 to 1.10 and coefficients of determination from 0.63 to 0.97. The least difference between the hourly and daily results was found at Leyendecker. The RMSE values were 0.98, 0.64, 0.21 and 0.35 mm/day at Fabian Garcia, Farmington, Leyendecker and Tucumcari, respectively. The adoption of the hourly ETo estimation method leads to 16.6, 5.5, -0.2, and 4.1% higher annual ETo at Fabian Garcia, Farmington, Leyendecker and Tucumcari respectively, and can help on accurate evapotranspiration estimation to meet crop water requirement under sustainable agriculture.

Variability of the Ratio of Alfalfa to Grass Reference Evapotranspiration under Semiarid Climate

Crop evapotranspiration estimation is critical for sustainable water management under the semiarid and arid climate in New Mexico. While irrigation scheduling is based on daily evapotranspiration through the two step approach, reference evapotranspiration and crop coefficients should be determined with accuracy. The utilization of grass reference evapotranspiration (ETo) or alfalfa reference evapotranspiration (ETr) and the conversion from one to the other calls for an understanding of the relationship between ETr and ETo. The objectives of this study were to develop the ratio of ETr to ETo values (Kr) and to determine the variability of Kr during the year for six locations across the State of New Mexico (USA). The results showed long term annual Kr values to vary from 1.28 to 1.45 and the coefficient of determination varied from 0.96 to 0.98. Kr value decreases from January to July and increases from August to December and was at its lowest Kr value at the peak daily reference evapotranspiration. Annual average Kr values were 1.31, 1.38, 1.43, 1.38, 1.38 and 1.48 at Alcalde, Fabian Garcia, Farmington, Leyendecker, Las Cruces and Tucumcari locations and the growing season average Kr values were 1.24, 1.32, 1.38, 1.31, 1.32 and 1.42 at the respective locations. The strong correlation between ETr and ETo allows the conversion of the grass reference evapotranspiration to alfalfa reference evapotranspiration and vice versa however, caution should be taken when using the crop coefficient values to convert either ETo or ETr to actual crop evapotranspiration for irrigation scheduling and water management.

Trend analysis of streamflow with different time scales: a case study of the upper Senegal River

Abstract This study investigates long-term trends of three different time scales including monthly, seasonally and annually at the upper Senegal River basin. Daily streamflows for the period 1961–2014 at Bafing Makana station were used and analyzed to conduct this research. The serial structural of the different time series (monthly, seasonal, and annual) were investigated in order to detect the presence of autocorrelation. Mann–Kendall test was applied to no autocorrelated series and the Modified Mann–Kendall test for the autocorrelated. Theil and Sen’s slope estimator test was used for finding the magnitude of change and Pettitt test was applied for detecting the most probable change year. Results exhibited a decreasing trend of the annual streamflow yet at the 5% significance level, streamflow series did not have any statistically significant trend for the whole period; however, integrating the different change years, decreasing trend is significant before the first breaking point (1976) and increasing trend is significant from first breaking point to the second change point (1993). For the monthly series, all months exhibit a non-significant decreasing trend except for the month of June. The seasonal series show a decreasing trend which a significant at MAMJ season. Change years were varying accordantly to the scale.

Evaluation of Valiantzas’ Simplified Forms of the FAO-56 Penman-Monteith Reference Evapotranspiration Model in a Humid Climate

AbstractThe unavailability of some meteorological variables, especially solar radiation and wind speed, is the main constraint for reference evapotranspiration (ETo) estimation using the standard U...

Managing Fertilizer Recommendations in Rice-Based Cropping Systems Challenges and Strategic Approaches

Improving agricultural productivity to facing the fast growing food demands is the huge challenge of Sub-Saharan Africa (SSA). Fertilizer is a powerful productivity-enhancing input, but farmers of SSA use only 5 to 9 kg ha−1 of fertilizer, ten time less than Latin America and Asia (50 and 80 kg ha−1, respectively). Rice (Oryza sativa) is one of the most important food crops of SSA and rice consumption is growing faster than the consumption of any other commodity in Africa. Rice-based systems have high potential for improving food production through an efficient management of fertilizers. The biophysical environment, cropping systems and, socio-economic environment of farmers including market opportunities are the main factors for development of appropriate fertilizer recommendations. This paper makes a critical review of rice-based systems in Africa and the main achievements on fertilizer recommendation, and further identifies the main challenges and opportunities to improve fertilizer use efficiency in rice-based systems. The opportunities offered by the new concepts, modeling and decision support tools that have been recently developed for better management of fertilizers in rice systems have been discussed. Beyond the traditional techniques of blanket fertilizer recommendations by country, some suggestions are proposed to improve the utilization of the new concepts and decisions support tools for better management of fertilizer in the rice-based systems.