1. Partial Nutrient Balance at Farm plot level under Different Irrigation Water Management for Tomato production
Muluye Gedfew1, Petra Schmitter2, Prossie Nakawuka2, Seifu Admasu Tilahun1, Tammo Steenhuis1,3, Simon Langan2
1 Faculty of Civil and Water Resource Engineering, Bahir Dar Institute of Technology, Bahir Dar University, Ethiopia; 2International Water Management Institute (IWMI), Addis Abeba, Ethiopia; 3Biological and Environmental Engineering, Cornell University, Ithaca, USA
Introduction
Method of study
The N, P and K content in the irrigation water, fruits and the crop residue did not differ significantly between the three WM treatments. The CWR and TDR treatment removed 211 kg ha-1 and 176 kg ha-1 N via the tomato fruits, respectively. This is significantly higher compared to the 112 kg ha-1 in the FARM treatment. Similarly the N removed with the residual biomass in the CWR was almost double compared to that in the FARM group. Hence, the differences in nutrients removed from the field through the tomato fruits and the crop residue in the three treatments was related to the differences in yield and biomass produced (Figure 4) leading to N depletion compared to FARM treatment.
Similar trends were observed for P and K. The fruits removed 1.0 kg ha-1 and 0.9 kg ha-1 of P in the CWR and TDR group compared to only 0.5 kg ha-1 in the FARM treatment. The biomass results were similar for all treatments (i.e kg ha-1). For K the CWR and TDR treatments removed 166 and 170 kg ha-1, respectively compared to a low 77 kg ha-1 in the FARM treatment. Similarly as for N, the biomass produced in the CWR and the TDR treatment removed twice as much K compared to the FARM group.
Rainfed agriculture is to date still the main cropping system in Ethiopia providing food and income for its population. Increasing rainfall variability such as the relatively dry rainy season of 2015 puts tremendous challenges on rainfed agriculture. Irrigated agriculture does not only provide resilience under variable climatic conditions but also ensures agricultural products outside of the main cropping season. Sustainable water management in irrigation plays a vital role in water and crop productivity, safe nutrient movement in the soil and sustainable use of land resources. Traditional irrigation practices does not consider the daily crop water requirement as per the prevailing climatic conditions, crop stage as well as the existing soil moisture content. As such, many of the irrigation practices result either in under- or over irrigation and suboptimal use of inputs (e.g; fertilizer, seeds) leading to low crop productivity, and potentially water, soil and nutrient losses.
The main objective of this study was to assess the effect of different irrigation scheduling practices on water & crop productivity and partial nutrient balances under dry season irrigation of tomato.
Three water management (WM) practices were tested: i) crop water requirement (CWR) ; ii) soil moisture based (TDR) and iii) farmer practice (FARM). The crop water requirement was estimated using 10 years of meteorological data ( ) whereas the soil moisture treatment made use of a TDR (time domain reflectometer) to bring soil moisutre levels back to field capacity. Soil samples were taken in all fields to assess the standard physico-chemical paramters including the major plant nutrients (N, P and K), field capacity and wilting point). Additionally irrigation water, rainfall and the produces were sampled and analyzed for N, P and K).
Figure 3: Water productivity in function of the obtained yield for the plots under CWR (blue), TDR (orange) and FARM (grey) treatment.
Result
The soil physiochemical parameters did not show a significant variation between the three WM treatments at the onset of the study. Hence, potentially differences in irrigation quantities or N, P and K concentrations found between the three WM treatments are unlikely to originate from significant soil variability.
The differences in yield and water productivity were translated in the differences obtained in the nutrient balances. a)
Conclusion
The total water applied during the cropping season was on average 476 mm, 590 mm and 575 mm for CWR, TDR and FARM, respectively. No significant differences were found between the three water management treatments. However, there was a difference between the amount of water applied in each of the cropping stages for all three WM treatments (Figure 2). According to the measured water balance deep percolation could be neglected.
Study Area Description
Both the climate based as well as the soil moisture based scheduling improved crop yield but did neither increase nor decrease the total amount of water used during the irrigation season. Results indicate that the farmers apply approximately the right amount of water but potentially not at the right time.
The effect of improved water management resulted not only in higher yields but also increased the N, P and K removal from the fields both via the product of fruits and via the crop residue. The largest removal of nutrients was found for CWR followed by TDR and the farmers practice.
To improve yield on smallholder farmers plots irrigation scheduling is not sufficient, nutrient scheduling is equally important. Hence, the conversion of rainfed plots into intensified production systems requires a well balanced approach where the nutrients are sufficiently replenished on a continuous bases through a good combination of both inorganic and organic fertilizer to compensate for the increased nutrient removal by additional cropping seasons even if improved irrigation management techniques are not applied.
The farmers are located within the Robit watershed ( N and E), northeast (approximately 10 km) of Bahir Dar city (Figure 1). The average annual rainfall is 1400 mm with a minimum average temperature of 23 °C and maximum average temperature of 31 °C. The Bahir Dar to Gondar road crosses the watershed from south to north. b) c)
Figure 2: Irrigation water used within each WM treatment for during the initial, development, mid and maturity stages.
Differences in irrigation water applied throughout the different cropping stages influenced both the crop as well as the water productivity (Figure 3). The average tomato yield produced in the CWR, TDR and FARM fields were 33.2 t ha-1, 31.7 t ha-1 and 20.8 t ha-1, respectively. Traditional irrigation resulted in significant lower yields compared to the two irrigation scheduling treatments.
Acknowledgements
This research was sponsored by the Innovation Laboratory For Small Scale Irrigation project (#AID-OAA-A SS) which is funded by Feed the Future through the U.S. Agency for International Development (USAID). The research was implemented under a collaborative partnership between the International Water Management Institute and Bahir Dar University. The contents of the paper are the responsibility of the authors and do not necessarily reflect the views of USAID or the United States government.
Figure 1: Overview of Robit watershed and the location of the tomato producing farmers in the project.
Figure 4: Input and output drivers behind the N (a), P (b) and K (c) balance for the three WM treatments (CWR, TDR and FARM).