Field evaluation of urea fertilizer and water use efficiency by tomato under trickle fertigation and furrow irrigation in the Islamic Republic of Iran

Urea fertilizer and water use efficiency by tomato (Early Urbana VF) were studied in a sandy loam soil, comparing trickle fertigation and conventional furrow irrigation -- band fertilization systems. During the period of 1995-1998, a conventional treatment, NS, with band application of 50, 150 and 100 kg N as urea, P as diammonium phosphate and K as potassium sulfate respectively was carried out. The average concentration of N in the total irrigation water was 0, 38, 76 and 114 mg/L for the N0, N1, N2 and N3 fertigation treatments, respectively. All fertigation treatments also received equally 24 and 16 mg/L P and K, respectively. An increase of K for the conventional treatment to 1200 kg/ha in 1998 coincided with the increase of the same element to 190 mg/L for the trickle irrigated treatments. To evaluate the urea-N use efficiency, the plants of isotope subplots received 2% 15N a.e. urea. The soil moisture in all treatments was measured by the neutron moisture gauge. During the first 3 years of experimentation there was no significant difference between the yields of the treatments. For the years 1995 through 1997 the average tomato yield was low in comparison to the yield shown in most reports. The yield variance among treatments and years was negligible. The highest fruit yield, 27.3 t/ha for the N1 treatment was observed in 1997. In this experiment, the low yield and urea-N use efficiency can be primarily attributed to unbalanced applied fertilizers in the trickle irrigation system. The highest urea-N use efficiency was 12.3% for the fertigation N1 treatment in 1997. In the 1998, a repetition of the experiment with increasing K rates for all treatments at the same experimental site, led to a considerable increase in yield and urea-N use efficiency as compared to previous years. The tomato fresh fruit yield attained for N0, N1, N2, N3 and NS respectively 84, 76, 69, 36 and 26 t/ha. Based on the 14N/15N ratio analysis of the dry matter the urea-N use efficiency was 42, 25, 11 and 6 for the N1, N2, N3, and NS treatments, respectively. All N treatments under trickle irrigation and conventional furrow irrigation received on average a total amount of 6,536 and 12,286 m3/ha irrigation water (1996-1998). The total water use efficiency for the NS treatment was the lowest (24 kg/ha.cm) of all treatments and was the highest for the fertigation treatment N1 (51 kg/ha.cm) (1996-1997). The yield increase of the fertigation treatments enhanced the water use efficiency for 1998 as compared to 1996 and 1997. The overall water use efficiency was the lowest for the NS treatment (33.3 kg/ha.cm) and the highest for urea-N0 treatment (155.4 kg/ha.cm) and urea-N1 treatment (154.1 kg/ha.cm) for 1998. This investigation indicates that application of conventional quantities of fertilizers via trickle irrigation is not suitable. In the second phase (1999-2000) of this project, with the application of proper amounts and proportions of fertilizers plus microelements, it is expected to obtain better results. (author)