Efficient Irrigation and N Management for Lemons: Results for 1993-1996

Abstract

Studies are being conducted which aim to improve the efficiency of irrigation and N fertilization for lemons produced on sandy soils in the low desert The first experiment evaluates the response of 'Lisbon' lemons to various flood irrigation intervals. Irrigation intervals are based on soil moisture depletion (SMD) as calculated from frequent neutron probe soil moisture measurements. Individual treatments were irrigated when total SMI) was 25 %, 40 %, 55 %, and 70 %, respectively. The second experiment compares the performance of young lemons produced under flood, trickle, and micro-spray irrigation systems. The third experiment evaluates the response of young lemons to water and N combinations (3 by 3 factorial) under micro - spray irrigation. The three irrigation rates were targeted for 30 cnbar, 20 cnbar, and 10 cnbar tension. The three N rates were 0.1, 0.2, and 0.4 kg N/tree. One flood irrigation treatment was added for comparative purposes. Overall, results obtained in experiment 1 during 1994, 1995, and 1996 indicate optimal fruit growth and yield is obtained at approximately 40% SMD. The results of experiment 2 show that after 3 years, only micro-jet irrigation produced less tree growth than flood irrigation. In 1995, first year fruit yields were significantly greater for pressurized irrigation compared to flood irrigation. However, by 1996 there were no differences in yield to irrigation treatment. Results from experiment 3 show a linear response in tree growth to irrigation. In 1994 and 1995, tree growth at the high micro - spray soil moisture regime was significantly greater than trees irrigated by flood. However, in 1996 where we failed to increase the micro-spay irrigation time to meet the increased water demand by the trees, the flood irrigation regime was superior. Yields were also increased to irrigation. There were no significant differences in tree growth to N fertilization rates in 1994 and 1995. However, there was increased tree growth in 1996 and a yield increase to N fertilizer rate at the highest soil moisture regime.