Irrigation frequency is one of the most important factors in drip irrigation scheduling that affects the soil water regime, the water and fertilization use efficiency and the crop yield, although the same quantity of water is applied. Therefore, field experiments were conducted for 2 years in the summer season of 2005 and 2006 on sandy soils to investigate the effects of irrigation frequency and their interaction with nitrogen fertilization on water distribution, grain yield, yield components and water use efficiency (WUE) of two white grain maize hybrids (Zea mays L.). The experiment was conducted by using a randomized complete block split‐split plot design, with four irrigation frequencies (once every 2, 3, 4 and 5 days), two nitrogen levels (190 and 380 kg N ha−1), and two maize hybrids (three‐way cross 310 and single cross 10) as the main‐plot, split‐plot, and split‐split plot treatments respectively. The results indicate that drip irrigation frequency did affect soil water content and retained soil water, depending on soil depth. Grain yield with the application of 190 kg N ha−1 was not statistically different from that at 380 kg N ha−1 at the irrigation frequency once every 5 days. However, the application of 190 kg N ha−1 resulted in a significant yield reduction of 25 %, 18 % and 9 % in 2005 and 20 %, 13 % and 6 % in 2006 compared with 380 kg N ha−1 at the irrigation frequencies once every 2, 3 and 4 days respectively. The response function between yield components and irrigation frequency treatments was quadratic in both growing seasons except for 100‐grain weight, where the function was linear. WUE increased with increasing irrigation frequency and nitrogen levels, and reached the maximum values at once every 2 and 3 days and at 380 kg N ha−1. In order to improve the WUE and grain yield for drip‐irrigated maize in sandy soils, it is recommended that irrigation frequency should be once every 2 or 3 days at the investigated nitrogen levels of 380 kg N ha−1 regardless of maize varieties. However, further optimization with a reduced nitrogen application rate should be aimed at and will have to be investigated.

No abstract

Differences in soil moisture and wetting pattern under different irrigation frequencies mean that vegetative growth and nitrogen use efficiency in maize can differ even when the same total amount of irrigated water is applied under different frequency regimes. The goal of this study was to evaluate the effects of drip irrigation frequency and its interaction with nitrogen fertilization on vegetative growth and nitrogen use efficiency of a maize crop at different growth stages and on grain quality at maturity stage in a sandy soil. The experiment was conducted for 2 years (2005 and 2006) using a randomized complete block split–split plot design with four irrigation frequencies (once every 2, 3, 4 and 5 days), two nitrogen levels (190 and 380 kg N ha−1) and two maize hybrids (three‐way cross 310 and single cross 10) as the main‐plot, split‐plot and split–split plot variables, respectively. Irrigation water, totalling 524 mm ha−1, applied for each irrigation frequency was divided into 28, 21, 17 and 14 doses for the F2, F3, F4 and F5 treatments, respectively. Results indicated that vegetative growth, crop growth and nitrogen efficiency parameters at the 10‐leaf and tasseling growth stages increased with increasing drip irrigation frequency, whereas grain protein content decreased. Although the values of the vegetative growth and crop growth parameters increased with increasing nitrogen levels, significant decreases in nitrogen efficiency parameters were also observed indicating the need for further optimization with a reduced nitrogen application rate. Significant interaction effects between irrigation frequency and nitrogen levels were detected for all parameters measured. In most cases, the parameters were not significantly different between the two nitrogen levels at an irrigation frequency of once every 5 days, but did differ significantly at irrigation frequencies of once every 2, 3 or 4 days. The relationship between the nitrogen use efficiency parameters and retained available soil water content at the 10‐leaf and tasseling growth stages was best represented by a second order polynomial equation with an R2 ranging from 0.73 to 0.98. Based on our findings, an irrigation frequency of once every 2 and 3 days is recommended to enhance growth and nitrogen use efficiency of drip‐irrigated maize in sandy soil in Egypt.

This study is an attempt to quantify the effect of different water qualities interacted with different moisture depletion levels on crop yield and leaching requirement for salt affected soil. Barley crop was cultivated on sandy soil as a pots experiment in the open field, in Ismailia, Egypt. Three water qualities were collected from different resources to represent three different water qualities: 1) Nile water, 0.4 dS m-1 , 2) Salam Canal, 0.8 dS m-1 and 3) Diluted Sea water, 7.4 dS m-1. Winter barley has been irrigated with the three different waters, where each type was applied under three different levels of soil moisture depletion: 25 %, 50 % and 75 % of soil field capacity. An empirical model to predict yield production was developed and evaluated in comparison to some common models such as models of Stewart and Maas-Hoffman's models. The results showed that the suggested model could be used as reliable approach to predict the relative yield of barley cultivated in sandy soil under different water salinities and soil moisture depletion levels, as well as the leaching requirement of such salt affected soils irrigated with saline water. The validation of the common used Hoffman's equation for leaching requirements, LR, had been tested based on leaching curve experiment. The results indicated that the developed model for yield prediction may be successfully adapted to estimate the relative yield as a function of both water salinity and depletion level of soil moisture. Based on the data of leaching experiment a relative over-estimation of the LR was obtained using Hoffman's equation compared to that estimated from Oster's equation. The amounts of water applied based on Oster's equation could be reduced to about one-third of that calculated according to Hoffman and led to the provision of large amounts of water available for irrigation.

No abstract