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A field experiment was carried out to study the effect of different rates of potassium (K) fertilizer [0, 50, 100, and 150 potassium oxide (K 2 O) ha -1 ] in the presence of increased supply of nitrogen (N) (120, 180, and 240 kg N ha -1 ) on cotton (Gossypium hirsutum L.) yield and the N and K use efficiencies using the 15 N isotopic dilution technique. Potassium fertilizer increased cotton yield, which was significant and more pronounced with the application of N in the high level (N3). The greatest cotton yield (6442 kg ha -1 ) was obtained in N2K3 treatment with an increase of 14% over the control. In addition, K fertilizer significantly increased N uptake efficiency in the N2 and N3 treatments. The greatest N uptake efficiency (98%) was in N2K3 treatment. The greatest K uptake efficiency (42%) was occurred in N3K1 treatment. In conclusion, the use of K fertilizer could be useful when growing cotton in soils of moderate to high N content to improve N uptake efficiency and consequently increase cotton yield.

Background:A pot experiment was conducted to determine the effects of alternate irrigation with saline (S) and fresh (F) water on growth, nitrogen uptake and nitrogen use efficiency in Sorghum crop (Sorghum bicolor L.) manured with Elaeagnus angustifolia leaves (GM) using 15 N. Method:Five types of irrigation systems abbreviated as (F, 2F:1S, 1F:1S, 1F:2S and S) and one rate of Green Manure (GM) were employed. Result:Results showed reductions in both Dry Matter yield (DM) and nitrogen uptake (NY) in sorghum grown under different types of irrigation systems as compared with the control (F). The reduction rates of these two parameters increased with increasing number of irrigations with saline water. However, E. angustifolia leaves applied as green manure mitigated the harmful effect of salinity on plant growth parameters. The percent increments as a result of GM application were 9, 19, 43, 43 and 65% for DM, and 33, 30, 42, 36 and 60% for NY in F, 2F:1S, 1F:1S, 1F:2S and S, respectively. Nitrogen use efficiency of added green manure ranged between 25 and 47% in the different types of irrigation systems. Our results indicated that increment of NY in green manured sorghum plants was mainly attributed to its nitrogen availability. According to the availability of S and F water resources, and the economic returns aimed by farmers in the semi-arid regions, it is recommended to use (2F:1S, 1F:1S and 1F:2S) in combination with E. angustifolia leaf GM. Such a procedure can be considered as a promising agricultural practice to improve yield with a proper water resource investment.

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