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Agronomy Journal Abstract -

Interrelationships of Irrigation Frequency, Urea Nitrogen, and Gypsum on Forage Sorghum Growth on a Saline Sodic Clay Soil1


This article in AJ

  1. Vol. 74 No. 3, p. 447-451
    Received: July 18, 1980

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  1. M. A. Mustafa and
  2. E. A. Abdelmagid2



Two field experiments were conducted in June, 1978, and April, 1979, at the Khartoum University Farm, Sudan, to study the effect of irrigation frequency, urea-nitrogen, and gypsum on the yield of forage sorghum (Sorghum vulgare L.) grown on a semi-arid, salinesodic clay soil. Each experiment had four nitrogen levels: 0N, 1N, 2N, and 3N (1N = 43.8 kg N/ha) applied as urea; three irrigation frequencies: 7, 10, and 15 days; and zero or 11.9 tonnes/ha gypsum, each replicated thrice in a split-split plot design. The seasonal quantity of water applied was the same for all frequencies of irrigation and was slightly higher than evaporation from a U.S. class A pan.

The two seasons data consistently showed that dry matter yield of the first cuts of forage sorghum increased significantly with increase in N-level, with decrease in irrigation interval, and with gypsum application. Decreased irrigation frequency had greater effect than 3N fertilization. The benefits from gypsum application were low (5%) at the 7-day irrigation interval. Dry matter yields were increased from 1.84 to 6.12 tonnes/ha in 1978 and from 3.20 to 7.23 tonnes/ha in 1979, by irrigating every 7 days instead of 15 days, application of 3N and 11.9 tonnes/ha gypsum.

Plant height and leaf area index increased with N fertilization, with gypsum and with reduction of irrigation interval from 15 to 7 days, whereas germination percentage was significantly increased by gypsum only. Dry matter yield significantly correlated (P = 0.01) with leaf area index and plant height but not with germination percentage. Multiple regression analysis showed that the first two growth attributes accounted for about 87% of the variability of yield. The dry matter yields of the second cuts were similarly affected by treatments but were about one-half to one-third those of the first cuts in 1978 and 1979 seasons, respectively.

For the two seasons the average seasonal water-use was about 1.02 times that of the U.S. class A pan evaporation. Water-use efficiency increased from 15.6 to 43.9 kg/ha-cm in 1978 and from 19.1 to 51.2 kg/ha-cm in 1979, by irrigating every 7 days instead of 15 days, and applying 3N urea and 11.9 tonnes/ha gypsum.

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