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This article in AJ

  1. Vol. 77 No. 2, p. 299-304
    Received: May 29, 1984

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Soybean Irrigation Serially Timed During Stages R1 to R6. 11. Yield Component Responses1

  1. F. A. Kadhem,
  2. J. E. Specht and
  3. J. H. Williams2



Soybean [Glycine max (L.) Merr.] seed yield components are established and fixed in a temporally ordered sequence during stages R1 to R6. To determine the effect of irrigation timing during R1 to R6 on these traits, we examined the seed yield component responses of 16 soybean cultivars to nine irrigation treatments in a 3-year experiment. Treatments T1 thru T7 consisted of only a single irrigation coinciding with the average R stages 1.1, 2.5, 3.7, 4.7, 5.6, 5.9, and 6.4, respectively. ‘Check’ treatments included TO, which was not irrigated, and T8 which received seven total irrigations coincident with those for T0 and T7. Averaged over cultivars and years, the mean number of seeds/plant were: T0: 87f, T1: 121a, T2: lllbc, T3: 115ab, T4: 105cd, T5: 99def, T6: 102de, T7: 95ef, and T8: 122a. T0 and T8 thus established the minimum and maximum ‘limits’ in the seeds/plant response, respectively, with declining responses as irrigation was delayed from T1 to T7. The 100-seed weight (9) means were: T0: 19.lb, T1: 17.8c, T2: 17.8c, T3: 18.3c, T4: 20.3a, T5: 20.4a, T6: 19.8ab, T7: 20.3a, and T8: 18.3c. Seed size for T8 was thus smaller than T0. The T4 thru T7 responses were significantly greater than T0, while the T1 thru T3 responses were significantly less than T0. Average seed yields were greatest for the T3 and T4 treatments, although for determinate cultivars, T8 also resulted in high yields. Only minimal changes in seed number and size were affected by irrigation in the determinate cultivars (in contrast to indeterminates), which may have accounted for the greater yield responsiveness of determinate cultivars to irrigation. Based on both the seed yield and yield component data, it would appear that stage R3.5 to R4.5 represents the reproductive period in soybeans most responsive to irrigation.

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