EFFECT OF EARLY GROWING SEASON MOISTURE STRESS ON BARLEY UTILIZATION OF BROADCAST-INCORPORATED AND DEEP-BANDED UREA

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Abstract
A field experiment was conducted to examine the interaction of fertilizer placement and moisture level on barley (Hordeum vulgare 'Gait') utilization of urea-N during early growth. The 15N labelled urea (50 kg ha−1) was either deep-banded or broadcast-incorporated, and plant samples were taken from the two-leaf stage until anthesis, then again at maturity. Five moisture regimes were created using rain shelters, with 0, 10, 15, 20 and 25 mm water applied per week until anthesis. A natural precipitation treatment was also included. All barley plants were unsheltered from anthesis to maturity. Weekly fertilizer recoveries by the crop with no water additions were much less for broadcast-incorporated N than deep placement. The differences narrowed with increasing rates of water additions. Apparently, broadcast-incorporated fertilizer N remained in dry surface layers of the no-water treatment, and was positionally unavailable for absorption by the crop. Compared to deep-banded N, broadcast-incorporated N resulted in 37% less grain when drought stress occurred from seeding to anthesis. Broadcast-incorporated N was more susceptible to immobilization by the soil than was deep-banded N. Key words: Barley, drought stress, 15N-urea, fertilizer positional unavailability, N immobilization