Effect of uneven emergence on rice yield, milling yield, and yield components

Establishing a uniform rice (Oryza sativa L.) stand is an important beginning to managing a rice crop and attaining high yields. Most rice management practices in the United States are timed according to rice growth stages. Non-uniform rice stands, and subsequently non-uniform growth stages, present problems for the timely application of management practices for attaining high yields. Our objective was the determination of the effects of uneven emergence on rice yield, milling yield, and yield components. Experiments were conducted in 1988 and 1989 on a Hebert silt loam (Vertic Hapludoll) at the Southeast Branch Experiment Station near Rohwer, Arkansas. Uneven emergence was simulated by delayed (18 days from emergence) interseeding of rice to achieve 0, 20, 40, 60, and 80% uneven emergence. Each experiment was planted with the cultivars Lemont (semi-dwarf) and Tebonnet (tall) and was replicated 4 times. Rice yields for the uneven emergence treatment levels were significantly less than the rice yields seeded exclusively at PD1 (planting date 1), except for the uneven emergence levels 80-20 (80% planted at PD1 and 20% planted at PD2) and 60-40 for Tebonnet, and 60-40 in 1988 for Lemont. In 1989, there was a trend for head rice yields to decrease as uneven emergence levels increased. Average panicle density and number of grains per panicle for both Lemont and Tebonnet decreased with increasing uneven emergence, indicating a failure in the typical compensatory relationship between panicle density and grain per panicle. Lemont exhibited reduced average grain weights due to uneven emergence, especially at 80-20, 60-40, and 40-60 uneven emergence levels. Harvest indices were higher for PD1 than for PD2, except at 20-80 uneven emergence level. Essentially, the later emerging rice from the second planting acted much like a weed by competing against rather than contributing to rice yields. Late interseeding to enhance poor rice stands is unlikely to produce an economic return that could be expected from an adequate initial plant stand.