Rice Ratoon Crop Yield Linked to Main Crop Stem Carbohydrates

Ratooning of rice (Oryza satira L.) may be agronomically possible in climates where the crop season is to short too produce two rice crops, but factors influencing ratoon rice yields are not well understood. The influence of main crop total nonstructural carbohydrate (TNC) and main crop N topdfessing on ratoon crop yield of four contrasting field‐grown riee cultivars were evaluated in Texas during 1988 and 1989. Allowing panicles to develop normally or removing the upper two‐thirds of each main crop panicle 10 d after initial main crop heading created a range in TNC of the culm and leaves during later stages of main crop development for determining TNC effects on ratooning. Nitrogen applied 10 d after initial main crop heading corrected, any possible N deficiency, but did not increase main crop yield, TNC, or ratoon crop yield, indicating no benefits to N applied immediately after main crop heading. During main crop grain filling, culm and leaf TNC levels of plants with normal panicles decreased to low levels (0‐90 g kg‐1), then gradually increased and ranged from 40 to 170 g kg‐1 at harvest. In contrast, TNC in culms and leaves of plants with incomplete panicles gradually increased during main crop grain filling reaching 140 to 310 g kg‐1 at main crop harvest. Main crop plants with elevated TNC levels produced ratoon yields up to 5.3 Mg ha‐1, averaging 48 and 33% higher than plants with low TNC at main crop harvest in 1988 and 1989, respectively. These data illustrate a moderate positive correlation (R2 = 0.66) between ratoon yields and TNC in cuim and leaves at main crop harvest for effects due to years, panicle removal, and cultivars.