Upland rice yield as affected by previous summer crop rotation (soybean or upland rice) and glyphosate management on cover crops

The appropriate chemical management of cover crops in no-tillage aims to obtain greater benefits with its employment in agricultural systems. The objective of this study was to assess upland rice yield as affected by the previous summer crop, species and desiccation timing of cover crops by glyphosate. Sown cover crops were sown (November 2007), followed by rice in half of the experimental area and soybean in the other half (November 2008). After the harvesting of these crops, the same cover crops were sown again (March 2009) and followed by upland rice in the total area (November 2009). The experiment consisted of the combination of five cover crops (fallow, Panicum maximum, Brachiaria ruziziensis, B. brizantha and Pennisetum glaucum), four desiccation timings (30, 20, 10 and 0 days before rice sowing), and two antecedents of the summer crop (rice or soybean) under no-tillage system (NTS), plus two control treatments at conventional tillage system (CTS). Cover crops significantly affect rice grain yield and its components. There is a significant tendency to highest yield when cover crop desiccation is conducted farther from the rice sowing date (from 2,577.1 kg ha-1 - desiccation at rice sowing to 3,115.30 kg ha-1 - desiccation 30 days before rice sowing). Soybean as an antecedent of summer crop allows better upland rice yield (3,754 kg ha-1) than rice as an antecedent of summer crop (2,635 kg ha-1); fallow/soybean/fallow (4,507 kg ha-1) and millet/soybean/millet (4,765 kg ha-1) rotation at no-tillage system, and incorporated fallow /soybean/ incorporated fallow (4,427 kg ha-1) at conventional tillage system allow the highest rice yield; upland rice yield is similar at no-till (3,194 kg ha-1) and till system (2,878 kg ha-1).

Germination ecology of Rhynchosia capitata: an emerging summer weed in Asia

Rhynchosia capitata is becoming an increasing problem in summer crops, such as cotton, soybean, pearl millet and mungbean in many Asian countries. Laboratory and greenhouse studies have been conducted to determine the effects of several environmental factors on seed germination patterns and seedling emergence of R. capitata. We investigated whether the diverse ecological factors such as temperature, light, salinity, moisture stress, pH, and soil depth affected germination and seedling emergence of R. capitata. Germination increased as temperature increased from 25ºC and significantly reduced at 45ºC. Presence or absence of light did not influence germination. Germination of R. capitata was sensitive to increased salt and moisture stress, as well as to seed burial depth. Only 48% of seeds germinated at 150 mM salt concentration compared to 100% in control (distilled water). Similarly, 15% of seeds germinated at an osmotic potential of ‑0.8 MPa compared to 88% at ‑0.2 MPa. The optimum pH for seed germination of R. capitata was 7 (98% germination), but the seeds also germinated at lower level of pH 5 (85%) and at higher level of pH 10 (75%). In seed burial trial, maximum seedling emergence of 93% occurred at 2 cm depth, and seedling did not emerge from a depth of 12 cm. The high germination ability of R. capitata under a wide range of ecological factors suggests that this species is likely to be the one to cause more problems in a near future, if not managed appropriately.

Assessing the Competitive Ability of Rhynchosia capitata; an Emerging Summer Weed in Asia

Rhynchosia capitata is a newly emerging threatening weed of summer crops in many Asian countries. We conducted 2-yr experiments to evaluate R. capitata competition with mungbean under irrigated conditions. Rhynchosia capitata was allowed to compete with mungbean for 0, 3, 4, 5, 6, 7 weeks after planting and for full crop season. The competitive ability of R. capitata was assessed by measuring its dry weight, micro and macro nutrient contents and uptake; and its effects on mungbean growth and yield parameters. The results showed that full season weed competition produced highest dry weight of R. capitata and its macro and micronutrient contents and uptake. Yield and yield components of mungbean decreased in a linear fashion with increase in competition period of Rhynchosia capitata. Full season competition of R. capitata reduced the seed yield of mungbean by 49% and 46% during 2011 and 2012 respectively. In conclusion, damaging effect of R. capitata intrusion on mungbean yield is associated with duration of its presence in crop, accumulation of dry matter and the nutrient uptake by R. capitata, which otherwise should be available to crop.