Soybean canopy formation effects on pitted morningglory (Ipomoea lacunosa), common cocklebur (Xanthium strumarium), and sicklepod (Senna obtusifolia) emergence

Abstract

Field studies were conducted in 2002 and 2003 to determine whether canopy formation influences pitted morningglory, common cocklebur, and sicklepod emergence in surface-tilled soybean. Each weed species was broadcast seeded before planting soybean in 19- and 97-cm-wide rows. Weed emergence beneath soybean was monitored after soybean emergence and compared with weed emergence in the absence of soybean (bareground treatment). Magnitude of daily diurnal soil temperature fluctuations diminished after soybean canopy formation, and light interception by soybean was positively related to the reduction in soil temperature. Canopy formation (50% light interception) occurred 16 to 17 d later in wide compared with narrow rows in both years. The red/far-red ratio of light available to seed on or near the soil surface was reduced from as much as 1.2 in full sunlight to less than 0.1 in the presence of a dense soybean canopy. Pitted morningglory emergence was not influenced by soybean canopy formation, whereas common cocklebur and sicklepod emergence were reduced as much as 33 and 68%, respectively. Although common cocklebur and sicklepod emergence diminished after soybean canopy formation, a small portion of the seedbank of both species emerged beneath the canopy. This research indicates that in a tilled system, emergence of some weed species is diminished by presence of an overlying canopy, but emergence does not completely cease with canopy formation. Late-season emergence of sicklepod and common cocklebur beneath a soybean canopy may contribute to replenishment of the soil seedbank, especially if these late-emerging cohorts are capable of surviving until the light environment is favorable for seed production.

Spatial Analysis of Digital Imagery of Weeds in a Maize Crop

“…The disturbance, caused either by the turnover of the soil or compaction, or both, stimulates the weeds to emerge because of the short exposure of seeds to light and changes in the ratios of soil gases and in water content [14,15,[39][40][41]. Compaction can also limit the available oxygen in soil, and competition from crop plants in the crop rows can reduce the density of weeds [42,43]. Thornapple responded positively to compaction under the tractor wheels and, to a lesser degree, by the press wheel of the planter in the crop rows (Figure 4).…”

Weed Problems, Ecology, and Management Options in Conservation Agriculture: Issues and Perspectives

“…Soybean canopy closure caused reductions in soil thermal amplitudes and an increase in light interception following soybean canopy formation resulted in reduced Palmer amaranth (Amaranthus palmeri) emergence, especially under NT (Jha and Norsworthy, 2009). Reduced PAR, and increased FR transmitted light due to canopy coverage (Norsworthy, 2004) inhibited germination of Amaranthus species, (Leon and Owen, 2003).…”

Root penetration through a high bulk density soil layer: differential response of a crop and weed species

“…It is not unusual, however, for large populations to emerge through a partially closed soybean canopy. In part, this can be explained by sicklepod seeds germinating throughout the summer (Norsworthy 2004) and an exceptional etiolation response (Nice et al 2001). But, a key question has been 'how are soil resources acquired to drive shoot growth processes when the larger soybean plants dominate the root zone?'…”