Study on the Effect of Adding Substrates on the Quantitative Characteristics and Germination Dynamic of Soil Seed Banks

In order to study the effect of adding substrates on soil seed banks (SSBs) germination characteristics, vermiculite (inorganic substrates), rice husk char (organic substrates) and their mixed substrates were selected to be added to SSBs by different ratios. After the germination test, the results show that SSBs in different treatments present different germination characteristics. In this test, the nutrition of organic substrates is more important for promoting the rate of seeding emergence, while the inorganic substrates is better for greater density and seeding community diversity. T1(rice husk char: soil=1:9), T5(rice husk char: vermiculite: soil=2:1:7) and T4(vermiculite: soil=3:7) correspond the best promoting effect on these three aspects. Thus the substrates selection should be determined according to specific objectives during vegetation restoration. Mixed substrates combine the advantages of organic and inorganic substrates, which leads to comparative advantages in all aspects.

Potential Pollen and Seed Production from Early- and Late-Emerging Common Ragweed in Corn and Soybean

Despite the abundance of common ragweed in crops and the potency of ragweed pollen as an allergen, pollen production in agricultural fields has hardly been evaluated. Our goal was to evaluate pollen and seed production of early- (i.e., plants missed by weed control) and late- (i.e., after weed control) emerging common ragweed growing in corn and soybean. Allocation and gender distribution were also evaluated. The experiment included 2 yr (2008, 2009), three competition treatments, two seeding/emergence dates, three densities, and four replicates. Competition treatments (main plots) included no crop or weeds (bare), corn, or soybean. Crops were glyphosate resistant. Subplots were seeded with common ragweed before or after glyphosate application at densities of 1 (4 m−2), 3 (12 m−2), or 6 (24 m−2) plants per plot. Ragweed plants were harvested in mid-October and measured (aboveground biomass, length of all male inflorescences, stem diameter, and seed production). Based on our estimates, mean (backtransformed from ln[x+ 1]) pollen production values were: 6.25 (bare), 0.74 (corn), and 1.13 (soybean) × 108pollen grains per ragweed. Biomass and diameter were good predictors of ragweed male and female fitness. Plant height was not correlated with maleness. In crops, ragweed gender distribution was shifted toward maleness. Estimations indicate early-emerging (June 18 to 23) ragweed produced three times more pollen than late (July 7 to 11) plants.

Influence of Canopy Removal by Burning or Clipping on Emergence of Eragrostis lehmanniana Seedlings

Eragrostis lehmmniana (Lehrnann lovegrass) is a warm-season bunchgrass native to South Africa which dominates many desert grassland sites in southern Arizona. To determine why fire results in high seedling recruitment of this species, we measured germination of seeds in the seedbank and field seedling emergence following 1) no treatment, 2) burning, 3) clipping and herbicide and 4) herbicide d y . Treatments were designed to compare the effects of initial fire heat treatment with those of canopy removal, as affecting seedbed temperatwe, light and water availability, on seedling emergence. Treatments were replicated over 2 years on a stand of Lehrnann lovegrass at the Santa Rita Experimental Range. Canopy removal, by either clipping or burning, increased seedling emergence in seedbank samples taken prior to summer rains and greatly increased field seeding emergence. High seedling emer- gence after canopy removal was not the result of greater seedbed water availability but probably the result of a greater range in diurnal soil temperatures and increases in red light reaching the seedbed, both of which stimulate germination. The ability of E. lehmanniana to persist after fire indicates that prescribed burning could be used to control associated woody plants and improve forage palat- ability of E. lehmanniana dominated grasslands.

EFFECT OF SEEDING DEPTH, SEEDING DATE AND SEED SIZE ON COMMON ROOT ROT OF SPRING BARLEY

The effects of variable seeding depth and dates of seeding of barley on the incidence of root rot, and on emergence and grain yield were investigated in field trials at Saskatoon and Scott, Saskatchewan. The effect of variable seeding depth of barley on intensity of root rot, grain yield, loss of yield due to root rot, and the effect of variable seed size of barley on incidence of root rot and yield were also investigated in field trials at Lacombe, Alberta. Symptoms of common root rot, based on lesions on the subcrown internode, were not influenced by seed size or seeding date but the disease increased with depth of seeding. Grain yield decreased with depth and with late seeding. Emergence was not affected by seeding date but decreased with depth of seeding. Common root rot was not associated with the reduced yields of later seeding dates but was associated with reduced yields of increased seeding depths. The increased emergence and reduced disease at shallow depths resulted in a greater number of clean plants which probably accounts for some of the increased grain yield at shallow seeding depths.