Fredrick A. Bliss
William R. Graves, Sandra R. Anfinson, and Kathryn K. Lappegard
Scotch laburnum [Laburnum alpinum (Mill.) Bercht.], Amur maackia (Maackia amurensis Rupr. & Maxim.), and Chinese wisteria [Wisteria sinensis (Sims) Sweet] were inoculated with compatible rhizobia and treated with leaching fractions (LF) of 0, 0.2, and 0.4 using fertilizer solutions with 3.6 and 10.7 mol N/m3 for 10 weeks. LF did not affect plant dry mass, leaf area, or stem length. Growth was higher among plants provided 10.7 mol N/m3, but only plants provided 3.6 mol N/m3 formed root nodules. We conclude that growth is not reduced by eliminating leaching during the first 10 weeks of seedling development, and that application of 10.7 mol N/m3 prevents nodulation of these species.
Wilfred Singogo, William J. Lamont Jr., and Charles W. Marr
Wheeler G. Foshee, William D. Goff, Michael G. Patterson, and Donald M. Ball
Hairy vetch (Vicia villosa Roth), common vetch (V. sativa L. `Cahaba White'), arrowleaf clover (Trifolium vesiculosum Savi `Yuchi'), crimson clover (T. incarnatum L. `Tibbee'), red clover (T. pratense L. `Redland II'), yellow nutsedge (Cyperus esculentus L.), buckwheat (Fagopyrum sagittatum Gilbert), hairy indigo (Indigofera hirsuta L.), bahiagrass (Paspalum notatum Flugge `Pensacola'), common bermudagrass [Cynodon dactylon (L.) Pers.], and centipedegrass [Eremochloa ophiuroides (Munro) Hack] were grown for 3 years in a 3 × 3-m spacing around young pecan [Carya illinoinensis (Wangenh.) K. Koch] trees. Compared to weed-free plots, all cover crops suppressed tree growth substantially, and there were no differences among cover crops in the degree of suppression. Mean trunk cross-sectional area of weed-free trees increased 26-fold by the end of the third growing season but increased only 13-fold for trees grown with any cover crop. These results suggest that cover crops, if grown in young pecan orchards to promote beneficial insects, should be excluded from the immediate area around the young trees.
Lin Wu and Armando Torres
The effect of tall fescue turf on growth, flowering, modulation, and nitrogen fixing potential of Lupinus albifrons Benth. was examined for greenhouse and field grown plants. No allelopathic effect was observed for lupine plants treated with tall fescue leachates. The nitrogen-fixing potential measured by nodule dry weight and acetylene reduction rates was not significantly affected by either tall fescue turf or low nitrogen fertilization. Both the greenhouse and field studies showed that the growth, sexual reproductive allocation, and number of inflorescences were significantly reduced when lupine plants were grown with tall fescue. The root length densities of tall fescue turf and lupine monoculture were measured. The tall fescue turf had 20 times higher root length density (20 cm cm-3 soil) than the lupine plants monoculture. This suggests that intense competition at the root zone may be a dominant factor which limits the growth of the lupine plants. The reproductive characters of the lupine plants was improved by phosphorus fertilization. Transplanting of older lupine plants into the turf substantially alleviated the tall fescue turf competitive effect.
William R. Graves' and Wilhelmina van de Poll
The capacity to form nitrogen-fixing symbioses with rhizobia is common among species in the Papilionoideae subfamily of the Leguminosae, but nodulation and nitrogen fixation have never been documented in Cladrastis kentukea (Dum.-Cours.) Rudd (American yellowwood). The purpose of this study was to test the hypothesis that C. kentukea is nodulated by rhizobia. Seedlings were grown in sterile vermiculite and irrigated with a nitrogen-free nutrient solution. In one experiment, the vermiculite was inoculated with rhizobia that nodulate Maackia amurensis Rupr. & Maxim., a closely related tree species. During a second experiment, the vermiculite was inoculated with samples of soil collected near trees of C. kentukea in a native stand in Alexander County, Illinois. There were no nodules on roots of seedlings harvested 6 weeks after inoculation in either experiment. These results represent strong additional evidence that C. kentukea does not form nitrogen-fixing symbioses with rhizobia.
Gary R. Cline and Anthony F. Silvernail
A split-plot factorial experiment was conducted to examine effects of tillage and winter cover crops on sweet corn. Main plots received tillage or no tillage. Cover crops consisted of hairy vetch, winter rye, or a mix. Nitrogen treatments consisted of either adding or not adding NH4NO3 at recommended rates. No significant effects of tillage on sweet corn yields were detected, although yields with tillage were slightly greater. Following rye winter cover crops, adding NH4NO3 to corn significantly (P ≤ 0.05) increased yields by 56% compared to treatments not receiving N. However, following vetch, corn yields obtained without N fertilization equaled those obtained with N fertilization following rye or vetch. It was concluded that 1) nontilled sweet corn was successful and 2) N2 fixed by vetch was able to sustain sweet corn production completely and was equivalent to a minimum of 70 kg N/ha.
DeFrank and Charles R. Clement
Pejibaye (Bactris gasipaes, Palmae) is being evaluated for palm heart production in Hawaii. Counts of parasitic nematodes and yields at 18 months and weed control were evaluated in response to: Arachis pintoi, Cassia rotundifolia cv. Wynn, Desmodium ovalifolium, Chloris gayana, and woven black polypropylene mat. Four open-pollinated progenies from the Benjamin Constant population of the Putumayo landrace were used as replications. Twenty five percent of the plants were harvested, with means of 5, 20, 15, 15, and 70%, respectively. Individual heart weights did not vary significantly among treatments (mean = 169 g). Actual yields were significantly different, with means of 31, 125, 92, 99, and 440 kg/ha, respectively. All vegetative ground covers competed with pejibaye for nutrients, which explains the harvest percentages and yields. D. ovalifolium and C. gayana provided acceptable weed control. A. pintoi provided good ground cover, but reduced weed control.
Wayne F. Whitehead and Bharat P. Singh
The goal of this study was to compare the effect of leguminous and non-leguminous cover crops alone or in mixture with fertilizer nitrogen rates on kernel weight, ear number, and yield of Bt sweet corn. The following fall-spring fertility treatments were applied using randomized complete-block design with three replications: 1) fall-0 N, fallow; spring-0 N, 2) fall-0 N, abruzzi rye; spring-0 N, 3) fall-0 N, hairy vetch; spring-0 N, 4) fall-0 N, abruzzi rye+hairy vetch; spring-0 N, 5) fall-0 N, fallow; spring-101 kg N/ha, 6) fall-0 N, abruzzi rye; spring-101 kg N/ha, 7) fall-0 N, hairy vetch; spring-101 kg N/ha, 8) fall-0 N, abruzzi rye+hairy vetch; spring-101 kg N/ha, 9) fall-0 N, fallow; spring-202 kg N/ha, 10) fall-0 N, abruzzi rye; spring-202 kg N/ha, 11) fall-0 N, hairy vetch; spring-202 kg N/ha, and 12) fall-0 N, abruzzi rye+hairy vetch; spring-202 kg N/ha. In Spring of 2005, `Attribute BSS0977' bi-color (BC) supersweet (sh2) corn seeds were field planted. Total unhusked ear yield and ear number were harvested 74 days after planting, while kernel weight was measured from three randomly chosen ears. Maximum kernel fresh weight (111.6 g/ear), ear number (101,773/ha) and total yield (17.3 Mg/ha) were produced by hairy vetch; spring-101 kg N/ha. Minimum kernel fresh weight (23.0 g/ear) and ear number (51,485/ha) were produced by fallow; spring-0 N, while minimum total yield (2.2 Mg/ha) was produced by abruzzi rye; spring-0 N. Results indicate that hairy vetch supplemented with N at 101 kg/ha is most effective in supporting kernel fresh weight, ear number and yield of this BCsh2 corn variety.
Dan TerAvest, Jeffrey L. Smith, Lynne Carpenter-Boggs, David Granatstein, Lori Hoagland, and John P. Reganold
the composition of the soil microbial community ( Laakso et al., 2000 ; Wardle et al., 2001 ). However, improvements in soil quality have not always translated into improved leaf and fruit N levels or greater yields. For example, legume and non-legume