Environmental concerns have led to renewed interest in use of sustainable green manure legume cropping systems. Field experiments were undertaken to determine whether cowpea [Vigna unguiculata L. (VValp.)] crop residues could be used to reduce fertilizer N inputs with fall broccoli [Brassica oleracea L. (Italica Group)]. Studies in 1992,1993, and 1994 involved broccoli preceded by cowpeas, with or without factorial combinations of preplant N and sidedress N from urea on the broccoli. Control broccoli plants were grown on fallowed ground and supplied with 168 kg ha−1 of N from urea. Cowpea crop residues alone did not provide sufficient N for optimum production of marketable broccoli. Marketable broccoli yields sometimes showed no significant differences between controls and cowpea residue treatments receiving only 84 kg ha−1 of fertilizer N. However, there was a tendency for increased broccoli transplant mortality in cowpea residue plots. A fourth study in 1994 indicated a negative main effect of cowpeas on broccoli stand establishment, and a complex interaction of cowpeas and trifluralin treatments on broccoli yield. Petiole N concentrations of broccoli plants with reduced fertilizer N inputs which succeeded cowpeas usually were lower than those of control plants. Soil nitrate levels at 15‐ to 30‐cm soil depths at the time of broccoli planting were consistent indicators of apparent nitrate utilization by microbial decomposition of cowpea crop residues. We were unable to demonstrate a cowpea‐broccoli succession cropping system which consistently reduced fertilizer N inputs without some type of adverse effect on the broccoli crop. Therefore, the use of cowpea crop residues to reduce fertilizer N inputs with fall broccoli is not recommended.

Swiss 3T3 cells exhibit contact-regulated cell growth and have a lower ability to transport 2-deoxyglucose than polyoma (Py)-transformed 3T3 cells. Py3T3 cells treated with dibutyryl cyclic adenosine 3'5' monophosphate (dBcAMP) and theophylline have reduced cell growth and transport 2-deoxyglucose at the same rate as normal 3T3 cells. Evidence that the cessation of cell growth and reduced transport abilities in Py3T3 cells does not represent a return to contact-regulated growth comes from the following observations. First, treating high density Py3T3 cells with dBcAMP allows more than two doublings of cell number, even though ability to transport 2-deoxyglucose is returned to levels equal to those of normal 3T3 cells. Second, dBcAMP prevents serum-stimulated increases in 2-deoxyglucose transport in Py3T3 but not in 3T3 cells.

Field experiments were conducted in Oklahoma in 1993 and 1994. Cowpeas [Vigna unguiculata (L.) Walp.] were grown using either noninoculated seed and 23 kg·ha -1 of preplant nitrogen (N) fertilizer (conventional) or Rhizobium-inoculated seed and no preplant N fertilizer (reduced input). Sample plants were excavated at first pod set and analyzed for nodulation and root morphology. Additional plants were harvested at the green-shell stage to determine seed yield and plant N concentration. Conventional and reduced input cowpeas did not differ in dry weight of root mass components, total root dry weight, shoot dry weight, shoot : root ratio, nodule distribution among root morphological components, total nodule fresh weight, plant N concentration, or green-shell seed yield. Most of the nodule fresh weight generally was associated with nodules on the basal and lateral roots. Results indicate that cowpea root characteristics are not necessarily altered by the presence or absence of added N fertilizer at a given location.

Field experiments were conducted in Oklahoma in 1993 and 1994. Cowpeas [Vigna unguiculata (L.) Walp.] were grown using either non-inoculated seed and 23 kg·ha–1 of preplant nitrogen fertilizer (conventional) or inoculated seed and no preplant nitrogen fertilizer (reduced input). Sample plants were excavated at first pod set and analyzed for nodulation and root morphology. Additional plants were excavated at the green-shell stage and were analyzed for nitrogen concentration. Conventional and reduced input cowpeas did not differ in nodule distribution among root morphological components, total nodule fresh weight, total root dry weight, or nitrogen concentration. Most nodules generally were located on the basal and lateral roots. Results indicate that cowpea root characteristics are not necessarily altered by differing cultural systems at a given location.