essential to successful management of no-till systems (Peterson et al., 1996;Zentner et al., 2002). MontanaThe productivity and cropping sequence effects of broadleaf crops farmers recognize their reliance on the cereal grain marare not well known within no-till systems in the semiarid northern Great Plains. We compared productivity of cool-and warm-season ket sector and the growing need for nutrient and pestibroadleaf crops with spring wheat (Triticum aestivum L.), measured cide inputs required to maintain productivity in cereal cropping sequence effects of broadleaf crops on subsequent cereal monoculture systems. However, with scant research incrops, and tested if different cereal crops interacted with previous formation, undeveloped market infrastructure for broadcrops. During 1999-2001 we conducted 2-yr cropping sequence experileaf crops, and low returns from their traditional comments at five sites in Montana under climatic conditions ranging from modities, alternative cropping ventures are especially severe drought to average rainfall. Grain yield and quality were mearisky in Montana. sured for chickpea (Cicer arietinum L.), flax (Linum usitatissimum Diversified no-till cropping systems have been pro-L.), pea (Pisum sativum L.), proso millet (Panicum miliaceum L.), moted to increase environmental and economic sussunflower (Helianthus annuus L.), and wheat in Year 1. In Year 2, tainability (Tanaka et al., 2002; Zentner et al., 2002). four cereal test crops [barley (Hordeum vulgare L.), durum (Triticum durum L.), spring wheat, and winter wheat] were grown following Oilseed and pulse crops increase market diversification the Year 1 crops and a fallow control to measure cropping sequence since these crop prices respond somewhat indepeneffects. Comparative productivity varied among crops by site, afdently of cereal grain markets (Zentner et al., 2002). firming that crop diversity mitigates production risk. Under averageOilseed and pulse crops also increase production diverrainfall, the cereal test crop yields following flax, pea, and chickpea sification due to differential responses to growing season ranged from 84 to 101% of the fallow control and were greater than rainfall and temperature patterns (Johnston et al., 2002; that following wheat in seven of nine cases. However, yields following Miller et al., 2002a). Crop diversity may also add value sunflower were equal or less than those following wheat. Under severe to cropping systems by increasing the efficiency of cereal drought, cereal test crop yields following broadleaf crops ranged from crop production (Johnston et al., 2002; 21 to 41% of the fallow control and were equal or less than those 2002a). Rotational benefits to wheat and barley from following wheat. Previous crops affected four cereal test crop species similarly.

Annual legumes permit intensified cropping in no‐till systems in the drought‐prone northern Great Plains. Our objectives were to compare cropping sequence effects of pea (Pisum sativum L.) with fallow, mustard (Sinapis alba L.), and wheat (Triticum aestivum L.), and to measure the effects of pea harvest timing and shoot biomass presence on soil water use and N contribution, and yield and grain quality of subsequent wheat. Pea, mustard, wheat, and fallow preceded spring wheat at three sites in Montana. In the first year, two harvest timings (anthesis and maturity) were included and managed for presence or absence of crop shoot biomass. In the second year, a wheat test crop was grown at four N fertilizer rates. Regardless of management, pea used equal or less soil water, contributed equal or greater soil N, and had equal or greater positive impact on subsequent wheat growth than mustard or wheat. Compared with maturity, midseason harvest timing of pea increased soil N (30–39 kg NO3–N ha−1) and soil water (19–39 mm) available in the spring to the subsequent wheat test crop at two of three sites. Under severe drought, midseason harvest of pea increased wheat yield 50% and critically increased grain density compared with the mature pea harvest. At the N‐limited site, midseason harvest of pea increased wheat yield 14% and grain protein 9% compared with mature pea harvest. Pea shoot biomass presence did not affect soil water or N, or growth of a subsequent wheat crop.

Pea (Pisum sativum L.) is increasingly being rotated with wheat (Triticum aestivum L.) in Montana. Our objective was to compare economic net returns among wheat-only and pea-wheat systems during an established 4-yr crop rotation. e experimental design included three wheat-only (tilled fallow-wheat, no-till fallow-wheat, no-till continuous wheat) and three no-till peawheat (pea-wheat, pea brown manure-wheat, and pea forage-wheat) systems as main plots, and high and low available N rates as subplots. Net returns were calculated as the di erence between market revenues and operation and input costs associated with machinery, seed and seed treatment, fertilizer, and pesticides. Gross returns for wheat were adjusted to re ect grain protein at " at" and "sharp" discount/premium schedules based on historical Montana elevator schedules. Cumulative net returns were calculated for four scenarios including high and low available N rates and at and sharp protein discount/premium schedules. Pea-wheat consistently had the greatest net returns among the six systems studied. Pea fallow-wheat systems exhibited greater economic stability across scenarios but had greater 4-yr returns (US$287 ha -1 ) than fallow-wheat systems only under the low N rate and sharp protein discount schedule scenario. We concluded that pea-wheat systems can reduce net return uncertainties relative to wheat-only systems under contrasting N fertility regimes, and variable wheat protein discount schedules in southwestern Montana. is implies that pea-wheat rotations, which protected wheat yield and/or protein levels under varying N fertility management, can reduce farmers' exposure to annual economic variability.

A gronomy J our n al • Volume 10 0 , I s sue 3 • 2 0 0 8 591

The bld2-1 mutation in the green alga Chlamydomonas reinhardtii is the only known mutation that results in the loss of centrioles/basal bodies and the loss of coordination between spindle position and cleavage furrow position during cell division. Based on several different assays, bld2-1 cells lack basal bodies in > 99% of cells. The stereotypical cytoskeletal morphology and precise positioning of the cleavage furrow observed in wild-type cells is disrupted in bld2-1 cells. The positions of the mitotic spindle and of the cleavage furrow are not correlated with respect to each other or with a specific cellular landmark during cell division in bld2-1 cells. Actin has a variable distribution during mitosis in bld2-1 cells, but this aberrant distribution is not correlated with the spindle positioning defect. In both wild-type and bld2-1 cells, the position of the cleavage furrow is coincident with a specialized set of microtubules found in green algae known as the rootlet microtubules. We propose that the rootlet microtubules perform the functions of astral microtubules and that functional centrioles are necessary for the organization of the cytoskeletal superstructure critical for correct spindle and cleavage furrow placement in Chlamydomonas.