1960; Walton, 1975; Carr et al., 1998; Chapko et al., 1991). Robinson (1960) reported that pea improved oat (Avena Intercropping barley (Hordeum vulgare L.) with Austrian winter sativa L.) forage yield. In a 2-yr pea-barley and pea-oat pea (Pisum sativum ssp. arvense L. Poir) may increase the use efficienintercropping study, Carr et al. (1998) found that total cies of growth resources and reduce fertilizer N requirements. The forage yield was unaffected by intercropping when the objectives of this study were to determine (i) row configuration and (ii) fertilizer N effects on yield, protein content, and the land equiva-cereal crop was sown at a rate equal to or greater than lent ratio (LER) of barley-pea intercropping systems. A 3-yr barleythe sole crop seeding rate. However, less forage was pea intercropping study was conducted at the Western and Central produced when the cereal component was sown at half Agricultural Research Centers (WARC and CARC) of Montana State the sole crop seeding rate. They also found that the University from 2000 to 2002 with three row configurations (4 rows intercropping forage yield was unaffected by the pea barley ϫ 4 rows pea, 2 rows barley ϫ 2 rows pea, and barley-pea mixed seeding rate. In other studies, forage and grain yield of within rows) and three N application treatments (0, 67, and 134 kg legumes were suppressed by cereal components (Ofori N ha Ϫ1 ). Barley biomass production increased 41% at WARC and and Stern, 1987; Hauggaard-Nielsen and Jensen, 2001; CARC, whereas pea biomass production decreased 34% at WARC Hauggaard-Nielsen et al., 2001). Seeding rates for comand 46% at CARC with the row configuration changing from the 4 ϫ 4 ponent crops in cereal-pea mixtures are commonly less to the mixed configuration. The LER ranged from 1.05 to 1.24 on a biomass basis and from 1.05 to 1.26 on a protein basis, indicating a than when either the cereal crop or pea is sown alone production advantage of intercropping. Barley is a more competitive (Carter and Larson, 1964; Droushiotis, 1989). component than pea. Separated row arrangements are advantageous The efficiency of an intercropping system can be evalwhere the desired outcome is a greater pea component in the harvested uated by the land equivalent ratio (LER), defined as forage, but the mixed arrangement has a greater total biomass yield the total area required under sole cropping to produce and LER. Fertilizer N increased total biomass yield and protein level the equivalent yields obtained under intercropping (De in barley-pea intercrops, but high N rates could decrease the LER Wit and Van Den Bergh, 1965; Willey, 1979; Mohta and and result in toxic levels of nitrate in the forage. De, 1980). It is expressed as:

Row spacing, plant density, and N application timing can be manipulated to optimize plant growth and spatial distribution, therefore maximizing sunlight, nutrients, soil water use effi ciency and grain yield. A 2-yr fi eld study to evaluate the eff ects of four seeding rates (108, 215, 323, and 430 seeds m -2 ), two row spacings (15 and 30 cm), and three N treatments (FA1, 100% at seeding; FA2, 50% at seeding and 50% at tiller formation; and FA3, 50% at seeding and 50% at shoot elongation) on grain yield of McNeal hard red spring wheat (Triticum aestivum L.) was conducted in central Montana. Spring wheat accumulated greater biomass at a faster rate under the 15-cm row spacing than the 30-cm row spacing. Grain yield was 410 and 412 kg ha -1 greater at 15-cm than at 30-cm row spacings in 2004 and 2005, and the yield increase was primarily attributed to 44 and 40 more spikes m -2 at 15-cm than at 30-cm row spacing in 2004 and 2005, respectively. Grain yield was not signifi cantly aff ected by the N treatments, thus all N should be applied at seeding. Th e optimum seeding rate was 215 seeds m -2 . Tillers at higher seeding rates had larger phyllochrons and greater mortalities. Low protein content was found in FA3 and high seeding rate treatments in 2005. Narrow row spacing is recommended for high spring wheat yield in the northern Great Plains. Th is yield increase cannot be achieved by increasing seeding rate at wide row spacing.

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Sprinkler irrigation of rice (Oryza sativa L.) has recently been considered to reduce water use and increase grower flexibility in U.S. production areas where flood irrigation is predominant. Tests were conducted for 2 yr on a Sharkey clay (Vertic Haplaquept) to evaluate selected rice cultivars under sprinkler vs. flood irrigation. Irrigation methods were main plots and three cultivars in 1983 and six cultivars in 1984 were subplots. Sub-subplots in 1984 were single or split application of 101 kg N ha-•. Sprinkler irrigation consisted of three weekly applications of 0.038 m water each in 1983 and a similar scheduling to maintain soil moisture tension above -30 kPa in 1984.In 1983, sprinkler irrigation increased sheath blight (Rhizoctonia solanr") incidence and decreased grain yield (4448 kg ha-• vs. 7139 kg ha-' under flood irrigation), dry matter production, harvest index, and florets per panicle compared to flood irrigation. In 1984, despite chemical control of sheath blight, yields averaged 5901 kg ha -• under sprinkler irrigation vs. 7846 kg ha -• under flood irrigation. Nitrogen timing did not significantly affect yields, but a weak N timing X irrigation method interaction (p=0.061) denoted that split Napplications may benefit yields under sprinkler irrigation. Multiple regression indicated fewer florets per panicle was the primary source of yield loss with sprinkler irrigation. Sprinkler irrigation of rice might decrease water use but it lowers yields and increases need for fungicides compared with flood irrigation.

Critical nutrient concentrations (CNC), below which a yield reduction occurs, for potato (Solanum tuberosum L.) petiole nitrate (PN) have been reported for the Pacific Northwest growing region but differences in method of determination or definition of this parameter have resulted in some discrepancies in values. The objectives of this research were to document seasonal PN levels with varying levels of applied N, to determine CNC at three growth dates [tuber initiation, TI; 21 d after TI(TI + 21); and 42 d after TI (TI + 42)], and to establish the relationship between yield responses to midseason N application and CNC. Experiments were conducted at two sites on a Typic Argiboroll and three sites on a Pachic Haploxeroll in western Montana. Treatments included six or eight N rates between 0 and 336 kg N ha−1 applied as NH4NO3 before hilling and a topdressing of 67 kg N ha−1 broadcast on subplots at TI + 21. Early season PN depended on applied N, with maximum values of 25 to 30 g NO3‐N kg−1 at TI. Values declined with seasonal progression and became increasingly dependent on fertilizer N rates. The N topdressed at TI + 21 increased PN level 6 g kg−1 at TI + 42 compared to non‐topdressed areas. Linear plateau regression of relative yield against PN revealed CNC values of 25 g kg−1 at TI 14 g kg−1 at TI + 21, and 10 g kg−1 at TI + 42. Statistical analysis, could not separate the TI + 21 and TI + 42 regressions, indicating a CNC of 13 g NO3‐N kg−1 throughout the period of tuber bulking. Yield responses to topdressed N, however, were documented only when PN values were below 11 g NO3‐N kg−1 at TI + 21. Conservative interpretation of critical nutrient concentration is justified.

Plant breeders have attempted to use extended green leaf duration (EGLD) traits for spring wheat (Triticum aestivum L.) yield improvement in Montana. The objective of this study was to investigate the yield, protein, harvest index (HI), remobilization of water‐soluble carbohydrate (WSCRM) and nitrogen (NRM), N uptake, nitrogen harvest index (NHI) and nitrogen recovery in grains (NRG) of two spring wheat cultivars with EGLD (Vida and Reeder) and one without the traits (Outlook) as influenced by N input rates at dryland and irrigated environments. Vida, selected from a cross between Reeder and Scholar, exhibited a greater grain yield but lower protein content compared with Reeder and Outlook; this yield advantage likely resulted from higher HI, as well as greater postanthesis biomass (PABM) accumulation of Vida under irrigation. The yield advantage was greater at the irrigated site (23%) than at dryland (7–12%). The average contribution of WSCRM to grain yield (WSCCGY) was 8 and 12%, and NRM to grain N (NRCGN) was 67 and 60% at the dryland and irrigated site, respectively. No evidence showed Reeder and Vida had a greater WSCCGY or NRCGN than Outlook. The WSCRM and NRM were influenced by N input rates. Lower grain protein contents in Vida than in Reeder and Outlook was attributed to higher N contents in the straw and greater biomass yields of Vida even though Vida took up more N from soil. High N application rates reduced the NHI and NRG for all cultivars at both dryland and irrigated environments.

Annual legume plowdown systems, which utilize fall regrowth for N contributions to rotational crops, have not been adapted to irrigated, intermountain areas of the Northern Rockies. Our objective was to evaluate plowdown systems using ‘Nitro’ alfalfa (Medicago sativa L.) and ‘Bigbee’ berseem clover (Trifolium alexandrinum L.). These two legumes were grown under five harvest management systems (zero to three forage harvests prior to fall plowdown of regrowth, or a standard three harvest system with no herbage plowdown) at two sites in western MT differing in soil characteristics. They were assayed for forage and plowdown production and for N benefits to ‘Clark’ barley (Hordeum vulgare L.; syn. H. distichon L.) for two subsequent years. Maximum herbage plowdown N was 125 to over 200 kg N ha−1 for berseem clover and 87 kg N ha−1 for alfalfa. A two‐harvest system resulted in 3.6 to 6.6 Mg ha−1 forage and 45 to 78 kg N ha−1 in herbage plowdown. Effects of plowdown were measured directly in increased soil N availability and correlated increases in N uptake in subsequent barley; benefits were expressed in increased grain yields and/or grain N concentrations and were apparent for two successive years at the site of lower native fertility. Alfalfa N benefits were superior to berseem clover, though disproportionate to herbage plowdown N quantities, possibly due to greater root and crown N in alfalfa. Where the management goal is primarily forage production with moderate benefit of plowdown N, berseem clover works well in a two‐harvest system; Nitro alfalfa is preferred where greater benefits of plowdown N are desired.