The model most widely used for path analysis of grain yield in small grains assumes bidirectional causal pathways between yield components; however, because yield components develop sequentially, it is questionable from a biological standpoint whether a yield component could influence others that develop earlier. The purpose of this research is to describe the theory and application of an alternative model for path analysis of grain yield that takes into account the sequential development of yield components. Path analysis was performed assuming bidirectional and unidirectional causal relationships among yield components of eight spring barley (Hordeum vulgare L.) cultivars grown at Palmer and Fairbanks, AK, in each of two years. Yield and the yield components spikes per square meter, kernels per spike, and kernel weight were estimated. The unidirectional model seems to reflect operative causal pathways more realisitically, and results in simpler estimates that present a clearer picture of the relationships among grain yield and yield components. Of the three yield components, spikes per square meter resulted in the greatest positive contribution to yield, while the effect of kernels per spike on kernel weight was the most negative compensatory response among yield components.

Urea is the predominant form of fertilizer N used in Alaska. However, little information is available on the N‐recovery efficiency (NRE) or the ultimate fate of urea‐N in subarctic soils. This study was conducted to determine the NRE and the ultimate fate of urea‐N applied in the spring for barley (Hordeum vulgare L.) production in interior Alaska. Urea and Ca(NO3)2 were applied at 100 kg N ha−1 and either incorporated into or left on the soil surface in each of three cropping years. Also, 15N‐labeled urea was applied to small plots. Ammonia traps and soil and plant samples were used to track the form and movement of the applied N. Ammonia volatilization losses were negligible. Deep soil samplings indicated negligible leaching of N. The NRE, as determined by the difference method, was estimated to be about 60% for urea and 73% for Ca(NO3)2. By the isotope dilution method, NRE for urea was calculated to be about 41%. An apparent added nitrogen interaction (ANI) accounted for an additional 16.5%. Approximately 43% of the applied urea‐N was recovered in the soil organic matter at the end of the season, 1% remained in the soil as inorganic N, and 15% was unaccounted for and assumed lost through denitrification. Grain yields did not differ due to N source or placement, but total plant N uptake was greater from the Ca(NO3)2 than from the urea source. Nitrogen placement did not affect N uptake. Fertilizer N cycling in this subarctic soil did not differ greatly from fertilizer N cycling in more temperate regions.

Long-term tillage and crop residue management in the subarctic: fluxes of methane and nitrous oxide. Can. J. Soil Sci. 77: 565-570. Methane and nitrous oxide are important radiatively active gases that are influenced by agricultural practices. This study assesses long-term tillage, crop residue management, and N fertilization rates on the flux of these two gases at a high latitude site representing the northern fringe of large-scale agriculture. Cumulative methane uptake for the summer was higher from no-tillage plots than tilled plots. This was associated with lower soil water contents with tillage. Thus, the reduction in CH 4 uptake was attributed to water stress on methane oxidizers. At planting, soil water contents were near field capacity, and the no-till plots had the lowest uptake which was attributed to restricted diffusion of methane to active sites. A similar pattern of methane uptake to soil water content was found with the residue management treatments. Removing the straw lowered the soil water content and for most of the season methane uptake was also lower than where the straw had been left on the plots. Nitrogen fertilizer rate had little effect on methane uptake over the summer, but high N rates lowered consumption during the time of active nitrification early in the season. This corresponded to the time of maximum efflux of nitrous oxide. Nitrous oxide efflux was greatest at the high N rate where straw was retained on the plots. L'absorption cumulative de méthane durant l'été était plus abondante à partir des parcelles en régime de culture sans travail du sol que dans celles travaillées selon les méthodes classiques. Cette plus forte absorption était associée à l'abaissement de la teneur en eau du sol par les façons culturales répétées. Ainsi la moins forte absorption de CH 4 en régime de travail classique était attribuée au stress hydrique exercé sur les oxydants du méthane. Aux semailles, époque où la teneur en eau du sol est presque à la capacité au champ, ce sont les parcelles conduites en culture sans labour qui manifestaient la plus faible absorption, ce qui s'expliquait par une diffusion réduite du méthane vers les sites d'activité. Un rapport similaire de l'absorption du méthane avec la teneur en eau du sol était observé dans les traitements de gestion des restes de culture. L'enlèvement de la paille provoquait l'abaissement de la teneur en eau du sol, et pour la plus grande partie de la saison, l'absorption du méthane était elle aussi plus faible que là où la paille était laissée sur place. La dose de fumure N n'avait que peu d'effet sur l'absorption du méthane pour la totalité de l'été, mais la dose supérieure causait une réduction de la consommation de méthane dans la phase de nitrification active du début de la saison de végétation, qui coïncidait avec celle d'efflux maximum d'oxyde nitreux. L'efflux de N 2 O était particulièrement abondant à la dose supérieure de fumure N lorsque la paille était laissée sur place.

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