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Estimates of heritability and various gene effects were obtained for a number of agronomic traits in grain sorghum. The material studied included the parental lines and the F1, F2 B1 (P1 ✕ F1), and B2 (P2 ✕ F1), derivatives of the crosses ‘Redlan’ ✕ ‘Martin’, ‘Redlan’ ✕ ‘Combine 7078’, and ‘Plainsman’ ✕ ‘KS 7.’ It appeared that heritabilities of grain yield and kernel number were of lower magnitude than those of head weight, kernel weight, stalk diameter, and half blooming. Heritabilities of plant height and germination percentage were of a still higher order. The magnitude of heritability estimates varied greatly among crosses for some traits. Inadequacy of the original scale was indicated by a scaling test. Heritability estimates were also obtained based on logarithmically transformated data. Additive, dominance, and digenic epistatic gene effects were expressed in terms of parental, first and second filial, and backcrosses population means. Additive gene effects seemed to have a minor contribution to the inheritance for grain yield, head weight, kernel weight, and kernel number but appeared to be more important for other traits. Dominance gene effects seem to be important in the inheritance of most of the traits. Among the 3 types of epistatic gene effects it appeared additive ✕ additive and dominance ✕ dominance were important types of epistasis. Additive ✕ dominance gene effects were of minor importance, in general, except for germination percentage. The magnitude of additive ✕ additive gene effects was comparable to that of dominance gene effect and greater than additive gene effect. Dominance ✕ dominance gene effects were also of large magnitude. The effect of epistasis perhaps cannot be considered as negligible. Genetic models assuming negligible epistasis may be somewhat biased.
The purpose of this study was to obtain estimates of the relative magnitudes of the various types of variety ✕ environment interactions in variety tests, and to consider the significance of these interactions on variety evaluation procedures. Ten varieties of winter wheat at 13 locations, 4 varities of winter barley at 10 locations, and 5 spring oat varieties at 5 locations were evaluated in Kansas for a 3‐year period. The variety ✕ year interactions were small and nonsignificant, but the second‐order interactions of variety ✕ location ✕ year were of considerable magnitude and highly significant. The significant three‐factor interaction was not accounted for by grouping locations, and in general, must be regarded as an error variance to be controlled by the number of locations used and number of years of testing. Significant variety ✕ location interactions were obtained for wheat and barley, indicating the state could be divided into subareas. By grouping appropriate locations together, a reduction of the magnitude of variety ✕ location mean square was generally observed. However, it is suggested that each subarea should be considered as an independent unit in testing the significance of variety ✕ location interaction because the decrease or increase in the magnitude of variety ✕ location mean squares of subareas compared to that of the state as a whole does not always provide the true picture of its significance.
Pyrogenic carbon (PyC) is important because of its role in the global organic C (OC) cycle and in modifying soil properties. However, our understanding of PyC movement from terrestrial to fluvial ecosystems is not robust. This study examined (i) whether erosion or subsurface transport was more important for PyC export from headwaters, (ii) whether PyC was exported preferentially to total OC (TOC), and (iii) whether the movement of PyC from terrestrial to aquatic ecosystems provides an explanation for the coupling of PyC and non‐PyC observed in rivers at a global scale. In the Guineo‐Congolian highland forest region of western Kenya, duplicate catchments with sizes of 1–12 ha were equipped with stream gauges in primary forest and adjacent mixed agricultural landscapes that were cleared by fire 10, 16, or 62 years before. Stream water samples were taken weekly throughout 1 year and compared with runoff to assess PyC movement. Additional stream samples were taken from all major tributaries of the White Nile watershed of Lake Victoria. PyC was not found to be preferentially eroded relative to TOC or non‐PyC, as topsoil (0–0.15 m) PyC concentrations (6.3 ± 0.3% of TOC; means and standard errors) were greater than runoff sediment (1.9 ± 0.4%) and dissolved PyC concentrations (2.0 ± 0.4%, n = 252). In addition, PyC proportions in eroded sediment were lower than and uncorrelated (r2 = 0.04; P = 0.14) with topsoil PyC. An enrichment of PyC was found with depth in the soil, from 6.3 ± 0.3% of TOC in the topsoil (0–0.15 m) to 12.3 ± 0.3% of TOC at 1–2 m. Base flow PyC proportions of TOC correlated well with subsoil PyC (r2 = 0.57; P < 0.05) but not with topsoil PyC (r2 = 0.18; P > 0.05). Similar PyC proportions were found in the studied headwater streams (2.7 ± 0.2%), their downstream inflow into Lake Victoria (3.7%), the other nine major rivers into Lake Victoria (4.9 ± 0.8%), and its outflow into the White Nile (1.1%). A strong positive correlation between dissolved PyC and non‐PyC (r2 = 0.91; P < 0.0001) in the headwater streams reflect relationships previously seen for a range of globally important rivers, and contrasts with a negative relationship for suspended sediments (r2 = −0.5; P < 0.0001). The estimated PyC export from the Lake Victoria watershed of 11 Gg yr−1 may therefore originate to a large extent from subsoil pathways in dissolved form that appeared to be an important source of PyC in aquatic environments and may explain the coupling of PyC and non‐PyC at a global scale.
Natural soils are generally populated with a wide variety of macropores formed from physical processes and/or biological activity. These macropores can have a large influence on the lateral flow of water in hillslope soils even when those macropores are not continuous or connected directly to ponded water. The concept of self-organization of flow paths described by SIDLE et al. (2001) is analyzed through numerical simulation of variably-saturated flow in a large cylinder of soil containing a population of disconnected macropores. It is demonstrated that there is a threshold water pressure at which the macropores will become active, and above this threshold the then active network of macropores significantly increases the effective conductance of the soil volume. In the case examined here the increase exceeded 40%. The analysis presented provides a context for the explanation of soil pipe formation by the process of seepage erosion. An analogy is drawn between percolation theory in porous media and the concept of self-organization of flow pathways at the hillslope scale.
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