More precise effects of soil t e m p e r a t u r e on t h e direction of corn root g r o w t h were d e t e r m i n e d b y growing seedlings in soil for s h o r t periods in g r o w t h c a b i n e t s controlled to give a range of soil t e m p e r a t u r e conditions.The angle of g r o w t h (relative to t h e horizontal} was f o u n d to be m i n i m u m (10 °) at c o n s t a n t 17°C. A b o v e or below this t e m p e r a t u r e (I0-30°C), a more vertical direction occurred. Cyclic t e m p e r a t u r e s also influenced direction, w i t h t h e m a x i m u m of t h e cycle a p p a r e n t l y d e t e r m i n i n g the angle. The duration of t h e m a x i m u m t e m p e r a t u r e period in a cycle necessary to initiate a direction effect was n o t d e t e r m i n e d , however.The significance of these findings in t h e field is t h a t modifications of soil t e m p e r a t u r e s b y mulches, etc. p r o b a b l y influence t h e d i s t r i b u t i o n of roots in t h e rooting zone of soils. This in t u r n m e a n s t h a t p l a n t b e h a v i o u r such as moisture a n d n u t r i e n t u p t a k e can be b e t t e r explained or m a n a g e d for maxim u m performance. * Former graduate student. Present address, Ministry of the Environment,
Bands of corn stover placed on soil in different positions relative to corn (Zea mays L.) rows decreased soil temperature at a 10‐cm depth 2.5C for maxima, doubled the proportion of root growth in the surface 5 cm of soil, and tripled fertilizer uptake from a surface‐applied band of 32P‐labeled phosphorus fertilizer. The greatest increase in uptake occurred with the band of stover on both sides of the row. Total root growth to a depth of 15 cm was not greater with stover than without it.The increase in uptake was credited to the relatively greater root growth near the surface, which in turn was believed due to the temperature depression and a tendency for a more horizontal direction of root growth. While a more favorable soil moisture level, as found under mulch, would be necessary for root growth and proliferation, it was not considered initially responsible for directing roots closer to the soil surface.
A set of morphological te-rms was selected rheir respeclive nodes. From the second node from varying terminology in the literature the second apparent leaf develops, but beto serve as a model for uniform descriptions cause its fohar nature is not universally of treatment efiects on growth and develop-accepted it is termed the "coleoptile". Ihe ment of corn seedlings. In this model, the leaf developing from the third node is termed first root to emerge is termed the "primary the "first leaf" and those developing f'om root". Those emerging from just above specific successively higher nodes are designated in nodes are interpreted as adventitious roots ascending numerical order.and termed "adventitious root whorls" of RESUME On a 6tabli, )r partir de la terminologie relev6e de racines adventives" du noeud correspondans Ia bibliographie, une s6rre de termes sus-dant. Le second noeud donne naissance ir la ceptibies d'undormiser Ia descriptron des ellets seconde feuilie apparente, appei6e ''col6optile" de traitements divers sur la crorssance de pian-du fait qu'elle n'a pas vraiment ia mcrphologie tules de mais. La premrdre racine ir apparaitre d'une feuille vraie. La premidle feuilie "vrare" est d6sign6e du nom de "racrne pnmarre". Les est celle qui nait du troisidme noeud, les racines n6es imm6diatement au-dessus d'un feuilies produites des noeuds suivants 6tant noeud sont consid6r6es comme 6tant des d6sign6es en ordre num6rique ascendant.
Cultural practices can modify losses of soil and nutrients from cropland, but little quantitative information is available on the extent. In this study the effect of stover on soil and phosphorus (P) removal was determined for a well‐drained till soil (Guelph loam) with 7% slope. Corn (Zea mays L.) was planted without tillage after 32P‐tagged P fertilizer was applied broadcast and covered with a corn stover mulch in one treatment or left bare in a second treatment. Run‐off was collected and analysed from one simulated and from two natural rainfall events. Stover reduced soil P in run‐off by 65% and fertilizer P by 97%. These reductions were achieved by a decrease in total run‐off and by a decrease in the concentration of suspended soil in it. Of the 29 kg of fertilizer P applied per ha, 3.85 kg (13%) and 0.13 kg (<1%) were removed over all run‐off events from the no stover and stover treatments, respectively. This corresponded to 8.5 and 1.3%, respectively, of the total P removal, which varied from 45 kg/ha without stover to 10 kg/ha with stover. The liquid fraction of the run‐off carried the least amounts of either soil or fertilizer P. Proportionately more fertilizer P was found in the coarse (>50μ) soil than in the fine fraction (<50μ), whereas proportionately more soil P was found in the latter than in the former, suggesting that fertilizer P is preferentially associated with the coarse fraction.
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