In:
Crop Science, Wiley, Vol. 29, No. 3 ( 1989-05), p. 758-763
Abstract:
Considerable variation exists in recommendations for the use of N during establishment of forage legumes. Abundant literature documents the inhibition of N 2 fixation by applied N, but few experiments determined the consequences of its subsequent removal. In this study the effects of NH 4 NO 3 on the growth and N 2 fixation of subterranean clover ( Trifolium subterraneum L.) were investigated. Plants were grown in a greenhouse from seed with a modified Hoagland's solution containing 0, 2, 4, 6, 8, and 12 m M NH 4 NO 3 for 80 d. The plants were then divided into two groups, the N treatments continued for one (+ N) group and the other group given an N‐free Hoagland's solution (−N) for an additional 21 d. Total dry wt. (DM), apparent N 2 fixation (ANF), leaf area (LA), and shoot N concentration were measured and levels of photosynthetically active radiation (PAR) were monitored continuously during daylight hours. Per plant DM accumulation increased exponentially over 101 d. Neither DM nor LA accumulation was influenced by NH 4 NO 3 at 50 and 80 d. At 101 d, both DM and LA were greater ( P 〈 0.01) for the 2 m M treatment than for the control, and each declined linearly ( P 〈 0.01 for ± NPM and −NLA; P 〈 0.05 for +NLA) with increasing NH 4 NO 3 levels. Differences in slopes were not significant (P 〉 0.05). Leaf area ratio (LAR) was not influenced by NH 4 NO 3 treatments at any of the sampling dates. Nitrogen per plant was greater than the control (P 〈 0.01) for both ± N at 2 m M , and it declined linearly ( P 〈 0.05 for +N; P 〈 0.01 for −N) with increasing NH 4 NO 3 levels. A reduction in per‐plant ANF was significant ( P 〈 0.01) over all NH 4 NO 3 levels at 50 and 101 d and over 6 to 12 m M levels at 80 d. Plants previously grown at 6 to 12 m M levels (−N) recovered much of their ANF ability at 101 d, while ANF for + N plants declined (P 〈 0.01) across all N levels. Expression of ANF on a per unit DM or LA basis improved interpretation of these data. Nitrogen concentration of shoots for all treatments except 12 m M −N was similar to the control at 101 d. Overall, N yields per plant were best explained by DM accumulation from 80 to 101 d. The ability to rapidly recover N 2 ‐fixing ability following depletion of inorganic soil solution N provides opportunity for early season use of N fertilizer in annual range systems.
Type of Medium:
Online Resource
ISSN:
0011-183X
,
1435-0653
DOI:
10.2135/cropsci1989.0011183X002900030044x
Language:
English
Publisher:
Wiley
Publication Date:
1989
detail.hit.zdb_id:
1480918-7
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