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Accueil du site → Doctorat → États-Unis → 1987 → EFFECTS OF MOISTURE STATUS ON ALFALFA GROWTH, QUALITY, AND GAS EXCHANGE

New Mexico State University (1987)

EFFECTS OF MOISTURE STATUS ON ALFALFA GROWTH, QUALITY, AND GAS EXCHANGE

GOMEZ BELTRAN, JOSE FRANCISCO

Titre : EFFECTS OF MOISTURE STATUS ON ALFALFA GROWTH, QUALITY, AND GAS EXCHANGE

Auteur : GOMEZ BELTRAN, JOSE FRANCISCO

Université de soutenance : New Mexico State University

Grade : Doctor of Philosophy (PhD) 1987

Résumé
Scheduling alfalfa harvest for optimum yield and quality is not well defined. Therefore, the objectives were to determine (1) if quantitative relationships exist between transpiration (T) and yield, maturity, leaf to stem mass ratio (LSR), nitrogen (N), neutral detergent fiber (NDF), in vitro dry matter disappearance (IVDMD), potassium (K), magnesium (Mg), calcium (Ca), phosphorus (P), and Ca to P ratio (2) if mean stage by weight (MSW) could be used for scheduling harvest for optimum quality and (3) if estimates of canopy resistance and net photosynthesis could be improved for plant growth models. Alfalfa (cv. ’Moapa’) was irrigated at Las Cruces, NM with a line-source sprinkler system where T was calculated. In 1983 and 1984, forage yield was measured. In 1984 and 1985, plants were separated into leaves and stems, and plant values were calculated for N, P, K, Ca, Mg, NDF, and IVDMD. In 1983, 1984, and 1985, LSR and MSW were determined. In 1985, leaf and canopy resistance and photosynthesis were measured at three moisture levels (ML 1, 2, and 3). Forage yields ; MSW ; and leaf, stem, and plant NDF increased linearly with T. Conversely, LSR ; plant N content ; and leaf, stem, and plant IVDMD decreased linearly with T. However, relationships between T and yield and quality parameters varied significantly (P $\leq$ 0.05) among cuts ; therefore, single functions could not be developed for the entire experimental period. Leaf and stem N content and K, Mg, Ca, and P did not vary with T. With advancing crop maturity the leaf, stem, and plant N and IVDMD decreased while NDF increased. The MSW appears inadequate for estimating forage quality. The stem rather than the leaf fraction had a greater influence on quality. Generally, canopy (Rc) and sunlit leaf (R$\sb\rm s$) resistances were higher while canopy (P$\sb\rm c$) and sunlit leaf (P$\sb\rm s)$ photosynthesis were lower with lower moisture levels. Shaded leaf resistance (R$\sb\rm o$) (and P$\sb\rm s$) were higher (P $\leq$ 0.05) than R$\sb\rm s$ (and shaded leaf photosynthesis) at ML 1 and 2, but not at ML 3 due primarily to a more open canopy. Estimates of R$\sb\rm c$ and P$\sb\rm c$ were greatly improved by integrating measurements of sunlit and shaded leaves as compared to using only sunlit leaves.

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