Growth of spring barley under drought: crop development, photosynthesis, dry-matter accumulation and nutrient content

Abstract

The effects of water deficit on growth of spring barley were analysed under five irrigation treatments. One crop was irrigated at weekly intervals from emergence throughout the growing season, and one was not irrigated at all after emergence. Soil water deficits in the other treatments were allowed to develop early, intermediate or late in the crop's development.Weekly irrigation produced a crop with a large leaf area index (maximum value 4) and maintained green leaf and awns throughout the grain-filling period. Early drought decreased leaf area index (maximum value 2) by slowing expansion of main-stem leaves and decreasing the number and growth of tiller leaves. Leaf senescence was also increased with drought. Drought late in the development of ears and leaves and during the grain-filling period caused leaves and awns to senesce so that the total photosynthetic areas decreased faster than with irrigation. Photosynthetic rate per unit leaf area was little affected by drought so total dry-matter production was most affected by differences in leaf area.Early drought gave fewer tillers (550/m 2 ) and fewer grains per ear (18) than did irrigation (760 tillers/m 2 and 21 grains per ear). Late irrigation after drought increased the number of grains per ear slightly but not the number of ears/m 2 . Thus at the start of the grain-filling period crops which had suffered drought early had fewer grains than irrigated (9-5 and 18-8 x 10 3 /m 2 respectively) or crops which suffered drought later in development (14 x 10 3 /m a ).During the first 2 weeks of filling, grains grew at almost the same rate in all treatments. Current assimilate supply was probably insufficient to provide this growth in crops which had suffered drought, and stem reserves were mobilized, as shown by the decrease in stem mass during the period. Grains filled for 8 days longer with irrigation and were heavier (36-38 mg) than without irrigation (29-30 mg). Drought throughout the grainfilling period after irrigation earlier in the season resulted in the smallest grains (29 mg).Grain yield depended on the number of ears, the number of grains per ear and mass per grain. Early drought decreased tillering and tiller ear production and the number of grains that filled in each ear. Late drought affected grain size via the effects on photosynthetic surface area.Drought decreased the concentrations of phosphorus, potassium and magnesium in the dry matter of crops, and irrigation after drought increased them. Concentration of nitrogen was little affected by treatment. Possible mechanisms by which water deficits and nutrient supply affect crop growth and yield are discussed.

Nitrogen and dry matter partitioning of barley grown in a dryland environment

“…However, N dynamics are also strongly influenced by the environment. In the instance of DM, reduced contributions of preanthesis assimilate to grain in dry years or during water stress have often been reported (Aspinall 1965;Gallagher et al 1975;Bidinger et al 1977;Austin et al 1980;Lawlor et al 1981).…”

Efeitos de potenciais de água no solo, em diferentes estádios fenológicos da cultura da cevada (Hordeum vulgare L.)

“…Vários trabalhos citados na literatura, concordam com os resultados obtidos no presente estudo, afirmando existir aumento do número de espigas chochas, com a diminuição do potencial de água no solo, sobretudo no período compreendido entre a emergência e a antese, sendo um dos principais responsáveis pelo decréscimo da produtividade em plantas de cevada (LAWLOR et al, 1981).…”

“…Por outro lado, vários trabalhos na literatura têm revelado que os efeitos de défices hídricos, sobre a produtividade das espécies vegetais, variam com o estádio, em que o mesmo se manifesta, existindo períodos críticos, onde as plantas são mais sensíveis à diminuição da disponibilidade de água no solo (ROBINS & DOMINGO, 1953;DENMEAD & SHAW, 1960;ASPINAL et al, 1964;SALTER & GOODE, 1967;KRAMER, 1969;SCALOPPI, 1973;LAWLOR et al, 1981;URCHEI, 1992).…”

“…LAWLOR et al (1981), verificaram que o período compreendido entre a emergência e a antese na cultura da cevada, foi particularmente sensível à défice hídrico, diminuindo significativamente o índice de área foliar, além de antecipar a senescência das folhas. URCHEI (1992), verificou que os efeitos de défices hídricos, sobre a produção de grãos de cevada, variaram com a intensidade, duração e estádio fenológico da cultura, onde o estádio de florescimento caracterizou-se como o mais sensível à défices de água.…”

Déficit Hídrico E Os Processos Morfológico E Fisiológico Das Plantas

“…Lawlor et al (1981), estudando os efeitos do déficit hídrico na cultura da cevada, verificaram que no período compreendido entre a emergência e a antese, o índice de área foliar, diminuiu significativamente em função da menor expansão e do número de folhas, além de antecipar a senescência. Para Belaygue et al (1996) em muitas espécies, como o milho ou girassol, o número de folhas já é determinado geneticamente; entretanto, NeSmith & Ritchie (1992) relatam que ocorrência de déficit hídrico antes do florescimento das plantas reduz o número de folhas do milho.…”