Print version ISSN 0103-9016
Sci. agric. vol. 53 n. 2-3 Piracicaba May/Dec. 1996
WHEAT CULTIVARS: RESPONSE TO IRRIGATION AND SOWING DATES1
A.E. KLAR2,4; T. HOSSOKAWA3
2Depto. de Engenharia Rural-FCA/UNESP, C.P. 237, CEP: 18603-970 - Botucatu, SP.
3Estudante de Graduação da FCA/UNESP.
4Bolsista do CNPq.
ABSTRACT: This study was carried out in an Alfisol-Oxisol transition sandy-clay texture, using six wheat cultivars (Triticum aestivum, L.): two tall and tolerant to soil aluminium toxicity (BH-1146, and IAC-18), and four semi-dwarf cultivars - Anahuac, IAC-162, IAC-24, and IAC-60 - of which only the first two are sensitive to soil aluminium toxicity. Two minimum soil water potentials (Ys) levels were used: 1. watered, when Ys reached about -0.05 MPa; 2. dry, when the water potential reached around -1.5 MPa. Two sowing dates, 05/22/92 and 06/11/92, were used. The results showed that Anahuac and IAC-60 are the most indicated cultivars for the studied region; when irrigated all cultivars presented similar yield level under no irrigation conditions; the irrigation was not sufficient to avoid yield differences between the two growing seasons; differences in rainfall were important for the crop in the dry treatment for both seasons.
Key words: irrigation, growing season, and semi-dwarf and dwarf wheat plants
CULTIVARES DE TRIGO: RESPOSTAS À IRRIGAÇÃO E DIFERENTES ÉPOCAS DE PLANTIO1
RESUMO: Este trabalho foi desenvolvido em um solo Alfisol intergrade para Oxisol, textura areno-argilosa, utilizando-se seis cultivares de trigo (Triticum aestivum, L.): dois de porte alto e tolerantes ao alumínio tóxico do solo (BH-1146 e IAC-18) e quatro de porte semi-anão (Anahuac, IAC-162, IAC-24 e IAC-60, sendo apenas os dois primeiros sensíveis ao alumínio tóxico do solo). Dois potenciais de umidade do solo (Ys) mínimos definiam dois tratamentos de umidade do solo: 1. Úmido, as plantas eram irrigadas quando Ys atingia as imediações de -0,05 MPa; e 2. Seco, quando as plantas receberiam irrigação com Ys em torno de -1,5 MPa. Duas épocas de plantio foram usadas: 22/05/96 e 11/06/96. Os resultados permitiram as seguintes conclusões principais: os cultivares Anahuac e IAC-60 são os mais indicados para a regão estudada; todos os cultivares apresentaram produtividade semelhante quando não se procedeu à aplicação artificial de água; a irrigação não foi suficiente para para evitar diferenças de rendimento entre as duas épocas de plantio deste ensaio; as diferenças que ocorreram nas precipitações pluviométricas entre as duas épocas afetaram a produtividade das plantas no tratamento que não recebeu irrigação.
Descritores: irrigação, épocas de plantio, plantas de trigo de porte alto e de porte anão
According to the WORLD OUTLOOK (1992), world wheat production for 1992/93 was expected to be 539.4 x 109 kg, down 3.6 x 109 kg from 1991/92. In order to compensate the increase production in the USA, Australia, China, India, and the former Soviet Union, smaller crops from Canada, Argentina, the European Community, and Eastern Europe are primarily responsible for the slight decrease in world production. The decrease wheat trade (8 x 109 kg) can be attributed to import reductions in the former Soviet Union and China. Wheat was grown on 220.6 million ha in the world, essentially the same area from 1978/79 to 1992/93, but the average yield grew from 1,920 to 2,450 kg/ha, a 27,6% increase, due to more efficient genotypes and better crop management where good irrigation practices were salient factors.
In Brazil, the southern region provides a sufficiently cold and humid autumn and winter for spring wheat. In the State of São Paulo and surrounding regions, the yield exceed 2,000 kg/ha, a greater value than the southern states of the country and some other traditional wheat export countries. Wheat is one of the few options for Brazilian growers immediately after summer. It is sowed from March to May, and can probably suffer frost and drought in this period of the year (Prognóstico Agrícola, 1988).
Espinoza et al. (1980) showed that soil water potentials lower than -0.08 MPa promoted 82% decrease in the water use efficiency, and the greatest grain yields were obtained with soil water content near field capacity, reaching 4,100 kg/ha, under "cerrado" conditions. Klar et al. (1992) observed that nine genotypes had significant differences in the grain yield under similar soil water potentials. On the other hand, Fisher & Maurer (1978) related that the reproductive phase was the most critical when subjected to water deficits.
Through physiological measurements, Klar (1988) showed that the cultivar IAC-5 presented good drought adaptation. The water relative contents and the water potentials of plant leaves were higher in the reproductive than in the vegetative phase at the same soil water potential.
Several authors showed sowing date as an important factor affecting grain yield (Moreira & Ignaczak, 1988). In Capão Bonito, São Paulo, Felício et al. (1988) reported that 18 wheat cultivars had the best behavior when planted in the last ten days of March in 1985. That period and the first ten days of April were shown as the best planting periods for South-West of São Paulo (Camargo et al. 1985). However, these authors recommend that periods with 1-2oC air temperature or less for this crop showed be avoided.
Camargo (1984), Camargo et al. (1988) and Freitas et al. (1985) reported that the most resistant plants to aluminium toxicity showed more visual symptoms of drought resistance than the sensitive ones. Studies focusing water effects on the yield and other characteristics of plants in conjunction with the different genotypes and sowing dates are needed in order to enlarge the knowledge of wheat subjected to drought, mainly under the specific condition found in São Paulo.
The aim of this study was to evaluate the influence of irrigation and different sowing dates on grain yield, and other characteristics of six wheat cultivars.
MATERIAL AND METHODS
The experiment was set up at the Agricultural Engineering Department of FCA-UNESP - Botucatu, SP (800 m altitude). The soil used was an Alfisol intergrade to Oxisol, sandy-clay texture with 49% clay, 1.28 g/cm3 bulk density at the 0-30 cm layer. The soil moisture characteristic curve is showed in the Figure 1. Chemical soil analysis showed pH = 5.3 (H2O), P (resin) = 3.0 mg/cm3, and K+, Ca2+, Mg2+, Al3+, and H+ were 0.84, l.8, 0.80, l.0, and 2.2 meq/l00 cm3, respectively. The organic matter content was 1.6%. The soil was fertilized according to the recommendation of the Soil Science Department - FCA-UNESP.
Figure 1 - Soil Moisture Characteristic Curve.
Six spring wheat cultivars were used: two tall and tolerant to soil aluminium toxicity (BH-1146, and IAC-18), and four semi-dwarf, of which two are tolerant (IAC-24, and IAC-60), and two sensitive to soil aluminium toxicity (IAC-162, and Anahuac).
Seeds were sown on two dates: May 22, and June 6, 1992 in field conditions. There were two water treatments: (1) irrigated - received water when soil water potentials reached nearly -0,05 MPa in the 0-20 cm layer and (2) the dry one - water was supplied around -1.5 MPa soil water potential, in the same layer. The cultivar x irrigation x sowing date interaction was replicated three times. The total area of each plot was 16 m2, with 4 m2 of useful area. Sprinkler irrigation was used. The soil moisture characteristic curve, tensiometers placed at 20, 40, and 60 cm of depth together with the gravimetric method were used to control daily soil water content and the figure 2 presents the measured results. The figures 3 and 4 show the results of a class A pan and a pluviometer placed in the center of the experiment.
Figure 2 - Soil water potencial at 0-20 cm depth
Figure 3 - Weekly evaporation of class a pan
Figure 4 - Rainfall
The following variables were studied in each plot: grain yield in 4 m2, grain number average in 20 spikes, spike length average of 20 spikes, spikelet number average in 20 spikes, weight of 1000 seeds, weight average of 20 fresh and dry whole plants, height average of 20 plants, and hectoliter mass (HM).
RESULTS AND DISCUSSION
Irrigation caused increases on: grain yield, grain and spikelet number per spike, spike length, weight of 1000 seeds, fresh and dry plant weight at 70oC, plant height, and decreases in hectoliter mass (TABLE l).
Leaf water potential is responsible, together with other factors, for cell size expansion by mechanical action. If water stress appears, turgor potential falls and results in less cell expansion and leaf area. The increase in leaf area amplifies photosynthetic production and, consequently, dry matter and grain yield per plant. Certainly, the wheat plants had osmotic adjustment and lower threshold leaf water potentials for stomatal closure in order to maintain the physiological activities (Klar, 1988).
Faria & Olitta (1987) showed that irrigation incresed 60% in wheat grain yield, and Klar et al. (1992) showed 103% increase average, working with nine cultivars, from which Anahuac reached 210% in relation to those non-irrigated (-1.5 MPa minimum soil water potential). That work showed that the cultivars IAC-24 and IAC-18 had 138% and 52% increases with irrigation, respectively. In this study (Klar et al., 1992), Anahuac presented 137% increase, IAC-24, 80% and IAC-18, 83% with irrigation in relation to the dry treatment. The variations came from climatic factors, mainly rain and photoperiod, since other factors, such as soil, were the same.
In this paper, where two sowing dates were tested, Anahuac was the most productive with 96% increase in relation to the plants subjected to drought in the first sowing, and 221% in the second.
Besides climate, the photoperiod and the genotipic effect appear: the cultivar Anahuac (watered) produced 6.963 kg/ha in the first, and 5.505 kg/ha in the second sowing; the IAC-24, 5.174 kg/ha, and 4.938 kg/ha, and the average of all six watered cultivars yielded 5.402, and 4.983 kg/ha, respectively. On the other hand, the dry treatment had important effects from rain deficits, with about 69% decreases of grain yields, from the first to second sowing. Rains were not significantly absent in the plant critical period (reproductive phase) in the first sowing, but were insufficient in the second one (Figure 4). Fisher & Maurer (1978) verified that wheat plants had the physiological activities dramaticaly decreased when water deficits occurred in the reproductive phase. Wardlaw (1971) asserts that wheat is more affected by drought in the phase of spikelets without grains, due to polen sensitivity to water deficit. However, Tripathi (1992) showed the vegetative phase (20-25 days after sowing) as the most affected by drought.
Mcpherson & Boyer (1977) related that water stress affects photosynthetic material movement. Machado et al. (1992) showed varietal differences in the photosynthetic rates and in the reserve removal in the vegetative organs during plant growth.
Wheat can maintain high leaf water potentials under water stress, using higher root-shoot-ratio, lower threshold leaf water potentials for stomatal closure, osmotic adjustment, etc. Therefore, it is classified among the "avoidance plants", according to Levitt (1972).
The selection program affects the yield of genotypes. Cultivars selected under irrigation, without soil water stress, usually have large yield decreases when subjected to drought. A good example is the cultivar Anahuac, selected in the arid regions of Mexico. It only has high grain yield under irrigation. A cultivar developed in humid regions shows lower decreases in dry conditions, because it usually does not receive supplemental irrigation and, consequentely, has been subjected to some drought (Klar et al., 1992).
Dwarf and semi-dwarf varieties, based on the Rht genes, have showed the greatest yield in the irrigated and humid regions. It has been suggested that they have not been as successful in non-irrigated drier regions because of their greater susceptibility to water shortage (Innes & Blackwell, 1984). These same authors, under mobile plot shelters, found, on average, the semi-dwarf lines yielded more grain than the tall or dwarf lines, the dwarf ones being intermediate. Tall and semi-dwarf lines were equally susceptible to drought either when it occurred before anthesis or during grain filling. Dwarf lines were less susceptible to the drought before anthesis than either the semi-dwarf or tall lines. The experiments of these authors provide no evidence that semi-dwarf lines are more susceptible to drought than the tall ones. All these conclusions were based on the grain yields. In this experiment, Anahuac, a semi-dwarf plant, was the least productive in green matter (5.98 g) in comparison to other non-irrigated cultivars. Therefore, it was selected for sending a large part of its energy for grain production.
Tall plants, like `IAC-18', reached 115 cm height with irrigation and 96 cm when subjected to drought, and yielded less grains than the semi dwarf ones. For instance, the cultivar Anahuac was about 52% and 55% smaller than IAC-18 under irrigation and drought conditions, respectively. On the other hand, dwarf plants receive nearly 50% of carbohydrates for grain formation, while the tall ones, around 30% for the same purpose, therefore those are more efficient for grain productivity (Hanson et al., 1985).
Irrigation affected grain quality. The weight of 1,000 seeds was larger in plants under irrigation for all cultivars. There were 14.6% increase in the first sowing in relation to the second for watered plants, and 32.2% difference for non-irrigated plants. The justifications for these differences are the same used for the differences in the yield. However, the most grain-productive cultivars did not have the heaviest grains, but IAC-162 had the heaviest grains, mainly under drought.
The hectolitre mass (HM) showed the effects of irrigation: the dry treatment had 82,48 kg/100 1, and the watered one, 76,61 kg/l00 1, on average, for all cultivars. Therefore, irrigation decreased grain density. The decrease was statistically significant between the two seeding dates: 85,11 and 73,97 kg/100 1, respectively, the first and second ones. Probably, there was a higher number of completely developed grains in the plants from the first sowing date. Anahuac and IAC-24 in the dry, and Anahuac in the irrigated treatment showed the highest HW. Both are semi-dwarf and also had high yield.
Brazilian rules specify 78 kg/100 1 HM as a reference. When HM is lower than 78 kg/100 1, the prices also are lower (Brasil, 1976).
Plants have different genotypic configuration for different photosynthetic efficiencies. The plant growth differs according to the genotype and the environment conditions. For example, an increase in grain protein content means decrease in grain yield. There is always an energy cost for each plant product and it is different for each genotype and the conditions influencing growth. Irrigation increases grain productivity and decreases grain protein content. Therefore, this factor is an important instrument for wheat flour quality, mainly for the bread industry. However, fibre, water, oil, and carbohydrate content are higher in the watered than in the dry plants (Klar et al. 1992).
Felício et al. (1990) showed that the best period for sowing wheat is the last ten days of March for l8 cultivars in Capão Bonito - SP. Wheat has a wide geographical distribution throughout the world, with several studies showing the best sowing date but, in this study, the main objective was to determine if soil water potential control can avoid significant grain yield decreases under different sowing dates. Under high soil water potentials, there was a 8.4% decrease between both sowing seasons, considering the six cultivars. Spike length, weight of 1,000 seeds, plant height, and fresh vegetative weight also were slightly affected by sowing dates.
- Anahuac and IAC-60 are the most appropriate cultivars for the studied region when irrigated;
- All cultivars presented similar productivity level under no irrigation conditions;
- The irrigation was not enough to avoid yield differences between the two growing seasons;
- Differences in rainfall were important for the crop in the dry treatment for both seasons.
The authors thank S. Sabatini for the drawings, Rita C.M. Araujo for the typewriting, G. Winckler and V.J. Vasconcelos for the field work, Dr. C.E.O. Camargo for the seeds and suggestions, and Mr. H.W. Smith for the English corrections.
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Recebido para publicação em 13.11.95
Aceito para publicação em 09.09.96
1Financiado pela FAPESP (91/0660) e FUNDUNESP (035/92 - DFP/FCAV).