WATER NEEDS FOR WINTER BEAN CROP¹

 

A.E. KLAR²; M.A. FERNANDES^2
2Depto. Engenharia Rural-FCA/UNESP, C.P. 237, CEP: 18603-970 - Botucatu, SP.

 

 

SUMMARY: A study of water use by bean winter crop (Phaseolus vulgaris, L., cv. Carioca) was carried out in a Red Yellow Latosol, clay texture. A furrow irrigation system maintained soil water potentials higher than -40 KPa. Two broadcast nitrogen treatments (0 and 30 kg N/ha) were applied 25 days after planting. The major objectives were to study the nitrogen and evapotranspiration interaction and measure the crop coefficients (Kc). The maximum average evapotranspiration (ETm) was 1.71 mm/day, or 157.16 mm over 92 days of observations; the ETm values for the vegetative (1), flowering (2) and pod formation (3) phases were 1.48, 2.35, and 1.50 mm/day, respectively, for the 30 kg/ha nitrogen treatment, and 1.48, 1.88 and 1.45 mm/day for the no nitrogen treatment. The crop coefficients (Kc = ETm / ETo) were 0.62 and 0.78 for the phase 1, 0.80 and 1.10 for the phase 2, 0.45 and 0.55 for the phase 3 and 0.61 and 0.80 for the entire cycle, based on the FAO-Penman and Class A Pan reference methods (ETo), respectively. The latter one was the best approach to estimate maximum water use by winter bean crop. Nitrogen treatments did not affect evapotranspiration significantly. However, the measured evapotranspiration obtained from the water balance method was 59.78 and 27.12% higher in the flowering than in the vegetative phase, respectively, under 30 and 0 kg N/ha.
Key Words: evapotranspiration, crop coefficient, irrigation

 

NECESSIDADE DE ÁGUA PARA O FEIJOEIRO DE INVERNO

RESUMO: Um estudo sobre o uso de água do feijoeiro de inverno (Phaseolus vulgaris L. cv. Carioca) foi realizado num solo Latossol Vermelho Amarelo de textura argilosa. Um sistema de sulcos de infiltração foi usado para proceder a irrigação com o intuito de manter o solo em potenciais de água superiores a -40,0 KPa. Duas doses de aplicação de N em cobertura (0 a 30 Kg N/ha) foram colocados 25 dias após o plantio. Os principais objetivos do estudo foram: avaliar a interação entre as duas doses de N com a evapotranspiração e medir os coeficientes de cultura (Kc). A evapotranspiração média máxima (ETm) foi 1,71 mm/dia, ou 157,16 mm nos 92 dias de observações; os valores de ETm para as fases vegetativa (1), florescimento (2) e formação de vagens (3) foram 1,48; 2,35 e 1,50 mm/dia, respectivamente, para a dose de 30 Kg/ha e 1,48, 1,88 e 1,45 mm/dia para o tratamento sem aplicação de N em cobertura. Os coeficientes de cultura (Kc = ETm/ETo) foram 0,62 e 0,78 para a fase 1, 0,80 e 1,10 para a 2, 0,45 e 0,55 para a 3 e 0,61 e 0,80 para o ciclo todo, respectivamente, baseados no método de FAO-Penman e do Tanque Classe "A". Este mostrou melhores resultados para estimar o máximo uso de água pelo feijoeiro de inverno. Os tratamentos de N não afetaram a evapotranspiração significativamente. Entretanto, a evapotranspiração, medida pelo método do balanço de água, foi 59,78 e 27,12% maior no estágio do florescimento que no estádio vegetativo, respectivamente, nas doses de 30 e 0 Kg N/ha.
Descritores: evapotranspiração, coeficiente de cultura e irrigação

 

 

INTRODUCTION

There are three bean cultivation possibilities in a year in the South-East region of Brazil: 1^st - sowed from August to October; 2^nd - sowed from December to February; and 3^rd - the winter crop, sowed from May to June and harvested in August and September.

Deficit or excess of rainfall are the major problems of the yield stability of the crop. The seasonal price variation also affects the planting area from one year to another. The use of irrigation is necessary to maintain good yield and the bean quality, mainly in the North-East (arid region). In spite of the nearly 1500 mm rainfall per year in the South-East also need water for complement, because water there is also a need for water complement deficit is very common during the crop cycle, mainly in the winter.

Irrigation systems are expensive, not only in relation to equipment prices, but due to energy, water, specialized labor cost etc. Therefore, adequate water application is necessary.

The evapotranspiration depends more on atmospheric factors under high soil water potentials, but soil and plant resistances become more important when soil water potentials are not suitable for the best crop development (Lemon, apud Klar, 1988).

Stanhill (1965) improved the evapotranspiration concept of Thorthwaite (1944) and Penman (1956): "Potential evapotranspiration is the maximum water loss of an extensive area covered with an uniform, low height of an active growth vegetation, without water deficit for the plants". Doorenbos & Pruitt (1975) defined the "Reference Evapotranspiration (ETo)" which is based on the same conditions established by Stanhill, but they included grass with 8 to 15 cm height, as a standart crop. On the other hand, Doorenbos & Kassan (1979) called "Maximum Evapotranspiration (ETm)" as the evapotranspiration of any agricultural crop for the same ETo conditions.

Doorenbos & Pruitt (1975) modified Penman's equation, suggesting the use of 1.0 for aw and 0.864 for bw for wind speed (m/s) 2 m above soil surface. The calculation of water vapor saturation pressure based on the daily air temperature average is required. They called this procedure: "FAO-Penman Method" which demands a covered grass surface. According to Allen (1986), the FAO-Penman equation is adequate for several situations.

Encarnação (1980) verified that the Class A Pan evaporation supplied the best approach to estimate water demand of a bean crop in Piracicaba - SP in comparison to other evapotranspiration methods, and the Kc's were very near to the values suggested by Doorenbos & Kassan (1979).

The soil water balance (SWB) supplies the best estimation of evapotranspiration under high water atmospheric demand and low rainfall, however, if soil water storage has no positive variation, the SWB is not applicable. Another problem of this method is the deep drainage determination (Black et al., 1970).

The crop coefficient (Kc) is mainly affected by phases of development, characteristics and cycle of the crop and climatic factors (Doorenbos & Pruitt, 1975). It is convenient, however, to include soil water availability, conductivity and fertility in the model. Pavani (1985) reported that Kc had the same behavior of the leaf area index (LAI) of a bean crop, mainly sixty days after sowing. Azevedo (1984), studying beans, showed that the highest evapotranspiration values occurred on the flowering and pod formation phases. In the same crop irrigated by sprinkler fertigation, showed that the best treatment yielded 2,247 ton beans/ha, applying 368 mm of water and 45 kg N/ha before flowering and 45 kg N /ha after flowering. Other treatments received from 272 to 416 mm of water, all receiving 90 kg N/ha (urea) divided into several applications.

The main objective of this study was to evaluate the influence of nitrogen fertilization on the evapotranspiration and on crop coefficients of a winter bean crop in field conditions.

 

MATERIAL AND METHODS

Experiments were carried out during 1987 at the Faculty of Agricultural Sciences-UNESP, Botucatu-SP. The soil was a Red-Yellow Latosol, clayey texture. Some physical and chemical characteris-tics of the soil are presented in TABLES 1 and 2.

 

 

 

 

A complete randomized block design with 16 replications and two nitrogen treatments; 0 and 30 kg N/ha (ammonium sulphate) applied 25 days after sowing were used. The furrows of the irrigation system were 50 m long and spaced 0.6 m. Three rows of beans per plot spaced 0.6 cm were used. Only 30 m of the central row were used experimentally. Irrigation frequency was based on a minimum soil water potential of -40 KPa and measured using the gravimetric method, tensiometers and soil water chararacteristic curve for the 0-20 cm surface layer. Four hundred kg/ha of of 4-14-8 fertilizer formula was applied before sowing.

Reference evapotranspiration (ETo) was measured through the U.S. Weather Bureau Class A Pan (EToA = ECA x Kp; ECA = tank evaporation and Kp = tank coefficient) and the FAO-Penman methods (Doorenbos & Pruitt, 1975). In the FAO-Penman calculation, the equation indicated by Hill (apud Cuenca & Nicholson, 1982) was used for the aerodynamic term (Ea). The vapour saturation pressure at daily average air temperature (ea) was taken as the product between average daily air relative humidity and the vapor saturation deficit tension; the vapor saturation deficit was calculated from a polynomial empirical equation according to Wright (1982). The average daily temperature (^oC) and the relationship between the temperature and altitude, according to Wright (1982), were used to define the moderator (1-W) in the aerodynamic term.

The maximum evapotranspiration of the crop (ETm) was measured by the water balance method, according to Reichardt (1975). The soil water storage variations in the soil profile was obtained from soil water content versus depth (0-20 surface layer) products.

The intervals between balance calculations were mobile with superpositions of the extremes, in order to optimize procedures. Sometimes, it was difficult to calculate evapotranspiration with some precision due to rainfall. Therefore, for some intervals, a relationship between evapotranspiration and Kcp values for the crop phase and climatic conditions was used (Doorenbos & Pruitt, 1975). This approach was adequate, because the relationship ETm/ETo followed a general tendency without significative deviations. The Kc values followed the equations:

Kcp = ETm/ETPo

Kca = ETm/EToA

The Kc values were daily determined and are presented according to the development phases of the crop (VP - Vegetative Phase; FLP - Flowering Phase; and PF - Pod Formation Phase). The maximum evapotranspiration obtained from the water balance method in each treatment was added in twelve intervals. The intervals 1,4 and 5 were obtained from the product of FAO-Penman method and the Kc indicated by FAO (Doorenbos & Pruitt, 1975).

 

RESULTS AND DISCUSSION

The average of the maximum evapotranspiration per treatment (ETm) in each interval and phase are presented in TABLE 3. For the same intervals, the evapotranspiration values were estimated by the FAO-Penman (ETPo) and by the Class A Pan (EToA) and are also presented in TABLE 3. The evapotranspiration values during the crop cycle, vegetative, flowering and pod formation phases were not statistically different in both nitrogen treatments. Hatfield et al. (1988) reported an increase of biomass and grain yield of wheat plants following an increase of nitrogen doses, but without affecting evapotranspiration values.

 

 

The measured (ETm) and estimated (ETPo and EToA) evapotranspirations always were lower than those found in other studies for the same crop (Garrido & Teixeira, 1978; Silveira & Stone, 1979; Garrido et al., 1979 and Costa, 1986), certainly due to a low atmospheric water demand (AWD) during the crop cycle. The results obtained from the Class A Pan method were intermediate of the FAO-Penman method and ETm, with the latter showing the lowest values.

The daily evapotranspirations in the flowering period, obtained from the Class A Pan and FAO-Penman methods, were, respectively, 14.20 and 19.32 % higher than in the vegetative, and 16.19 and 32.20% smaller than in the pod formation period (TABLE4). The measured evapotranspirations, obtained from the water balance method, followed the same trend and were 59.78 and 27.12 % higher in the flowering than in the vegetative phase, respectively under 30 kg N/ha and 0 kg N/ha doses. In part, that variation between the two doses can be explained by the large difference of leaf area indexes, higher in the treatment that received nitrogen after 25 days of sowing. On the other hand, the average of the evapotranspiration intensities of the phases and cycle, measured by the water balance method for both nitrogen doses, were always lower than those obtained from the reference evapotranspiration methods EToA was slightly lower than ETm in the 30 kg N/ha treatment in the flowering phase, but not statistically different.

 

 

The results of evapotranspiration intensity measured by the water balance method had the largest values at the flowering phase, following the leaf area index behavior (TABLE 4), and are very similar to those reported by Silveira & Stone (1979).

The maximum evapotranspiration (30 kg N/ha treatment) for the entire cycle were 32.95 and 62.78% smaller than those obtained for the Class A Pan and FAO-Penman methods, respectively, showing mainly the influence of plant resistance mechanisms to decrease transpiration for satisfying atmospheric water demand.

TABLE 5 presents the relationships between the maximum and the reference evapotranspirations for each hydric interval and each phase and cycle. In general, the Kcp and Kca values were statistically significant related to those indicated by Doorenbos & Kassan (1979). However, at the pod formation phase, there were larger differences between ETm and ETo, being Kcp significantly smaller than those obtained by Doorenbos & Kassan (1979).

 

 

Encarnação (1980), studying the same crop in Piracicaba - SP, found Kcs (obtained from the Class A pan method) between 0.70 for vegetative phase and 1.40 for the association of flowering and pod formation phase. The significant decrease of maximum evapotranspiration (ETm), caused by the low atmospheric water demand during the entire cycle is a good explanation for the differences among the data of Encarnação (1978) and these ones. Luchiari (1978) measured the evapotranspiration of beans through the water balance method for beans in Piracicaba - SP and found 3.06 mm/day and Kca = 0.88 as an average for the entire cycle. On the other hand, Wright (1982) showed Kc values from 0.30 to 0.90 for several soil moisture contents in arid conditions, after effective soil covering by plants. Obviously, climate, plant and soil are important factors to control maximum evapotranspiration of crops with emphasis to the atmospheric water demand, mainly under optimum soil water potentials. In this experiment, there were no soil and plant restrictions in relation to water use for the development of the crop and these results can be used for bean crops under similar soil and climatic conditions.

 

CONCLUSIONS

The average maximum evapotranspiration of winter bean crop cycle in Botucatu - SP is about 1.71 mm/day and Kc average is 0.61 for Kcp and 0.78 for Kca. The maximum evapotranspiration average for vegetative, flowering and pod formation were 1.48, 2.35 and 1.50 mm/day , respectively. The Kcp was 0.62, 0.80 and 0.45 and Kca was 0.78, 1.10 and 0.55, respectively, for vegetative, flowering and pod formation phases.

The measured evapotranspiration obtained from the water balance method was 59.78 and 27.12% higher in the flowering than in the vegetative phase, respectively, under 30 and 0 kg N /ha treatments.

 

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Recebido para publicação em 08.02.96
Aceito para publicação em 25.04.97

 

 

¹Apresentado no XXI Congresso Brasileiro de Engenharia Agrícola, Santa Maria, R.S, 1992.