Crop water parameters of irrigated wine and table grapes to support water productivity analysis in the São Francisco river basin, Brazil

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Abstract

Energy and water balance parameters were measured in two commercial vineyards in the semiarid region of the São Francisco river basin, Brazil. Actual evapotranspiration (ET) was acquired with the Bowen ratio surface energy balance method. The ratio of the latent heat flux to the available energy, or evaporative fraction (EF), was 81% on average for two growing cycles in wine grape and 88% for two growing seasons in table grape. Energy partitioning in this last vineyard was higher due to microsprinkler irrigation conditions and greater soil cover promoted by the overhead horizontal trellis systems. The accumulated ET from pruning to harvest in wine grape was 438 and 517 mm for the first and second growing cycles, respectively. Table grape consumed less water than wine grape (393 and 352 mm for the first and second growing seasons, respectively) due to shorter crop stages. Beneficial transpiration (T) was 89 and 81% of total ET for wine and table grape, respectively. Brazilian semiarid climate allows 2.5 production cycles per year for vineyards. The yield was in average of 6183 kg ha−1 for two cycles of wine grape and 11,200 kg ha−1 for one short growing season of table grape, corresponding to a bio-physical water productivity per unit ET of 1.06 kg m−3 (or 1.02 L wine m−3) and 3.18 kg m−3, respectively. Table grape showed a significantly higher economic water productivity (US$ 6.51 m−3) than wine grape (US$ 0.93 m−3). These values are much favorable than for staple crops.

Introduction

Irrigated crops in the semiarid region of São Francisco river basin in Brazil consist mainly of fruit crops, such as grapes, mangos, bananas and guavas. The average rainfall in this region is 570 mm year−1, and the rainy period is concentrated from January to April. The reference evapotranspiration (ETo) is around 1600 mm year−1. The monthly average air temperature varies between 24 and 30 °C only. Under such high evaporative atmospheric demand and low and irregular rainfall, irrigation becomes necessary for commercial agriculture.

The vineyards growing under these permanently warm conditions exhibit an agronomic behaviour being different from the temperate climates. While in these last climates, a typical winter season induces dormancy in grapes, the continuous physiological processes in the semiarid region of Brazil are accelerated and the propagation is very fast allowing the first production after 1.5 years.

With proper irrigation and cultural management practices, the farmers in São Francisco valley can produce grapes and wine in any time of the year, allowing on average 2.5 production cycles per year and the harvests in periods with higher prices, although for seedless table grapes, the rainy period is avoided due to the direct damage to the fruits and the high occurrence of diseases.

Crop water productivity (CPW) – or its equivalent water use efficiency for irrigated crops – represents the fresh fruit or wine production per unit of water applied or consumed. It is preferred to analyse CPW in terms of consumptive use because it includes also non-irrigation sources of water, such as rainfall, seepage and soil moisture changes.

The amount of applied water is partitioned into evapotranspiration and deep percolation. Actual evapotranspiration (ET) represents the water that is vapourized and not longer available to downstream users of a river basin. Percolated water can be recycled, and should therefore not be ascribed to the production of a certain irrigated crop.

The term “water productivity” reflects the link between production of an intended good and its resource input (Molden and Satkhivadivel, 1999, Kijne et al., 2003, Bos et al., 2005, Molden et al., 2007), having a more general basis than the term “water use efficiency”, and makes it suitable to compare the economic performance with other water use sectors.

It is deemed necessary to study the energy and water balances of vineyards for understanding and predicting CPW (Bastiaanssen et al., in press). As wine and table grapes are cultivated in different trellis and irrigation systems in the São Francisco river basin, it is important to quantify various grape water parameters under these differences, being ET the most important of them.

ET from vineyards can be obtained accurately using weighing lysimeters (Evans et al., 1993, Williams et al., 2003, Williams and Ayars, 2005b), eddy correlation techniques (Oliver and Sene, 1992, Sene, 1994, Trambouze et al., 1998, Ortega-Farias et al., 2007) and the Bowen ratio energy balance method (Heilman et al., 1994, Heilman et al., 1996, Rana et al., 2004, Yunusa et al., 2004).

These studies reveal a significant variation in water consumption due to different irrigation strategies and cultural practices. While certain farmers prefer the production of high quantities of berries, others like a high quality product introducing significant water stress levels by partial root zone drying and deficit irrigation.

The extrapolation of field measurements to irrigation schemes, regions and river basins are, therefore, cumbersome (Williams and Ayars, 2005b). With simultaneous measurements of ET and ETo, it is possible to determine the crop coefficient (kc) that normalizes ET for climatic influences. This coefficient reflects the canopy development and vineyard water status as the crop stages progress (Snyder et al., 1989).

As Brazil is a developing country on fast track with a growing export of fresh fruits and wines, on-farm water management in vineyards is the cornerstone for a productive use of scarce water resources at the basin scale. The objective of this study was the determination of water parameters related to ET such as crop coefficients, evaporative fraction, soil evaporation and canopy transpiration, bulk surface and canopy resistances and crop water productivity for wine and table grapes growing under different trellis and irrigation systems. Upscaling of these data sets is a good bio-physical basis for appraising the options for increasing total CPW at the regional scale.

Section snippets

Wine grapes with drip irrigation and vertical trellis

The wine grape investigated stands at Vitivinícola Santa Maria farm near the town of Lagoa Grande in Pernambuco state (latitude 09°02′S; longitude 40°11′W). The cultivar is Petite Syrah, and the vineyard was 11 years old during the field investigation in 2002.

The plants are spaced at 1.20 m × 3.50 m, trained vertically to a bilateral cordon and spur pruned. The cordon wire was at a height of 1.6 m with no foliage wires (a sprawl type canopy developed). There was no cover crop between the rows, and

Methodology

The energy balance equation of a vineyard can be expressed by means of bulk energy and heat fluxes:RnλEvGHv=0where Rn is the net radiation, λEv the latent heat flux from the vineyard, Hv the sensible heat flux from the vineyard and G is the soil heat flux. λEv was obtained by a partitioning parameter:λEv=RnG1+βwhere β is the Bowen ratio:β=γΔTΔeand γ (kPa °C−1) is the psychrometric constant, ΔT (°C) the temperature gradient measured by the dry thermocouples and Δe (kPa) is the vapour pressure

Soil moisture and weather conditions

The values of soil moisture (SM) are shown in Fig. 1. SM at 20 cm depth showed more variations with time, than at deeper soil layers in both vineyards. This is an expected result because of the dynamics of infiltration and subsequent depletion by root water uptake and soil evaporation.

The maximum values of SM in the wine grape were found at 60 cm depth pinpointing that moisture assembles in the lower root zone and is not easily drained away. This could be related to the increasing retention

Conclusions

Albedo, evaporative fractions, beneficial/non-beneficial water consumption, aerodynamic resistance, bulk surface resistance and canopy resistance were derived from the field data set and compared with the international literature. The results allowed expressing water consumption from vineyards in more specific bio-physical parameters, rather than in crop coefficients that lump together other crop water parameters.

The seasonal evapotranspiration of table grape was less (352–393 mm) than for wine

Acknowledgements

The research herein was supported by CAPES (Ministry of Education, Brazil), and Embrapa (Brazilian Agricultural Research Corporation). CAPES is funding a Ph.D. grant for the first author. EMBRAPA is acknowledged for the resources to design and execute the field measurements.

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