9 research outputs found
Model parameters of four important vegetable crops for improved water use and yield estimation
High-value vegetable crops are typically grown under irrigation to reduce production risk. For water resource planning it is essential to be able to accurately estimate water use of irrigated crops under a wide range of climatic conditions. Crop water use models provide a means to make water use and yield estimates, but need crop- and even cultivar-specific parameters. There is generally a lack of crop-specific model parameters for some important commercially grown vegetable crops, especially parameters determined over both summer and winter seasons. The experimental site used in this study was on the Steenkoppies Aquifer, a catchment under stress and an important vegetable production area in South Africa. Crop-specific growth parameters and water use for 4 selected high-value vegetable crops (beetroot, cabbage, carrots and broccoli) were measured over multiple seasons (two summers and one winter). These were used to parameterise the Soil Water Balance (SWB) generic crop growth model for both summer and winter seasons. In seasons where the same cultivar was planted, a single set of model parameters could be used to successfully simulate crop growth and water use. Results show that the amount of irrigation water required is dependent on season and rainfall, with broccoli having the lowest (1.8–2.7 kg m−3) and beetroot the highest (12.2–23.4 kg m−3) water productivity (WPFM), defined as fresh mass of marketable product per unit water consumed. The root crops had a greater harvest index (HIDM) than cabbage and broccoli. The parameters obtained expand the current database of SWB crop growth parameters for vegetables and can be used in a wide range of mechanistic simulation models to improve water management at field and catchment levels.Keywords: SWB model, Steenkoppies Aquifer, carrot, broccoli, beetroot, cabbag
Estimating water footprints of vegetable crops : influence of growing season, solar radiation data and functional unit
Water footprint (WF) accounting as proposed by the Water Footprint Network (WFN)
can potentially provide important information for water resource management, especially in water
scarce countries relying on irrigation to help meet their food requirements. However, calculating
accurate WFs of short-season vegetable crops such as carrots, cabbage, beetroot, broccoli and lettuce
presented some challenges. Planting dates and inter-annual weather conditions impact WF results.
Joining weather datasets of just rainfall, minimum and maximum temperature with ones that include
solar radiation and wind-speed affected crop model estimates and WF results. The functional unit
selected can also have a major impact on results. For example, WFs according to the WFN approach
do not account for crop residues used for other purposes, like composting and animal feed. Using
yields in dry matter rather than fresh mass also impacts WF metrics, making comparisons difficult.
To overcome this, using the nutritional value of crops as a functional unit can connect water use
more directly to potential benefits derived from different crops and allow more straightforward
comparisons. Grey WFs based on nitrogen only disregards water pollution caused by phosphates,
pesticides and salinization. Poor understanding of the fate of nitrogen complicates estimation of
nitrogen loads into the aquifer.The first author, Betsie le Roux, conducted this research and wrote the paper as part of
her Ph.D. studies; Michael van der Laan supervised the research.The Water Research Commission (WRC) and the National Research Foundation (NRF) of South Africa.http://www.mdpi.com/journal/wateram2017Plant Production and Soil Scienc
Water footprints of vegetable crop wastage along the supply chain in Gauteng, South Africa
Food production in water-scarce countries like South Africa will become more challenging
in the future because of the growing population and intensifying water shortages. Reducing food
wastage is one way of addressing this challenge. The wastage of carrots, cabbage, beetroot, broccoli
and lettuce, produced on the Steenkoppies Aquifer in Gauteng, South Africa, was estimated for each
step along the supply chain from the farm to the consumer. Water footprints for these vegetables were
used to determine the volume of water lost indirectly as a result of this wastage. Highest percentage
wastage occurs at the packhouse level, which is consistent with published literature. Some crops
like lettuce have higher average wastage percentages (38%) compared to other crops like broccoli
(13%) and cabbage (14%), and wastage varied between seasons. Care should therefore be taken when
applying general wastage values reported for vegetables. The classification of “waste” presented
a challenge, because “wasted” vegetables are often used for other beneficial purposes, including
livestock feed and composting. It was estimated that blue water lost on the Steenkoppies Aquifer
due to vegetable crop wastage (4 Mm3 year-1) represented 25% of the estimated blue water volume
that exceeded sustainable limits (17 Mm3 year-1).The Water Research
Commission (WRC project No. K5/2273//4). The first author,
Betsie le Roux, received financial support for research from the WRC and a bursary from the National Research
Foundation (NRF) of South Africa (NRF Grant number: 88572).http://www.mdpi.com/journal/wateram2019Plant Production and Soil Scienc
Crop coefficient approaches based on fixed estimates of leaf resistance are not appropriate for estimating water use of citrus
The estimation of crop water use is critical for accurate irrigation scheduling and
water licenses. However, the direct measurement of crop water use is too expensive
and time consuming to be performed under all possible conditions, which
necessitates the use of water use models. The FAO-56 procedure is a simple,
convenient and reproducible method, but as canopy cover and height vary greatly
among different orchards, crop coefficients may not be readily transferrable from one
orchard to another. Allen and Pereira (2009) therefore incorporated a procedure into
the FAO-56 approach which estimates crop coefficients based on a physical
description of the vegetation and an adjustment for relative crop stomatal control
over transpiration. Transpiration crop coefficients derived using this procedure and
fixed values for citrus, did not provide good estimates of water use in three citrus
orchards. However, when mean monthly leaf resistance was taken into account, good agreement was found with measured values. A relationship between monthly
reference evapotranspiration and mean leaf resistance provided a means of
estimating mean leaf resistance which estimated transpiration crop coefficients with
a reasonable degree of accuracy. The use of a dynamic estimate of mean leaf
resistance therefore provided reasonable estimates of transpiration in citrus.South Africa‟s Water Research Commission (Project K5/1770, Water use of fruit tree orchards), with cofounding from the South African National Department of Agriculture, Forestry and Fisheries.http://link.springer.com/journal/2712016-12-30hb201
Modelling water use of subtropical fruit crops : the challenges
Subtropical fruit crops form an important part of the fruit industry in many countries. Many of these crops are grown in semi-arid regions or subtropical regions where rainfall is seasonal and as a result the vast majority of these perennial, evergreen orchards are under irrigation. This represents a significant irrigation requirement and with more emphasis being placed on the conservation of water and orchard profitability, it is becoming increasingly important to accurately estimate water use of these crops and schedule irrigation accordingly. The FAO-56 procedure is a simple, convenient and reproducible method for estimating water use. However, the transferability of crop coefficients between different orchards and growing regions is not always readily achieved, due largely to differences in canopy size and management practices. In addition, as subtropical crops tend to exhibit a higher degree of stomatal control over transpiration than most other agricultural crops, some measure of canopy or leaf resistance must be taken into account when using models based on atmospheric demand. The challenge is therefore to provide reliable and dynamic estimates of canopy resistance from relatively simple parameters which can be of use to irrigation consultants and farmers for determining the water requirements of these crops. The challenge remains to ensure that these dynamic estimates are realistic and readily applicable to a number of growing regions. The derivation of transpiration crop coefficients, based on canopy cover and height and a dynamic estimate of leaf resistance, provided reasonable estimates of transpiration in three orchards in contrasting climates, suggesting that this approach could prove useful in future for subtropical crops.http://www.actahort.org2018-05-10hj2017Plant Production and Soil Scienc
Modelling water use of subtropical fruit crops: the challenges
Subtropical fruit crops form an important part of the fruit industry in many countries. Many of these crops are grown in semi-arid regions or subtropical regions where rainfall is seasonal and as a result the vast majority of these perennial, evergreen orchards are under irrigation. This represents a significant irrigation requirement and with more emphasis being placed on the conservation of water and orchard profitability, it is becoming increasingly important to accurately estimate water use of these crops and schedule irrigation accordingly. The FAO-56 procedure is a simple, convenient and reproducible method for estimating water use. However, the transferability of crop coefficients between different orchards and growing regions is not always readily achieved, due largely to differences in canopy size and management practices. In addition, as subtropical crops tend to exhibit a higher degree of stomatal control over transpiration than most other agricultural crops, some measure of canopy or leaf resistance must be taken into account when using models based on atmospheric demand. The challenge is therefore to provide reliable and dynamic estimates of canopy resistance from relatively simple parameters which can be of use to irrigation consultants and farmers for determining the water requirements of these crops. The challenge remains to ensure that these dynamic estimates are realistic and readily applicable to a number of growing regions. The derivation of transpiration crop coefficients, based on canopy cover and height and a dynamic estimate of leaf resistance, provided reasonable estimates of transpiration in three orchards in contrasting climates, suggesting that this approach could prove useful in future for subtropical crops
Crop coefficient approaches based on fixed estimates of leaf resistance are not appropriate for estimating water use of citrus
The estimation of crop water use is critical for accurate irrigation scheduling and water licenses. However, the direct measurement of crop water use is too expensive and time-consuming to be performed under all possible conditions, which necessitates the use of water use models. The FAO-56 procedure is a simple, convenient and reproducible method, but as canopy cover and height vary greatly among different orchards, crop coefficients may not be readily transferrable from one orchard to another. Allen and Pereira (Irrig Sci 28:17–34, 2009) therefore incorporated a procedure into the FAO-56 approach which estimates crop coefficients based on a physical description of the vegetation and an adjustment for relative crop stomatal control over transpiration. Transpiration crop coefficients derived using this procedure and fixed values for citrus did not provide good estimates of water use in three citrus orchards. However, when mean monthly leaf resistance was taken into account, good agreement was found with measured values. A relationship between monthly reference evapotranspiration and mean leaf resistance provided a means of estimating mean leaf resistance which estimated transpiration crop coefficients with a reasonable degree of accuracy. The use of a dynamic estimate of mean leaf resistance therefore provided reasonable estimates of transpiration in citrus
Model parameters of four important vegetable crops for improved water use and yield estimation
High-value vegetable crops are typically grown under irrigation to reduce production risk. For water resource planning it is
essential to be able to accurately estimate water use of irrigated crops under a wide range of climatic conditions. Crop water
use models provide a means to make water use and yield estimates, but need crop- and even cultivar-specific parameters.
There is generally a lack of crop-specific model parameters for some important commercially grown vegetable crops,
especially parameters determined over both summer and winter seasons. The experimental site used in this study was on the
Steenkoppies Aquifer, a catchment under stress and an important vegetable production area in South Africa. Crop-specific
growth parameters and water use for 4 selected high-value vegetable crops (beetroot, cabbage, carrots and broccoli) were
measured over multiple seasons (two summers and one winter). These were used to parameterise the Soil Water Balance
(SWB) generic crop growth model for both summer and winter seasons. In seasons where the same cultivar was planted,
a single set of model parameters could be used to successfully simulate crop growth and water use. Results show that the
amount of irrigation water required is dependent on season and rainfall, with broccoli having the lowest (1.8–2.7 kg m−3) and
beetroot the highest (12.2–23.4 kg m−3) water productivity (WPFM), defined as fresh mass of marketable product per unit water
consumed. The root crops had a greater harvest index (HIDM) than cabbage and broccoli. The parameters obtained expand the
current database of SWB crop growth parameters for vegetables and can be used in a wide range of mechanistic simulation
models to improve water management at field and catchment levels.This research formed
part of a solicited project, WRC K5/1482/4 (standards and
guidelines for improved efficiency of irrigation water use from
dam wall release to root zone application).The South African Water Research Commissionhttp://www.wrc.org.zaam2019Plant Production and Soil Scienc
The water use of selected fruit tree orchards (volume 2) : technical report on measurement and modelling
Final report to the water research commission and department of agriculture, forestry and fisheries.
The water use of selected fruit tree orchards (Volume 2) : technical report on measurements and modelling