Module No. 4

WATER NEEDS ON A FARM: A Tool for Efficiency in Production

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Module 4: Water Needs on a Farm

Introduction

The Problem

Agriculture is the primary consumer of water and is likely to encounter the most severe threats due to water scarcity.

Any shortage of this critical natural resource puts farmers’ livelihood in jeopardy.

At the same time, demographic shifts, economic development and lifestyle changes are expected to intensify the competition between agriculture and other uses of water, including municipal and industrial uses.

Long-term imbalances in supply and demand for irrigation water are expected to intensify as limited and unequally distributed rainfall follows a declining trend, whereas mean temperature increases.

The Solution

Knowing water requirements for crops and animals is advisable for farmers to better prepare for farm planning, droughts, and upgrading water infrastructure.

Estimating crop water needs are pre-requisites for implementing adaptation strategies and agricultural water management in general.

Contents

1.1. Transpiration, Evaporation and Evapotranspiration of Crops

1.2. Water Needs of Crops

1.3. Water Needs of Irrigation

1. How much water does my farm need?

Crops need water for transpiration and evaporation

  • Transpiration is the water loss of plants, mainly from the leaves.
  • Evaporation is the amount of water vaporised into the atmosphere from sources such as soil surface.
  • Evapotranspiration (ET) is the total water loss of evaporation and plant transpiration (fig.1).
  • The crop water needs coincide with the ET, and they are usually expressed in mm/day, mm/month, mm/year, or mm/season.
Fig. 1: Crop Water Need (Evapotranspiration)
Fig. 2 Major Climatic Factors Influencing Crop Water Needs

Mainly three (3) factors influence crop water needs:

  1. Climate
  2. Crop Type
  3. Growth Stage Of The Crop

Climate

The principal climatic factors which influence the crop water needs are solar radiation, temperature, humidity, and windspeed (fig. 2). Their effects on the crop’s water needs are shown in this table:

Climatic Factor Crop water need
High Low
Solar radiation Sun No Sun
Temperature Hot Cool
Humidity Low (Dry) High (Humid)
Windspeed Windy Little Wind

Water needs for a specific crop in a specific location vary significantly depending on spatial and temporal variations in evapotranspiration and net water requirements.

From the previous, it is clear that evapotranspiration of a specific crop (and thus its water needs) is sensitive to climatic change in different regions due to variations in radiation, temperature, windspeed and humidity. For example, a specific citrus tree variety grown in a cool climate will need less water per day than the same citrus tree variety grown in a hotter climate.

For more efficient water management, it is helpful to take a particular standard crop or reference crop and determine how much water this crop needs per day in the various climatic regions.

Crop Type

Crop type has an influence on the crop water needs concerning:

  • Daily Water Needs Of A Fully Grown Crop. For example, the peak daily water needs for a fully developed watermelon will need more water per day than a fully developed crop of onions.
  • Duration Of The Total Growing Season Of The Crop. For instance, peas have higher daily water needs than melons. However, the seasonal water needs of peas are lower than melons because peas have a shorter duration of the total growing season (90-100 days, compared to melons, which have a duration of the total growing season of 120-160 days).

Growth stage of the crop

A fully grown crop will need more water than a plant crop that has just been planted (fig. 3).

Crop water needed at planting and during the initial stage is estimated at 50 per cent of the crop water needed during the mid-season stage when the crop is fully developed. Regarding the late-season stage, which is the period during which the crop matures and is harvested, the water needs are diversified accordingly to:

  • Freshly harvested crops (e.g., lettuce, cabbage, etc.) where the crop water need remains the same during the late-season stage as during the mid-season stage.
  • Dry harvested crops (such as cotton or maize), where their water needs during the late-season stage are minimal, and therefore no irrigation is needed for these crops during the late-season stage.
Fig. 3 Growth Stages of A Plant Crop
Fig. 4: A Crop Water Need Of 15 Mm/Day

EXAMPLE: Crop water requirements of a general crop in a very hot and dry climate

Assume the water need of a particular crop in a very hot, dry climate is 15 mm/day. This means that the crop needs a water layer of 15 mm over the whole area on which the crop is grown (fig. 4). It does not mean that this 15 mm has to be indeed supplied by rain or irrigation every day.

For example, the crop could be provided with irrigated water, with 60 mm every four days. The irrigation water will then be stored in the root zone and gradually be used by the crop: 15mm for every day, given that irrigation water will not be lost due to leaching, runoff or evaporation.

Water Needs of Irrigation

Without water, crops cannot grow. The most well-known source of water for plant growth is rainwater. But, what to do if there is too little rainwater?

If there is too little rain, then irrigation is needed to supplement the extra water needs

The two Factors which Determine The Amount Of Irrigation Water which is needed are:

  • the total water needs of the various crops
  • the amount of rain water which is available to the crops
Effective Rainfall – Things to Consider
  • Part of the rainfall is not effective. Part of it percolates below the root zone of the plants, and another part flows away over the soil surface as run-off. The plants cannot use deep percolation water and run-off water. A relatively large part of the water is lost through deep percolation and run-off (fig.5).
  • The remaining part, the so-called effective rainfall, is stored in the root zone and can be used by the plants.
  • Variation of the rainfall over the years. Especially in low rainfall climates, the little rain that falls is unreliable; one year may be relatively dry, and another year may be relatively wet.
  • Before planting a crop, it is, therefore, useful to consider factors like topography, prevailing soil type, the soil texture, the soil structure and the depth of the root zone, but especially the microclimate of the region and the region’s rainfall reliability.
Fig. 5 Non Effective Precipitation
  • For each crop, the water need is determined monthly and can be found from different sources, like local authorities or literature.
  • The effective precipitation is estimated every month using measured rainfall data (or local information, if available).

The Agricultural Research Institute (ARI) has developed an essential tool for Cypriot farmers who want to know monthly water needs for their cultivations in different locations of Cyprus Farming Land. Further details can be found in the link below:

http://news.ari.gov.cy/apps/irrigation.html

2. Adaptation Strategies to Water Needs

Drip Irrigation

  • Drip irrigation systems deliver water directly to a plant’s roots, reducing the evaporation with sprinkler watering systems.
  • Timers can be used to schedule watering for the cooler parts of the day, further reducing water loss.
  • Adequately installed drip irrigation can save up to 80 per cent more water than surface irrigation and even contribute to increased crop yields.

Irrigation Scheduling

  • Innovative water management is not just about how water is delivered but also when, how often, and how much.
  • To avoid under-or overwatering their crops, it is necessary to monitor the weather forecast, soil and plant moisture carefully and adapt their irrigation schedule to the current conditions.
  • For example, farmers can water at night to slow down evaporation, allowing water to seep down into the soil and replenish the water table.

Drought-Tolerant Crops

  • Growing crops appropriate to the region’s climate is another way farmers get more crops per drop.
  • Crop species native to arid regions are naturally drought-tolerant, while other crop varieties have been selected over time for their low water needs.

Dry Farming

  • Dry farming relies on soil moisture to produce crops during the dry season, avoiding artificial irrigation.
  • Examples of practices supporting dry farming: early soil preparation and planting; selecting drought-tolerant, resistant or early-maturing cultivars; lower planting density; minimizing soil disturbance.
  • It is likely to enhance flavours but produces lower yields than irrigated crops.

Rotational Grazing

  • Rotational grazing is a process in which livestock are moved between pastures to promote regrowth.
  • Good grazing management increases the fields’ water absorption and decreases water runoff, making pastures more drought-resistant and increasing soil organic matter.

Compost and Mulch

  • Compost, or decomposed organic matter used as fertilizer, has improved soil structure and increased its water-holding capacity.
  • Mulch is a material spread on top of the soil to conserve moisture. Mulch made from organic materials such as straw or wood chips will break down into compost, further increasing the soil’s ability to retain water.
  • Compost and mulch help farmers retain more water in the soil during the dry season.

Cover Crops

  • Cover crops reduce weeds, increase soil fertility and organic matter and help prevent erosion and compaction. This allows water to penetrate the soil more quickly and improves its water-holding capacity.
  • Fields planted with cover crops are more productive than conventional fields during years of drought.

Conservation Tillage

  • Conservation tillage uses specialized ploughs or implements that partially till the soil but leave at least 30 per cent of vegetative crop residue on the surface. Such practices help increase water absorption and reduce evaporation, erosion, and compaction.
  • To make the most of their water use for a crop, conservation agriculture’s whole set of practices should be implemented: mulch, compost, cover crops, and no/minimum tillage.

Going Organic

  • Organic agriculture has greater yields than conventional fields in drought because organic methods contribute to retaining soil moisture.
  • Healthy soil rich in organic matter and microbial life serves as a sponge that delivers moisture to plants.
  • Organic fields can recharge groundwater supplies up to 20 per cent.

Sources and Links

Christou, A., Dalias, P. and Neocleous, D. 2017. Spatial and temporal variations in evapotranspiration and net water requirements of typical Mediterranean crops on the island of Cyprus. Journal of Agricultural Science, 155, 1311-1323

Dalias, P., Christou, A. and Neocleous, D. 2018. Adjustment of Irrigation Schedules as a Strategy to Mitigate Climate Change Impacts on Agriculture in Cyprus. Agriculture 9,4.

https://agriculture.vic.gov.au/farm-management/water/farm-water-solutions/how-much-water-does-my-farm-need

https://www.fao.org/3/s2022e/s2022e00.htm#Contents

https://www.sciencedaily.com/terms/evapotranspiration.htm

https://cuesa.org/article/10-ways-farmers-are-saving-water

https://dryfarming.org/about/what-is-dry-farming

AGRIWATER project has been funded with the support from the European Commission, with the reference number 2020-1-CZ01-KA204-078212. The content of this website reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

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