Review: Clay pot Sub-Surface Irrigation as Water Saving Technology for Small-Farmer Irrigation (Daka, 2002)

Table of Contents

Objective of the study
Description of the experiments


Title: Clay pot Sub-Surface Irrigation as Water Saving Technology for Small-Farmer Irrigation
Authors: Daka, Angel Elias
Type of Study: Dissertation Thesis, Experimental
Journal: Chapter 7 in: Development of A Technological Package for Sustainable Use of Dambos by Small-Scale Farmers, Ph.D. Thesis, University of Pretoria, South Africa.
Open Access: Yes


Objectives of the study

“(1) To compare the water requirements and yield responses of some vegetable crops grown under clay pot sub-surface irrigation and the conventional watering can.
(2) To establish the water use efficiencies of these vegetable crops and derive irrigation intervals and water savings with the clay pot system, compared with the conventional watering can irrigation system.
(3) To assess the suitability of clay pot irrigation to small-scale farmer-irrigation with regards to system performance and crop adaptability.
(4) To establish the radius of a wetting front for water distribution from clay pots in a sandy clay loam soil.”



Type of experiment: Field study, Completely Randomized Block Design with three replications
Country: Zambia
Place: Noole Dambo, Agroecological zone II, Southern Province
Crops: Beans, cauliflower, cabbage, maize, onion, rape, tomato; Mexican apple, citrus, coffee
Soil Type:
Number of pitchers: 168?
Parameters analysed: yield, crop water requirement, water use efficiency; mortality rates, hight, stem diameter


Content of Chapter 7

7.1. Introduction
7.1.1 Objectives
7.1.2 The Clay Pot as Sub-surface Irrigation

7.2. Experimental Procedures
7.2.1 Site Selection
7.2.2 Materials and Experimental Methods
7.2.3 Statistical Analysis of Yields

7.3. Test Procedure
7.3.1 Yield Responses
7.3.2 Crop Water Requirements and Water Use Efficiency
7.3.4 Application of Clay Pot Irrigation to Perennial Crops
7.3.3 Fertigation in Clay Pots
7.3.4 Advantages and Disadvantages of the Clay Pot Irrigation System Advantages of the System Disadvantages of the System

7.4 Manufacturing Of Clay Pots

7.5 Principles Of Operation

7.6 Maintenance Of Clay Pots

7.7 Sustainability And Economics

7.8 Optimizing The Clay Pot System By Combining It With
Treadle Pump Technology

7.9 Conclusions

Note: Section 7.3.4 occurs twice. There is no reference section to chapter 2.


Description of the experiments

Pitcher characteristics

“The clay pots are made from a mixture of clay and sand in the ratio of 4:1 and with an effective porosity ranging from 10-15%. The clay pots are made by rural women using their hands to mould them into different shapes, i.e. cylindrical/round with somewhat flat bottom. After they are made, glazing is not done so as to retain their natural porosity i.e. the walls remain micro-porous. The pots are then tempered by burning them in a pit fire from firewood at undetermined temperature. Small-scale earthen-ware manufacturers use kilns to temper such ceramic pots at 1200°C. This is done in order to eliminate the swelling and shrinking properties of clay, which would cause cracking of the pots. Women believe that the type of clay used to make the pots is very important and it requires an experienced old woman to identify clay that would not crack unduly during the tempering process and indeed when installed under field conditions.” [192]

Pitcher Volume (ml) Height (cm) Average wall thickness (cm) Maximum outside diameter (cm) Neck diameter (cm) Base diameter (cm) Surface area (cm2)
1-168 5

No more information concerning the clay pots is provided.


Soil characteristics

No information provided.


Experimental Set-up
It seems that there were 21 seed beds of which seven were prepared with 8 pots each resulting in 56 clay pots but this cannot be established for sure since the author writes: “Eight clay pots were required for each configuration in a given seed bed. Twenty one such seed beds were prepared (…) Control plots were established, which had similar arrangement and used the same crops but without clay pots.” [175-176]

“A completely randomized block design with three replications was used for all the vegetable and cereal (maize) crop trials. Study plots measuring 4 m x 1 m were prepared by cultivating the soil to a fine tilth with a hand hoe after the soil was brought to field capacity. Beans, cauliflower, cabbage, maize, onion, rape and tomato were evaluated in this experiment.” [175]

“Eight clay pots were required for each configuration in a given seed bed. Twenty one such seed beds were prepared and except for beans which was directly seeded, seedlings were transplanted adjacent to either sides of the clay pots in such a way that the first seedlings and last seedlings in a given study plot were 45 cm away from the clay pot and 10 cm away from the edge of the bed. The crop spacing in this configuration was as per horticultural recommendations of 30 cm x 90 cm for cabbage, cauliflower, maize, rape and tomatoes. Beans and onion were spaced at 10 cm x 15 cm drilled and transplanted in rows respectively between and on the side of the pots (Figure 31).” [175]

“Control plots were established, which had similar arrangement and used the same crops but without clay pots. Irrigation was done by the traditional conventional method which employs irrigating with watering cans.” [176]

“Clay pots were refilled every time they reached a 50% depletion level and /or when index tensiometers recorded between -20 kPa and -40 kPa, whichever occurred first (…)” [176]

“Yield was measured by weighing actual harvested produce from the crops in the study plots on a standard hanging scale. The yield was measured in kilogrammes but translated to ton/ha for both treatments. Results by the Vegetable Research Team (VRT, 1996) on water requirements and yields of the same crops irrigated by sprinklers were used to compare with those obtained from this trial.” [177]

“A statistical computer package called AGSTATS was used to analyze the statistical significance in yield differences.” [177]

“In view of the difficulty to irrigate and establish tree crops under conventional irrigation systems that use buckets or watering cans, the use of clay pots was tried with coffee, citrus and mexican sugar apples on an observational basis. Yield results are not reported here as the crops take a long time to start fruiting. However, experiences elsewhere are discussed in relation to observations made in this observational trial.” [177]


Clay pot irrigated crops compared to irrigation with watering cans provide an increase in yield for all crops besides onions (clay pot: 36.13 t/ha, water can: 36.62 t/ha).

“In the present study statistically significantly higher yields with the clay pot irrigation system than with the watering can system were obtained for three of the seven crops, viz. cauliflower, maize and rape (Table 24). The yields with the clay pot system for these crops were also substantially higher than for the sprinkler system, although they cannot be compared statistically.” [180]

“In no case did the clay pot system give significantly lower yields than the watering can system or substantially lower yields than the sprinkler system. Even more noteworthy than the statistical significance of the increases in yield with the clay pot system over the watering can system are the large magnitudes of these increases on a percentage basis. For cauliflower it was 38%, for maize 58% and for rape 26%.” [180-181]


Crop Water Requirements and Water Use Efficiency
“it is observed that water savings between 50% and 70% are achievable with the clay pot irrigation system as compared to the conventional watering can system (…)” [181]

“The irrigation cycle was thus found to be 7 days for clay pot irrigation and 4 days for conventional watering can systems.” [181]

“Peculiarly low water requirements were observed under both the clay pot and the conventional irrigation systems for cabbage and onion, a head and bulb forming vegetable respectively.” [182]

“The vast reduction in water use by crops under clay pots did not, however, reduce yields.” [182]

“It is observed from Table 26 that all crops grown under the clay pot sub-irrigation system manifest much higher water use efficiencies than those under the conventional system. This means that crops under clay pots only require less water to produce a unit biomass yield as compared to the conventional traditional watering can irrigation system or produce a higher yield per unit water applied.” [183]

“The surface soil in clay pot irrigation systems remains dry thereby reducing weed prolification and direct evaporation of water. However, this does not mean that the clay pot which wets only part of the soil volume in the field reduces water consumption by plants but rather cuts back on the waste of water due to evaporation, deep percolation and competitive consumption of water by weeds.” [184]

“The conventional system whose soil surface is usually heavily wetted at each irrigation cycle remains vulnerable to weed infestation.” [184]

“At the end of the trial, it was found that the tomato plants had formed mats of fibrous roots all around the clay pot. In this way the crop enjoyed direct abstraction of water as it oozed out of the pot under atmospheric pressure head. Similarly rape, cauliflower and maize exhibited rooting systems that ramified the soil deeply, but were confined within the wetting zone of the pot.” [184]

“A concentration of thin fibrous roots in the confined volume of irrigated soil under claypots will therefore have a tremendous capacity to supply water to the above ground canopy due to increased root surface area, a relative low dependence on water movement to the roots in the soil.” [184]

“Observations have also shown that cabbage and onion have shallow rooting which is also not fibrous. Despite their shallow, non-fibrous roots, both cabbage and onions had absolutely incredibly high water use efficiencies. Although yields of cabbage and onion were slightly lower under clay pot irrigation than the conventional system, their water use efficiencies were highly superior with this system because the rootzone remains moist whereas it quickly dries up under the conventional watering can irrigation system.” [185]


Application of Clay Pot Irrigation to Perennial Crops
“The clay pot system, as observed in mexican apple and citrus tree seedlings, performed very well in terms of growth and establishment as compared to the slower growth rates and high mortality rates experienced with conventional plantings four months from transplanting in August 1996” [185]

“Clay pots also ensure better establishment of trees as plant mortality is reduced to reasonable levels with more plant seedlings surviving. The system also reduces the frequency of irrigation during establishment of tree plants as well as the total amount of water applied. [187]

“Plant height increases of 87.5% and 90% for mexican apple and citrus, respectively, were observed in clay pot irrigation compared to 19.5% and 18.5% increases for the same crops under conventional watering can (Table 27).” [187-188]

“Higher stem growth rates are also observed for clay pots than the conventional watering can. Table 28 illustrates better tree seedling establishment under clay pot irrigation (94% – 98.75%) than the conventional watering can (64% – 83.75%).” [188]


Fertigation in Clay Pots
“Half of the recommended doses for conventional systems proved to be suitable for the clay pot irrigation system. This is a tremendous advantage, since high fertilizer costs often pose severe limitations to small-scale resource poor farmers.” [190]



“Clay pot sub-surface irrigation is a drip irrigation system by way of its water application to the plants. Water oozes out through the micro-pores of the pot and wets the surrounding soil. The crops grown around the pot take up the water as they need it.” [185]

“It has been found that as long as the water is not completely depleted in clay pots, it will be in continuous phase of moving out of the pot as long as water uptake by a crop takes place. In this way the surrounding soil is kept moist.” [185]

“The technology is a conservation irrigation system, which saves between 50% and 70% water when compared to the conventional watering can irrigation system. Water is a scarce resource and thus its use must be optimized.” [185]

“Clay pots reduce water use without reducing yields. Therefore it is a water saving technology which optimizes yields per unit water.” [185]

“The clay pot irrigation system is a labour saving technology, both because of less labour required for irrigation and less labour required for weeding.” [185]

“The fact that most rural women of Africa locally make clay pots, means that making clay pots for irrigation will potentially contribute towards creation of employment for them by means of a technology that they are proficient in.” [185]

“The clay pot irrigation system greatly reduces fertilizer requirements, which greatly improves the economy of small-scale irrigation farming.” [185]

“The clay pot irrigation system could be optimized by combining it with treadle pump technology.”


Additional statements within the text :

“The clay pot technology is sustainable since the pots are made from readily and locally available materials which are in abundance. They are low-cost and are made by rural women whose activity to manufacture them at village level offers possibilities of rural income generation at household level.

At a cost of US$0.25 they are affordable by the majority of end users. When properly used and maintained, they can be re-used year in and out for a period of up to 5 years. The fact that very little water is required to raise crops, offers a high potential for their demand particularly in regions with scarce water. No skill is required to operate and maintain the system. The low fertilizer requirements, as compared to conventional recommendations, greatly enhances the economic benefit of the system.” [194]

The author suggests to install a treadle pump because they “provide a much more efficient and less laborious system for abstracting water from wells or rivers than the rope-and-bucket system. By connecting a hosepipe to the treadle pump, water can be delivered at the point where it is needed. The pots can be filled directly from the hosepipe or watering cans can be filled close to the point where they are used to fill pots. Combining the two technologies in this way can clearly optimize the clay pot system.” [195]




This is a solid presentation of a well designed experiment. What is missing is precise information about the soil and the characteristics of the pitchers – the only given informationen concerns their volume and material composition.

It would have been useful to provide information concerning the process and the results of the entire experiment, e.g., was the yield of each pot similar or were there noticeable individual differences.

The author classifies yield data in table 24 as “significant” and “non significant” but does not outline the criteria for this classification. In the same table the abbreviations “LSD(5%)” and “CV(%)” are used but not explained anywhere in the text.

The exact set-up of the experiment cannot be reconstructed. The author writes:
“Eight clay pots were required for each configuration in a given seed bed. Twenty one such seed beds were prepared (…) Control plots were established, which had similar arrangement and used the same crops but without clay pots.” [175-176]

“A completely randomized block design with three replications was used for all the vegetable and cereal (maize) crop trials. Study plots measuring 4 m x 1 m were prepared by cultivating the soil to a fine tilth with a hand hoe after the soil was brought to field capacity. Beans, cauliflower, cabbage, maize, onion, rape and tomato were evaluated in this experiment.” [175]

Since there were seven individual crops involved in the study and the experimental design included three replications this would make 21 plots for clay pot irrigated crops with each plot consisting of eight clay pots totalling to 168 clay pots alltogether. It remains unclear if “similar arrangement” of the control plots refers to the layout of the seed beds or of the total number of 21 control plots.

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