Chapter Cropping in soil with drip irrigation

The drip irrigation cropping system is similar to but better than the conventional soil cropping system because it can be used to control crop growth through a regulated supply of water and nutrients. In addition, the system allows reduced relative humidity in the greenhouse because not all the soil is irrigated and because it is compatible with the use of white polyethylene film as a light-reflecting mulch. Resources, including energy, are thus used more efficiently with this system.

Irrigate the crop up to four times a day, and use the irrigation system to apply fertilizer to the crop. Fertigation is the application of fertilizer through the irrigation system and is a popular method of fertilizing greenhouse vegetables. Fertilizers are either dissolved in a large holding tank and the solution is pumped to the crop or they are mixed in concentrated stock solutions, which are then incorporated, with fertilizer injectors, into the irrigation water

Several makes and models of fertilizer injectors are available at varying costs and offer varying degrees of fertigation control. A sophisticated fertilizer injection system capable of meeting the nutrient requirements of a series of crops automatically from the same set of stock solutions was developed recently at the Agriculture Canada Research Station in Harrow, Ont. (Plate 2).

The Harrow FM uses an IBM-compatible computer to activate a series of dosimetric pumps at varying frequencies for the preprogrammed application of a desired concentration of individual nutrients. In addition, the Harrow FM automatically adjusts the supply of water and nutrients to the crops in accordance with both expert information stored in the memory of the computer and with crop and environmental conditions as monitored by appropriate sensors.

Introducing drip irrigation and fertigation has made it necessary to consider the fertilizer needs of a crop in terms of the concentration of fertilizer (and therefore the concentration of nutrients) in the irrigation water rather than on the basis of the cropped area. Base fertilizers are not normally applied when drip irrigation is used; the exceptions are peat and lime, which might be desirable for the benefit of soil structure and soil pH adjustment.

Plate 2 The Harrow Fertigation Manager, a computerized multifertilizer injection system. (Harrow Fertigation Manager and HFM are registered trademarks of Labbate Climate Control Systems Inc., 1 Wilkinson Drive, Leamington, Ont.)

Plate 3 An early spring tomato crop in rockwool. Artificial light is used for growth enhancement, fine misting (fogging) for relative humidity control, and white plastic on the ground for light reflection, dust control, and evaporation control. Other services, not visible in this modern greenhouse, include computerized environmental control, liquid carbon dioxide supply, hot-water heating, and thermocurtains.

Plate 4 The deep-flow, or deep-culture, technique (DFT) was developed in Japan and is practicedwidely in the Far East. The modular construction of the cropping system includes plant support, extensive use of preformed polystyrene in trough construction, coextruded black-and-white polyethylene film used for protecting the nutrient solution from contamination and light exposure, and white plastic surfaces on the ground and the troughs for light reflection.

Table 10 illustrates a fertilizer feeding program recommended for most soils in the Loam to Sandy Loam categories.

Table 10 Fertigation schedule for drip-irrigated crops (kilograms of fertilizer per 1000 L of stock solution)

Potas

Ammo-

Mono-

Potas

Magne

Week from

Calcium

sium

nium

potassium

sium

sium

EC

planting

nitrate

nitrate

nitrate

phosphate

sulfate

sulfate

L/day Qj.S/cm

Spring crop

M-3, 4,

44.0

6.0

0

22.0

126.0

50.0

0.4

3500

5, 6, 7, 8

44.0

25.0

0

22.0

108.0

50.0

0.6

3000

9, 10, 11

44.0

44.0

0

22.0

68.0

50.0

1.0

2500

12, 13

44.0

64.0

0

22.0

0

50.0

1.2

2300

14, 15

60.0

64.0

0

22.0

0

50.0

1.4

2200

16, 17

76.0

64.0

7.0

22.0

0

50.0

1.6

2000

18, 19, 20

76.0

64.0

22.0

22.0

0

50.0

1.6

1800

21, 22, 23, 24,

25

76.0

64.0

30.0

22.0

0

50.0

1.6

1600

26, 27, 28, 29,

30

76.0

64.0

30.0

22.0

0

50.0

1.6

1400

Fall crop

1,2,5, 4

76.0

64.0

7.0

22.0

0

50.0

0.6

1400

5, 6, 7, 8

60.0

64.0

0

22.0

0

50.0

0.8

1500

9, 10

44.0

64.0

0

22.0

0

50.0

1.0

1800

11, 12

44.0

44.0

0

22.0

68.0

50.0

1.0

2000

13, 14

44.0

25.0

0

22.0

108.0

50.0

0.8

2200

15, 16, 17, 18

44.0

6.0

0

22.0

126.0

50.0

0.4

2500

  • Trace elements (e.g. 0.7 kg of STEM) and 0.5 kg of iron chelate (13% iron) must also be added to all the above fertilizer feeds; atypical trace element mix, e.g. Peters soluble trace element mix (STEM) contains 1.45% boron, 3.2% copper, 7.5% iron, 8.15% manganese, 0.046% molybdenum, and 4.5% zinc.
  • Dissolve given amount of each fertilizer, includingtrace elements, in 1000 L of water and add to the irrigation water in equal doses, ideally with a mult.ihead fertilizer injector. Start injection at a very low rate and increase progressively until the desired EC is achieved. Adjust the pH of the fertigation solution to 5.5 by injecting a dilute solution of phosphoric, nitric, or sulfuric acid.
  • The recommended strength of the stock solutions is within the working range of a fertilizer injector with a 1:100 mixing ratio. If a fertilizer injector with a 1:200 mixing ratio is used, double the amount of each fertilizer. Similar adjustments can be made foi fertilizer injectors with other mixing ratios. If the solubility limit, of a fertilizer (e.g., potassium sulfate) is exceeded, more than one stock solution of the same fertilizer can be prepared and the amount, of the fertilizer divided equally between the stocks.
Growing Soilless

Growing Soilless

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