Chapter Conventional cropping in soil

Conventional cropping in soil is the simplest cropping system and involves the planting and raising of a crop as would be done outdoors. The actual planting is an important stage in the growth of the crop. First, dig a trench at least 10 cm deep and 15 cm wide. Then place the plants in soil blocks or peat pots in the trench and heel in with 0.25 L of starter fertilizer solution (5 g of 10-52-17 per litre of water) per plant; pull only a little soil around them. Spot-water plants as needed for 2 weeks after transplanting. Once the plants are established, general watering usually is not needed for 4-6

weeks, depending on soil type and light intensity On light soils general irrigation begins sooner than on the heavier soil.

What type of soil to look for

To achieve maximum production, greenhouse vegetables in general need a well-aerated soil with a high water-holding capacity, rich in nutrients and free from pathogens. Although greenhouse tomatoes can be grown on a wide variety of soils, the most suitable are those classified as loams, sandy loams, and some silty loams, all with a high organic-matter content, if possible (see Fig. 8). Other types of soils can be used, but they are more difficult and expensive to manage. For example, coarse sandy soils have low water-holding capacity, poor nutrient retention, and poor cone formation when drip-irrigated; silty soils have an unstable structure that breaks down with heavy watering; and clay loams are poorly drained, difficult to leach, and their structure is damaged by cultivation when wet. Proper management can render almost any soil suitable for greenhouse production. For example, both light and heavy soils can be improved by adding organic matter. If natural drainage is poor, as in most clay, silty clay, and sandy clay loams, a tile or pipe drainage system is necessary. The main purpose of the soil is to provide a medium in which there is a proper balance between air, water, and nutrients. If this balance is ensured, the roots can easily obtain water and nutrients, resulting in rapid growth.

Drainage

Install tile drainage in ground beds to ensure that all excess water is carried away. For drainage, use perforated or nonperforated clay tiles, 10 cm in diameter, and lay them with a small space between them to allow for expansion; a few 7.5-cm tiles make effective slip joints for 10-cm tiles. To improve the effectiveness of drainage, cover the tile lines with glass fiber matting made for this purpose or with 2-cm gravel. Set tiles at a depth that prevents their being broken by rototilling or other cultural practices. Place tiles 35 cm deep and 45 cm apart, with a slope of 10 cm for every 150 m of 10-cm clay tiles. The same tiles, with perforations on the bottom or the sides, are also used for steam sterilization. Loop adjacent rows of tile together at the ends, with elbows and tees for more equalized steaming from line to line. Introduce steam into the rows of tile through a header. This header, with a 50-cm capped riser on each end for steam input, extends across the width of the house and is equipped with nipples 2-3 cm in diameter and about 25 cm long; one nipple corresponds to, and is cemented into, each row of tile. Both the header and the rows of tile should be no longer than 15 m because beyond that length steam condenses into water and sterilization is poor.

Table 6 Leaching requirements after steaming

Electrical conductivity ((j-S/cm)

Water required (L/m2)

Saturated-paste

Water

method

extract

Sandy soils

Other soils

up to 1.5

up to 0.5

15

25

1.5-3.0

0.5-1.0

30

50

3.0-5.0

1.0-1.5

70

100

Over 5

Over 1.5

100

150

  • The numbers suggested for litres per square metre of required water also indicate equivalent rates of rain in millimetres.
  • The rates apply to leaching and are added to the requirement for bringing the soil to field capacity (usually 20-50 L/m2).
  • The rates apply to use of overhead sprinklers at intervals over 2-5 days.

It is difficult to leach salts from heavy-textured soils, especially if no effort is made to improve their structure.

If the conductivity before leaching is higher than the recommended range, it must be checked again after leaching and before planting.

Flooding reduces nitrates and conductivity markedly, and may reduce potassium reserves slightly, but it produces little change in other nutrient levels.

  • The numbers suggested for litres per square metre of required water also indicate equivalent rates of rain in millimetres.
  • The rates apply to leaching and are added to the requirement for bringing the soil to field capacity (usually 20-50 L/m2).
  • The rates apply to use of overhead sprinklers at intervals over 2-5 days.

It is difficult to leach salts from heavy-textured soils, especially if no effort is made to improve their structure.

If the conductivity before leaching is higher than the recommended range, it must be checked again after leaching and before planting.

Flooding reduces nitrates and conductivity markedly, and may reduce potassium reserves slightly, but it produces little change in other nutrient levels.

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