The preferred pH* is in the range of 6 -7.2. When the soil pH drops below 5.5, magnesium, calcium, potassium and molybdenum availability drops.
Use of lime to increase soil pH, and gypsum to improve soil structure and calcium saturation, will help to increase yield (Figure 2). The sulfur from gypsum complexes with free aluminum reducing the toxicity to the plants.
Soil pH also affects the activity of triazine herbicides, which, where approved for use, can provide complete weed control. Triazine herbicides are most effective when the soil pH is between 5.8 and 6.5.
Maize is less tolerant of salinity post germination, than cereals or alfalfa. While maize will germinate in saline conditions, early leaf and root growth is restricted. An EC of around 8.8mS/ cm will reduce alfalfa yields by around 50%; the equivalent yield loss in maize occurs at an EC of 3.9mS/cm.
Soil analysis is used to provide baseline initial information for a fertilizer program – particularly as an indication of potassium and phosphorus requirements and to assess plant available soil mineral nitrogen for nitrogen recommendations. It is also used to assess soil pH, and organic matter levels.
Plant tissue analysis is important to confirm that the balance between elements within a fertilizer program is effective to maximize crop production. Tissue analysis will also confirm visible deficiency symptoms, reveal hidden deficiencies where visual plant symptoms are not yet present and show excessive nutrient concentrations which may be causing other nutrients to beneficent – e.g. too much phosphorus and poor zinc supply.
• At the seedling stage – when the plant is less than 30cm in height, sample the entire plant from 2 cm above ground – bulking together 15–20 plants.
• Prior to tasseling, sample the last fully expanded leaf from 20–25 plants.
• From tasseling to silk stage, take the leaf opposite and below the ear, again collecting from 20–25 plants Table 8 gives interpretative nutrient ranges across a range of growth stages up to flowering: These figures are guidelines and could vary according to variety as well as local research.