Nitrogen deficiency
The most important soil attributes for lucerne production are:
• high organic matter content with an organic carbon level of 30/o or better, which contributes to a friable soil structure;
• a deep, free-draining soil profile not subject to waterlogging;
• good surface drainage;
• neutral to alkaline pH of 6.5 to 8.
Lucerne for intensive hay production is grown mainly on naturally fertile, alluvial creek flats and river valleys where, traditionally, little fertiliser has been used. There is ample evidence that in these soils, which have been cropped to irrigated lucerne for hay production, fertility has been depleted and significant fertiliser responses are obtainable. Hay production removes large quantities of soil nutrients because large tonnages of crop are transported from the paddock each year. Approximate nutrient removal with each tonne of lucerne hay is shown in Table 6.1.
Before planting lucerne, a comprehensive soil test from a reliable laboratory is recommended to assess paddock fertility. Growers can then develop a fertiliser application program to replace nutrients that arelimiting.
Nutrient deficiencies have specified visual diagnostic symptoms. It is unwise to rely entirely on these symptoms as indicators of lucerne nutrient deficiencies because losses in yield, quality and longevity will normally be experienced well before symptoms become evident.
The elements most commonly deficient are phosphorus, sulfur, potassium, nitrogen and calcium. The minor elements, which are most commonly deficient, include molybdenum, boron, and zinc, although the other trace elements can also cause problems.
Table 6.1 indicates the critical soil levels of the major plant nutrients needed by lucerne in most Queensland soils. Soil test results should be used in conjunction with local knowledge and experience when deciding on a fertiliser program. The process of identifying deficient nutrients should include grower-applied fertiliser test strips, which are harvested to assess yield and quality benefits.
The nutritional status of established lucerne stands can be monitored using tissue-testing techniques now available, and widely used, in a range of crops. To obtain useful results when tissue sampling, strict procedures must be followed. Seek advice on tissue-sampling techniques and interpretation of laboratory results from the specially trained personnel of a fertiliser company or retailer, reliable local analytical laboratory, or from local DPI extension agronomists. These people are trained to interpret soil test results and to suggest fertiliser practices for individual paddocks.
Table 6.1 Major elements needed by lucerne
.
