Residual effects of applied chemical fertilisers on growth and seed yields of sunflower (Helianthus annuus cv. high sun 33) after the harvests of initial main crops of maize (Zea mays L.), soybean (Glycine max L.) and sunflower (Helianthus annuus).

The experiments consisted of two locations, i.e., the first one was carried out on a growers's upland area at Saraburi Province, Central Plane region of Thailand with the use of Chatturat soil series (Typic Haplustalfs, fine, mixed) and the second experiment was carried out at Suranaree Technology university Experimental Farm, Suranaree Technology University Northeast Thailand with the use of Korat soil series (Oxic Paleustults). The experiments aimed to investigate the effect of residual effects of applied chemical fertilisers on growth and seed yields of sunflower (Helianthus annuus) after the harvests of initial main crops of maize, soybean and sunflower. The experiments consisted of four cultural methods being practiced by growers in both regions. For Methods 1 and 2, each had four fertiliser treatments; Method 3 consisted of two fertiliser treatments and Method 4 was used as a control treatment. The results showed that soil pH, organic matter and nutrients of Korat soil series were most suited soil conditions for growth of sunflower plants, whilst that of Chatturat soil series at Saraburi province was an alkaline soil with a mean value of soil pH of 7.8. Chatturat soil series, in most cases, gave higher amounts of seed yields (1,943.75 kg ha(-1)) than Korat soil series. Residual effects of applied chemical fertilisers to main crops of soybean gave better growth and seed yields of sunflower plants and it is considered to be the first choice. The use of sunflower and maize as main crops gave a second choice for subsequent crop of sunflower.