Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2006
Publication Date: 5/3/2006
Citation: Pettigrew, W.T., Adamczyk Jr, J.J. 2006. Nitrogen fertility and planting date effects on lint yield and cryl ac (bt) endotoxin production.. Agronomy Journal. 98:691-697
Interpretive Summary: The early planted cotton production system offers greater lint yield potential for Mid-South cotton producers. To achieve the full benefits from this new production system, some of the inputs employed in traditional production systems needed to be reexamined to determine their appropriate utilization in an early planting scenario. In addition, most of the cotton being currently grown in the Mid-South is "trangenic" cotton, containing novel traits that were derived from outside source material. An example of this is the "Bt" trait that conveys resistance to certain insects and came for a microorganism found naturally in the soil. It is not clear whether the current nitrogen fertilization recommendations remain appropriate for these new cotton production options. Therefore, this research investigated how varying the amount, timing of application, or source of nitrogen fertilization affected cotton growth and development, lint yield, and the expression level of the Bt trait. The cotton grown in this study was planted both early in the season (early April) and at a later more traditional planting date (early May). Varying the nitrogen fertility treatments had no effect on lint yield or any of the components of growth. However, plants that received the highest nitrogen application (150 lbs per acre) exhibited 14% greater leaf Bt concentration and a 3% greater leaf chlorophyll (green color pigment) concentration than plants which only received 100 lbs of nitrogen per acre. Early planted cotton yielded 10% more than cotton planted on the more normal planting date. This early planted cotton also had 5% greater leaf chlorophyll concentration but a 12% lower leaf Bt concentration. Because alterations in certain production practices have been identified to affect the level of these novel traits in the transgenic plants, most production practices may need to be reexamined to ensure optimal levels of these traits in the desired plant tissue.
Technical Abstract: An early planted cotton (Gossypium hirustum L.) production system and varieties expressing the Bacillus thuringiensis (Bt) insecticidal gene offer cotton producers improved lint yield potential. It is not clear whether the current nitrogen fertilization recommendations remain appropriate for these new production options. The objectives of this study was to determine how varying rates, application timing, and sources of N fertilization affected cotton dry matter partitioning, leaf chlorophyll (Chl) concentration, leaf Bt (Cry1Ac) endotoxin concentration, lint yield, yield components, and fiber quality. Four varying N fertility treatments were applied to three cotton varieties planted on either an early or normal planting date from 2001 through 2004. The N fertility treatment response was consistent across planting dates and varieties across all data collected as shown by the lack of any significant interactions with these variables. Although the N fertility treatments had no effect on lint yield or any of the dry matter partitioning components, plants that received the 112/56 kg N ha-1 split application (168 total N) treatment exhibited 14% greater leaf Cry1Ac endotoxin concentration and a 3% greater leaf Chl concentration than plants from the other N treatments, which only received 112 kg N ha-1. Early planted cotton had 5% greater leaf Chl concentration but a 12% lower leaf Cry1Ac concentration than the normal planted cotton. This lower Cry1Ac concentration may reflect enhanced remobilization of the leaf protein to feed the faster developing boll load of the early planted cotton. The early planted cotton yielded 10% more than the normal planted cotton because it produced 9% more bolls per unit ground area. Because environmental factors have been identified that affect the level of trangenically produced proteins, production practices may need to be reexamined to ensure optimal levels of the transgenic proteins are present in the desired tissue.