Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 30, 1997
Publication Date: N/A
Interpretive Summary: Microirrigation (trickle) can be used to precisely place water and fertilizers near plant roots. One drawback of microirrigation is that systems are expensive to install because of the high costs of materials. Thus for crops that do not have a high value per acre, like cotton, installation costs have kept farmers from using microirrigation. We conducted this experiment to find out if costs can be reduced by using fewer materials in the system. Secondly, we tested whether nitrogen fertilizer efficiency could be increased by feeding the plants a small amount of nitrogen fertilizer through the microirrigation system when a computer plant growth model predicted nitrogen stress was about to occur. We found that burying trickle lines between two rows was as effective as burying them under every row in supplying water and fertilizer nitrogen to cotton plants. We also found that by using the plant growth model to prescribe nitrogen application, 30% less nitrogen was put into the environment than with current cotton production recommendations. These results are important to the irrigation industry and to scientists who are trying to develop improved water management systems for the southeast USA. They are also important because they provide a way to potentially reduce environmental contamination by nitrogen.
Technical Abstract: No information is available on optimal management of water and N fertility with buried microirrigation systems for cotton (Gossypium hirsutum L.) in the southeastern USA. Our objectives were 1) to determine the effect of buried microirrigation lateral spacing on flower production and on plant water and N status, and 2) to determine the effect of N application scheduling method on plant N status. Treatments were three irrigation levels (rainfed, laterals placed in-row, and laterals placed in alternate mid-rows) and three sidedress-N scheduling application methods (112 kg N ha-1 before first bloom, five weekly applications of 22.4 kg N ha-1 beginning before first bloom, and 11.2 to 22.4 kg N ha-1 applications applied as dictated by the GOSSYM-COMAX simulation model). Soil type was Eunola loamy sand (fine-loamy, siliceous, thermic Aquic Hapludult). Flower number and leaf water potentials did not differ between in-row and alternate mid-row placement in any year. Rainfed cotton had water potentials up to 0.49 MPa lower than irrigated cotton. Leaf petiole NO3-N and blade N concentrations for all treatment combinations were above the deficiency range at first bloom in each year. The results suggest that a lateral spacing wider than in-row placement is adequate for supplying both water and N to cotton on these soils and that N management can be improved by using simulation models for predicting N fertilizer needs.