Part I. Real-time use of soil moisture data for refined greenseeker sensor based N recommendations in winter wheat (Triticum aestivum L.). The Sensor Based Nitrogen Rate Calculator enables producers to estimate yield potential and obtain nitrogen (N) fertilization rates based on GreenSeeker sensor measurements and the response index, number of days where GDD (growing degree days)>0, agronomic maximum yield, expected grain price, and fertilizer price. Soil moisture levels can vary significantly both site-to-site and year-to-year. Furthermore, soil moisture is known to significantly affect both yield potential and fertilizer use efficiency. The current Sensor Based Nitrogen Rate Calculator does not take in account profile soil moisture at the time of sensing. Limited soil profile moisture leads to overestimation of yield potential and, low fertilizer use efficiency. At-sensing knowledge of the amount of water present in the soil profile can help to more accurately predict yield potential. This will in turn reduce the risk of applying N when it is not required, and to identify years when sufficient moisture is present in the soil profile to produce near maximum yields where more N is needed.
Part II. Effect of foliar P fertilization on corn (Zea mays L.) grain yield and phosphorus use efficiency. Application of foliar phosphorus (P) fertilizer to corn could allow for P deficiency correction if it occurs mid-season. This would supply the crop with the P supplement needed to achieve higher grain yield as well as increase phosphorus use efficiency (PUE). The experiment was established in the spring of 2006 at Lake Carl Blackwell (Port-oscar silt loam, fine-silty, mixed, super active, thermic Cumulic Haplustolls) Oklahoma to evaluate the response to various rates and sources of foliar P fertilizer application of in corn. The experiment employed a randomized complete block design with three replications and 15 treatments. All treatments received N fertilizer at a rate of 168 kg ha−1 applied preplant as urea (46-0-0) and incorporated into the soil. Topdress fertilizer P was applied foliar one day prior to sprinkler irrigation: at V6 in late May, and at V10 in the beginning of June. The sources of foliar P fertilizer applied were KH2PO4 (potassium phosphate monobasic), DAP (diammonium phosphate), APP (ammonium polyphosphate), and TSP (triple super phosphate). Two rates (3 kg P ha−1 and 7 kg P ha −1) were evaluated using were KH2PO4, DAP, APP, and TSP was applied at 22 kg P ha−1 and 168 kg P ha−1 (phosphorus-rich treatment). In general, highest corn grain yields were achieved when 3 kg P ha−1 were applied at the V10 growth stage as KH2PO4 and DAP. Phosphorus use efficiencies were very low for both growing seasons due to lack of response to P fertilizer applied. The results of the study were inconclusive due to the lack of good quality data caused by adverse weather conditions. Further studies are necessary to determine how foliar P fertilization might benefit corn production.
|Advisor:||Raun, William R.|
|Commitee:||Godsey, Chad B., Klatt, Arthur R., Solie, John B.|
|School:||Oklahoma State University|
|Department:||Plant & Soil Science|
|School Location:||United States -- Oklahoma|
|Source:||DAI-B 73/07(E), Dissertation Abstracts International|
|Subjects:||Agronomy, Agriculture, Soil sciences|
|Keywords:||Corn, Grain yield, Greenseeker sensors, Nitrogen, Soil moisture data, Winter wheat|
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