NRES 201 Lecture 40 Outline of Last Lecture I. Some fundamentalsII. Nutrient deficiency symptomsIII. Plant analysisIV. Basic aspects of soil testingOutline of Current Lecture V. Practical aspects of soil testingVI. Yield - based nitrogen managementVII. Soil - based nitrogen managementCurrent LectureField Sampling - - Fundamental Assumption - Samples for soil testing accurately represent the entire field.- Depth of Sampling - A crucial factor has been overlooked. 7 inches for pH, P, and K are there to represent the plow layer and simplify sampling. - Method of sampling - o A 1 - inch soil probe is recommended. Automated soil samplers can also be used.- Time of sampling - o Every 4 years, in late summer or fall to reduce seasonal variability in K tests. o Sample before applying lime or fertilizer, otherwise you'll need to wait a few monthsExtraction - - Significance: It is the crucial step in any soil test procedure that determines selectivity in estimating the plant - available forms of a nutrient. - A potential source of problems - o Extraction procedures modified for the sake of speed and convenienceo It can lead to invalid fertilizer recommendationso Soil testing labs should be certifiedChemical Analysis- Requirements - Accuracy, Speed, Convenience - Implications of new methodology -o The modern trend is toward multi - nutrient testing with inductively coupled plasma (ICP) spectroscopy These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o This has changed what is being measured and requires recalibration with crop responseCalibration - - Factors that affect soil test calibrations: Soil factors, Cropping factors, Fertilizer factors, and Tillage- The usual tests are for pH, P, and K. Other tests can be done, but calibration may be unreliable. This is especially a problem for micronutrients. N recommendations - - Corn - 1.2 x yield goal with adjustments for a previous legume, manure, or late planting- Soybean - N is not recommended- Late planting - o Reduce the N rate by 20 lb/A for each week delay in planting after the optimum date: Apr 10 - 15 in Southern IL Apr 20 - May 1 in Central IL May 1 - May 10 in Northern ILo Later planting lowers the yield potential so less N will be needed and a rate adjustment should be made if N will be applied to the growing crop (side-dressed) There is more crop N uptake from fertilizer than from soil The Illinois Soil N Test (ISNT)- A simple diffusion method that estimates soil N - supplying power by measuring Alkali - labile organic N and NH4 but not NO3. - Valuable insights about the ISNT - o Management affects the critical rangeo Calibration shifts upward: With low soil pH, P, or K With low subsoil fertility With higher plant populations With accumulation of carbonaceous residues- Potential applications for the ISNTo Estimation of soil N - supplying powero Site - specific management of N fertilization and planting rateo Land
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