NRES 201 Lecture 41 Outline of Last Lecture I. Practical aspects of soil testingII. Yield - based nitrogen managementIII. Soil - based nitrogen managementOutline of Current Lecture IV. Nitrogen fertilization and soil organic matterV. Phosphorus and potassium managementCurrent LectureN fertilization and soil organic matter - - Fable - N fertilizers build up soil organic matter by increasing the input of crop residues.- Fact - Intensive N fertilization depletes soil organic matter by stimulating microbial conversion (mineralization) of organic C to CO2 with the loss of residue C and also soil organic C. Evidence from the Morrow Plots - - Corn yields have increased since NPK fertilization began in 1955, but all the residue C is gone with the loss of SOC. - There are greater SOC losses for C - S than C - C for the subsoil than the plow later with higher N rates. - These has been a parallel decline in soil total N and a greater loss of potentially mineralizable N as measured with the ISNT. A global dilemma - - Synthetic N fertilization has artificially inflated cereal production and world population while most contributing to atmospheric enrichment of CO2 and N2O. - The loss of organic matter jeopardizes soil productivity with adverse implications for: Food supplies, living standards, social unrest, and world population. P and K recommendations: Buildup - Based on: P or K supplying power of the soil as well as soil test value. - Correlations - o 9 lb P205 = 1 lb increase in P testo 4 lb K20 = 1 l increase in K test- Limitations - o Soils differ: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. In P - Buffering capacity, which depends on:- Clay content and composition- pH- Organic matter In K - Buffering capacity, which depends on:- CEC, - Clay content and compositiono Soils must differ in buildup efficiency o Calibrations are obsolete - Developed in the 1940s and 1950s When corn populations were much lower More plants need more food Cropping systems and tillage practices have also changedP and K recommendations: Maintenance- Based on the amount of P or K removed in the harvested portion of the crop.- It is determined from the type of crop and the yield goal- However, it does not depend on soil type or soil test level. - Limitations - o Superfluous with a properly calibrated soil testo Uptake efficiency will vary with soil propertiesP and K fertilizer recommendations: relationship to soil - test level- Below soil - test goal: Buildup and maintenance- At or up to 20 lb/Acre above sol - test goal: Maintenance only- More than 20 lb/ Acre above soil - test goalo No P fertilizero Retest the soil in 4 yearso K - Retest in 2 years if alfalfa is being grown and the K test is 400 -
View Full Document
Unlocking...