NRES 201 Lecture 41 Outline of Last Lecture I Practical aspects of soil testing II Yield based nitrogen management III Soil based nitrogen management Outline of Current Lecture IV Nitrogen fertilization and soil organic matter V Phosphorus and potassium management Current Lecture N 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 test o 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 composition o 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 changed P 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 test o Uptake efficiency will vary with soil properties P 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 goal o No P fertilizer o Retest the soil in 4 years o K Retest in 2 years if alfalfa is being grown and the K test is 400 600
View Full Document
Unlocking...