Download Soil Analysis - Fertility Soil Fertility - Slides | SSC 051 and more Study notes Agricultural engineering in PDF only on Docsity! SOIL ANALYSIS Objectives of soil tests provide an index of nutrient availability or supply in a given soil predict the probability of obtaining a profitable response to lime and fertilizer provide a basis for recommendations on the amount of lime and fertilizer to apply Soil testing – nutrient recommendation system Collect a representative soil sample from the field Determine the quantity of plant available nutrient in the soil sample (soil test). Interpret the soil test results (soil test calibration). Estimate the quantity of nutrient required by the crop (nutrient recommendation). General Methods Collecting the sample – The largest source of error in the system!!!! Field average sampling dividing the field into units that have similar management history and can be managed differently for the current crop. Site-specific sampling dividing the field into a grid with cells from 1-5 a in size, then sampling the entire cell or the taking samples around a grid point. Cell Sample Point Sample Mobile nutrients (NO3- SO42- Cl- ) crop yield is proportional to the total quantity of nutrient present in the root zone , thus the recommendation is based on nutrient present (i.e. N) in the profile and a yield goal. For example N recommendations are based on quantity of N needed to produce expected crop yield or yield goal (Ncrop) quantity of N supplied or available in the soil during the growing season (Nsoil) Nrec = Ncrop - Nsoil Ncrop is determined by yield goal (bu/ac) x N coefficient (lbs N / bu yield) = lbs N/ac Ncrop varies between crops, regions or climates, and laboratories making the N recommendation. For example, corn contains 0.7 lb N /bu (assuming all N applied recovered in the grain). Unfortunately, N recovered in grain can vary between 40 and 70%; thus, usually 0.9 - 1.7 lb N/bu is used for Ncrop. In winter wheat, 1.8 - 2.4 lb N/bu yield goal is required (2.1 lb N/bu average). For a 60 bu/a yield goal: Ncrop = 60 bu/a x 2.1 lb N/bu = 126 Ib N/a So the recommendation now becomes: Nrec = Ncrop - [ Nsoil ] Nrec = Ncrop - [ Profile NO3- - Nmin (OM) - Nmin (legume) - Nmin (Manure) ] The Nsoil factors are determined for each specific field by the laboratory Immobile nutrients crop yield is proportional to the quantity of nutrient near the root surface and the soil test provide an index of the nutrient availability Management strategies A. build up – when soil test levels are below the critical level, nutrients should be added to increase soil test level. B. maintenance – when soil test levels are above the critical level nutrients are added to replace the nutrients removed by the harvested crop.
