1. SOIL NITRATE-N VARIABILITY ON CORN FIELDS WITH HIGH
MINERALIZATION POTENTIAL
Silva*, G. H1. and Dahl, J. G2. www.msue.msu.edu
1Michigan State University Senior Extension Educator, 551 Courthouse Drive, Charlotte, MI 48813.
2Manager, MSU Soil and Plant Testing Laboratory, Michigan State University, East Lansing, MI 48824.
Abstract Results and Discussion
The nitrogen (N) mineralization potential on 20 corn The Pre-sidedress Soil Nitrate Test (PSNT) for corn The soil nitrate-N ranged from 7 to 35 ppm with an
fields, each with a history of manure practices was was developed to identify manure applied fields that average of 22 ppm (Fig 1). The coefficient of variation
studied in 2011 using the pre-sidedress soil nitrate test will not respond to additional N fertilizer. A critical soil was 36% reflecting the high degree of dispersion in
(PSNT). Manure types were dairy, swine, poultry and nitrate-N level of 25 ppm at V6-V8 growth stage was the nitrate-N levels between fields.
sheep. They were applied within a year before corn established. Currently the test is adapted to MSU’s
Fig 2. The soil nitrate-N concentration on
planting. Representative PSNT soil samples were Maximum Returns to Nitrogen (MRTN) corn fertilizer
20 manure applied corn fields - June 2011
taken during June 5–20 at V6-V8 growth stage. The recommendation. The test provides N fertilizer credit
for fields based on the soil nitrate-N levels. 9
soil nitrate-N concentration varied from 7 to 35 ppm 8 Average = 22 ppm
CV = 36%
with an average of 22 ppm. The coefficient of variation
Number of fields
7
was 36%. Forty percent of fields exceeded the critical 6
5
PSNT level of 25 ppm and required no additional N 4 8
fertilizer. Based on the Maximum Return to Nitrogen 3
(MRTN) fertilizer recommendation, growers received 2 4 4
3
1
an average N credit of 80 lb/acre, equivalent to about 1
0
$50/acre in fertilizer cost savings. The results showed < 10 11-15. 16-20 21-25 >26
that N mineralized from manure was quite variable Soil nitrate-N concentration
from field to field. This study provided further evidence parts per million (ppm)
that PSNT is a valuable diagnostic tool to estimate soil
Eight fields (40%) exceeded the critical nitrate-N level
N availability from manure and economically and
Objectives of 25 ppm and required no additional N fertilizer. Two
environmentally manage N fertilizer use on corn.
• To assess the nitrate-N mineralization on fields of these fields were ‘certified organic’ receiving N as
with previous manure practices; dairy manure. Based on the MRTN, four fields (20%)
Introduction with nitrate-N levels of 11-15 ppm, 3 fields (15%) with
• To demonstrate the economic and environmental
Efficient Nitrogen(N) management is a vital aspect of benefits of PSNT as a tool to manage N fertilizer. 16-20 ppm and 4 fields (20%) with 21-25 ppm,
profitable corn production. Determining the optimum received soil N credits of 30, 60 and 90 lb/acre,
N fertilizer rate is critical to reducing fertilizer cost and respectively. All four manure types were represented
Materials and Methods
potential environmental losses. Livestock manure is a in these three categories. Only one field tested less
valuable source of N to corn. However, manure type This study included 20 corn fields each with a history than 10 ppm nitrate-N and received no soil N credit.
and nutrient composition varies considerably from of manure practices. Dairy manure was used on 10, This field had 10,000 gals/acre of a diluted dairy
farm to farm (Table 1). The manure nutrient value will swine manure on 3 and poultry manure on 6 fields. manure liquid from an open pit, injected soon after
also depend on application rate, timing, and method, Sheep manure was used on 1 field. Ten corn growers wheat harvest in 2010. The average soil N credit
animal diet, and storage conditions. The typical rates from Eaton, Ingham, Barry and Shiawassee counties recommended for all fields was 80 lb/acre, equivalent
vary from 5 to 30 tons/acre for dairy and swine and 2 collaborated. The manure was applied within a year of to about $50/acre savings from reduced fertilizer cost.
to 5 tons/acre for poultry and sheep. Frequent corn planting. Some fields received multiple
applications. Representative PSNT samples were The observed variability in nitrate-N could not be
manure analysis and average ‘book values’ are
taken June 5-20 at the V6-V8 growth stage. This predicted based only on the type and rate of manure
helpful in creating manure management plans but not
period coincided with the onset of peak N uptake by because of site-specific variables such as soil and
very useful in predicting N availability in specific
corn. Soil cores were taken midway between the corn climate and manure practices before 2011. Some
situations. Furthermore, organic matter mineralization
rows as prescribed by the PSNT procedure (Fig. 2). fields received 4-5 inches rainfall in May and June of
(Fig.1) that converts organic-N to plant available N, is
2011 favoring nitrate leaching and denitrification. It is
a biological component of the N cycle that is largely The sampling depth was conceivable that some nitrate-N was lost particularly
influenced by interactions of soil microorganisms, 12 inches. The samples on light textured soils. However, the early season
management practices and weather. were analyzed at the MSU mineralization rate was slow and most the manure N
Table 1. The range in nutrient composition of Soil and Plant Testing was in the organic form. The results reinforced the
animal manures from Michigan farms Laboratory for nitrate-N. diagnostic value of PSNT in determining the site-
Manure N P2 05 K20 N P205 K20
The cost was $10.00 a specific N requirements to corn, irrespective of the
type -------------lb/Ton------------- -----------lb/1,000 gals----------- sample and the turn- manure type and rate.
around time was 24
Dairy 5-16 2-16 2-31 3-51 2-21 2-58 References
hours. Fig. 2. Soil sampling area
Swine 3-27 1-62 2-18 1-61 1-63 1-49 Silva. G. H . 2011. Prep work for PSNT. MSUE Field Crops News
between rows for PSNT
Poultry 1-111 1-96 2-55 35-75 13-91 13-39 Silva G. H. 1998. Alternate approaches to monitor excess
nitrogen fertilizer use on seed corn. Michigan State University
Sheep 2- 28 2-15 3-43 NA NA NA Research Report 558.