Long-Term Nitrogen and Phosphorus Fertilization of Irrigated Grain Sorghum
Kansas Agricultural Experiment Station Research Reports Long-Term Nitrogen and Phosphorus Fertilization of Irrigated
A. Schlegel 0 1 2
H. D. Bond 0 1 2
Kansas State University 0 1 2
0 1 2
0 Kansas State University , USA
1 This report is brought to you for free and open access by New Prairie Press. It has been accepted for inclusion in Kansas Agricultural Experiment Station Research Reports by an authorized administrator of New Prairie Press. Copyright , USA
2 Kansas State University Agricultural Experiment Station and Cooperative Extension Service , USA
Follow this and additional works at: https://newprairiepress.org/kaesrr Part of the Agronomy and Crop Sciences Commons Recommended Citation Schlegel, A. and Bond, H. D. (2016) "Long-Term Nitrogen and Phosphorus Fertilization of Irrigated Grain Sorghum," Kansas Agricultural Experiment Station Research Reports: Vol. 2: Iss. 6. https://doi.org/
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Long-Term Nitrogen and Phosphorus Fertilization of Irrigated Grain Sorghum
Abstract
Long-term research shows that phosphorus (P) and nitrogen (N) fertilizer must be applied to optimize
production of irrigated grain sorghum in western Kansas. In 2015, N applied alone increased yields 66 bu/
a, whereas N and P applied together increased yields up to 92 bu/a. Averaged across the past 10 years, N
and P fertilization increased sorghum yields up to 76 bu/a. Application of 40 lb/a N (with P) was sufficient
to produce 88% of maximum yield in 2015 which is slightly above the 10-year average. Application of
potassium (K) has had no effect on sorghum yield throughout the study period. Average grain N content
reached a maximum of ~0.7 lb/bu while grain P content reached a maximum of 0.15 lb/bu (0.34 lb
P2O5/bu) and grain K content reached a maximum of 0.19 lb/bu (0.23 lb K2O/bu).
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Kansas Fertilizer
Research 2016
Long-Term Nitrogen and Phosphorus
Fertilization of Irrigated Grain Sorghum
Summary
Long-term research shows that phosphorus (P) and nitrogen (N) fertilizer must be
applied to optimize production of irrigated grain sorghum in western Kansas. In 2015,
N applied alone increased yields 66 bu/a, whereas N and P applied together increased
yields up to 92 bu/a. Averaged across the past 10 years, N and P fertilization increased
sorghum yields up to 76 bu/a. Application of 40 lb/a N (with P) was sufficient to
produce 88% of maximum yield in 2015 which is slightly above the 10-year average.
Application of potassium (K) has had no effect on sorghum yield throughout the study
period. Average grain N content reached a maximum of ~0.7 lb/bu while grain P
content reached a maximum of 0.15 lb/bu (0.34 lb P2O5/bu) and grain K content reached a
maximum of 0.19 lb/bu (0.23 lb K2O/bu).
Introduction
This study was initiated in 1961 to determine responses of continuous grain sorghum
grown under flood irrigation to N, P, and K fertilization. The study is conducted on
a Ulysses silt loam soil with an inherently high K content. The irrigation system was
changed from flood to sprinkler in 2001.
Procedures
This field study is conducted at the Tribune Unit of the Southwest Research-Extension
Center. Fertilizer treatments initiated in 1961 are N rates of 0, 40, 80, 120, 160, and
200 lb/a N without P and K; with 40 lb/a P2O5 and zero K; and with 40 lb/a P2O5
and 40 lb/a K2O. All fertilizers are broadcast by hand in the spring and incorporated
before planting. The soil is a Ulysses silt loam. Sorghum (Pioneer 8500/8505 from
2006–2007, Pioneer 85G46 in 2008–2011, Pioneer 84G62 in 2012-2014, and Pioneer
86G32 in 2015) was planted in late May or early June. Irrigation is used to minimize
water stress. Sprinkler irrigation has been used since 2001. The center two rows of each
plot are machine harvested after physiological maturity. Grain yields are adjusted to
12.5% moisture. Grain samples were collected at harvest, dried, ground, and analyzed
for N, P, and K concentrations. Grain N, P, and K content (lb/bu) and removal (lb/a)
were calculated.
Results
Grain sorghum yields in 2015 were 22% greater than the 10-year average (Table 1).
Nitrogen alone increased yields 66 bu/a while P alone increased yields 13 bu/a. However,
N and P applied together increased yields up to 92 bu/a. Averaged across the past 10
years, N and P applied together increased yields up to 76 bu/a. In 2015, 40 lb/a N (with
P) produced about 88% of maximum yield, which is slightly above the 10-year
average of 84%; 120 lb/a N (with P) and 160 lb/a N (with P) produced 98% and 100% of
maximum yield, respectively. Sorghum yields were not affected by K fertilization, which
has been the case throughout the study period.
The 10-year average grain N concentration (%) increased with N rates but tended to
decrease when P was al (...truncated)