Response of Sunflower to Nitrogen Fertilizer*
B. Schatz, B. Miller, S. Zwinger, and B. Henson

* Adapted from "Sunflower response to nitrogen fertilizer." Proceedings of the 21st Sunflower Research Workshop, Fargo, ND, 14-15 January 1999. p. 193-97.

In an environment of high production costs and low grain prices, efficient use of inputs is essential for maintaining economic viability of farming operations. Application of excessive amounts of nitrogen (N) fertilizer may reduce profitability and create groundwater pollution hazards. On the other hand, yield responses to N frequently make this technology cost effective, but determination of the optimum level of fertilizer is necessary to maximize profit.

Current North Dakota fertility recommendations for sunflower suggest 5 pounds N/cwt. yield goal (Dahnke, 1994). Thus, a 2,000 pound yield goal would require 100 pounds of total N (soil test nitrate-N + credit for a previous legume crop + applied fertilizer). However, experiment station trials sometimes show no yield benefit from N fertilization of sunflower and usage under production conditions varies greatly. The objectives of this study were to determine the effects of N fertilizer on sunflower yield and soil nitrate-N levels and the influence of tillage practices on these effects.

Sunflower data were analyzed from the Spring Wheat Sunflower Barley Fallow rotation in a long-term cropping systems experiment, which was initiated in 1987. Fertilizer N levels (see below) and tillage practices (conventional, reduced, no-till) were arranged in perpendicular strips. Sunflowers were planted in 30" rows and managed to maximize yield by optimizing P fertility and pest control. Fall soil samples from two replicates were analyzed for nitrate-N concentration. Yield was measured on all three replicates.

Fertility Treatments (lbs N/acre)

Low

Medium

High

1987-1990

30

60

90

1991-1997

0

40

80

Soil Nitrate-N Level (0-24")

Averaged across years, a nearly linear increase in fall soil nitrate-N concentration was observed with increases in the level of spring N fertilizer (Table 1). Over the nine years covered by data, N fertilization not only increased yield (see below), but improved the N-status of soil for the next crop in the rotation.

Tillage practice had essentially no effect on fall soil nitrate-N level within a given year (data not shown). Averaged across years, significantly lower nitrate concentration in the no-till plots was likely due to uptake by weeds, which were more prevalent in this system. Higher water accumulation in these high-residue plots may have contributed to increased N losses by leaching.

Comparing the average fall nitrate-N values for years 88-90 (relatively low rainfall) with those for 93-95 (relatively high rainfall) points out the susceptibility of soil N to leaching and denitrification. The range of 4.3 to 47.3 pounds/acre stresses the importance of annual soil sampling to quantify the N-status of fields.

Yield

In most years, sunflower yield increased slightly with increases in N fertilization, but differences were not statistically significant (Table 2). However, the average across years shows an incremental increase in yield with applied N and the differences among treatments are highly significant.

In some years, significant yield reductions were observed in the no-till treatment (Table 3). These differences are attributed to inferior weed control in these plots, which will become less of a limiting factor as more post-emergence herbicides are labeled for use in sunflower. Yields under minimum tillage and conventional tillage were statistically similar in all nine years, which indicates the possibility of reducing tillage costs without affecting yield.

Dahnke, W.C. 1994. Fertilizer recommendations. p. 11-12. In D.R. Berglund (ed.) Sunflower Production. Extension Bulletin 25 (revised), North Dakota State University, Fargo. 98 p.

Table 1. Effect of N Fertilization on Soil Nitrate-N Levels (ppm, 0-24") in Sunflower,
NDSU Carrington Research Extension Center, 1988-1997.

N Fertilizer Applied

Year Low Medium High Average LSD (0.05) LSD (0.01)
1988 24.2 34.8 88.8 47.3 29.7 43.2
1989 22.9 43.2 53 39.7 NS1 NS
1990 5.9 30.5 22.3 18.9 10.2 14.9
1992 3.2 4 12 6.4 3.3 4.8
1993 3.2 4.1 5.4 4.3 NS NS
1994 2.7 3.6 8.9 5 4.1
1995 3.1 3.1 8.1 4.8 2.1
1996 3.8 7.1 25.5 12.1 8.5
1997 3.1 8.5 26.8 12.8 10.9 15.9
X 8 15.1 27.9 17 4.4
1NS = non-significant difference
Table 2. Effect of N Fertilization on Yield (lbs/acre) of Sunflower,

NDSU Carrington Research Extension Center, 1988-1997.

N Fertilizer Applied
Year  Low Medium High Average LSD (0.05) LSD (0.01)
1988 1098 1328 1430 1285 NS1 NS
1989 1250 1277 1154 1227 NS NS
1990 1615 1753 1603 1657 NS NS
1991 1548 1594 1632 1691 NS NS
1992 777 785 897 820 NS NS
1993 650 708 858 739 NS NS
1995 1061 1110 1598 1257 206 284
1996 1537 1879 2099 1838 320 441
1997 696 745 868 770 NS NS
   X 1137 1242 1349 1243 103 137
1NS = non-significant difference
Table 3. Effect of Tillage Practices on Yield (lbs/acre) of Sunflower,
NDSU Carrington Research Extension Center, 1988-1997.
Tillage
Year No Till Minimum Conventional LSD (0.05) LSD (0.01)
1988 986 1430 1440    NS1  NS
1989 1076 1254 1352    NS  NS
1990 1803 1670 1498    NS  NS
1991 1470 1732 1572    NS  NS
1992 202 1070 1187 195 268
1993 463 794 960 272 375
1995 619 1655 1496 206 284
1996 1918 1682 1915    NS  NS
1997 287 1051 971 235 324
   X 980 1371 1377 103 137
1NS = non-significant difference


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