On-Farm Tests Show Manure Impacts on Corn Yields

Over-application of manure did not improve yield and can harm soil and water quality.

Field studies were established in Weld County in 1997 to evaluate beef feedlot manure impacts in irrigated cropping systems. One field had a clay soil (Nunn series) with no manure applications in the last eight years (except for one application in the fall of 1995). The other field had a sandy loam soil (Vona series) with a long history (>50 years) of beef manure applications. In 1998, the sandy site was relocated to another sandy field (Valent loamy sand) with a long history of turkey and beef manure applications. All three fields were irrigated through center-pivot systems. Each field was laid out with four replications, four manure treatments (0, 10, 20, and 30 tons manure per acre), and two sidedress nitrogen treatments (0 and 50 lbs/acre) in split-plot designs, with manure treatments as the main treatments and sidedress nitrogen as the split plots.

Pre-season soil sampling showed that no additional nitrogen fertilizer was required for the Nunn clay and about 90 lbs of nitrogen per acre were required for the Vona soil. The Valent soil required nearly 180 lbs nitrogen per acre based on soil testing. In the second year, the Nunn clay soil showed trends of increasing soil NO3-N, P, K, and salts with increasing manure application rates. Therefore, the plots receiving the higher manure rates required less nitrogen fertilizer.

Analyses of Beef Feedlot Manure Used on Field Plots

Field	D.M.	pH	Soluble Salts	Total N	P2O5	K2O
	%		mmhos/cm	--------lbs/ton-------
Nunn Clay (1997)	78.9	7.9	37.1	16	27	36
Vona sandy loam (1997)	45.0	8.6	43.7	20	11	23
Nunn Clay (1998)	62.2	8.6	33.5	24	36	26
Valent loamy sand (1998)	50.8	8.6	41.0	15	14	25

Manure came from on-farm or nearby beef cattle feedlots. The manure used in the experiments was sampled during application and analyzed by the CSU Soil, Water, and Plant Testing Lab. The manures differed in dry matter content (D.M.) and nutrient content due to their different ages and management practices.

The manure treatments were applied in the early spring, one month before planting. Manure for each plot was weighed, carried to the plot by hand or with a dumptruck, and spread with rakes. The manure was incorporated immediately after application, either by disking or by rototiller.

Harvest
In 1997, both fields were damaged by hail, and yields were higher at the sandy site with a long-term manure history than on the clayey site with limited manure history. There were no effects from sidedress nitrogen applications at either field, nor any effect from manure treatments on yield at the sandy site. There was a significant impact of manure rates on corn yield at the clayey site, however. The higher manure application rates improved stand in the clayey soil, and, subsequently, increased yield. In 1998, neither field was hailed, and yields at the two fields were similar. There were no effects from sidedress nitrogen applications at either field, nor any effect from manure treatments on either soil.

Corn Yields (Bushels/acre) as Influenced by Manure Application Rate

Manure Rate (tons/acre)	Sandy Site: 1997	Sandy Site: 1998	Clayey site: 1997	Clayey site: 1998
0	177 A*	156 A	116 B	149 A
10	168 A	152 A	124 AB	149 A
20	164 A	142 A	129 A	148 A
30	169 A	146 A	136 A	146 A

*Manure rates with a common letter are not sifnificantly different according to Tukey's test for mean separation at p<0.05.

Three of the four sites evaluated had no significant yield differences due to manure application rates. This is probably due to the long-term manure application histories on the sandy sites and the long-term fertilization of the clayey site. Over-application of manure (30 ton/acre rate) did not improve yield at any location and can harm soil and water quality. Many other measurements were made on these on-farm tests. Those results are reported in subsequent articles.

by Kirk Iversen and Jessica Davis
Former Research Associate and Extension Soil Specialist
Soil and Crop Sciences