Influence of Residue Management Tillage Systems
with Solid Beef Manure Application on Snow Melt and Annual Runoff, Sediment and Phosphorus Losses

J.F. Moncrief, S.D. Evans, and G.A. Nelson
West Central Experiment Station
University of Minnesota, Morris, MN

D Ginting, S.C. Gupta, and E.C. Dorsey
Department of Soil, Water, and Climate
University of Minnesota, Saint Paul, MN

Introduction

The method of manure storage and application that results in the most efficient nutrient recovery is liquid storage systems with field injection. Injection of course is not an option with solid manure sources. A major challenge in utilization of solid manure sources is deciding on the optimum amount of soil tillage to incorporate manure for enhanced nutrient value but leave enough crop residues for reduction of erosive losses. Of particular importance is P. Algal growth in most of the lakes in the Midwest are limited by P. When lake P levels are raised due urban or agricultural sources of runoff algae increase in numbers. When they die their degradation consumes dissolved oxygen. This is what is responsible for stressed fish and unpleasant odors.

Soil test P levels are high near the soil surface when tillage for incorporation is reduced. This is true for all noninversion tillage systems such as no till, ridge till, chisel plowing, and spring discing or field cultivation approaches. The obvious question is "What is the net effect of increased P levels near the surface (increases the probability of increased P losses) and reduced sediment loss due to the presence of crop residues (decreases the probability of runoff P losses associated with sediment)?". This problem is complicated by the relative proportions of soluble and particulate P present under different tillage systems. Crop residues themselves and manure can be a major source of soluble P. The first leaching rains or snow melt after crop senescence or freezing will carry a large portion of soluble P from the dead plant material in the runoff. A high percentage of this P is available to the algae responsible for eutrophication. In a tillage system that leaves little soil cover most of the P losses are associated with erosive losses of sediments and organic matter. Only a portion of this P becomes available to algae.

This study was conducted to evaluate the impact of tillage system in combination with a one-time application of solid beef manure on annual runoff and sediment loss from 1992 to 1994 at Morris, MN.

The soil was a complex of a Udic Argiboroll and Typic Calciboroll (Foreman-Buse loam) with a uniform 12 % slope and easterly aspect. The initial soil test P (Olsen P) was in the medium range (~10ppm). A one-time application of 330 pounds per acre of P2O5 as solid beef manure (25 tons manure per acre) was applied in the spring of 1992. About 40% and 60% of the manure P was in the dissolved molybdate reactive P (DMRP) and particulate P (PP) form, respectively. In 1992 (establishment year) the manure was incorporated with moldboard plowing and ridge formation. For the remainder of the study the tillage treatments were fall moldboard plowing followed by spring field cultivation (MP) and ridge tillage (RT, two row cultivations) with or without manure. Over the three-year study, the one time application of manure was mixed three times with moldboard plowing to a depth of 8 inches, or with planting and cultivation in the ridge-till plots. Surface runoff and the associated sediment as well as total P (TP), particulate P (PP), and dissolved molybdate reactive P (DMRP) were measured from runoff plots for each runoff event (snow melt and rainfall) and summed on an annual basis. The crop was continuous corn (Zea mays L.).

Runoff plots were defined with corrugated steel borders and were four rows wide and 70 feet long. Tillage and planting were done up and down the slope. Runoff was directed to a series of three plastic 55-gallon barrels with a collector and polyvinyl chloride pipe (PVC). The first barrel collected coarse sediments. The overflow from the first barrel was then channeled to a second barrel with nine openings near the rim of the barrel. One ninth of the excess runoff in the second barrel was then diverted to a third barrel. The runoff suspension in each barrel was thoroughly stirred and sampled for measurement of sediment, TP, and DMRP. The PP was determined by the difference between TP and DMRP.

The 1993 and 1994 runoff and yield data (second and third year of corn since manure application) are shown in table 1. The soil test P in the spring of 1994 (0-6") was increased by the manure application more with the ridge-till system than the moldboard system. This is due to less mixing and fixation in this calcareous soil (formation of insoluble P compounds with Calcium). In 1993 there was no statistically significant increase in yield due to manure with either system. There was a decrease in yield with the ridge-till system compared to the moldboard plowing system in this year however. This decrease in yield was not due to stand loss, weed control, or N availability. In 1994 there was no grain yield benefit to the higher soil test P levels associated with manure addition with moldboard plowing. It does appear that the higher soil test did, however, increase grain yields 21 bushels per acre with the ridge-till system.

The effect of tillage and manure on snow melt losses are shown in table 2. The RT system resulted in about 6 times the runoff of the MP system in 1993. This is due to more snow caught by standing corn stalks and less surface storage with the RT system. In 1994 the snow pack before melting was measured and in this year there was about twice as much water as snow with the RT system. The trend in runoff in 1994 was higher with the RT system although not statistically significant. Manure did not affect runoff. Because of the increased runoff with the RT system there was more sediment lost due to snow melt runoff in both years. There are two things to keep in mind when interpreting these data. The sediment amounts are very low and the runoff plots are up and down the slope. A ridge till system farmed on the contour would undoubtedly result in less runoff.

The rainfall induced runoff data are shown in table 3. Rainfall in 1993 was at an all time record. There was a four inch rain on July 4^th that came in about 2 hours that was responsible for most of the runoff losses. Manure and crop residue both reduced runoff and sediment losses in this erosive year. The MP system had about 15 and 59 times more runoff and sediment loss, respectively than the RT system. Manure reduced runoff and sediment loss with both tillage systems. Without manure applied on average there was about 2 and 3 times more runoff and sediment loss, respectively. Although 1994 was a much less erosive year than 1993, the manure and tillage trends were similar. Recall that the manure was applied in 1992. It's effects were still apparent three years after application. In 1995, a year with very low erosion levels, manure effects were not present (data not shown).

Because of lack of space the snow melt and rainfall P losses are not shown separately. Generally there was more soluble or DMRP loss with snow melt runoff with manure applied especially with the RT system in 1993. Manure effects on DMRP were not evident in 1994. The PP was reduced greatly by manure application in the erosive year of 1993. Since the PP values are much higher than the DMRP this trend is also seen with the TP losses.

The sum of snow melt and rainfall runoff P losses (annual total) are shown in table 4. In 1993 manure reduced PP and TP losses for both tillage systems. Although manure reduced runoff and sediment losses in 1994, there were no statistically significant manure effects on P losses. This is a significant finding since the P soil concentration was much higher with manure applied, but P losses were similar to the much lower P testing soil without manure applied.

Tillage did have an effect on P losses in 1994. Both PP and TP were reduced with the RT system (1/4 and ½ respectively) . However, the soluble or DMRP was increased with the RT system by about a factor of 3. The increased losses of DMRP with RT was due to a combination of leaching of crop residue and the increased soil P near the surface. Laboratory leaching studies associated with this project have shown corn residue to be a major source of DMRP. The increase in shallow soil P with the RT system is due to both phytocycling (deposition of P near the surface due to plant residue release) and shallow manure incorporation (data also not shown).

Application of solid manure greatly reduced runoff and sediment losses with both a RT and MP tillage system. An associated reduction in PP was also present with manure addition with both tillage systems. Since PP was lost at much higher levels compared to DMRP, TP was also reduced due to manure addition. The DMRP losses were higher when crop residues and manure were not incorporated with moldboard plowing, however.

This study should be interpreted with the limitation of small runoff plots oriented "up and down" the slope in mind. The RT system may perform better when farmed on the contour. Research needs to be conducted on a field or small watershed scale to better reflect tillage and manure effects on a landscape basis.

Table 2. The effect of tillage and manure on snow melt runoff and sediment loss, West Central Experiment Station, Morris, MN.

	Winter 1993		Winter 1994
	Runoff (inches)	Sediment (lbs/acre)	Snow (inches of water)	Runoff (inches of water)	Sediment (lbs/acre)
Ridge till
No manure	0.90	72	2.7	0.94	39
Manure	0.39	23	3.4	1.30	42
Average	0.59	40	3.0	1.10	40
Moldboard
No manure	0.10	3.8	1.3	0.40	20
Manure	0.10	6.4	1.7	0.70	33
Average	0.10	4.9	1.5	0.53	25
Average
No manure	0.30	16	2.0	0.61	28
Manure	0.20	12	2.5	0.95	36
P>F values1
Tillage (T)	.003	.023	.044	.309	.090
Manure (M)	.209	.389	.107	.560	.686
T x M	.207	.251	.483	.868	.759
1 If this value is less than ~100, differences in the treatment averages are due to the treatment and not due to unexplained variability.

Table 3. The effect of tillage and manure on rainfall runoff and sediment loss, West Central Experiment Station, Morris, MN.

	------- 1993 -------		-------- 1994 -------
	Runoff inches	Sediment tons/acre	Runoff inches	Sediment tons/acre
Ridge till
no manure	0.26	0.26	0.33	0.05
manure	0.07	0.04	0.30	0.04
average	0.14	0.12	0.31	0.04
Moldboard
no manure	2.39	10.1	1.19	1.12
manure	1.95	5.1	0.86	0.55
average	2.16	7.1	1.01	0.79
Average
no manure	0.78	1.58	0.63	0.23
manure	0.39	0.46	0.50	0.15
P>F values 1
tillage (T)	0.017	0.032	0.007	0.002
manure (M)	0.103	0.037	0.060	0.095
T x M	0.207	0.251	0.294	0.256
1. If this value is less than ~.100, differences in the treatment averages are due to the treatment and not due to unexplained variability.

Table 4. The effect of tillage and manure on annual (snow melt plus rainfall runoff) total P (TP), particulate P (PP), and dissolved molybdate reactive P (DMRP) losses.

	------- 1993 ------- pounds/acre			-------- 1994 ------- pounds/acre
	TP	PP	DMRP	TP	PP	DMRP
Ridge till
no manure	1.95	1.84	0.11	0.28	0.15	0.13
manure	0.47	0.28	0.20	0.41	0.15	0.26
average	0.96	0.81	0.15	0.34	0.15	0.18
Moldboard
no manure	2.28	2.21	0.08	0.76	0.71	0.04
manure	1.46	1.44	0.07	0.56	0.50	0.06
average	1.86	1.78	0.07	0.65	0.60	0.05
Average
no manure	2.11	2.10	0.09	0.46	0.38	0.07
manure	0.84	0.72	0.12	0.48	0.36	0.13
P>F values1
tillage (T)	0.161	0.091	0.160	0.104	0.018	0.064
manure (M)	0.070	0.105	0.196	0.914	0.415	0.344
T x M	0.248	0.343	0.455	0.449	0.449	0.714
1. If this value is less than ~100, differences in the treatment averages are due to the treatment and not due to unexplained variability.

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