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Research Report  4.2

An Investigation into the Management of Manure-Nitrogen
to Safeguard the Quality of Groundwater

Dr. M.J. Goss, and P.S. Smith,
Centre for Land and Water Stewardship,
Univ. of Guelph, Guelph, ONT N1G 2W1
COESA Report No.: LMAP-013/95

Objectives & Expected Outputs
Executive Summary

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Objectives and Expected Outputs
Objectives: To study the fate of nitrogen from liquid dairy cattle and composted cattle manures in two field experiments (at the Elora Research Station, and at the Winchester research Station of Kemptville College), in which cover crops are grown to investigate the cycling of manure nitrogen between soil and crops in the fall, and to identify whether significant nitrogen is transferred from the cover crop to corn planted in the following spring.
Expected Outputs: This study will improve the understanding of nitrogen cycling from animal manures into soils and crops, and show the role of cover crops in nitrogen transformations.
Type: 93-94: $38.8 K
Status: Available January 1996


Executive Summary

In this study the fate of nitrogen from liquid dairy cattle manure and from composted cattle manure was investigated in two field experiments. These were conducted at the Elora Research Station of the Ontario Ministry of Agriculture, Food and Rural Affairs in collaboration with Drs. D.L Burton, E.G. Beauchamp and R.G Kachanoski, and at Winchester Research Station of Kemptville College of Agricultural Technology in collaboration with W.E. Curnoe.

In the first experiment carried out at Elora in 1991-1992, the soil was a Conestogo silt loam (Gleyed Melanic Brunisol). The particle size fraction of the Ap horizon consisted of sand (0.26), silt (0.55), clay (0.18); the organic matter fraction was 0.056, and the pH was 7.0. A sub-program of a larger investigation was established with the objective of evaluating the risk of nitrate leaching from spring-applied manure, and identify how much of the mineral N from the liquid cattle manure (LCM) was incorporated into a corn crop. The contribution to N in the crop due to mineralization of soil organic matter was also investigated. Liquid cattle manure was applied in spring before planting corn on a randomized complete block design with fourfold replication. Corn was also planted in 1992.

In the second experiment carried out at Winchester in 1991-1993, the soil was a Dalhousie clay loam (Humic Gleysol). The particle size fraction of the Ap horizon consisted of sand (0.20), silt (0.52), clay (0.28); the organic matter fraction was 0.037, and pH was 6.3. Both liquid manure from dairy cattle and composted cattle manure were applied to ploughed-down alfalfa forage during late summer. The liquid cattle manure was injected, and the solid manure applied with a conventional spreader. The objective of the program was to evaluate the risk of nitrate leaching over the fall, winter and spring from fall-applied manure, and evaluate whether this could be alleviated by timely agronomic practices without impairing the productivity of the land. The following ten experimental treatments were replicated fourfold in 4 randomized blocks, and test crops planted:

  1. Alfalfa ploughed in; grass (Timothy); no manure; corn (Control)

  2. Alfalfa ploughed in; grass (Timothy); 172 x 103 L ha-1 liquid cattle manure; corn (manure control - LCM)

  3. Alfalfa ploughed in; 54 t ha-1 composted cattle manure; corn (CCM)

  4. Alfalfa ploughed in; liquid manure; barley ; wheat (LCM + barley)

  5. Alfalfa ploughed in; liquid manure; oilseed radish cover crop; corn (LCM + OSR)

  6. Alfalfa ploughed in; liquid manure; 3.8 t ha-1 straw (dry weight) incorporated; corn (LCM+straw)

  7. Alfalfa ploughed in; liquid manure, straw; oilseed radish cover crop; corn (LCM + straw +OSR)

  8. Alfalfa ploughed in; liquid manure; winter wheat, corn (LCM + winter wheat)

  9. Alfalfa ploughed in; winter wheat, corn (Control + winter wheat)

  10. Alfalfa ploughed in; barley; wheat. (Control + barley)

Winter wheat was sown in the fall of 1992 on the plots where spring barley had been grown. In the spring of 1993 all plots not growing winter wheat were planted with corn.

The soil, soil water, and plant material was sampled to assess the availability of the nitrogen to crops, determine the presence of mineral nitrogen, including nitrate, in the soil, and determine the magnitude of the fluxes of nitrogen. 15N was used to trace the fate of the nitrogen present in the mineral fraction of the manures at both experimental sites. Tracer was also applied directly to the soil to identify the fate of mineral nitrogen produced by mineralization of soil organic matter prior to the application of manure, and to help identify potential sources of the nitrogen mineralized after manure application.

From 15N tracing, it was shown that the loss of mineral nitrogen from manure was greater during surface spreading and mechanical incorporation in spring than after early fall application to recently cultivated land followed immediately by hand-digging.

At Winchester, the soil at the time of manure application contained about 80 kg ha-1 mineral nitrogen. Only 16 kg ha-1 of mineral nitrogen was present in the 320 kg N ha-1 from the composted cattle manure, but of the 301 kg N ha-1 applied in the liquid manure 216 kg N ha-1 was mineral nitrogen. The volumetric water content of the top 100 mm of soil was approximately 0.15 at the time the manure was applied at the end of August. This was ideal for injection, but severely impaired the establishment of the grass. Growth of the winter wheat, oilseed radish was good in the fall of 1991. There was considerable growth of volunteer oats from seeds present in the incorporated straw, and wild mustard weeds grew on plots where liquid cattle manure was applied but no crop was planted in the fall. The uptake of mineral nitrogen (y, kg N ha-1) by all crops in the fall was directly related to the dry matter produced (x, t ha-1) according to the equation: y = 43x - 10.2 (p <0.001). However, less than 10% of mineral-N applied in the liquid cattle manure was taken up by the sown cover crop. By the end of November much of the mineral nitrogen applied in the manure could be accounted for in the soil and plants. In un-manured plots there was 55 kg NO3 - N ha-1, 78 kg NO3-N ha-1 in plots that received composted manure, and 134 kg NO3-N ha-1 in plots given liquid manure. All this nitrogen was at risk of leaching. However, from analysis of the 15N present in the soil it appeared that only about 60 kg N ha-1 had been derived from the mineral fraction of the liquid cattle manure, at least 50% of that fraction had already transferred into the organic pool of the soil. Re-mineralization of a small part of this fraction appeared to take place in early spring. But much of the 15N was still retained in the soil organic matter after two years. Only small amounts became available even in the second year.

The winter was cold and the snow cover was ended by heavy rain on 14 January, after which the temperature dropped sharply and killed the winter wheat crop.

There was little through drainage in the early spring of 1992, and all plots contained at least as much mineral nitrogen at planting in May than in November. Nonetheless, loss of 15N over this period was consistent with about 50 kg N ha-1 of the nitrogen present in the mineral fraction of the liquid cattle manure being lost from the soil over winter. The loss was about 25%; less where cover crops were grown and straw had been incorporated. Two further periods of leaching were identified in late spring and early summer. The maximum concentration of nitrate-N recorded in the water draining from the rooting zone for all treatments exceeded the Ontario Drinking Water Objective of 10 mg L-1 during one or both periods.

Growth of the corn crop on the microplots at Elora was good in both years, and there was no significant benefit to yield from application of manure compared with control plots in either season. Previously corn had been grown continuously on the site, so the lack of any effect on yield due to manure application in the first season was probably due to residual nitrogen from the management of those crops. The crops at Winchester grown on land injected with liquid manure produced significantly greater grain yields than the Control treatment when harvested by hand, except where straw had been incorporated or oilseed radish planted, but this was not converted into significantly more combinable yield. The yield of barley was influenced by the lodging that took place preferentially on the manured plots. Although earlier in the season nitrogen uptake by barley was greater on manured plots than on plots that received no manure, there was no significant difference at harvest. In the first cropping year the uptake by corn of nitrogen derived from the mineral-N in manure was greater from a spring application (39 kg N ha-1) than from a fall application (31 kg N ha-1). Uptake in the second season was about 5% of the mineral nitrogen in the manure at application in both cases. Only 16% of the nitrogen in the cover crop was transferred to the following corn crop. Evidence from crop sampling indicated that much of the nitrogen from the cover crop did not become available until after 20 August. This was also true for nitrogen from the organic fraction of the manure. There was no clear evidence that nitrogen was released from the organic fraction of the liquid cattle manure to the crop planted after the spring application. There was evidence that some of the organic nitrogen in manure became mineralized in the late summer, twelve months after application, when it was at risk to leaching over winter.

Nitrogen released by the ploughing of the soil under alfalfa-hay at Winchester provided sufficient nitrogen for the corn crop. The total nitrogen in the control treatment at harvest was 150 kg N ha-1. The crop on land injected with liquid manure contained 225 kg N ha-1, but this was not converted into significantly more combinable yield. About half of the additional nitrogen was present in the grain, but the remainder was in the harvest residues that contribute to the organic matter pool of the soil and therefore could be remineralized in the future. The results indicated that a value of 110 kg N ha-1, currently used in Ontario, was an appropriate credit for the underground residues of the alfalfa hay.

The Ontario soil nitrogen test suggested that the un-manured plots would require some fertilizer nitrogen to obtain the maximum economic yield, but all manured plots contained sufficient nitrogen. Since yields of corn were unaffected by the treatments imposed despite the indications of the soil nitrogen test, it is clear that adjustments are needed when making fertilizer recommendations based on the test to ensure that the nitrogen from crop residues (straw or cover crop) is included. The soil N test, which only takes account of nitrate-N, clearly underestimated the amount of mineral nitrogen available in the soil on all treatments.

Total loss over two cropping years, estimated as 15N not present in soil or crop, were 35% for the spring application and 40% for the fall application. The potential for leaching loss to occur in the period following the fall application was considerable. The application of manure in the early fall resulted in a large amount of mineral nitrogen in the soil, much of it in the nitrate form. In that experiment, the prevailing weather conditions were not conducive to leaching, but incorporating composted cattle manure at the same time of year did not have a significant impact on the soil pool of mineral nitrogen.

The study strongly indicated that applying liquid manure in the fall was potentially hazardous to water resources. The risk from leaching was high in the fall immediately after application, in the following spring, and in the next fall period, especially if cereals were grown in the spring. None of the fall treatments designed to immobilize nitrogen were adequate to reduce the risk significantly.

Combining straw incorporation and growing a cover crop that would be removed for forage in late fall appeared to offer the best solution to minimize loss of nitrogen from manure applied in early fall. However, in a wet fall the impact of this treatment might not be as great as the results for a relatively dry fall. Furthermore, smaller yields may also result.



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