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<p> </p> <p>The dairy operation used in this evaluation was located in western Washington and lactating dairy cattle diets were based on grass silage. The forage was intensively managed for six or seven cuttings per year. The Holstein herd milk production average at the initiation of the evaluation was approximately 13000 kg yr<sup>–1</sup>, a high level of milk production for Holstein dairy cows. The dairy producer's management practices were to harvest "old-seeding" grass for silage (grass that was not planted in the current harvest year) approximately every 28 d and to harvest "new-seeding" grass for silage (grass that was planted in the current harvest year) every 21 d. Within 10 d after each cutting, liquid manure was applied to the grass fields with a self-retrieving irrigation system at an application rate of approximately 126945 L ha<sup>–1</sup>. No manure was applied before first cutting. </p> <p><strong>Manure Application Evaluation</strong><br>The producer wanted to increase the CP content of the old-seeding grass. Therefore, in 2001, a study was designed to evaluate the potential to increase CP content in grass silage by applying manure in excess of previous practices (previous practice was to apply manure at approximately 126945 L ha<sup>–1</sup> after each cutting). </p> <p>Perennial ryegrass (<em>Lolium perenne</em> L.) and orchardgrass (<em>Dactylis glomerata</em> L.) were planted at 39.2 and 2.24 kg ha<sup>–1</sup>, respectively, in the spring of 2000 in a 15.8-ha field at the dairy. Data collection for this demonstration project began in 2001, and the grass forage was harvested for silage seven times throughout the growing season starting on 25 Apr. and concluding on 3 Oct. 2001. The 15.8-ha field was divided into three sections, and three different manure application schedules were established. The treatments were not replicated. The treatments were: (i) control; (ii) 2x rate, three times; and (iii) 2x rate, four times. All treatments received a 1x manure application after all seven cuttings in 2001 at 126945 L ha<sup>–1</sup>. The 2x rate, three times treatment received an additional application of manure after Cuttings 4, 5, and 6, and the 2x rate, four times treatment received an additional application of manure after Cuttings 3, 4, 5, and 6. The additional application of 2x rate, three times resulted in an additional 128.7 kg ha<sup>–1</sup> of manure ammonia N applied over the growing season. The additional application of 2x rate, four times resulted in an additional 205.3 kg ha<sup>–1</sup> of manure ammonia N applied over the growing season. Manure from the storage lagoon on the dairy was applied using a self-retrieving irrigation system. Water was added to the lagoon periodically throughout the growing season to provide enough liquid for irrigating the crops. </p> <p><strong>Quality and Quantity of Old Seeding versus New Seeding Grass Silage</strong><br>Another evaluation was conducted in tandem with the manure application evaluation in 2001. A significant portion of the dairy producer's grass acreage was reseeded annually because the quality and quantity of the grass stands diminish rapidly after the second year. Therefore, two distinctly different grass forages (old and new seeding) were harvested throughout the growing season. Quality and quantity differences between new- and old-seeding grass stands were measured. The intent was to determine if alternative management strategies should be adopted. </p> <p>Five fields were included in the old- versus new-seeding evaluation in 2001. Fields 1a, 2, and 3 were old seeding, and Fields 4 and 5 were new seeding. Field 1a data were included in both the manure application evaluation and old- versus new-seeding evaluation. Field 2 was a 15.8-ha field planted in 1999. Field 3 was a 17.8-ha field planted in 2000. Fields 4 (28.8 ha) and 5 (25.9 ha) were planted in the spring of 2001. </p> <p><strong>Old Seeding versus New Seeding Evaluation in 2002</strong><br>Data collection was continued into 2002 to evaluate trends in N management over time. Of particular interest was the effect of tilling old-seeding grass and replanting on soil nitrate concentrations and new-seeding grass nitrate concentrations over the 2002 growing season. </p> <p>A second year of data (similar to that collected in 2001) was collected in 2002 on Fields 1a, 1b, 1c, 2, 4, and 5. An additional field (Field 6) was planted into grass in 2002. The seeding rate for the fields that were reseeded in 2002 (Fields 2 and 6) was 1.12 kg ha<sup>–1</sup> ‘Penlate’ orchardgrass and 42.8 kg ha<sup>–1</sup> ‘Citadel’ ryegrass. </p> <p><strong>Nutrient Content in Grass Silage and Lactating Dairy Cow Rations</strong><br>Nutrient analyses of grass from (i) one of the old-seeding grass fields after it had been ensiled, (ii) one of the new-seeding grass fields after it had been ensiled, and (iii) a malfermented silage were sent to a commercial laboratory and analyzed for nutrient content. The nutrient analysis was entered into the Cornell–Penn–Minor (CPM) version of the Cornell Net Carbohydrate Protein System ration evaluator (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB7">Fox et al., 1990</a>). Differences in grass silage nutrient profile effects on lactating dairy cattle ration formulation were evaluated. Performance parameters such as predicted milk production, predicted microbial efficiency in the rumen of dairy cows, and predicted milk urea N were also monitored using CPM. The evaluation demonstrated how common differences observed in grass silage quality on a dairy farm in a given year could affect lactating dairy cattle nutrition and performance characteristics. The malfermented silage was included in the evaluation because it is a situation that occurs occasionally in real-world situations. It is not uncommon for producers to incorporate malfermented silage into lactating dairy cattle rations at a reduced feeding rate. The theory is that it is better to feed the silage instead of disposing of the silage. Feeding the silage can have negative implications to the lactating dairy cow. </p> <p>Three samples of grass (old seeding, new seeding, and malfermented) were obtained after fermentation in the silo for >60 d. These samples were used to evaluate differences in ration formulation and predicted performance characteristics observed in feeding lactating dairy cattle grass silage of differing nutrient content grown and harvested on the dairy during the same growing season. The grass silage samples were dried and ground to pass a 1-mm screen using a Wiley mill (Arthur H. Thomas, Philadelphia, PA). Tissue was analyzed for dry matter (adapted from <a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB9">Goering and VanSoest, 1970</a>), ash (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB1">AOAC International, 1990</a>), CP (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB2">AOAC International, 2000</a>), ammonia N (Kjeltec Auto 1030 Analyzer; Tecator Foss, Eden Prairie, MN), nitrate (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB1">AOAC International, 1990</a>), soluble crude protein (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB14">Krishnamoorthy et al., 1982</a>), neutral detergent fiber (NDF) (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB16">Mertens 2002</a>), acid detergent fiber (ADF) (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB1">AOAC International, 1990</a>), lignin (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB9">Goering and Van Soest, 1970</a>), volatile fatty acids (Shimadzu [Kyoto, Japan] GC-14A gas chromatograph and Supelco [Bellefonte, PA] column packed with Carbowax 20M8), and lactate (Model 2700 Select biochemistry analyzer; YSI, Yellow Springs, Ohio). Wet samples of grass silage were also analyzed for pH (DL 12 titrator; Mettler-Toledo, Columbus, OH). </p> <p><strong>Data Collection and Analysis</strong><br>The same procedure was used to measure grass yield and N content, soil N, and manure application in all evaluations. One to eight days before harvest of each cutting, grass yield was estimated on each of the three plots by randomly clipping four 0.608- by 0.608-m squares of forage. The forage from each square was dried and weighed to estimate dry-matter yield. Yield estimate samples were composited by treatment for each cutting and N (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB1">AOAC International, 1990</a>) and nitrate (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB1">AOAC International, 1990</a>) were measured on the composited sample. Soil samples were taken for each treatment 1 to 8 d before harvest of each cutting and analyzed for soil nitrate [<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB8">Gavlak et al. (2003)</a> for soil nitrate nitrogen determination method and <a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB12">Keeny and Nelson (1982)</a> for extract method]. Field manure application rates were calculated by measuring the volume of manure present in three 18.9-L buckets randomly placed under a self-retrieving irrigation system. Collected manure was analyzed for total and ammonia N via the Kjeldahl procedure (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB1">AOAC International, 1990</a>). </p> <p>Nitrogen available for crop uptake was calculated by summing commercial fertilizer N, 50% of the manure ammonia N [see Table 11-6 in USDA Soil Conservation Service (1992)], and estimated soil N available. A portion of the manure ammonia N will volatilize before it reaches the crop. Volatilization losses were not measured in this evaluation, therefore an estimate from Table 11-6 in USDA Soil Conservation Service (1992) was used. Fields in this study had received manure for many years, therefore it was assumed that there was a buildup of organic matter in the soil. The amount of available soil N was estimated at 22.4 kg N ha<sup>–1</sup> yr<sup>–1</sup> for each 1% organic matter in the soil, and was based on grass N uptake studies conducted in western Washington (<a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB5">Cogger et al., 2001</a>; <a href="http://www.biology-online.org/articles/references-manure_management_effects_on_grass_production_nutritive_content_and_soil_nitrogen_for_a_grass_silagebased_dairy_farm.htm#BIB18">Sullivan et al., 2000</a>). </p>
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