PEAQ PREDICTION OF ALFALFA QUALITY

PEAQ PREDICTION OF ALFALFA QUALITY David B. Fischer TAKE HOME MESSAGES Select 1 st cut harvest date by quality vs. calendar Accurate methods are available to determine quality of standing alfalfa RFV calculated from scissor clip NIR and PEAQ are very comparable Prioritize 1 st cut alfalfa harvest over other field work Alfalfa is an important component of dairy rations and can be a profitable cash crop. High quality alfalfa can reduce feed costs and increase profitability. The key management strategy in producing high quality alfalfa forage is knowing when to select the optimum harvest date for the first cutting. Second and successive cuttings should then be harvested every 28 to 30 days thereafter. A common approach to determining the optimum harvest date for quality and quantity is by observing the growth stage of the plants. There is a direct correlation between the morphological development of the plant and the quality and quantity of alfalfa harvested. It is well documented that alfalfa nutrient quality decreases as the plant matures from the vegetative stage to full flower. At the same time, the pounds of plant material harvested per acre increases as the plant matures. The optimum harvest date is a compromise between the feed quality and the tonnage produced. Producers need to monitor the first cut alfalfa growth in order to determine the optimum harvest date. To assist alfalfa producers in monitoring plant growth and quality, University of Illinois Extension specialists conducted an Illinois scissor clip project on eighteen fields in eight regions throughout the state during spring 1998. This project is supported by a Partnership Illinois grant. SCISSOR CLIP VS. PEAQ Alfalfa fields were monitored based on the alfalfa scissor clipping procedure developed by the University of Wisconsin and the Wisconsin Forage Council. Samples were collected twice weekly from 2 or 3 fields per region. Sampling began at the late vegetative stage and continued to harvest. Alfalfa clippings were taken from the same area of the field, approximately the same time of the day and clipped at 2 inches above soil line. All clip samples were sent to Agri-King, Inc. Laboratory in Fulton, Illinois and analyzed by the near infrared reflectance spectroscopy (NIR) method. The analysis included the relative feed value (RFV) which is computed from the acid detergent fiber (ADF) and neutral detergent fiber (NDF) results using the following formula: RFV = [88.9 - (0.779 x % ADF)] x (120 % NDF) 1.29

A second method for monitoring the alfalfa quality was used in the study with the predictive equations for alfalfa quality (PEAQ). PEAQ is an in-field prediction of fiber composition based on plant height and maturity. Plant height measurements, soil to stem tip, were taken and averaged from the tallest plants in a 2 sq. ft. area. The maturity ratings were taken from a modified version of the Kalu-Fick morphological stages of legume development scale (Table 1). PEAQ values for ADF and NDF were computed using the following formula: ADF = 10.78 + (0.53 x height) + (0.79 x maturity value) NDF = 15.86 + (0.69 x height) + (0.81 x maturity value) The RFV based on the PEAQ fiber values were calculated as a comparison to the lab tested relative feed values. The relative feed value (RFV) is a measure of the fiber fractions which dictate the digestibility and feed intake potential. The higher RFV, the higher quality feed value is obtained from the alfalfa. Relative feed value is a way to compare two or more similar forages for energy intake. Dairy producers with high producing cows often look for alfalfa with a RFV of 140 to 160 and higher. The crude protein content is not taken into account in the RFV calculation and needs to be evaluated separately. A common goal for dairy producers is to raise or buy alfalfa that has 20% or higher CP, 30% or lower ADF, and 40% or lower NDF which will equate to a RFV of near 150. In order to achieve a 150 RFV to the cow, it is recommended to harvest the first cutting when the RFV reaches 170 in the field. The optimum harvest date for first cutting alfalfa in 1998, based on a RFV of 170, for Southern Illinois (Clinton County) was approximately May 4 and for Northern Illinois (Stephenson County) approximately May 18. Using the RFV as a first cutting harvest guide is preferable to the cutting by the calendar method often used by producers. From previous years data the optimum harvest date can vary about three weeks from year to year, depending on the growing season as shown in Table 2. Based on the averaged data from two fields in Clinton County, the RFV declined 3 to 4 points per day during the sampling period (Table 3). This decline is consistent with the sampling from the other Illinois regions. However, growing conditions can effect the decline of quality and the RFV loss per day can range from 3 to 7 points as reported in various studies. The data in Table 3 represents the changes in alfalfa forage quality comparing PEAQ to NIR values. This data shows a close correlation between PEAQ and NIR values. Alfalfa quality evaluations were also conducted on the harvested hay or silage to determine the amount of nutrient loss from field clip to harvest. The average decline in RFV for the two fields harvested in Clinton County was 18.4 points as shown in Table 4. This data supports the concept to harvest alfalfa when the scissor clip data is near the RFV of 170 in order to achieve a harvested crop value of 150 RFV.

CONCLUSIONS The Illinois alfalfa scissor clip project provided information and awareness to producers to enhance their ability to produce higher quality forages through timely harvest. Improved forage quality will allow dairy producers to reduce feed costs and improve profitability. These producers will have less dependence on importation of alfalfa from other states to meet animal production requirements. Monitoring the RFV for alfalfa quality in the field via scissor clip or PEAQ can be an excellent management tool as demonstrated by this Partnership Illinois project. Efforts to build on the confidence of using the PEAQ method and the ease of checking RFV in the field will be continued through further studies. Table 5 is shown as a quick reference chart to determine RFV with the PEAQ method. First cutting alfalfa needs to be harvested near 170 RFV in order to get adequate quality and to set-up the cutting schedule for the rest of the growing season. Subsequent cuttings should be taken every 28 to 30 days. The first cutting must be taken in the bud stage since quality reduces rapidly as the plant matures. It may be difficult to make top quality first cutting alfalfa due to weather factors, coarse plant material, and possible weed and insect infestations. However, by prioritizing hay harvesting over all other cropping chores, many dairy and hay producers are able to make satisfactory first crop alfalfa. TABLE 1. Alfalfa Growth Stages for Determining Maturity Value Maturity Value Name Description 0 early vegetative stem length < 6 inches 1 mid vegetative stem length 6 to 12 inches 2 late vegetative stem length > 12 inches 3 early bud one or two nodes with visible buds 4 late bud three or more nodes with visible buds 5 early flower one node with at least one open flower 6 late flower two or more nodes with an open flower TABLE 2. Optimum Harvest Date for 1st cutting Alfalfa in Southern Illinois - 1994 to 1998 Year Date RFV 1994 May 6 168 1995 April 21 172 1996 May 2 172 1997 May 13 171 1998 May 4 174

TABLE 3. 1998 Alfalfa Quality Results - Clinton County, Illinois NIR PEAQ Date % CP % ADF % NDF RFV RFV 4-16 31.9 23.5 32.8 232.3 246.4 4-20 30.4 20.6 29.6 229.6 233.1 4-23 30.7 23.2 32.3 204.6 214.3 4-27 29.3 24.0 33.8 193.7 193.5 4-30 28.7 25.0 34.7 186.6 181.4 5-4 26.5 27.0 36.2 174.5 169.2 5-7 26.1 29.4 39.4 156.2 158.2 5-11 25.8 29.3 39.1 157.0 143.3 TABLE 4. Average Nutrient Comparison (Dry Matter Basis) of Scissor Clip and Harvested Samples Tested by NIR - Clinton County, Illinois Date Description CP % ADF % NDF % RFV 5-11-98 standing in field 25.8 29.3 39.1 157.0 5-12-98 harvested 22.0 32.9 42.5 138.6 Partially supported by a Partnership Illinois Grants Program

TABLE 5. Monitoring Illinois Alfalfa Quality Using Predictive Equations for Alfalfa Quality (PEAQ) Height of tallest stem (soil surface to stem tip) Late vegetative > 12" tall, no bud visible Early bud 1-2 nodes, visible buds Late bud > 2 nodes, visible buds Early flower 1 node, visible flowers Late flower 2 nodes, open flowers Inches Relative Feed Values 16 237 229 220 213 206 17 230 222 214 207 200 18 224 216 208 201 195 19 217 210 203 196 190 20 211 204 197 191 185 21 205 199 192 186 180 22 200 193 187 181 175 23 195 188 182 177 171 24 190 184 178 172 167 25 185 179 173 168 163 26 180 174 169 164 159 27 175 170 165 160 155 28 171 166 161 156 152 29 167 162 157 153 148 30 163 158 153 149 145 31 159 154 150 146 141 32 155 151 146 142 138 33 152 147 143 139 135 34 148 144 140 136 132 35 145 141 137 133 129 36 142 138 134 130 126 37 138 135 131 127 124 38 135 132 128 124 121 39 132 129 125 122 119 40 129 126 123 119 116 41 127 123 120 117 114 42 124 121 117 114 111 43 121 118 115 112 109 44 119 116 113 110 107 45 116 113 110 107 105