By S. Ray Smith Extension Forage Specialist, University of Kentucky - Have you ever given advice and then not taken that advice yourself. I’m sure my kids could tell you a few stories about that. At almost every forage meeting I speak at I emphasize the importance of soil testing hay and pasture fields. I say something like: “if you do not take a soil test, then how do you know if you are over-fertilizing or under-fertilizing.” If you over-fertilize, then you are spending money that could be used for other things. If you under-fertilize, you are giving up forage production and usually growing weeds, like bromestraw.

Since I don’t have a farm, my grass production is in my backyard. Every other year or so I apply a bag (35 lbs) of 10-10-10 to the 5000 sq feet of grass in the backyard whether it needs it or not. That’s about 35 lbs/acre each of Nitrogen, Phosphorus and Potassium (N,P,K). I also apply a few bags of pelleted lime. Then every fall (usually October) I apply the equivalent of 40 lbs/acre N in the form of urea. The fall N application doesn’t grow more grass, but it helps the existing bluegrass and fescue produce new shoots for next year and strengthen root systems going into the winter.

I have decided to follow my own advice. Until this past year I just never got around to soil testing, or one time I took a sample and put it aside and it never got to the lab. So in early September I took soil cores to 4” deep from several places in my yard, mixed them together, and dropped them by the Jessamine County extension office. Then about a week later, I got anxious and since I was sure that my pH and fertility was low, I was on my way to the local Ag Store to buy 8 bags of pelleted lime at $4 per bag (about 1 ton per acre). And while I was at it I was going to buy a couple of bags of 10-10-10 at $12 per bag. Just before heading out though I checked the mailbox, and there was my soil test report. To my surprise the P and K levels were in the very high range (675 lbs P and 499 lbs K/acre) and the pH was fine at 6.5. Not only did I not need to buy any lime, but the P and K levels were high enough that I probably do not need any fertilizer (except N) for 10 years or more. Apparently the previous owner of our property must have added a fair bit of fertilizer over the years. So my soil test saved $56 dollars in lime and fertilizer just this year alone. If you over applied the same rate of commercial lime and fertilizer I was about to on your pasture or hayfield you would have saved almost $100 per acre.

I hope your soil test report shows you do not need much fertilizer, but you may like the KY farmer who got back the soil test report on his grass hay field this spring. It showed P in the low range (12 lbs/A), K in the very low range (90 lbs/acre), and pH of 6.0. This farmer definitely needed to add P and K and lime according to the soil test recommendations and then add N in the spring to enhance grass growth. Or he could frost seed red and ladino clover to obtain free nitrogen from nitrogen fixation. An additional rule of thumb for hay production is to apply fertilizer based on how much is removed from the field. On page 4 of UK’s AGR-1 publication “2014-2015 Lime and Nutrient Recommendations” crop nutrient removal values are listed. For example, a 5 ton crop of alfalfa removes 250 lbs/acre of N, 70 lbs/acre of P and 275 lbs/acre of K. Fortunately, the nitrogen removed in alfalfa hay is replaced for free by nitrogen fixation.

Nutrients Removed per ton of hay
P205 K20
Forage Croplbs removed per ton
Alfalfa hay50 1455
Grass/legume hay35 1253
Fescue hay351850

So how do I take a soil test?

Soil tests should be taken every 3 years in pastures and every year for hay fields. Separate samples and separate analysis should be done for each pasture and hay field or unique areas in the field. For example, a feeding area or shaded area where livestock spend extended periods of time build up manure and may have much higher nutrient levels. Spring and fall are the best times to perform a soil test. Take soil samples at a depth of approximately 4 inches in 10 to 12 different areas of the field. Samples need to be thoroughly mixed in a plastic bucket and then a representative amount put into a soil sample bag provided by your county extension office and clearly labeled. The sample bag can then be returned to the county extension office and they will ship it to the UK Soil Testing Lab. Your county agent will send back the results and will assist you in interpreting results and developing a fertility program for each field. For more information on how to take soil samples, refer to UK AGR-16 “Taking Soil Test Samples”.

Weed control

Fall is a great time of the year for weed control. The UK publication AGR-207 “Broadleaf Weeds of Kentucky Pastures” shows pictures of weeds on one side and a chart on the other side with a list of the weeds, the herbicides that will control each one, and the time of the year that is best to spray. For weeds that grow or germinate in cooler months like Bull, Musk and Plumeless thistle the time to spray is Oct-Nov or Feb-March. Spraying during these months kills the thistle plants when they are small. On the other hand, weeds like Buttercup and Poison Hemlock often do not germinate until late winter, so the most effective time to spray is March-April. Other problem weeds only grow in the summer months so the best time to spray Tall Ironweed is June-August or to spray Ragweed is May-July. Spray at the right time and use the recommended products and soon your pastures and hayfields will be almost weed free. Remember though, that the best weed control is good grazing and cutting management and a well fertilized forage stand has the best chance to outcompete weeds.

Forage Seeding Dates

Normally, fall is considered an ideal time to seed cool season forages. For example, AGR-18 “Grain and Forage Crop Guide for Kentucky” shows that October 1 is the cut-off date for seeding Tall Fescue. From this same publication, the recommended deadline for seeding clovers and alfalfa is September 15. Fortunately, clover establishes well by frost seeding in February. Now is a great time to soil test the pasture or hay field where you want to add clover and then apply lime, P and K according to soil test recommendations. That way, the pH has time to increase prior to seeding and the fertilizer is already in place.