Impacts of grazing cattle in a pecan grove

Beef cattle grazing in a native pecan grove

   One of the most common forms of ground cover management in native pecan groves is to pasture cattle. Cattle grazing offers two advantages for a pecan producer: A second source of income from the same parcel of land (pecans + beef) and a significant reduction in orchard mowing costs. 
    The grazing of animals under tree crops is an age old agricultural practice that started soon after man first learned to tend livestock. Travel to almost any Mediterranean coastal area and you'll see the small, rock-walled sheep paddocks with ancient olive trees still dotting a landscape first created by ancient Romans.

   Cattle may help diversify farm income but grazing the pecan grove impacts the ground cover and the trees in ways not easily recognized.
    In the photo at left, the pecan grove on the left side of the fence is pastured while the grove on the right side is mowed. Cattle are picky eaters. Over time, intensive grazing will change the composition of the plants that make up the ground cover. The tall weed growing on the pastured side of the fence is ironweed. This plant has stems as tough as iron, can grow 5 feet tall and is totally avoided by grazing cattle. On the right side of the fence,  you see mostly Canadian wild rye, a common native in our river bottom and great cool season forage grass. You don't see wild rye in the grazed area because the cattle have already chewed it into the ground.
   Grazing has both positive and negative impacts on the pecan grove ground-cover composition. On the plus side, cattle will help control poison ivy and wild grape, keeping those troublesome vines from climbing trees. Over-grazing, on the other hand, fosters the growth of undesirable plants in the ground cover. Mowed-off ironweed stems can damage the rubber fingers of your pecan harvester. Nutsedge, another plant cattle will not eat, will quickly carpet the orchard floor during the summer months. Nutsedge secretes allelopathic substances into the soil that can inhibit the growth of other plants and possibly reduce pecan tree vigor.
    Last year, I saw and explosion of chickweed in thin, over grazed pecan groves. Chickweed is a winter annual weed that germinated in the fall after the cattle were removed from pecan groves in preparation for harvest. Chickweed made such a thick mat of intertwined vegetation that harvesters were unable to effectively pick up the nut crop.

    The biggest impact cattle have on the pecan grove is on soil nitrogen. In the past, I've talked to cattle experts and asked, what I thought was a simple question-- "How much nitrogen does cattle production use per acre?" The knee-jerk response I got was--"Cattle don't use nitrogen, they add nitrogen via urine and manure." Well I knew that couldn't be right. A 100 lb. calf in the spring turns into a 700 lb calf by fall and part of that weight gain is nitrogen containing proteins and amino acids.
   I finally discovered some beef research that estimated the nitrogen uptake by a grazing cow/calf pair. The only problem with reading beef research is everything is reported in animal units not on a per acre basis. So, in calculating nitrogen use by cattle, I will assume that each cow/calf pair utilizes 4 acres of grazing land.
    It is estimated that a cow/calf pair ingests 280 lb. of nitrogen during the grazing season. Of the nitrogen ingested, 10 lbs are retained by the animals and 270 lbs are excreted as urine and manure. But here's the problem. The nitrogen returned to the soil surface via urine and manure is so concentrated in a relatively small area that it overwhelms the soil system and 30-50% of the nitrogen contained in cattle excretions end up volatilizing into the air.
   On a per acre basis, grazing cattle remove only about 2.5 lbs. of N per acre as increased body weight. However, nitrogen volatilization from cattle urine and manure causes a net loss from the pecan grove of between 17.5 to 33.75 lbs. N/acre. Taken together, cattle grazing in the pecan grove removes between 20 and 36.25 lbs of nitrogen per acre.
   Cattle do have a place in native pecan groves but knowing the impacts of grazing on the system is important for growers to understand.  Growers should practice good pasture management techniques to limits the spread of troublesome weed species and be careful not to over graze the orchard floor. Growers should also consider increasing their spring fertilizer nitrogen application by 30 lbs N/acre to replace the N lost to cattle production.

Double row pecans: From intercrop to covercrop

    In 2003, we planted a new pecan orchard using a double row planting plan that created a wider spacing for intercropping while maintaining adequate tree numbers to allow for early economic returns from nut production.
    Over the years, we had planted and harvested wheat, oats, and soybeans all during a time when our young pecan trees were just getting established.  But last summer, we noticed a change in the relationship between our trees and the intercrop. The tree's root system was starting to out-compete the intercrop for water and nutrients (photo at right). Then last fall, these same trees had their first commercial crop. And by commercial crop, I mean the trees produced enough nuts to require shaking and mechanical harvest. 

   

    This summer we allowed the previously cropped areas of the field to remain fallow. It was time to convert from field crop to cover crop. Over the summer, we chiseled the soil to help reduce weed growth.  Last week we worked the ground with a heavy disk (photo at left) then used a spring tooth harrow to prepare a fine seed bed.

     This week we planted a combination of perennial rye grass and redtop; two cool season grasses (photo at right). The perennial rye should produce a quick and vigorous ground cover. The redtop will be a little slow to take off but once established, it should provide us with a flood tolerant grass that provides an excellent surface for pecan harvest. Now all we need is a little rain to bring this new covercrop to life.

Harvesting intercrop soybeans

   Today we took a break from pecan harvest to cut our soybean crop (photo above). The beans were planted within a block of pecan trees that were established in 2002 using a double row planting plan. We planted the beans back in early June and they fought their way through this past summer's heat and drought.  Amazingly our bean crop ended up yielding 27 bu./planted acre. This year we will also harvest a small pecan crop from the trees in this block adding to the total income/acre.

The fight for water

   We planted soybeans in our double-row intercrop study again this year. And for the first time, I've noticed that our young trees (11 years old) are starting to dominate over the intercrop. In the photo at left, you can see the perfect outline of the pecan tree root system's  area of influence. Soybeans were planted in the area that is now mostly bare soil (note the 7.5 inch planter rows) but the pecan tree out-competed the beans for water during this drought stricken growing season and the germinated soybeans died from a lack of water.

    I walked up the area in the bean field where the pecan tree's roots had their greatest impact and learned one more interesting thing. A huge soil crack has developed at the boundary between the pecan tree's root system and normal sized bean plants. This says to me that pecan roots are so efficient at extracting water from the soil that the soil has shrunk causing a crack in the soil.   
    This interaction between pecan trees and soybeans has got me thinking. Are the trees getting big enough for me to start thinking about seeding the entire field to a harvester-friendly covercrop?  Soybeans are bringing $16 per bushel: Can I pass up the economic opportunity of an intercrop while the trees are still producing less that 200 lbs. pecans/acre? All I know for certain is that the year to make the switch from intercrop to covercrop is coming soon. I just don't know if it will be 2013 or 2014. Most likely, a flood by the Neosho River will probably make that decision for me.

Intercropping with soybeans

  
     Last week we received some much needed rain. So, this week we had enough moisture to plant soybeans in our double pecan row/intercrop demonstration plots. The pecan trees in these plots are now 10 years old and nearing the point where they are getting large enough to warrant mechanical harvest. Depending on tree growth this summer, this may be the last year we crop this field. If this turns out to be the last crop of soybeans, we will establish a cool season grass in the tilled areas and switch over to hay production for 3 to 5 years before completely ending all intercropping practices. By year 16, our entire focus will be on pecan production with the trees producing more income per acre than any field crop that can be grown in SE Kansas. 

Harvesting intercrop soybeans

    Today we harvested the soybeans planted in our intercrop study. If you've been following this blog, you know that I've described the double-row intercrop system  in a previous post and also posted photos of this Spring's soybean planting. Like every field crop planted in SE Kansas this year, our soybean crop suffered from a lack of water. Yield was well below normal for full season beans. The final tally was 23 bushels/acre sold at $11.62/bu.

Double-row intercrop system: Pecans and soybeans.

     Back in June, I posted a photo of planting soybeans in our pecan intercrop study area.Today, the beans look good with plants averaging 30 inches tall (photo at right). However, just like area farmers, our soybean crop has struggled with drought all summer long. Fortunately, we had 4 inches of rain during the second week of August, giving the bean crop a needed boost. Plants grew nearly 2 feet taller in the week following the rain.
     Now, another dome of high pressure has settled over SE Kansas and we are back to hot dry conditions. Our bean crop looks good from the road, but on closer inspection you'll find very few pods setting on the plants. Poor pod set is directly related to the hot, dry weather. Needless to say, farming has been a challenge in 2011!

      Despite this year's drought, I still believe that our double-row, intercrop system has great potential for making a new pecan planting financially sustainable during the years of orchard establishment. The grass alleyway between each double row of trees is the unique feature of  this system. The alleyway allows for easy access to the trees for maintenance operations such as grafting, summer pruning and pest control; all without trampling the adjacent agronomic crop..  For those planning a new orchard, here's the planting plan for the double row system (below).

Haying a pecan grove effects nutrient budgets

    Many native pecan producers like to cut a hay crop from their groves as a good way to "clean up" the orchard floor. The grove pictured at left looks picture perfect and has a valuable hay crop that can be sold or fed.
    Unfortunately, most growers that regularly hay their groves do not figure in the cost of replacing the soil nutrients that are removed when the hay is trucked off the farm. For every ton of hay harvested, an estimated 30 pounds of nitrogen, 7 pounds of phosphorus and 42 pounds of potassium are removed from the pecan grove.
    Nitrogen and potassium are also used in large amounts to build pecan crops. By removing these important nutrients with a hay crop you are effectively robbing soil fertility away from the much more valuable pecan crop.
    There are two options in dealing with the ground cover. First you can just brush hog down all the vegetation and return all the nutrients and organic matter back into the soil. Or second, you can plan to cut the hay from the grove but increase the amount of N and K you apply in the spring to compensate for expected nutrient removal.

Intercropping pecans with soybeans

    Yesterday we spent the day preparing the soil and planting a soybean crop within our double row pecan orchard (photo at right). We established this pecan orchard back in the fall of 2002 and have raised soybeans, wheat, or oats between the trees since that time. 

   The double row system was designed to put tree care first. It features a grass alley way between each double row of pecan trees to allow easy access to the trees all season long.

    In this photo taken a few years ago, you can see recently grafted trees, an oat intercrop, and the grass alley between the double pecan rows The pecan trees are planted 40 ft apart within each row. Trees in adjacent rows are offset so that the distance between the double row is 22.5 feet and trees are 30 feet apart on the diagonal. The space between each set of double rows allows at least 50 feet for grain crop production.