There is almost no information on the use of cover crop in popcorn in general and organic popcorn production in particular. This work was initiated to better understand how cover crops could affect weed management practices, soil nutrients, and popcorn yield. Cover crops were chosen because compost is expensive due to transportation costs. Because of a serious decline in the number of farms in the area, animal manures are in short supply. Also, past farming practices have reduced the amount of organic matter in the soils. Lastly, we were seeking ways to provide the necessary nitrogen to produce a successful crop of popcorn.
Field experiments were conducted in 2004 and 2005 to evaluate organic popcorn production following different summer cover crops and winter cover crops. The summer cover crops were cowpea (legume) and sorghum sudangrass (grass). The winter cover crops were cereal rye (grass) hairy vetch (legume) and bare ground. At the end of summer 2004, each summer cover crop plot was split into three subplots, each receiving one of the winter cover crop treatments. The summer cover crops were planted on June 14, 2004 and the winter cover crops on on September 20, 2004. Cover crop seeding rates were 46, 38, 160 and 50 lbs/A for cowpea, sorghum sudangrass, rye, and hairy vetch. Baseline soil samples were collected at the beginning of the experiment in 2004 prior to planting cowpea and sorghum sudangrass. In fall of 2004, additional soil samples were collected prior to planting the winter cover crops. Finally in summer of 2005 (May 11), final soil samples were collected before popcorn sowing. On May 09, 2005, the cover crops were incorporated into the soil by disking and supplemental organic fertilizer (200 lbs of 0-2-12). Popcorn was sown on May 9, 2004 in 30 inch rows with spacing of 7-9 inches between plants. Weed management was conducted with one rotary hoeing on June 1, 2005 and two cultivations on June 18, 2005 and July 1, 2005. During the popcorn growing season, leaf chlorophyll content was estimated using the SPAD 502 Chlorophyll Meter. A total of 20 fully expanded leaves from different plants were used. Popcorn was harvested on October 22, 2005. Stalk number, ear number, weight of marketable ears, and total ears weight was recorded. Analysis of variance was used to test the differences among the cover crop treatments.
Weed Control: Excellent weed control was achieved using one rotary hoeing early in the growing season followed by two cultivations. During the popcorn season, the plot’s weed competition was minimal and all plots were clean as shown in Photo 1. The plot had the best weed suppression we have observed in many years of farming. The exception was a patch of thistle which required hand hoeing. [Editor’s Note: To see the photos and tables mentioned in this report, please contact the NCR-SARE office at: firstname.lastname@example.org or 1-800-529-1342.]
Soil Fertility: Soil analysis conducted after the summer cover crops indicate the cowpea increased N content by about 10lbs/A (Table 1). In the sorghum sundangrass system, soil N decreased by about 20 lbs/A. Other soil chemical properties were less affected by the cover crops. Prior to popcorn planting in summer 2005, cowpea plots had 45 lbs/A of N and the sorghum sudangrass plot only 35 lbs/A (Table 2). Sorghum sudangrass increased the level of K with 113 mg/kg compared to cowpea which had only 74 mg/kg. There did not seem to be a benefit for growing a winter cover crop after the summer cover crops for soil chemical properties (Table 2).
Popcorn leaf chlorophyll content: Popcorn plants in plots where cowpea was the summer cover crop had greener leaves. Estimates of leaf chlorophyll content showed 42 for cowpea plots and 39 for sorghum sudangrass plots.
Popcorn yield and yield components: The number of stalks was similar for cowpea and sorghum sudangrass; however, the number and weight of ears was significantly higher in the cowpea system (Figure 2, Table 3). This was observed for both marketable and total yield. Popcorn plants from the cowpea cover crop treatment produced more ears per plant and individual ears were heavier compared with sorghum sudangrass
Planting cereal rye or hairy vetch after the summer cover crops did not provided additional benefits for popcorn yield (Tables 4 and 5).
This study improved my understanding of the effect of cover crops on organic popcorn production. Two legumes and two grass cover crops were tested. Cowpea (legume) showed the most potential in terms of soil fertility and popcorn yield.
There was not a benefit to planting a winter cover crop after an initial summer cover crop. Therefore the best system would be to rotate popcorn with a legume cover crop like cowpea. During the project, the winter cover crops of rye and hairy vetch had very poor growth. A cold spring did not provide the expected growth before incorporation two weeks prior to the planting of the popcorn. A year involving better growing conditions for rye and hairy vetch before incorporation may effect the yield differently.