What's Cropping Up? Blog

Articles from the bi-monthly Cornell Field Crops newsletter

Wheat Emergence, Early Plant Populations, and Weed Densities Following Soybeans in Conventional and Organic Cropping Systems

Bill Cox1, Eric Sandsted1, and Jeff Stayton2
1Soil and Crop Sciences Section – School of Integrated Plant Science, Cornell University; 2Musgrave Research Farm, Cornell University Agricultural Experiment Station

Wheat harvest and stressed corn 064We initiated a 3-year study at the Aurora Research Farm in 2015 to compare the corn, soybean, and wheat/red clover rotation under conventional and organic cropping systems during the 3-year transition period (2015-2017) to an organic cropping system. We used three entry points or previous crops from 2014 to initiate the 2015-2017 study: 1) grain corn, 2) small grain, and 3) soybean. Three of the many objectives of the study are 1) to determine the best previous crop (2014) for the transition, 2) the best crop to plant in the first year (2015) during the transition and 3) do corn, soybean, and wheat respond similarly to management inputs (high and recommended) under conventional and organic cropping systems? This article will discuss days to wheat emergence, fall wheat populations on October 8, the one shoot stage (GS 1), and weed densities on November 3, tiller initiation (GS 2), under conventional and organic cropping systems under high and recommended management inputs.

Wheat is planted in the fall after soybean harvest in the corn-soybean-wheat/clover rotation in New York. We harvested soybean in all three entry points or fields with different 2014 crops (grain corn, soybean, and small grain) on September 23 and no-tilled wheat into soybean stubble the following day. We decided to no-till wheat in the conventional and organic cropping systems because of the paucity of visible weeds, especially perennial weeds.

We used a John Deere 1590 No-Till Grain Drill to plant the treated (insecticide/fungicide seed treatment) Pioneer soft red wheat variety, 25R46, in the conventional cropping system; and the untreated 25R46, in the organic cropping system at two seeding rates, ~1.2 million seeds/acre (recommended input treatment for a September planting date) and ~1.6 million seeds/acre (high input treatment). We applied about 200 lbs/acre of 10-20-20 as a starter fertilizer to wheat in both input treatments in the conventional cropping system. In the organic cropping system, we applied the maximum amount of Kreher’s composted manure (5-4-3 analysis) that would flow through the drill, or about 150 lbs of material/acre, as a starter fertilizer to both input treatments. We also broadcast Kreher’s composted manure to provide ~60 lbs of actual N /acre (assuming 50% available N from the composted manure) in the high input treatment in the organic cropping system. In addition, we also added Sabrex, an organic seed treatment with Tricoderma strains, to the seed hopper of 25R46 in the high input treatment in the organic cropping system. Finally, we also applied Harmony Extra (~0.75 oz/acre) to the high input conventional treatment at the GS 2 stage (November 5) for control of winter perennials (dandelion in particular).

We will frost-seed red clover into all the wheat treatments in mid to late March when wheat is greening up to provide N to the subsequent corn crop in 2017. We will apply ~60 lbs of actual N/acre (33-0-0, ammonium nitrate) in the recommended input treatment in the conventional cropping system during the early to mid-tillering stage (GS 3) in late March/early April. In the high input conventional cropping systems, we will apply a total of ~100 lbs of actual N/acre (33-0-0) during the spring with some applied at GS 3 and the remainder applied at early jointing stage (GS 6), based on the tiller count at GS 3. We will also apply a timely fungicide (s) to the high input treatment. We will apply Kreher’s composted manure to provide 60 lbs of available N/acre in the recommended input treatment in the organic cropping system at GS 3 in late March/early April. We will also apply Kreher’s composted manure to provide an additional 40 lbs of available N/acre to the high input treatment in the organic cropping system at GS 3

When comparing wheat emergence in the two cropping systems under their respective input treatments, emergence was more rapid in the organic cropping system (Table 1). It is not clear why the untreated 25R46 in the organic cropping system emerged more rapidly than the treated 25R46 in the conventional cropping system. Temperatures were exceptionally warm (average temperature of 62.70F) and dry (0.05 inches of precipitation) during the first 6 days after planting. Conceivably, the seed treatment in the conventional wheat made the seed somewhat more impermeable to soil water imbibition, resulting in delayed emergence in the conventional cropping system by ~ 1 day. We also noted the same pattern of emergence between the untreated organic and the conventional soybean seed (http://blogs.cornell.edu/whatscroppingup/2015/09/16/emergence-early-v2-stage-plant-populations-and-weed-densities-r4-in-soybeans-under-conventional-and-organic-cropping-systems/). It was noted in that news article, however, that soybean varieties differed so a valid comparison of emergence between treated and untreated seed was not possible. On the other hand, corn emergence was more rapid for the treated GMO hybrid, P9675AMXT, in the conventional cropping system compared with the untreated non-GMO isoline, P9675 in the organic cropping system (http://blogs.cornell.edu/whatscroppingup/2015/07/23/emergence-early-v4-stage-and-final-plant-populations-v10-psnt-values-v4-and-weed-densities-v12-in-corn-under-conventional-and-organic-cropping-systems/). So perhaps other factors rather than more rapid imbibition contributed to more rapid wheat emergence in the organic cropping system.

When comparing wheat populations at the GS 1 stage in the two cropping systems under their respective input treatments, there was an interaction between cropping systems and management input treatments because of the magnitude of higher populations in the organic cropping system (Table 1). Plant populations averaged ~10.5% higher in the organic compared with the conventional wheat in the recommended management input treatment (seeding rate of ~1.2M seeds/acre). In the high input management treatment (seeding rate of ~1.6M seeds/acre), wheat treated with Sabrex in the organic cropping system averaged ~25% greater than wheat treated with the insecticide/fungicide treatment under conventional management. Perhaps the Sabrex seed treatment greatly improved wheat stand establishment in the organic cropping system when compared with the insecticide/fungicide seed treatment in the conventional cropping system. It must be noted, however, that seed size differed between the untreated 25R46 (~11,500 seeds/lb) and the treated 25R46 (~14,000 seeds/lb) so drill settings were not consistent between the two plantings because we planted according to seeds/acre and not lbs or bushels/acre. Conceivably, changes in drill settings between the two treatments could have contributed so some of the wheat population differences between the two cropping systems.

Another surprising aspect of our data is that the conventional cropping system had greater weed density compared to the organic cropping system (Table 1). It must be noted, however, that weed densities were very low so yields will probably not be compromised except in a couple of the plots in the conventional cropping system under recommended inputs (no herbicide) when corn was the previous crop in 2014. Most of the observed weeds were dandelion with some mallow or cheese weed also observed. Apparently, the last cultivation of soybean on July 16 and the last cultivation of corn on July 6 removed existing or late-emerging dandelions or mallow, whereas the observed weeds in the conventional cropping system apparently emerged after the June 26 Roundup application.

In conclusion, the timely wheat planting (September 24) resulted in excellent wheat stands and the warm November temperatures resulted in an excellent wheat crop in appearance in all the treatments in late November. Overall, the organic wheat looked more robust than the conventional wheat, especially in the high input treatment, because of better stand establishment and perhaps the 60 lbs/acre of actual N applied as composted chicken manure. In addition, the organic compared to the conventional wheat surprisingly had fewer weeds, especially dandelion, in early November under no-till conditions. Soybean followed by wheat may prove to be excellent transition crops in the first 2 years going from conventional to an organic cropping system (http://blogs.cornell.edu/whatscroppingup/2015/11/09/soybean-yield-under-conventional-and-organic-cropping-systems-with-recommended-and-high-inputs-during-the-transition-year-to-organic/). Wheat, however, unlike soybean, requires fertilizer N to realize its yield potential, and this may prove to be a limiting factor to organic wheat yields, similar to corn yields. (http://blogs.cornell.edu/whatscroppingup/2015/11/09/corn-yield-under-conventional-and-organic-cropping-systems-with-recommended-and-high-inputs-during-the-transition-year-to-organic/). We will find out how organic wheat fares compared to conventional wheat when we harvest next July (2016).

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