Cover Crops

Pacific Gold Mustard Cover Crop

A cover crop is a plant, or mixes of plants, that are used as a green manure to improve soil health, reduce weeds, reduce soil erosion, enhance soil water infiltration, reduce pests and diseases, and to enhance soil nutrient recycling. A cover crop can remove residual soil nitrates deep into the soil profile, thus reduce leaching and improving groundwater quality. The USDA has over 60 plant species listed as use for cover crops. For my business, I have focused on just one mustard variety and that is Pacific Gold. It is considered an Oriental Mustard, sometimes referred as a Brown Mustard.

A glucosinolate is a compound produced by mustards that contain nitrogen and sulfur. The glucosinolate compound is similar to that found in Vapam and is considered a natural deterant to some soil borne pathogens.

The goal of a mustard cover crop is to produce heavy biomass of leaves versus stems.

In a green manure Pacific Gold, the leaves are where the majority of nutrients and glucosinolates are. Thus, it is imperative to grow lots of big, green leaves and then put those leaves into the ground as a green manure before leaf tissue starts yellowing. The root system provides valuable leachates when they are healthy.

"The goal of any cover crop is to improve soil health and the soil's ecosystem of beneficial organisms. This in turn improves food quality and the environment in which we must all live in." -Taberna

Pacific Gold can do that. Pacific Gold is a PVP variety owned by the University of Idaho. It is bred mostly for cover crop use and to enhance soil quality. The value of Pacific Gold is that you can attain 3-4 tons of biomass in less than 8 weeks. This 3-4 tons, if green, will have maximum values of NPKS leaf and glucosinolate content as long as it is 10 days before full flowering to 7 days after full flowering.

Unpublished research done by Western Ag Research in 2005 was to determine the best timing, or growth stage, of Pacific Gold mustard green manure for NPKS recycling and glucosinolate content that is worked into the soil. Western Labs ran the leaf tissue NPKS and we pulled other leaf samples for glucosinolates and sent them to the University of Idaho where Dr. Matt Morra analyzed leaf glucosinolate content. Western Ag Research compared the data set. Western Ag Research's data suggested that the best time to chop and groundwork Pacific Gold into the soil is 10 days before flowering to about 7-10 days after full flowering. After 10 days of full flowering, the NPKS and glucosinolate leaf content starts to drop steadily.

This photo shows a mustard plant about
7-10 days before flowering.
The beginning of flowering.

"We cannot solve our problems with the same thinking we used when we created them."
-Albert Einstein

This is true.

The positive variable about Pacific Gold is that it acts as a rotational crop in just the 6-8 weeks that they are raised. They are an excellent rotational crop because you do not lose a year as with raising a crop, or using other cover crops that require more time to achieve just 2 tons of biomass. Pacific Gold is raised as a green manure, not a harvested commodity, and the biomass is worked into the ground thus recycling nutrients and building organic matter, whereas a harvested commodity removes nutrients from the soil. Thus, a wheat-potato rotation can be more like a wheat-mustard-potato rotation in the same two year time frame.

Pacific Gold with flowering just starting. This is the best timing to work the mustard into the soil.
This field has 4 tons of biomass on October 2. It was planted August 2. It is ready.

Picture 4 shows the perfect timing to incorporate mustard green manure. In picture 4, the plants are still green with good biomass. In picture 5, the field is in full flower. At this point, leaf NPKS contents declines. The glucosinloate starts to decline as well. It would be best to incorporate the Pacific Gold as soon as possible in picture 5.

We must remember that a green manure is exactly a green manure. That is, the plants must be raised and then incorporated while still green. If not, then it is just a cover crop. One must remember, as plant flowering it ages and its' root system is also aging, as well as leaf tissue, and the effects of a mustard green manure starts to lessen as the plant continues to age. Healthy roots are an integral part of the Pacfic Gold system where the healthy roots provide pathogen suppressive leachates into the rhizosphere area. As root systems die-off, then their beneficial effects start to decline too.

Leaves and roots decline at flowering. They are at their healthiest point prior to flowering.

A green manure is most powerful when carbon to nitrogen ratios (C:N ratio) are 30:1 or less. You need biomass, but you also need good, fresh green material. C:N ratios 10 days before flowering are probably under 25:1. At flowering they may be around 25-30:1. After flowering the C:N ratios start to increase meaning that nutrient recycling will be slowed down.

The Pacific Gold to do list:

  1. Plant around 8 to 11 lb/acre seed in August 10 through August 25.
  2. Apply around 100 to 130 lb N/acre with sulfur following a wheat crop.
  3. Leave a 3-5 foot border around the perimeter of the field. This helps reduce escapes.
  4. Leave a border around the pivot point.
  5. Leave a 5 foot border near canals or rivers. This helps reduce escapes and good weed control.
  6. Chop mustard in time period of 10 days before flowering to around 7 days after full flowering.
  7. Spray the volunteer grain after the mustard has fully germinated.
  8. Make sure sprayer tank is cleaned or you may stunt or kill the mustard with another residual.
  9. Plant mustards in field(s) where needed most. Not all fields need a cover crop. Pick the best one.
  10. Pick a field(s) that have water or wind erosion issues. Mustards slow those down.
  11. Pick a potato field where rotations are short, like wheat-potato-wheat-potato-wheat-etc.
  12. Don't over fertilize.