The Big Question – How to Choose Cover Crop Species and Varieties

THE BIG QUESTION.

Without covering ‘why?’ too much, I have a big question.  And it won’t be easy to answer or discuss without some background and thoughts.  And I could keep it short and sweet, at the risk of being simplistic.  But that is rarely me.

So how about just ploughing in?

In the use of summer cover crops, should I aim for Maximum Biomass, or Maximising the lifespan of Biota via a long plant green-bridge?  What will benefit my system the most?

OK, let’s assume I want to use cover crops as one of the conservation farming principles, and one of the reasons is to increase the VAM &other biology lifespan over summer in the non-live crop periods ie Nov –April in our Mediterranean climate.  This is the main trigger message I was hearing from Dr  Jill Clapperton on her visit to Australia, and in the articles by Dr Kris Nichols. (plus Business Watch bio)  Let’s also assume that our winter crop is harvested during December, and winter crops are sown in late April, and our initial ccs are killed a month before sowing.  December to March is a 5 month window.  The mean rainfalls are 25mm Dec, 21mm Jan and Feb, median rainfalls a bit below.  That is certainly enough rain to germinate and sustain self-sown crops and summer weeds.  Having said that, we can also have near perfectly dry summers.

At the same time we/I must avoid introducing weeds, bridging cash-crop diseases, and creating too much mess to manage at the following sowing.  They are kept in mind, but not relevant for this post.

There is also a list of tertiary benefits I am not deliberately chasing.  And I have a rough plan with contingencies.

4 SCENARIOS:  So this all begs the question:  Do I aim for long season to keep roots growing to feed bugs (especially if we can still build a big biomass) and ‘harvest the sun’, or short season to build quick biomass?  What could happen?

1. Aim for Long season: dry summer eg 1″ rain for 2 months, decile 3.

2. Aim for Long season: wet summer eg 4″ rain for 2 months, rare.

3. Aim for Short season: dry summer eg 1″ rain for 2 months, decile 3.

4. Aim for Short season: wet summer. eg 4″ rain for 2 months, rare.

1. Long season – long season spp and cv only with low water use to stay alive.  If dry, we get high evaporation before plants grow much, either going dormant or dying.  If a dry summer and little biomass, I would not stock but “burn off” (the Yank jargon for kill with spray) when earliest sp goes to seed, leaving a short fallow (min 4 weeks) before next cash crop sown (April 15 earliest).  Drought tolerant sp may be only thrivers, but still go to seed within 10 weeks eg Tepary beans.

2. Long season – long season spp and cv with low water use to stay alive. If a wet summer and much biomass, may stock to reduce and flatten biomass before burning off, or not stock but roll and burn off.  Or could cut for haylage or hay.  Or roll, maybe if because of height it can’t be sprayed.  It would leave a  short fallow (min 4 weeks) before next cash crop sown (April 15 earliest).  If wet and long growth opportunity, everything could grow well, maximizing biomass?  Self sown cash crops will thrive, and probably go to seed before CCs, which is what the wheat did this year in the trial.

3. Short season (and long) sp and cv- aim for big biomass with mix of water-use styles. If dry, High evaporation before plants grow much, either going dormant or dying.  Dry summer – burn off between 4-10 weeks or when first sp goes to seed.  Don’t stock.  Drought tolerant sp may be only thrivers, but still go to seed within 10 weeks, more so if high water use sp dry ground more, or die off.

4. Short season (and long) sp and cv- aim for big biomass with mix of water-use styles. Wet summer with much biomass. Stock to reduce and flatten biomass, or hay/haylage.  Or roll, if only if height can’t be sprayed.  Either way, burn off between 4-10 weeks or when first sp goes to seed.

Self sown cash crops will thrive, but shouldn’t go to seed in 8 weeks.

The implication for a short growth covercrop is that I still end up with a short summer fallow of no growth afterwards.  That means moisture conservation for the following cash crop – a Good Thing.   And that seems to be a main point I read out of “Managing cover crops profitably, 3rd Ed” (google it and download pdf) – to control how much subsoil moisture gets used.  But the other factor is we are no longer feeding bugs with live root exudates – they then feed on dead roots, humus, and synthetic ferts (yes?).  That period, until the cash crop is sown, could be 3 months long.  Is that bad?

Some feedback so far, from Ed Winkle,  is to grow ‘as much biomass as possible until it gets in the way’.  And if I don’t use discs (another discussion) for a while, that means growing rows of erect and bush types, not sprawling or vines.

I hope the dilemma is clear.  Where should I be directing the thoughts?

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About covercropper

G'day, I'm a grain grower in the NW Wimmera area of Victoria, Australia. This blog is to share my journey of exploring cover cropping here, mostly summer mixes /cocktails. How to, what, when, will it work in improving our soils, productivity and profits?
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