Thursday, 30 August 2012

New strawberry bed

The new strawberry bed is finished now.  I have four rows of new plants and two rows of one year old plants.  That will be more than enough for me.

I was all ready to plant some rocket, American winter cress, lambs lettuce, spinach and winter lettuce until I discovered that I had left my seeds at home.  Not to worry.  The seed bed is raked and level ready for when I do remember to take the seeds to the allotment whenever that might be.

I dug over the old strawberry bed and dug in the old plants mixing in a little pigeon manure.  I was practising (NB I am writing in English) my digging techniques because I will be lecturing on how to dig effectively on the 30th of September.  I was just single digging throwing up the sods onto the top of the dug soil and slicing off the top 2 inches and letting it fall into the trench.  I kept the surface of the turned soil level by breaking up the sods with the back of the spade.

There is some thought that you should leave the soil rough and the clods unbroken so that the winter frosts can break them up.  This might work with some soils but it certainly doesn't with mine.  If I were to leave the soil rough dug then I would have to spend time in the spring breaking down great clods of soil that have set like concrete.  I will continue to break down the soil into a good friable texture and carefully level it as I dig  during the autumn and winter.  If the winter frosts then want to break it down even further then it is welcome to.

I wanted to continue to cover this bed with grazing rye and winter tares for the winter and this necessitates making a seed bed.

I raked over the ground but did not have time to plant green manure because I spent about an hour weeding between the rows I planted earlier.  The rye grass and tares mix will prevent weeds from growing but not until they have grown quite large and formed a good canopy of leaves to cover the ground.  Until then, I will  keep the weeds down.

I usually go along the rows with a hoe and cultivator and this seems to be adequate to remove most of the weeds.  However, I am experimenting with using the hand fork because I have seen Don use it very effectively to take off weeds from his allotment.  Not only does it enable you to hand weed more effectively, it also makes the soil very friable.  The soil looks very good when you have forked it over and broken all the lumps.

It does not necessarily make plants grow any better but it is pleasing to see neat rows with smooth, clean soil between.

There are several reasons for covering the soil with a green manure.

Using a fibrous rooted grass like grazing rye produces a really good soil  tilth when it is dug in.  The roots are incredibly adventitious and the soil in between them is fine and sandy.  These roots seem to be ideal for gleaning nutrients from the soil and fixing them within the structure of  the plant preventing  loss from leaching by heavy winter rain.

Although the leaves of grazing rye are soft and not very robust they are very effective in forming a barrier that is fairly impenetrable to light.  This will  prevent germination of weed seeds keeping the soil clean during the autumn and winter months.

Rye grass is used as green manure because it rots down quickly adding carbon and  nutrients to the soil speedily.

The tares forms a symbiotic relationship with soil bacteria such as Rhizobium leguminosarum biovar viciae  which can fix nitrogen from the air.  Rhizobium leguminosarum biovar viciae  can infect several leguminous plants including peas. Nitrogen is reduced through the action of several enzymes; the most important for this process being nitrogenase.   Nitrogen is an important plant nutrient.

So the Rhizobium captures the nitrogen from the atmosphere and passes it onto the plant that uses it for growth.  This process occurs within the plant root nodules and only benefits the infected plant.  Some say that nitrogen can be passed to other plants when growing close to an infected leguminous plant. I cannot see how this happens because of the intimate nature of the symbiosis.  However, there is a large turnover of roots in most plants and as the roots die they must give up their constituent nutrients to the soil which then could be used by other plants.

The only way that other plants can benefit from this symbiosis is when the infected plant dies and rots down releasing nutrients; including the nitrogen that was fixed by rhizobium.    The fixed nitrogen is transported and used throughout the plant and this means that all the plant should be dug into the soil to get the full benefit.

Some might say that rhizobium bacteria may well continue to fix nitrogen in plant roots even when the tops of peas, beans and tares have been cut off.  I would question this because nitrogen fixation is a very energy intensive process.  The energy to promote nitrogen fixation in the root nodule of legumes comes from the plant.  While there may be a small amount of stored food in the roots this will quickly be used up by the nitrogen fixing process. Once the energy from the food is used up, nitrogen fixation will cease because there are no photosynthesizing structures to replenish the food.  Any nitrogen that is fixed will pass straight into the root and will only be released when the roots decompose.

The benefit only comes when the dug in tares breaks down in the soil releasing nitrogen that was initially captured from the air.

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