## 2.1 Growing biomass

2.1.1 Growing conditions

How much biomass can be produced on a hectare of land? The figure below gives insight in all the factors that determine the eventual production of land plants. These factors are categorized in three groups: defining factors, limiting factors and reducing factors.

(Adapted from Langeveld et al, 2012)

Potential production is determined by light, ambient CO2 concentration, temperature and plant characteristics. Crop management is assumed not to hamper growth. Under conditions with water limitation, potential yields are reduced by water shortage. If nutrients are in short supply, but assuming perfect water supply and full crop protection, yields are denoted as nutrient limited. Of course most crop production suffer from a combination of water and nutrient shortage. In developing countries the loss of production due to water or nutrient shortage is larger than in, for example, The Netherlands. The availability of nutrients and water is strongly related to the soil quality. A high quality soil has a good water holding capacity and steady rate of mineralisation creating a continuous nutrient flow. A low quality soil retains no water and in this soil mineralisation hardly takes place because of a lack of organic matter. Actual production refers to yields reduced by pests, weeds and diseases and/or toxicities (e.g. pollution), often in combination with water and/or nutrient limitation. Reality is always more complex, several factors concurrently exerting their influence, but this framework can assist in analysing and understanding crop production situations. Potential growth varies with latitude, altitude and time of the year (Langeveld et al, 2010).

The actual agricultural yield of each country is lower than the potential production. But note that major differences in yield exist between countries indicating that the gap between the actual and potential production is gigantic in developing countries and smaller in developed countries such as The Netherlands. This phenomenon is explained by land specific climate and soil conditions but also by limited access to water and nutrients (artificial fertiliser) and chemicals for crop protection. Moreover level of education, means for investments etc. also play an important role. As an example the yield of cereals in kg/hectare for different countries is shown in the table below. The table shows that the total production of biomass worldwide has enormous potentials to increase. However, the yield is also dependent on the political situation of a country (e.g. war), which is also a reducing factor.

Cereal yield, measured as kilograms per hectare of harvested land in 1961 and 2016.

Country | Yield 1961 | Yield 2016
Sudan | 913 | 685
Mozambique | 877 | 824
Australia | 1,084 | 2,074
Russian Federation | Not known | 2,650
Pakistan | 856 | 3,064
Canada | 985 | 3,909
China | 1,193 | 6,029
Germany | 2,417 | 7,182
The Netherlands | 3,691 | 7,777

Source: http://data.worldbank.org/indicator/AG.YLD.CREL.KG

2.1.2 Breeding

To create new cultivars the plant breeder disposes of a multitude of possibilities. The most simple way - already applied for ages - is searching for the best plants in crop selection. More progress can be made by including plants from all over the world in the selection process to make optimal use of natural occurring genetic variation. A further step is making crosses by which characteristics of different plants are combined. Sometimes traits can be changed artificially through chemical treatment or radiation mutation. As a result of increasing knowledge on the organization and action of tissues and cells during the past decade, new techniques have become available such as fusion of cells of different species (cell fusion), exchange of pieces of genetic information between different organisms (transformation) or elimination of genes causing adverse effects. These new techniques are commonly indicated as genetic modification, though actually nearly all breeding activities are a kind of genetic modification. The latest technique used for genetic modification is the CRISPR/Cas technology. However, there is a debate whether this is really genetic modification as no new DNA is inserted in the host. See the movie for explanation of this technique. Both North and South American countries paved the way for development of gene-edited crops by removing regulatory uncertainty. The European Commission has banned biotech crops.

https://www.youtube.com/watch?v=KUApt4RIU1M

In relation to the biobased economy breeding is for example focussed on the plant cell walls for a better understanding of the cell wall biosynthesis and degradation pathways, both for first and second generation bio-fuels (chapter 2.4). First generation biomass is e.g. maize (corn), potatoes, sugar beet and sugar cane. Second generation biomass is made from side products like wood chips and potato peels. Third generation biomass like microalgae and seaweed do not need arable land. Moreover, breeding enables the identification of interesting compounds and genes for different industrial, food and medical applications.