## 2.2 Agricultural challenges

The contemporary economy is to a great extent powered by limited resources that are being depleted. As they are being depleted we will have to develop alternative sustainable sources of energy and raw materials; most likely with biomass as a cornerstone. The challenge is to develop an economy that does not undermine the long-term productivity of agriculture and natural ecosystems by depleting the natural capital that is the basis of the productivity. A biobased economy depends on a sustainable production of biomass. First priority in sustainable biomass production will be to ensure conservation, regeneration, recycling and substitution of the needed resources: fossil energy, nutrients, water, soil organic matter. The current agricultural practice is various aspects far from sustainable. In the text below the major challenges are summarized.

2.2.1 Dependency on fossil fuels

Today, the main part of agriculture is driven by fossil energy, either as direct energy for fuels in machinery or as indirect energy in mineral fertilizers and other inputs; for instance, US food production when evaluated at the consumer level consumes seven times more fossil energy than the energy value of the produced food. The out-phasing of fossil energy inputs in agro-ecosystems requires a radical change of agricultural practices. Biofuels can in theory substitute fossil fuels used for machinery. However, self-reliance at the farm level may require more than 10 to 20 per cent of the land (Langeveld et al, 2012).

Artificial fertilisers are made by the so-called Haber-Bosch process. Carbon and oxygen are also critical, but are easily obtained by plants from soil and air. Even though air contains 78% nitrogen (N2), atmospheric nitrogen is nutritionally unavailable; many plants are unable to use this form of nitrogen. Nitrogen is a strong limiting nutrient in plant growth. In 1913 Carl Bosch managed to converse nitrogen from the air in ammonia at full scale. Some people consider the Haber process to be the most important invention of the past 200 years! The primary reason that the Haber-Bosch process is important is because ammonia is used as a plant fertilizer, enabling farmers to grow enough crops to support an ever-increasing world population. The fixation of atmospheric nitrogen (N2) to ammonia (NH3) via the Haber-Bosch process is equivalent to 1-2% of the world's annual energy consumption. The process requires high temperatures and pressure. This is an important disadvantage of the process; it depends heavily on fossil energy.

Haber-Bosch process https://www.youtube.com/watch?v=VtQFiwHlnmY

Possible solutions for replacing artificial fertilisers are:

(1) The use of nitrogen fixating plants. Nitrogen fixation is a process by which nitrogen (N2) in the atmosphere is converted into ammonium (NH4+). Plants that contribute to nitrogen fixation include the legume family – Fabaceae – with taxa such as kudzu, clovers, soybeans, alfalfa, lupines, peanuts, and rooibos. They contain symbiotic bacteria called Rhizobia within nodules in their root systems (see figure below), producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the fixed nitrogen is released, making it available to other plants and this helps to fertilize the soil.

Nitrogen fixation legumes

(2) Switching to a (more) vegetarian diet. World meat consumption increased (see figure below) from 23 kilograms per person in 1961 to 43 kg in 2014, almost a doubling. Consumption of milk and eggs has also risen. In every society where incomes have risen, meat consumption has too, perhaps reflecting a taste that evolved over 4 million years of hunting and gathering. As shown below in the figure about “Useable protein per acre of farmland” the conversion of vegetable protein to meat leads to a loss of protein. So, a vegetarian diet stimulates the economically most wise consumption of protein.

One acre (=0.4 hectare) of soy produces 160 kg protein (1 lbs = 0.45 kg). One acre of land used for the production of cattle feed, for example beef, delivers 9 kg protein in the end product.

More information about the N-cycle is given in the following link:

PowerPoint about the N-cycle

2.2.2 Resources of phosphorus will be more and more difficult to mine

Phosphorus is one of the building blocks of all life. Every living cell requires it. Plants need phosphorus to grow as much as they need water. Many soils do not have enough to meet the demands for phosphorus of high production crops. By mining phosphate from rock and turning it into fertilizer to spread on the land phosphorus can be supplemented to the soil. Unlike nitrogen, phosphorus (P) is a finite mineral resource (current global reserves will depleted in 50–100 years and declining production will occur much earlier). Therefore, future crop production will increasingly have to rely on recycling of P from urban areas, as well as on the breeding of crops that are more efficient in utilizing the soil phosphorus.

Currently, only about 15 percent of phosphorus comes from mines in the Western Sahara and Morocco. But the only other large producers, the U. S. and China, mostly keep supplies for their own use. So Morocco is by far the biggest contributor to international trade, with more than half the total business.

A huge amount of phosphorus is transferred from the soil in one location to another as food is transported across the world, taking the phosphorus content with it. Once consumed by humans, it usually ends up in local rivers via the sewage system. An example of one such crop in South America that takes up large amounts of phosphorus is soy. At the end of its journey, the phosphorus often ends up in rivers in Europe and the USA. Possible solutions are:

- precision agriculture, making sure the plant is able to take up phosphorus at the right time at the right spot.

- reuse of phosphorus from urban areas, regaining the phosphorus form human and industrial waste.

More info about phosphorus scarcity is found here:

Fosfaat: tekort aan wat nooit opraakt?

PowerPoint about the P-cycle

2.2.3 Organic matter in soils

The soil is fundamental to biomass production, and there is a great challenge in developing new agricultural methods in Europe that can improve organic matter levels, soil biological activity and soil structure. Many cultivated soils show a steady decline of organic matter unless they receive frequent applications of organic matter (e.g. animal manure, compost). Soil organic matter improves the water holding capacity and the activity of living soil organisms and thus the soil structure and health.

Sustainable biomass production should lead to a maintained level of soil organic matter. As organic matter levels have been declining for many years, it could be argued that even an increase in the organic matter level would be desirable, trying to compensate for historic non-sustainable land use. Soil organic matter can be managed by inputs (growing perennial crops and use of organic fertilizers) and minimising the degree of disturbance, for example soil tillage (Langeveld et al, 2012) .