Lecture 3 - nutrients

Question 1

what is the issue with monocultures?

Answer 1

are pretty rare in nature so natural ecosystems don’t really support them
-Expected that more diverse mixtures of plants suffer less weed, pathogen and pest problems

Question 2

why is competition for nutrients more severe in monocultures?

Answer 2

• The elemental composition of different plants is very similar but what they use each element for can be very different so the competition for nutrients of the same species can be very strong

Question 3

positives of monocultures?

Answer 3

• Very efficient system in terms of labour costs for harvesting etc

Question 4

what are monocultures vulnerable too?

Answer 4

extremely vulnerable to pests, diseases and extremes of weather and to nutrient losses
- more diverse cropping systems spread the risks and can reduce nutrient losses

Question 5

what are the positive effects of increasing the diversity of crops?

Answer 5

may reduce pest and disease pressures, increase nutrient-use efficiency, reduce risks of large-scale crop failures, and improve soil quality. Increasing the diversity of crops grown may improve food security especially in relation to increasing threats from climate change and pest and disease resistance to chemical controls

Question 6

what was the issue with neonicotinoid seed treatments in oil seed rape monocultures?

Answer 6

• used as an insecticide
• because of the monocultures the the toxicity is so great that it seeped into the flowers and started to effect bees and accumulation in wildflowers and field margins
• now banned from use

Question 7

what is the EU common agricultural policy 3-crop rule?

Answer 7

rule requires UK farms of more than 30 ha of arable land to plant at least 3 crops, with 2 main crops not to exceed 95% of the arable area

Question 8

what is the issue with the 3 crop rule?

Answer 8

3 crops just isn’t enough - need much more diversification - not radical enough

Question 9

what is the incentive for farmer to produce monocultures?

Answer 9

yields of cereals and oil seed rape provide a high income and some plants are not as economically viable
-More diverse rotations currently give less profit

Question 10

why might diverse rotations of crops do better in the future?

Answer 10

because of the growing demand of pest and disease control might counter increased profits

Question 11

what does sustainable crop production depend highly on?

Answer 11

on sustainable nutrient supplies e.g. where they come from, how we use them and how they get recycled in the system

Question 12

what is the issue with adding fertiliser to soils?

Answer 12

when fertilizer is added to soil unless the soil has a good capacity to hold onto the nutrients, they may get washed out
- rates of nutrient loss from soil erosion and leaching by rainfall in crop production systems usually far exceed rates of natural replenishment of nutrients

Question 13

how can we sustainably add fertilisers to soil?

Answer 13

need to have an understanding of how nutrient additions interact with the soil

Question 14

what is the importance of clay in soil?

Answer 14

• key component of sustainable fertiliser use
• clay minerals and organic matter store nutrients - made up of layers of repeating sheets which increase the surface area of them - with the capacity to take up water and nutrients

Question 15

how do clay minerals form?

Answer 15

form in soils from the weathering of rocks

Question 16

what effects clays ability to hold on to nutrient ions in the soil?

Answer 16

nature of the structure’s give them their properties
- Clay is also electrostatically charged - some is permanent, and some is dependent on the ph - this effect the ability to attract and hold on to nutrient ions in the soil

Question 17

describe the difference between colloid and non colloid soil particles

Answer 17

colloids have a higher surface area and charge than non-colloids e.g. colloid humans has a really high negative charge that is very dependent on PH

Question 18

2 causes of negative charges on colloids?

Answer 18

1) Isomorphous substitution - Within the crystal structures ions are replaced - These substitutions give permanent charge
2) PH dependent charge-A strong negative charge will have a powerful attraction to positively charged ions and hold them there by electrostatic attraction

Question 19

how do fertilisers with positively charges ions in work?

Answer 19

diffuse into the spaces which the other ions have left as they have been attracted to the clay/colloid surfaces and are ready for uptake by the roots

Question 20

what is the issue with organic matter and clays in the soil?

Answer 20

these components are the most easily eroded- and in the case of organic matter can be lost by oxidation through tillage and other practices

Question 21

describe the charge of root cell walls

Answer 21

cell wall of roots are typically negatively charged and attract positively charged ions - therefore they perform similar functions to the organic matter and colloids in the soil however this is only local to the root system and adjacent soil

Question 22

summarise colloids

Answer 22

• very small charged particles
• some have permanent charge
• some have PH dependent charge
• some have combination of both
  they attract ions of the opposite charge

Question 23

describe biological ion exchange in roots

Answer 23

Hydrogen ions (protons) are held more strongly than all the other ions - so given that protons are what plant roots and microorganisms typically actively pump out into the soil those ions are able to displace other ions from the exchange complexes to release their nutrient ions back to the plants

Question 24

6 examples of how plants dont compete via niche specialisation?

Answer 24

1. Soil pore size/ root dimensions
2. Profile and spatial separation of roots e.g. differences in tolerance to water logging is linked to root anatomy or different rooting strategies to cope with water limitations - root densities are also effected by the biomes they exist in
3. Different root phonologies and root architecture- timings e.g. Bluebell Hyacinthoides non-scripta - A vernal woodland plant active in root growth when the deciduous over-storey trees are losing their leaves, and active in P uptake in the winter before the trees come into leaf again.
4. Different nutrient source preferences - different preferences could mean that a diversity of plants grown could be more effective than monocultures depending on the availability of nutrients
5. Abilities to use nutrients that are unavailable to other plants e.g. Symbiotic N fixation, Use of amino-acid N and organic N, Use of organic P, Mobilisation of insoluble minerals
6. Extensive vs. Intensive root systems. - e.g. ability to respond to patchy distribution of nutrients

Question 25

what are winter cover crops used for?

Answer 25

grown to protect the soil fertility and structure but not actually a crop - include deep rooted grasses and legumes etc

Question 26

why is it thought plant species richness is positively correlated with productivity (overall biomasss) ?

Answer 26

• Suggestion is this might be partly explained by niche complementarity and nutrient use
• Strong suggestion of nutrient benefits from mixtures - especially mixtures including legumes

Question 27

what are 4 suggested management strategies for sustainable ecosystems?

Answer 27

• Companion cropping e.g. clover cover crops under-sown in winter wheat increase yield of subsequent spring barley (however this system doesn’t always work - some combinations of crops work better than others)
• Green manures
• Crop rotation
• Agro-forestry - use of trees to recycle nutrients and water deep in soils- below the rooting depth of annual crops

Question 28

what does diversity mean in terms of food production?

Answer 28

productivity and dietary variety