Nutrient demand, storage, cycling

Question 1

Monocultures vs mixtures of plants co-existing-

intensive agriculture and ecosystems

Answer 1

Why are monocultures rare in nature?

Do more diverse mixtures of plants suffer less weed, pathogen, and pest problems?

The elemental composition of different plants is very similar

Do the same species of plants compete with each other more strongly for nutrients?

Do different species obtain some or all of their nutrients from different sources or niches?

Are monocultures inherently less nutrient-use efficient than mixtures of species?

Question 2

Spatio-temporal effects of monoculture cropping-

Answer 2

Huge areas growing the same limited numbers of crops/ varieties makes agricultural production 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.

Growing the same crop more frequently in rotations builds up pathogens and reduces yields.

Question 3

Increasing the diversity of crops 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.

Answer 3

Data from 2016 shows about 60% of the Cabbage Stem Flea Beetle population in the UK is pyrethroid resistant and this resistance applies across all pyrethroids.

EU Common Agricultural Policy 3-crop rule. … This 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 4

Unfavourable preceding crop reduced yield of wheat, barley and oilseed rape by 10% on average. Break crop benefits persisted to the second year.

Answer 4

“The wheat/wheat/rape rotation that has been the first choice for heavy (clay rich) land across much of the country is being called into serious question in terms of both black-grass management and oilseed rape pest and disease control,”

More diverse rotations currently give less profit

Question 5

Crop production depends on nutrient supplies

Answer 5

Sustainable crop production depends on sustainable nutrient supplies

The soil provides an important store of nutrients- and when fertilizer is added to soil unless the soil has a good capacity to hold onto the nutrients they may get washed out.

The 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 6

Clay structures, slabs

Answer 6

can store water, and more slab layers increases surface area

Question 7

What are the causes of negative charges on colloids?

Answer 7

Isomorphous subsitution
Within the crystal structures ions are replaced
e.g. Si4+ replaced by Al3+
Al3+ replaced by Mg2+

These substitutions give permanent charge.

Question 8

pH dependant charge

Answer 8

Increasing acidity in low pH clay means:

• high pH, low acidity, negative charge
• low pH, high acidity, positive charge

Question 9

Positively charged ions attracted in a swarm towards the negatively charged surface and held there by electrostatic attraction.

Answer 9

Organic matter and clays play a vital role in holding nutrient reserves in soil (e.g. during the winter) but 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 10

Colloid summary

Answer 10

Very small charged particles/macromolecules
Some have permanent charge
Some have pH dependant charge
Most have a combination of both
They attract ions of the opposite charge

Question 11

Biological ion exchange

Answer 11

• Roots and mycorrhizal fungi associated with roots selectively absorb nutrient elements.
• These organisms normally absorb more cations than anions.
• They actively release protons (H+) to maintain electrostatic balance.
• Roots and cell walls of microorganisms normally have net negative surface charge- attract cations.

Question 12

Do plants strongly compete with each other for nutrients or do different species obtain some or all of their nutrients from different sources or niches?

Answer 12

Examples of niche separation

1. Soil pore size/ root dimensions
2. Profile and spatial separation of roots
3. Different root phenologies and root architecture
4. Different nutrient source preferences.
5. Abilities to use nutrients that are unavailable to other plants.
6. Extensive vs. Intensive root systems.

Question 13

Has extensification of agriculture under more sustainable management been properly evaluated as an alternative to intensification?
Can we breed crops like wheat for light, water and nutrient use efficiency and no tillage?

Answer 13

Wheat bred to have high shoot and low root ratios

Natural ecosystems have variable root systems to maximise nutrition niche complementarity

Question 14

Management strategies for sustainable ecosystems.

Answer 14

Companion cropping
Green manures
Crop rotation
Agro-forestry

Question 15

Clover when under-sown with wheat increases yield of subsequent barley

Answer 15

Effect of N dose and companion grass

Question 16

Agro-forestry- use of trees to recycle nutrients and water deep in soils-

Answer 16

below the rooting depth of annual crops

Question 17

Banda Aceh after the 2004 Tsunami-

Fruit and vegetable garden- multi-tiered production.

Answer 17

Diversity= productivity and dietary variety

Question 18

Agroecological strategies

Answer 18

polycultures
animal integration
rotations
green manures
organic amendments

Question 19

Glover et al. 2010
Perennial grain crops would have similar advantages and also pro- duce food. Compared with annual counter- parts, perennial crops tend to have longer growing seasons and deeper rooting depths, and they intercept, retain, and utilize more precipitation (6–10). Longer photosyn- thetic seasons resulting from earlier canopy development and longer green leaf duration increase seasonal light interception efficien- cies, an important factor in plant productivity (7).

Answer 19

Greater root mass reduces erosion risks and maintains more soil carbon compared with annual crops (9). Annual grain crops can lose five times as much water and 35 times as much nitrate as perennial crops (10). Peren- nial crops require fewer passes of farm equip- ment and less fertilizer and herbicide (9), important attributes in regions most needing agricultural advancement.

Question 20

Sieling & Christen 2015
The current results revealed the importance of favourable preceding crops. During the last decades, increasing fertilizer and/or pesticide intensities more and more replaced the regulatory functions thus allowing for a simplification of the crop rotations.

Answer 20

However, evidence like the increasing problem with blackgrass suggests that the potential of the crop management is limited. A return to sustainable crop rotations providing informative results is required; however, unfortunately, the number of long-term rotation trials is still decreasing since their costs are very high and their need is not generally acknowledged.

Question 21

Hilton et al., 2013
Oilseed rape (OSR) grown in monoculture shows a decline in yield relative to virgin OSR of up to 25%, but the mechanisms responsible are unknown.

Answer 21

A long term field experiment of OSR grown in a range of rotations with wheat was used to determine whether shifts in fungal and bacterial populations of the rhizosphere and bulk soil were associated with the development of OSR yield decline. The communities of fungi and bacteria in the rhizosphere and bulk soil from the field experiment were profiled using terminal restriction fragment length polymorphism (TRFLP) and sequencing of cloned internal transcribed spacer regions and 16S rRNA genes, respectively. OSR cropping frequency had no effect on rhizosphere bacterial communities. However, the rhizosphere fungal communities from continuously grown OSR were significantly different to those from other rotations. This was due primarily to an increase in abundance of two fungi which showed 100% and 95% DNA identity to the plant pathogens Olpidium brassicae and Pyrenochaeta lycopersici, respectively. Real-time PCR confirmed that there was significantly more of these fungi in the continuously grown OSR than the other rotations. These two fungi were isolated from the field and used to inoculate OSR and Brassica oleracea grown under controlled conditions in a glasshouse to determine their effect on yield. At high doses, Olpidium brassicae reduced top growth and root biomass in seedlings and reduced branching and subsequent pod and seed production. Pyrenochaeta sp. formed lesions on the roots of seedlings, and at high doses delayed flowering and had a negative impact on seed quantity and quality.

Question 22

Berkgvist et al., 2010

Clover cover crops under-sown in winter wheat increase yield of subsequentspring barley—Effect of N dose and companion grass

Answer 22

The amount of spring-sown cover crops can be up to 2Mgha−1dry matter at wheat harvest without any notable effect on win-ter wheat yields. The amount of clover in a cover crop under-sownin winter wheat can be increased by reducing the N dose, whileincreasing the amount of clover can increase the yield of a subse-quent crop of spring barley by more than 2Mgha−1. The red cloverbiomass at wheat harvest was less affected by N than white clover,but no differences were found in residual effect between red andwhite clover. Large amounts of clover increase the risk of leaching ,as shown by the larger amount of SMN late in the autumn with clover, in particular pure white clover, than with ryegrass. The risk of leaching from cover crops with clover can be reduced by adding ryegrass to the seed mixture. The proportion of grass increases at higher N doses and thus the residual effect of the cover crop become smaller, but the risk of leaching also decreases

Question 23

FAO 2018

Answer 23

The total utilised agricultural area (UAA) in the UK has increased slightly to almost 17.5 million hectares. The area of total crops and uncropped arable land have also seen increases, helping to offset the 0.6% decrease in permanent grassland.