Leave crop residues on the field
System: Olive Orchards
Description
Applying organic material to soils, such as pruning debris or compost. Also leaf fall, bark fall, and fruit falls in the rainy season supply additional C input to the soil. In case the litter is removed during harvests, it is beneficial to apply it later back on the soil. This could replace mineral fertilizer applications without a reduction in productivity (Altieri et al., 2008). The use of olive mill waste requires an appropriate concept and strategy, as it is not suitable and, in some countries, not allowed to apply olive mill waste directly to the fields as a pure application of olive mill waste have a damaging impact . If added to compost, it can contribute to organic amendments. Studies showed that the application of olive mill waste compost affects a decrease in pH (García-Ruiz et al., 2012) which should be monitored and might required additional soil treatment to control the soil pH.
Mechanism of effect
Organic materials include carbon, which is added to the soil. This can be in form of pruning debris, litter (directly fallen from the trees or brought back to the field) and compost. Perennial crops produce more residues than annual crops. Keeping the residues on the soil or bringing them back after they are removed will increase soil organic carbon (SOC). Beside the higher rate of residue, perennial plant inputs from management interventions such us pruning and on-site retention of litter add to the overall carbon input (Ledo et al., 2018). Additionally, perennial crops develop larger and deeper roots which provide more carbon for the soil. Pruning, litter and compost are organic amendments that all increase SOC. Here, olive leaves seem to have a major impact (Lozano-García & Parras-Alcántara., 2013).
Effects on GHG emissions
Reference situation: No pruning, litter removed, no olivemill waste applied
Effect on soil organic carbon (SOC) stocks
| Relative change (%) in SOC%: | Change in t/ha | |||||
| Mean | (min-max) | Mean | (min-max) | Level of evidence | ||
| Apply organic amendments | ● ● | ● – ●●● | ● ● | ● – ●●● | Low | |
| ● – small increase (<10%) | ● – small decrease (<5%) | o – no effect |
| ●● – medium increase (10-25%) | ●●– large decrease (≥5%) | ? – unknown effect |
| ●●● – large increase (>25%) | ● – ● – Variable effect (depending on farm characteristics or way/level of implementation) |
Explanation of variable effect
Apply organic amendments
The impact of organic amendment on SOC in general depends on the amount of organic material applied. Additionally, local conditions (e.g. initial SOC, texture, climatic conditions) affect the impact on the soil. Therefore, the provided estimates for carbon gain will vary across different locations and cannot be generalised. The analysed studies include experimental locations that applied a very high amount of organic material. Therefore, the maximal values can be assumed to be over-optimistic for farm applications. Pruning is applied to allow aeration of the foliage and to enhance new shoots (Fraga et al., 2021). Further, leaving the pruning debris on the site will improve soil fertility and increase SOC. It is beneficial to use mulching to incorporate the pruning debris to the soil, while burning the debris will have a negative effect (due to increased emissions).
| Literature references | |
|---|---|
| Altieri et al., 2008 | Olive orchard amended with two experimental olive mill wastes mixtures: effects on soil organic carbon, plant growth and yield. Bioresource Technology, 99(17), 8390-8393. |
| Fraga et al., 2021 | Mediterranean Olive Orchards under Climate Change: A Review of Future Impacts and Adaptation Strategies. |
| García-Ruiz et al., 2012 | Improved soil quality after 16 years of olive mill pomace application in olive oil groves. |
| Lozano-García & Parras-Alcántara, 2013 | Short-term effects of olive mill by-products on soil organic carbon, total N, C: N ratio and stratification ratios in a Mediterranean olive grove. |
| Ledo et al., 2018 | Perennial-GHG: A new generic allometric model to estimate biomass accumulation and greenhouse gas emissions in perennial food and bioenergy crops. |