Nitrate leaching and slurry application in dairy grasslands

Broadcast application of cattle slurry to grassland soils is a natural means of fertilisation. However this practice is actually not optimised and leads to nitrogen loss to the atmosphere and groundwater. Novel application techniques such as injection into the soil are therefore tested. Kayser et al. found that the type of application technique has no effect on nitrate leaching. Whereas the amount of applied slurry has an effect on nitrate leaching.

 

Winter turnip rape, a Nordic catch crop that recycles nitrogen and decreases nitrate pollution

A catch crop is a crop planted between two regular crops grown in successive seasons or between two rows of crops in the same season. Catch crops are used in particular to reduce soil erosion and fertiliser leaching that occur when the soil surface is not planted. For instance nitrogen catch crops feed on nitrates and thus recycle soil nitrogen and decrease water pollution by nitrates. Catch crops are therefore a way to reduce the use of costly fertilisers. Tuulos et al. show that winter turnip rape, an oilseed crucifer, is an effective nitrogen catch crop adapted to the Nordic climate.

 

Biofertilisers to grow rice cheaper

Rice is a major food worlwide. The cost of rice fertilisation using mined fertilisers such as nitrogen (N), phosphorus (P), and potassium (K) amounts to 30-35% of the cropping cost, and is still increasing. This issue could be solved by replacing mined fertiliser by biofertilisers that contain microbes helping the plant to grow, so-called ‘plant growth-promoting microorganisms’. The report by Rose et al. indeed show that inoculant biofertilizers can replace up to 52% of mined nitrogen fertiliser without loss of yield.

 

Synthetic fertilisers: too much of a good thing

Today half of the world population would not be alive without the 68 million tons of nitrogen (N) fertiliser applied to agricultural soils yearly. However, synthetic N has become too much of a good thing because most applied N is not used by crop plants and escapes to pollute groundwater as nitrates and atmosphere as nitrogen oxides. An alternative and cheap solution is to return plant residues to the soil, thus producing ‘natural’ N by plant residue decomposition. Chen et al. reviewed the effects of crop residues on soil N behaviour to better understand the mechanisms of transformation, and to predict farming practices that optimise natural fertilisation.

 

Composted poultry litters fertilise soybean crops and increase soil quality

Composted and formulated poultry litters can be used as organic fertilizer for value added soybean crops such as edamame to maintain soil productivity and partially restore nutrients removed at harvest. However, applications may be limited by lack of understanding of properties and behavior in soil and impacts on plant and seed quality components in addition to yield. Greenhouse and field experiments by Blair et al. show that composted poultry litter is better for edamame production than formulated litters because composted poultry added a more stable organic substrate to soil.

 

Legumes are the future of food and fertilisation

Legumes are plants that do not need nitrogen (N) fertilisation because legumes are plants that are able to fix atmospheric nitrogen (N2). In addition legumes can be used as ‘green’ fertilisers because legumes are N-rich and thus cropping legumes provides the soil with a cheap, sustainable source of N fertiliser. Legumes are also an excellent source of protein for feed and food. Nonetheless legume cropping land in Europe represents only less than 4% of arable land. The grounds for such a low cropping surface are discussed by Voisin et al. who analyse the production of forage and grain legumes in France since 1950. The authors propose changes to improve legume production.

 

Silicon-rich manure for sustainable rice production

Rice is a plant that needs silicon (Si) as a nutrient to grow well. Silicon is an element of silica (SiO2) found commonly in sand. Rice yields decrease when soils are depleted in available silicon. A possible solution is to add silicon-rich manure to soils. Song et al performed a 10-year field experiment and found that adding silicon-rich manure doubled the amount of available silicon in soils. Using manure brings the additional benefit of recycling organic waste and providing other plant nutrients such as nitrogen and phosphorus

 

Benefits and risks of anaerobic digestate fertilisers

Intensive soil fertilization with mineral fertilizers has led to several issues such as high cost, nitrate pollution, and loss of soil carbon. Fertilization with organic wastes such as anaerobic digestates is an alternative for sustainable agriculture. Conflicting results in the literature have questioned the effectiveness of anaerobic digestates as organic fertilizers. The review by Roger Nkoa demonstrates the fertilizer values of anaerobic digestates. However, anaerobic digestates emit amonia (NH3) and contain copper (Cu), Zinc (Zn) and manganese (Mn) that could pollute the soil and the atmosphere upon repeated soil applications.

 

Benefits of compost in agriculture

Climate change and most actual world food issues are linked directly or indirectly to soil loss of carbon and fertility. Here composting appears as a cheap and sustainable solution.The review by Martínez-Blanco et al. presents nine benefits of compost application to the soil. Composting practices are classified into short-term, mid-term, and long-term benefits.