The latter case refers to the cultivation of, above all, legumes, are made to then pay the Earth. They also incorporate nitrogen. Often used e.g. alfalfa, beans, etc. In an urban garden, don’t usually have enough space to allocate to this type of fertiliser, but what you can do is to cultivate some vegetables for consumption and then use its leaves and stems to fertilize, they can be beans, beans or green beans (in my case, peas worked me very well). Manure surface, mulch, mulch or mulching another way to improve the fertility of the soil is placed about it, around the plants, a layer of organic matter, which will be decomposing; watering and rains take these nutrients to the roots. While more traditional is to use straw, they can be used different plant debris, such as leaves, freshly cut grass, bark or even girls branches, compost, etc.
I usually use a layer of remnants of cuisine that I know that it decomposes quickly; egg shells, you will be providing calcium slowly; very thin strips of banana (potassium) shells; compost or soil paying a half done; old grass, which is very good to keep moisture and above that a mixture of dry grass and bark, with a larger branch. When applied in a pot, should be larger than that you hope, because right away, with the risks and decomposition, it decreases its volume and settles. In addition to enriching the soil, has other benefits: keeps the humidity (because it prevents that you evaporate the water); It protects the land of the force of rain or irrigation (very useful potted balcony, that sometimes there are half inaccessible when it comes to watering and dropped water from a distance, with great force); It regulates the temperature and, although it is not common in urban gardens, prevents the emergence of weeds. For this reason, I also use it in seedbeds the first year that I had a macetohuerto, what he was doing is burying plant remains on the same land, because he understood that it would go decomposing and feeding the roots directly.