*4.1.4. Chickpea*

pods also showed low half‐life value (both of approximately 70 days). Those authors observed N and P release and half‐life following the residue decomposition rate, while the K release was faster (average half‐life of 18 days) and showed low difference regarding the material quality. In this case, N and P could be better used by the subsequent crop, while K can be reused by the same crop. The yield of 1350 kg/ha presented a potential for cycling 31.5 kg/ha N and

The species *Vigna mungo*, *Vigna radiata*, and *Vigna unguiculata* stand out in the *Vigna* genus, the latter being the most cultivated. These species have short cycle, low water requirement, and good development in low fertility soils; in addition, the BNF is capable of supplying more than 100 kg/ha of N [94, 95]. An increase in millet productivity of 9–24% was observed in an experiment carried out in three different locations in Niger, when cowpea was previous

A C/N ratio of 15.8 was found in cowpea residues grown in a field experiment evaluating N mineralization depending on the phosphorus content in tissues [97]. In the same experiment, the authors found an increasing in N mineralization (25, 32, and 34%) with increasing P concentration in tissues (1.0, 1.2, and 2 g/kg, respectively) in 8 weeks. This fact demonstrates the close relationship between nutrients interfering in the mineralization process, emphasizing the importance of fertilization management together with residues management. A potential mineralization from 6.8 to 9.2 g of N per kilogram of dry matter of cowpea residues is consid‐

India is largest producer of peanuts (*Arachis hypogaea*), which usually uses 10–20 kg/ha of N from ammonium sulfate. A large number of farmers in that country use crop rotation with groundnut to take advantage of its ability to improve soil fertility and increase the subsequent

The peanut cultivation in Brazil is also carried out with the same goal, but most in rotation with sugarcane. A C/N ratio of 15 and 24, and an addition of 70 and 38% of N from BNF in plant tissues, was, respectively, observed in the IAC‐Caiapó and IAC‐Tatu varieties, in acid soils [99]. These authors emphasized that the N values from BNF for IAC‐Tatu were low because the sampling, which was performed 120 days after sowing, when the plant was in an advanced stage of pods maturation and much of the N had translocated to the grains. About 90% of N was from the shoot in the average for these cultivars. In this same experiment, there was a yield increase of 12.2 (IAC‐Caiapó) and 15.5 t/ha (IAC‐Tatu) in the sugarcane crop compared with the control. Bagayoko et al. [96] also reported an increase of approximately 39% in average yield of sorghum after groundnut cultivation compared to subsequent sorghum crops; during 3 years of experiment in Kouaré (Burkina Faso), they found N mineral

The groundnut may also be infected by arbuscular mycorrhizal fungi [99], which favors the

2.37 kg/ha P from the bean residues [93].

68 Organic Fertilizers - From Basic Concepts to Applied Outcomes

ered as a practical reference.

crop yield, due to the BNF [98].

increment available for sorghum.

next culture infection [96] and improves the P cycling.

*4.1.3. Groundnut (peanut)*

cultivated compared to successive cultivation of millet [96].

The chickpea (*Cicer arietinum*) is the second more cultivated legume in the world to obtain grains. Most of the chickpeas production and consumption occur in developing countries (95%). A BNF evaluation by the 15N natural abundance method in different areas of Punjab showed that 58–86% of N (an average of 78%) could be derived from symbiosis, fixing 87– 186 kg/ha of N. The average balance of N left by chickpea was 28 kg/ha N in that experiment, the yield ranged from 0.6 to 2.0 t/ha and the N in the soil increased in 38%, on average. The yield increase in the wheat planted in the sequence ranged from 19 to 73%, even with shoot residues removed [100]. Around 90 kg/ha of N fixed was found in a cultivation field in Australia using similar methods [101]. Turpin et al. [102] suggest that chickpeas can fix 146– 214 kg/ha of N and contribute with 80–135 kg/ha of N, including the roots.

The ICRISAT work in Kenya reported that chickpea residues contributed from 30 to 35 kg/ha of N to the subsequent wheat crop [103], while the TSBF reported contributions of about 40 kg/ha of N for maize [104].

### *4.1.5. Difficulties*

The absorption and mineralization must be synchronized for an effective N supply by a leguminous species [105]. According Palm, organic residues release about 80% of their nutrients during decomposition, but <20% is absorbed by the crops, often because the lack of synchronization between the release and absorption [106]. There are several studies reporting the decomposition rate and mineralization depending on soil and climatic characteristics, but there is still a lack of field data in some major producing regions and data to create models to predict the nutrients mineralization and availability.

The contribution of N mineralization arising from the root system is noteworthy, for example, Evans et al. [107] and Larson et al. [108] reported negative contribution of N to some tropical legumes when considering only the N from the shoot, with different results found when they accounted the N contained in the nodulated roots. Another factors to consider in the experi‐ ments are the biochemical characteristics and C/N ratios of the residues. We must pay attention to the fact that how higher residue decomposition rate, lower will be the vegetation cover time.

#### **4.2. Perennial crop residues**

Different from annual crops, nutrients from perennial crop residues are normally used in the same culture, but similarly, they take advantage of nutrients not exported at harvest. A perennial crops peculiarity is the use of residues from processing in the farm. Once seen as an environmental impasse, such residues are currently good sources of nutrients.

#### *4.2.1. Sugarcane*

The estimated BNF in sugarcane may reach 0.5 Tg per year [109]. Although the N added by BNF generate savings for the system, the straw C/N ratio is around 97–149 [110, 111] and the stem around 118 [112], promoting an initial immobilization of N. Straw is the main residue left in field, which has high C/N ratio and high lignin content, about 21% [111]. It is estimated that each ton of sugarcane produces 150 kg of sugar, 140 kg of dry bagasse and 140 kg dry matter of straw [113], approximately 17 t/ha of straw [110].

In an experiment with 15N labeled straw, Gava et al. [110] found that the N use efficiency by ratoon cane was 9% (68 kg/ha N) and that the main contribution of N from straw was to maintain or increase the organic N in the soil. Furthermore, this N became available in the second half of the cycle.

Another effective contribution of the sector is the vinasse return to the crops. Each liter of ethanol produced in distillery produces between 12 and 14 L of vinasse, which has 0.5–1.0% of soluble carbon and high levels of K (typically 12 g/L), and contain considerable amounts of other nutrients [114]. Gava et al. [110] used vinasse with the following contents (kg/m3 ): 0.41 of N, 0.07 of P2O5, 2.72 of K2O, 0.91 of CaO, 0.38 of MgO, and pH (water) of 4.9. Typically, the dose applied is around 80–100 m<sup>3</sup> /ha.

Resende et al. observed a sugarcane yield increase of 12–13% after application of vinasse in a period of 16 years [115]. However, in some situations, vinasse is recurrently applied near of the distillery due to the cost of transportation, occurring concentrated applications with ground water salinization and/or contamination potential.

The filter cake is also a residue from the sugarcane processing used in the field. The sugarcane processing in Thailand produces 3.4% of filter cake and 25–30% of bagasse from the sugarcane fresh material [116]. Each ton of sugarcane crushed generates around 40 kg of filter cake [117], which has variable composition, but with high levels of organic matter (OM), P, N, Ca, substantial amounts of K and Mg [118], as well as Fe, Mn, Zn, and Cu [119].

Two works illustrate the variability of nutrient content in the filter cake. In Brazil, Fravet et al. [120] found pH of 4.5, C/N ratio of 20.9, C/P ratio of 17.65, OM of 20.1%, humidity of 71.4%; Ca of 2.43%, Mg of 0.26%, S of 0.39%, P (H2O) of 0.33%, P (CNA + H2O) of 0.40%, P (citric acid) of 0.40%; P2O5 (total) of 0.98% and K of 0.25%. In Thailand, Meunchang et al. [116] found pH (water 1:5) of 7.7, C/N ratio of 14, OM of 48%, P (total) of 0.96%, K of 0.39%, Ca of 7.1%, Mg of 0.4%, Cu of 1.9 mg/kg, Zn of 51 mg/kg, Mn of 257 mg/kg, and Fe of 803 mg/kg.

The filter cake can be applied in the entire area at pre‐planting in the furrow or planting lines. According to Nunes Júnior [118], 20 t/ha of filter cake on wet base or 5 t/ha on dry base can provide up to 100% of the N required by the plants and 50% of the P, 15% of K, 100% of Ca, and 50% of Mg. In ratoon cane, the application of 70 t/ha of filter cake provided the greatest productivity of sugarcane stalks, regardless of application mode [120].

### *4.2.2. Coffee*

Coffee is the second most traded commodity in the world, behind oil. The coffee husk is a common residue of the processing on farms, accounting for about 50% of the dry fruit harvested [121]. This residue can return to coffee plants for nutrients release, providing around 29 g/kg of N (mostly in the form of nitrate) and 45 g/kg of K [122].Values of 23 g/kg of K‐total (7.4 g/kg K‐soluble), 14.8 g/kg of N, C/N ratio of 30, and 21 g/kg of lignin have also been found in coffee husks naturally dry. The K release from husks is high (above 90%) and regardless of the coffee bean constitution, decomposition rate, or processing type [123].

Another processing variation is the pulping done by the wet method, which withdraws just the husks, and the pulp and grain are placed to dry along with the parchment. Afterward, the parchment is removed from the coffee bean, which constitutes 12% of the dry fruit harvested. The pulp and parchment have 3.65 and 0.38% of K and 1.85 and 0.59% of N, respectively [124]. The C/N ratio in the pulp is around 24 while in the parchment is 63. In the husk in the same processing, 38.9 g/kg K‐total (17.7 g/kg K‐soluble), 26.7 g/kg of N, C/N ratio of 16 and 20.9 g/kg of lignin were found [123].

The variation in nutrient content within the same post‐harvest processing must be taking into account, but mainly when they are from different processing (**Figure 3**). Composting is also a good option for husk use [125, 126].

**Figure 3.** Coffee pods stack after processing. This residue returns to farming by providing mainly K and N. Photo by Lucas de Ávila‐Silva.

#### *4.2.3. Eucalyptus*

in field, which has high C/N ratio and high lignin content, about 21% [111]. It is estimated that each ton of sugarcane produces 150 kg of sugar, 140 kg of dry bagasse and 140 kg dry matter

In an experiment with 15N labeled straw, Gava et al. [110] found that the N use efficiency by ratoon cane was 9% (68 kg/ha N) and that the main contribution of N from straw was to maintain or increase the organic N in the soil. Furthermore, this N became available in the

Another effective contribution of the sector is the vinasse return to the crops. Each liter of ethanol produced in distillery produces between 12 and 14 L of vinasse, which has 0.5–1.0% of soluble carbon and high levels of K (typically 12 g/L), and contain considerable amounts of other nutrients [114]. Gava et al. [110] used vinasse with the following contents (kg/m3

of N, 0.07 of P2O5, 2.72 of K2O, 0.91 of CaO, 0.38 of MgO, and pH (water) of 4.9. Typically, the

Resende et al. observed a sugarcane yield increase of 12–13% after application of vinasse in a period of 16 years [115]. However, in some situations, vinasse is recurrently applied near of the distillery due to the cost of transportation, occurring concentrated applications with

The filter cake is also a residue from the sugarcane processing used in the field. The sugarcane processing in Thailand produces 3.4% of filter cake and 25–30% of bagasse from the sugarcane fresh material [116]. Each ton of sugarcane crushed generates around 40 kg of filter cake [117], which has variable composition, but with high levels of organic matter (OM), P, N, Ca,

Two works illustrate the variability of nutrient content in the filter cake. In Brazil, Fravet et al. [120] found pH of 4.5, C/N ratio of 20.9, C/P ratio of 17.65, OM of 20.1%, humidity of 71.4%; Ca of 2.43%, Mg of 0.26%, S of 0.39%, P (H2O) of 0.33%, P (CNA + H2O) of 0.40%, P (citric acid) of 0.40%; P2O5 (total) of 0.98% and K of 0.25%. In Thailand, Meunchang et al. [116] found pH (water 1:5) of 7.7, C/N ratio of 14, OM of 48%, P (total) of 0.96%, K of 0.39%, Ca of 7.1%, Mg of

The filter cake can be applied in the entire area at pre‐planting in the furrow or planting lines. According to Nunes Júnior [118], 20 t/ha of filter cake on wet base or 5 t/ha on dry base can provide up to 100% of the N required by the plants and 50% of the P, 15% of K, 100% of Ca, and 50% of Mg. In ratoon cane, the application of 70 t/ha of filter cake provided the greatest

Coffee is the second most traded commodity in the world, behind oil. The coffee husk is a common residue of the processing on farms, accounting for about 50% of the dry fruit harvested [121]. This residue can return to coffee plants for nutrients release, providing around 29 g/kg of N (mostly in the form of nitrate) and 45 g/kg of K [122].Values of 23 g/kg of K‐total (7.4 g/kg K‐soluble), 14.8 g/kg of N, C/N ratio of 30, and 21 g/kg of lignin have also been found

/ha.

substantial amounts of K and Mg [118], as well as Fe, Mn, Zn, and Cu [119].

0.4%, Cu of 1.9 mg/kg, Zn of 51 mg/kg, Mn of 257 mg/kg, and Fe of 803 mg/kg.

productivity of sugarcane stalks, regardless of application mode [120].

ground water salinization and/or contamination potential.

): 0.41

of straw [113], approximately 17 t/ha of straw [110].

70 Organic Fertilizers - From Basic Concepts to Applied Outcomes

second half of the cycle.

*4.2.2. Coffee*

dose applied is around 80–100 m<sup>3</sup>

Eucalyptus crops with ever shorter cycles (6–7 years) are extremely dependent on the biogeo‐ chemical cycling of nutrients from the residues that are added to the soil over the cycle and also at harvest. A eucalypt forest produces an average of 75% of commercial wood, 1.5–3% of leaves, 4–6% of branches, 6–19% of barks, and 10–12% of roots, considering the total biomass, after 7 years [127].

Studies have shown that eucalyptus planted forests can deposit 7–84 tons of dry matter to the soil during 7 years, from old dead branches and dry fruits (25–30%), barks (10–15%) and leaves (55–65%) [128].

The treetops begin to close between the 1st and 2nd year after planting, and the competition causes the disposal of branches and lower leaves that are gradually deposited on the ground. The trees are taller and with small treetops from the 3rd to the 4th year, occurring the deposition of barks. However, the quantities of residue deposited to the ground depend on the eucalyptus species, climate, and evapotranspiration. The components of the eucalyptus forest deposited to the ground are called litterfall, which has great influence on the nutrients availability to the eucalypt [127].

Thus, considering that the estimated content of nutrients accumulated (in relation to the total accumulated in the plant) in the tree tops and eucalyptus bark after 6.5 years has on average 65% of N, 70% of P, 64% of K, 79% of Ca, and 79% of Mg [128], considerable amounts of nutrients are deposited to the ground and are considered in the fertilization management. In addition, the harvest of trees leaves in the area large amounts of residues such as leaves, branches, tree tops, and small trees discarded during harvest. The trees can be pruning and strips in the area or at companies, depending on the harvesting modules used. Some companies separate the so‐called woody debris (thick branches, tree tops and small trees) and sell as wood or trans‐ formed into wood chips to produce biomass fuel for the company itself, depending on the demand.

However, we must emphasize here the importance of the retention of crop residues in the area because during the harvest the accumulated litterfall on the soil surface has order values of 8– 14 t/ha [129, 130]. Studies have been shown that lower amounts of nutrients are required in fertilization when the bark is left in the field at harvest [131–133]. Moreover, the roots also remain in the area, since that the currently practice of stump removal is increasingly scarce due to the large impact on the soil.

The crop residues have nutrient availability potential remaining in the area and can reduce the impact on the soil due to the heavy‐machinery used [134, 135]. This is an important fact, since forestry operations can alter the physical and mechanical properties of the soil [136], increasing soil compaction. The productivity of eucalyptus forests may reduce with increasing soil compaction levels [137, 138], due to: (*i*) physical obstruction of developing roots; (*ii*) lower water and nutrients absorption; (*iii*) gas exchange reduction.

Many factors influence the residue decomposition rates in the soil, with later nutrients availability for plants as we mentioned in the item 2. Generally, the leaves have faster biode‐ gradation, since they have C/N ratios of 25–45 and C/P of 250–300, while the branches and trunk have C/N of 350–500 and C/P of 500–700 and the barks have C/N of 150–250 and C/P of 300–450 [127]. However, the nutrients allocated in the residues will not be fully available for eucalyptus plants; thus, many companies conduct tests in their crop areas trying to estimate the decomposition rates of the plant compartments and the recovery rates of applied fertilizers. Many companies use these data to establish the complementary fertilization management, seeking to minimize costs and make a more sustainable system.

Works describing the decomposition rates of different compartments in different environ‐ ments can be found in the literature [139–143], which can be used for fertilization estimates when perform the tests is not possible. Some modeling programs such as the Nutricalc‐UFV, allows us to estimate the different rates that will assist in the fertilization management. The residues have great importance on the nutrient balance of a system, and we cannot ignore the benefits of the construction and permanence of soil organic matter.
