**3. Sampling of leaves and soil in fruit orchards**

The soils in Brazil are mainly tropical, are low in fertility and normally show acid reaction. This is particularly due to their weathering during soil formation. This is one of the main reasons for applying lime and fertilizers in farmed areas. Another important factor is that because of Brazil's continental dimensions, it has a wide range of climate and soil character‐ istics, requiring different liming and fertilization regimes depending on orchard location.

Furthermore, different soils have different nutrient deficiencies, and plant species vary greatly in their nutritional demands. Therefore, the only reliable way to identify the best acidity corrective measure or fertilizer for use in a determined place for a particular crop is soil analysis.

Besides soil analysis, which is a well-established practice in agriculture, it is also important for the majority of fruit trees to analyze the leaves for determining the pattern of nutrient uptake over time [19]. Because adult fruit trees require a certain degree of nutritional stabili‐ ty, leaf diagnosis allows adjusting fertilization programs over the years so as not to impair fruit harvest in the same year. Hence, leaf sampling and soil analysis are useful methods to monitor the effects of liming and fertilization on plant nutrition. Growing fruit trees is a long-term activity where the plants continue exploiting practically the same volume of soil for many years. In this situation, chemical impediments (acidity) as well as physical ones (soil compaction) can reduce the efficiency of the roots in exploiting the soil. Therefore, the only way to determine to what extent plants are using the nutrients applied via fertilization and liming is to diagnose their nutritional status by leaf analysis.

Chemical analysis is the easiest and most practical way to assess soil fertility. Proper sam‐ pling is essential to obtain reliable results because if the samples are not representative, the results do not accurately reflect the true soil fertility. Soil sampling is a common practice among farmers for annual crops, but it has not been widely studied for perennial crops such as fruit trees, raising doubts on its reliability. The present recommendations are to sample the area that receives soil treatment. However, some works have shown a higher correlation between leaf nutrient levels of fruit trees and soil nutrient levels in the paths between rows than in the rows [12, 20]. So, which soil samples should be analyzed, those from the treated area or between the rows? How should correlations be interpreted? And at what depth should the soil be sampled? These are difficult questions to answer, and according to [8], it also is not easy to design studies for this purpose.

At the time of planting fruit orchards, the soil sampling procedure is the same as for annual crops, namely across the entire representative area. In producing orchards, it is important to sample the region under the projection of the tree crowns, which is the area that usually re‐ ceives fertilizers. Samples should be collected at the end of harvest from 20 points in each homogeneous plot (same cultivar, age, productivity, soil type, management and fertiliza‐ tion). At the same time, samples should be taken between the rows to measure lime require‐ ments if necessary. Studies have shown that acidification occurs more intensely under the projection of tree crowns due to nitrogen fertilization, application of organic wastes and ac‐ cumulation of plant material from pruning. As a rule, limestone is more often applied in strips under crown projection than onto areas between rows.

The most common method to calculate lime requirement in Brazil is base saturation [10]. The formula is as follows:

$$LN \text{ (ton } h \text{ } a^{-1}\text{)} = \frac{(V\_2 - V\_1) \times CEC}{TRNP \times 10}$$

where:

surface, because the incorporation of corrective materials into the soil may induce phytosa‐ nitary problems to the plants. Materials with finer particles can move more easily through

Considering the perennial nature and cultivation conditions of fruit trees, the path of limestone particles in the soil can vary along with various factors, including physical ones, through the channels left by the decomposition of roots [14]. According to [15] and [16], another explanation for particle flow through the soil profile is the formation of ion pairs

and RCOO-

weight that can be leached to deeper layers. Besides these mechanisms, according to [17] other compounds may form such as Ca(HCO3)2 and Mg(HCO3)2. Nitrogen fertilization, in turn, can promote the formation of soluble salts, such as calcium nitrate, which percolate down through the soil in forms dissolved in water [18]. According to [11], it is probable that the sum of the contributions of all these processes is more important than each one individually. Finally, the movement of these particles depends on the dose of the correc‐ tive measure employed, the time after application, soil type and the type of fertilization

The soils in Brazil are mainly tropical, are low in fertility and normally show acid reaction. This is particularly due to their weathering during soil formation. This is one of the main reasons for applying lime and fertilizers in farmed areas. Another important factor is that because of Brazil's continental dimensions, it has a wide range of climate and soil character‐ istics, requiring different liming and fertilization regimes depending on orchard location. Furthermore, different soils have different nutrient deficiencies, and plant species vary greatly in their nutritional demands. Therefore, the only reliable way to identify the best acidity corrective measure or fertilizer for use in a determined place for a particular crop is

Besides soil analysis, which is a well-established practice in agriculture, it is also important for the majority of fruit trees to analyze the leaves for determining the pattern of nutrient uptake over time [19]. Because adult fruit trees require a certain degree of nutritional stabili‐ ty, leaf diagnosis allows adjusting fertilization programs over the years so as not to impair fruit harvest in the same year. Hence, leaf sampling and soil analysis are useful methods to monitor the effects of liming and fertilization on plant nutrition. Growing fruit trees is a long-term activity where the plants continue exploiting practically the same volume of soil for many years. In this situation, chemical impediments (acidity) as well as physical ones (soil compaction) can reduce the efficiency of the roots in exploiting the soil. Therefore, the only way to determine to what extent plants are using the nutrients applied via fertilization

Chemical analysis is the easiest and most practical way to assess soil fertility. Proper sam‐ pling is essential to obtain reliable results because if the samples are not representative, the

) of high solubility and low molecular

the soil profile, correcting the acidity only in the surface layers.

**3. Sampling of leaves and soil in fruit orchards**

and liming is to diagnose their nutritional status by leaf analysis.

(Ca2+ and Mg2+) and organic acids (RO-

applied to the orchard.

176 Soil Fertility

soil analysis.

LN is the need for limestone, in ton ha-1;

V2 is the target base saturation for the crop;

V1 is base saturation of the soil;

CEC is soil's cation exchange capacity; and

TRNP is the total relative neutralization power, which considers the quantity of carbonates present in the limestone and lime's granulometry.

The soil layer typically sampled is the surface 0 to 20 cm. However, fruit trees exploit a much larger soil volume compared to annual plants, so it is important to analyze the proper‐ ties of the deeper layers, especially regarding calcium and aluminum concentrations. This may lead to gypsum application, which neutralizes toxic Al and allows increasing Ca con‐ centration in deeper layers, an important factor for the proliferation of the root system and its exploitation of a larger soil volume.

Gypsum is indicated, for crops in general, when analysis of the soil from the 20-40 cm layer reveals calcium concentrations lower than 4 mmolc dm-3 and/or aluminum saturation above 40%. The need for gypsum is estimated by the following equation [10]:

```
GN (kg h a −1
              )= 6 × clay
```
where:

GN is the need for gypsum, in kg ha-1; and

Clay is the soil clay content, in g kg-1.

For diagnosing the nutritional status of plants, leaf analysis is the most efficient technique, but also the one where errors occur most frequently. Each plant species has its own sam‐ pling procedure. Thus, the leaves to be collected and the time of the year are critical for suc‐ cessful diagnosis of the plant nutritional status. In the case of fruit trees, such as the guava tree, the third pair of leaves should be collected from each plant, with 25 pairs being collect‐ ed from each homogeneous plot. This should be done at the time of full flowering [21]. These leaves should be immediately taken to the laboratory for washing, drying, grinding and analysis. The next step is to interpret the results, based on studies conducted under field conditions in high-yielding orchards.

Fruit growing is an important activity in most Brazilian regions, especially those covered with latosols (oxisols) and argisols (ultisols), which are generally deep and permeable, hence providing ideal conditions for perennial crops that produce a broad and well developed root system. Nevertheless, these soils have a strong acid reaction and are low in nutrients, so

Soil Acidity and Liming in Tropical Fruit Orchards

http://dx.doi.org/10.5772/53345

179

Roots do not develop satisfactorily in highly acid soils. Among the acidity factors, alumi‐ num toxicity and calcium deficiency are indicated as the most relevant restrictions to root growth. Regarding acidity correction with application of limestone at soil surface without no incorporation, research reported low movement of the lime to deeper layers, depending

Knowledge to support adequate management of soil fertility and plant nutrition is particu‐ larly important for fruit growing systems, given the influence these production factors on the qualities of fruits, such as color, size, taste, aroma and appearance. Meeting plants' nu‐ trient needs is one of the key factors for the success of this activity, because besides affecting yield and quality, adequate nutrition increases plant growth, tolerance to pests and diseases and postharvest longevity. On the one hand, the demand of this group of plants for mineral elements is relatively high, while on the other tropical soils in which they are normally culti‐ vated are low in nutrients, making it imperative to apply nearly all the nutrients necessary for their full development. This leads to the use of high amounts of fertilizers [21, 11] and corrective measures [12, 13, 22] in orchards and requires technical competence for economi‐ cally rational use of these inputs. For Brazilian conditions, the analyses can be interpreted

Information on the effects of liming on the development and nutritional status of fructifer‐ ous plants is very limited in the literature despite the widespread scientific recognition of the importance of acidity correction. Much more attention has been paid to these aspects in annual cropping systems, but those findings cannot be transferred directly to perennial plants because the latter do not react the same way to liming and fertilization for a various

**a.** The roots of perennial plants like fructiferous ones exploit a large volume of soil, which increases as plant ages, and little is known about the nutritional reserves in deeper soil

**b.** Roots, trunk, branches and leaves of perennial plants form large reservoirs of nutrients. Therefore, these plants have hidden early deficiency that makes it difficult for the farm‐ er to implement corrective measures at the right time. Furthermore, it takes longer peri‐ ods of time for these reservoirs to replenish, making these plants slower to react to

**c.** The regular pruning of fructiferous plants complicates the problem of liming and fertili‐ zation. By restricting vegetative development, pruning hides even more deficiency symptoms and hence the effects of corrective measures. However, in many cases prun‐ ing is essential, because, as the saying goes, "hunger for light is just as harmful as hun‐

on the dose applied, the time elapsed and the fertilization regime.

they need liming and fertilization.

with the help of the Fert-Goiaba software [23].

reasons as follows [24]:

nutrient applications.

ger for nutrients."

layers.

In summary, when performed correctly, analysis of soil and leaf samples can allow making recommendations on liming and fertilization to improve fruit yield and quality, and hence increase the profits of fruit growers.
