**2. Establishment of** *Arachis pintoi* **Krapov & W.C. Greg. as a cover crop in citrus plantations of Veracruz, México**

The citrus crop in Mexico is one of the most important agricultural activities, both in area established as the value of marketing. At the end of 1999, 322.000 ha of orange (*Citrus sinen‐ sis* L.) and 32,000 ha of Persian lime (*Citrus latifolia* Tan), which depend altogether more than 15,000 families involved in the processes of production, harvesting, packing and marketing. In the case of the orange, the estimated production in 1997 was 3.9 million tonnes, while for the Persian lime was 244 thousand tons [3].

*Arachis pintoi* has shown a high potential as a cover crop in perennial crops such as citrus [4], peach [5], banana [6] and papaya [7]; thus, its incorporation in orange and lemon plantations in Mexico could be a viable alternative. Considering this, we evaluated the ecotypes *A*. *pintoi* CIAT 17434, 18744 and 18748 as options in citrus vegetation of Veracruz, Mexico.

#### **2.1. Materials and methods**

In April 1996 we established two experiments on commercial farms located in the munici‐ palities of Martinez de la Torre and Misantla, Veracruz, Mexico (20 º 03 'north latitude and 97 ° 03'longitud west), with hot and humid climate (24 º C average and 1980 mm annual rainfall), and no definite dry season, at 112-151 meters above sea level. Figure 1 presents the data of temperature and rainfall recorded during the course of the experiments, which is typical of the region, whereas data of 20 years, except for rain April, where the normal is half of that shown in graph mentioned.

#### **2.2. First experiment**

In the most recent experience, three land preparation management experiments were con‐ ducted, in order to evaluate the establishment of *Arachis pintoi* CIAT 17434. The results offer a range of practices to cattle producers from which they could select the best practice ac‐

Previously, in 2006, two experiments were carried out in order to assess the establishment of

Also, were evaluated two treaments to establish *Arachis pintoi* and *Pueraria phaseoloides*. The two treatments consisted of (1) weeding by slashing (S) and application of herbicides (H), and (2) burning (+B) or not (-B), as main plots. Phosphorus (simple superphosphate) appli‐

In other experiment, two methods of soil preparation were evaluated in a native pasture. The two methods, conventional tillage and minimum tillage were evaluated under the es‐ tablishment of *A*. *pintoi* CIAT 17434 with fertilization (T1 and T2) and without fertilization (T3 and T4). In terms of number of *A*. *pintoi* plants established and soil cover, with complete soil preaparation, gave the best results. The legume did not respond to fertilization because

**2. Establishment of** *Arachis pintoi* **Krapov & W.C. Greg. as a cover crop in**

The citrus crop in Mexico is one of the most important agricultural activities, both in area established as the value of marketing. At the end of 1999, 322.000 ha of orange (*Citrus sinen‐ sis* L.) and 32,000 ha of Persian lime (*Citrus latifolia* Tan), which depend altogether more than 15,000 families involved in the processes of production, harvesting, packing and marketing. In the case of the orange, the estimated production in 1997 was 3.9 million tonnes, while for

*Arachis pintoi* has shown a high potential as a cover crop in perennial crops such as citrus [4], peach [5], banana [6] and papaya [7]; thus, its incorporation in orange and lemon plantations in Mexico could be a viable alternative. Considering this, we evaluated the ecotypes *A*. *pintoi*

In April 1996 we established two experiments on commercial farms located in the munici‐ palities of Martinez de la Torre and Misantla, Veracruz, Mexico (20 º 03 'north latitude and 97 ° 03'longitud west), with hot and humid climate (24 º C average and 1980 mm annual rainfall), and no definite dry season, at 112-151 meters above sea level. Figure 1 presents the data of temperature and rainfall recorded during the course of the experiments, which is typical of the region, whereas data of 20 years, except for rain April, where the normal is

CIAT 17434, 18744 and 18748 as options in citrus vegetation of Veracruz, Mexico.

cording their specific conditions.

46 Soil Fertility

*Arachis pintoi* as a cover crop in citrus plantations.

**citrus plantations of Veracruz, México**

the Persian lime was 244 thousand tons [3].

**2.1. Materials and methods**

half of that shown in graph mentioned.

cation (-P, +P) was included as subplots.

of its slow initial growth.

This was done in a lemon orchard Persian 3-year-old plantation trees with 7 x 7 m. We eval‐ uated the establishment as cover crop of the ecotypes: CIAT 17434, 18744 and 18748. The field was prepared with cross harrowing, 20 cm deep. AP 17434 was used for vegetative ma‐ terial (stolons 20 cm in length) while the remaining were planted with seeds (two seeds per planting point). All ecotypes were inoculated with *Bradyrhizobium* strain CIAT 3101. Sowing was done in furrows separated by one meter and 50 cm between plants. For the availability of plant material or seed ecotypes had different number of test sites, with three repetitions of a square meter per site, so the 17434 had five sites, while the 18744, two, and the 18748, a site. The treatments were fertilized at planting date with superphosphate single at 50 kg/ha of P2O5, and 30, 90 and 180 days after planting date with KCl (83 kg/ha). Number of plants (plants/m2) and plant height (cm) was evaluated at 4, 8 and 12 weeks; and coverage (%) at 4, 8, 12, 16, 20 and 24 weeks. The data of number of plants were subjected to a logarithmic transformation to meet assumptions of analysis of variance. Analysis of variance were per‐ formed, and means were compared using the Tukey test. For plant height only averages were estimated. We used a completely randomized design, with *Ap* ecotypes as treatments, and a level of probability (P) for comparison of means of 0.05 was used.

**Figure 1.** Climatic conditions during the establishment period.

In the case of coverage, the trend of the data indicated the existence of an asymptotic re‐ sponse, so exponential models were fitted to a maximum, logistic and sigmoid, using the routine "Regression Wizard" program SigmaPlot [8]. The model that final showed the best fit to the data coverage with rational values, was the three-parameter sigmoid, which is de‐ scribed below:

$$\mathbf{Y} = \mathbf{a} / \left(\mathbf{1} + \mathbf{e}^{\cdot \left((\mathbf{x} - \lambda \mathbf{u}) \wedge \mathbf{b}\right)}\right) \tag{1}$$

**2.4. Results**

*2.4.1. First experiment*

weeks of sampling.

**CIAT accesion**

\* Standard error of the mean.

were greater than 0.8 (Table 2).

**CIAT accesion n**

ecotypes, after planting.

\*\* Probability level.

Veracruz, Mexico.

*Number of plants.*Table 1 shows the average number of plants (and its standard error) for each accession. For the first and the second accesion an increase from week 4 to 12 was reg‐ istered, while for the third accesion, the average remained constant during the period evalu‐

Soil Management for the Establishment of the Forage Legume Arachis pintoi as a Mean to Improve Soil Fertility...

not detect any statistically significant difference within each accession, considering the

**Weeks**

17434 2.5 ± 0.24\* 3.1 ± 0.28 3.2 ± 0.33 0.0875 18744 3.8 ± 0.76 3.8 ± 0.51 4.2 ± 0.48 0.5833 18748 8.3 ± 0.33 7.7 ± 1.45 8 ± 1.0 0.8153

**Table 1.** Number of plants/m2 from *Arachis pintoi* ecotypes established as cover crop in a citrus orchard soil of

the model parameters were different from zero at the same level of probability. R2

and the latter value was more frequent in ecotypes 18744 and 18748.

*Plant height*. Except for the evaluation at 4 weeks, the range was kept between 10 and 20 cm,

*Coverage*. In the three ecotypes the model was highly significant (P <0.0001), and in all cases

17434 90 95.0234 15.9488 3.9614 0.8332 18744 36 96.3046 12.3222 3.0102 0.9481 18748 18 94.1993 12.7762 3.4453 0.9105

¥ "Y" is the percentage of ground covered by the plant, "a" is the maximum coverage, "X0" is the time in weeks to

**Table 2.** Sigmoid model parameters: Y = a/(1 + e-((X - X0)/b)), applied to the increase in coverage of three *Arachis pintoi*

reach half of "a", 'X' is the time in weeks, since planting date; and "b" is a constant of proportionality.

**4 8 12 P\*\***

**Model parameters ¥ a X0 b R2**

. The analysis of variance did

http://dx.doi.org/10.5772/53318

49

values

ated; achieving at 12 weeks an overall average of 5.1 plants/m2

where "Y" is the coverage in percentage, at a "X" time, given in weeks; "a" is the maximum coverage value predicted by the model; "e" is the base of natural logarithms; "X0" is the time to "Y" reaches 50% of the value of "a"; and "b" is a constant of proportionality indicat‐ ing the slope of the "S" on the right side (the higher the value, the greater slope), ie how fast it reaches the value of "a".

#### **2.3. Second experiment**

In this case, the orchard was located in the municipality of Misantla, Veracruz, and consist‐ ed of an orange plantation with coffee plants from 14 and 8 years old, respectively. The ar‐ rangement of citrus planting was 6 x 6 m, with four coffee plants around each orange tree. A week before the start of the experiment, the native vegetation was controlled with mechani‐ cal slashing and application of glyphosate (2 L/ha). The establishment of *Arachis pintoi* CIAT 17434 was evaluated for three methods of site preparation: disking, chiseling and hoeing, with two *A*. *pintoi* plant arrangements: plants at 35 and 50 cm within furrows separated by 75 cm; and two fertilizer levels: with and without P+K+Mg. P was used as triple superphos‐ phate (50 kg/ha P2O5), for K, potassium chloride (50 kg/ha of K2O), and Mg, magnesium sul‐ fate (20 kg/ha) applied every 30 days post -planting. Plant material consisting of stolons of 20-25 cm was used, placing of 3-4 stolons per plant site.

A randomized blocks design was used, in an split-split plot arrangement, being fertilization treatment the main plot and subplot planting method, sub-divided into two planting densi‐ ties. This resulted in 12 treatments with four replicates each. The total area was 2268 m2 , and the experimental unit was 144 m2 .

We measured the percentage of coverage, number of plants/m2 and plant height (cm, five plants per replication), at 4, 8, 12, 16 and 20 weeks post planting. Coverage data, number of plants and plant height were subjected to analysis of variance, and means were compared using the Tukey test from the SAS statistical package [9]. The soil was analyzed at the begin‐ ning of the experiment and 16 months later to determine changes in organic matter, soil acidity, as well as levels of nitrogen, phosphorus and potassium. Economic estimates were made to determine costs of establishment, maintenance and return on investment, com‐ pared to traditional management of weed control in citrus plantations. Were considered: the cost of slashing of the land, legume plant material and its planting labor, fertilization (P, K, Mg), land preparation, with disking, hoeing; and herbicide application.

## **2.4. Results**

In the case of coverage, the trend of the data indicated the existence of an asymptotic re‐ sponse, so exponential models were fitted to a maximum, logistic and sigmoid, using the routine "Regression Wizard" program SigmaPlot [8]. The model that final showed the best fit to the data coverage with rational values, was the three-parameter sigmoid, which is de‐

> - X – X0 /b ( ) ( ) Y = a/ 1 + e æ ö ç ÷

where "Y" is the coverage in percentage, at a "X" time, given in weeks; "a" is the maximum coverage value predicted by the model; "e" is the base of natural logarithms; "X0" is the time to "Y" reaches 50% of the value of "a"; and "b" is a constant of proportionality indicat‐ ing the slope of the "S" on the right side (the higher the value, the greater slope), ie how fast

In this case, the orchard was located in the municipality of Misantla, Veracruz, and consist‐ ed of an orange plantation with coffee plants from 14 and 8 years old, respectively. The ar‐ rangement of citrus planting was 6 x 6 m, with four coffee plants around each orange tree. A week before the start of the experiment, the native vegetation was controlled with mechani‐ cal slashing and application of glyphosate (2 L/ha). The establishment of *Arachis pintoi* CIAT 17434 was evaluated for three methods of site preparation: disking, chiseling and hoeing, with two *A*. *pintoi* plant arrangements: plants at 35 and 50 cm within furrows separated by 75 cm; and two fertilizer levels: with and without P+K+Mg. P was used as triple superphos‐ phate (50 kg/ha P2O5), for K, potassium chloride (50 kg/ha of K2O), and Mg, magnesium sul‐ fate (20 kg/ha) applied every 30 days post -planting. Plant material consisting of stolons of

A randomized blocks design was used, in an split-split plot arrangement, being fertilization treatment the main plot and subplot planting method, sub-divided into two planting densi‐ ties. This resulted in 12 treatments with four replicates each. The total area was 2268 m2

plants per replication), at 4, 8, 12, 16 and 20 weeks post planting. Coverage data, number of plants and plant height were subjected to analysis of variance, and means were compared using the Tukey test from the SAS statistical package [9]. The soil was analyzed at the begin‐ ning of the experiment and 16 months later to determine changes in organic matter, soil acidity, as well as levels of nitrogen, phosphorus and potassium. Economic estimates were made to determine costs of establishment, maintenance and return on investment, com‐ pared to traditional management of weed control in citrus plantations. Were considered: the cost of slashing of the land, legume plant material and its planting labor, fertilization (P, K,

è ø (1)

, and

and plant height (cm, five

scribed below:

48 Soil Fertility

it reaches the value of "a".

20-25 cm was used, placing of 3-4 stolons per plant site.

.

Mg), land preparation, with disking, hoeing; and herbicide application.

We measured the percentage of coverage, number of plants/m2

the experimental unit was 144 m2

**2.3. Second experiment**

## *2.4.1. First experiment*

*Number of plants.*Table 1 shows the average number of plants (and its standard error) for each accession. For the first and the second accesion an increase from week 4 to 12 was reg‐ istered, while for the third accesion, the average remained constant during the period evalu‐ ated; achieving at 12 weeks an overall average of 5.1 plants/m2 . The analysis of variance did not detect any statistically significant difference within each accession, considering the weeks of sampling.


\* Standard error of the mean.

\*\* Probability level.

**Table 1.** Number of plants/m2 from *Arachis pintoi* ecotypes established as cover crop in a citrus orchard soil of Veracruz, Mexico.

*Plant height*. Except for the evaluation at 4 weeks, the range was kept between 10 and 20 cm, and the latter value was more frequent in ecotypes 18744 and 18748.

*Coverage*. In the three ecotypes the model was highly significant (P <0.0001), and in all cases the model parameters were different from zero at the same level of probability. R2 values were greater than 0.8 (Table 2).


¥ "Y" is the percentage of ground covered by the plant, "a" is the maximum coverage, "X0" is the time in weeks to reach half of "a", 'X' is the time in weeks, since planting date; and "b" is a constant of proportionality.

**Table 2.** Sigmoid model parameters: Y = a/(1 + e-((X - X0)/b)), applied to the increase in coverage of three *Arachis pintoi* ecotypes, after planting.

In round numbers, weeks to reach 50% and 100% coverage were 16 and 32; 12 and 24; and 13 and 26, for ecotypes 17434, 18744 and 18748, respectively;

**2.5. Discussion**

D\*

Ch

H

32.0 (0.81)

14.0 (1.65)

21.0 (2.28)

\*\*P: Probability level.

31.0 (1.11)

11.5 (1.93)

20.5 (1.71)

\*D=Disking, Ch=Chiseling, and H=Hoeing.

With respect to coverage, the R2

achieve 50% coverage.

34.5 (3.42)

13.5 (1.93)

18.2 (4.11)

PD1 and PD2= Plants sown at 35 and 50 cm within the furrow respectively.

weeks post planting date, regardless of the treatments.

cause the measurement time was only 24 weeks.

34.5 (2.89)

9.5 (0.50)

20.5 (4.42)

+F: With fertilization (kg/ha: 50 P2O5, 50 K2O, 20 Mg2SO4); and, -F: without fertilization.

*2.5.1. First experiment*

The number of plants for the three ecotypes at 12 weeks, was on average lower compared with those found by [10] in one of three experiments with *Arachis pintoi* in native pastures of that region. He observed that Ap 17434 presented at that time more than 10 plants/m2

Soil Management for the Establishment of the Forage Legume Arachis pintoi as a Mean to Improve Soil Fertility...

plant material grown in field where vegetation was controlled with a machete and herbi‐ cide, with or without burning the dead material and fertilized or not with P. The smaller number of plants found here could be due in part to the month after planting (May) was relatively dry (<50 mm), consequently affecting plant emergence. In the mentioned experi‐ ment [10] the growth period immediately to planting date had higher humidity (> 150 mm).

**Trat. PD1+F PD1-F PD2+F PD2-F \*\*P PD1+F PD1-F PD2+F PD2-F P**

0.2641

0.8672

0.6755

**Table 3.** Number of plants of *Arachis pintoi* and its height (Averages; standard error in parentheses), reached five months after planting date according to soil preparation, plant density (PD) and fertilizer application or not (F).

Moreover, it appears that the ecotypes evaluated here shown in the early stages of establish‐ ment a tendency of erect growth. It has been indicated [10] a range from 14.4 to 21.0 cm at 12

tal conditions during the study. No one model predicted a maximum coverage of 100%, be‐

In Colombia [4] evaluated in citrus plantations the same ecotypes, and found 8 months af‐ ter that Ap 17434 was much lower coverage (32%) compared with the other ones (73% on average). On native pastures [10], found in another experiment with Ap 17434 that its es‐ tablishment was even slower, since the accession planted with no-tillage or reduced till‐ age, with or without fertilization (P, K, Mg, Ca, Zn, Cu and B), needed 20 to 21 weeks to

**Plants/m2 Plant height (cm)**

11.6 (0.96)

4.6 (0.35)

9.5 (0.71)

8.2 (0.49)

5.0 (0.53)

10.2 (0.65)

values showed good predictive power for the environmen‐

12.0 (1.05)

5.6 (0.75)

8.3 (0.78)

8.0 (0.50)

http://dx.doi.org/10.5772/53318

3.5 (0.59)

10.9 (0.91) , using

51

0.5255

0.0193

0.2048

Showing the accesion 17434 the slowest establishment, considering that at 24 weeks, plants covered an average of 84%, compared to 18744 (94%) and 18748 (91%); these latter two, very close to the corresponding value of "a" (Table 2, Figure 2 ).

#### *2.4.2. Second experiment*

*Number of plants and plant height*. The information related to the number of plants and height of plants/m2 are shown in Table 3. The disking treatment showed, on average, higher values for number of plants and plant height. This last parameter represented a range of 3.5 to 12.2 cm.

Coverage. Table 4 shows the percentages of coverage, achieved five months after establish‐ ment. In all treatments the highest values were achieved with the higher plant densities and fertilization treatment, except for planting treatments with hoeing. Treatments involving the disking had values far above the other ones, regardless of the plant density and/or fertiliza‐ tion applied. Analyses of variance performed within each site preparation, indicated statisti‐ cally significant differences (P ≤ 0.05) considering the variables plant density and fe application or not of fertilizer.

Changes in the soil. In relation to changes in soil properties, increases were recorded for the content of nitrogen, phosphorus and potassium, although there was a decrease in organic matter content (Table 5).

Economic considerations. Economic estimates indicated that establishment costs per hectare (in U.S. dollars) for the year in which the experiment was performed, varied according to the evaluated treatments, being lower for those without fertilization (US \$ 294, 410 and 396) in compared with those receiving fertilizer (US \$ 356, 472 and 473) for treatments with disk‐ ing, weeding and hoeing, respectively. Moreover, the expenses incurred to control weeds in one hectare included the purchase of a commercial herbicide (glyphosate), an adherent and implementation of both. It imported US \$ 222.

**Figure 2.** Dispersion data coverage and lines fixed to three-parameter sigmoid model, shown in Table 2.

#### **2.5. Discussion**

In round numbers, weeks to reach 50% and 100% coverage were 16 and 32; 12 and 24; and

Showing the accesion 17434 the slowest establishment, considering that at 24 weeks, plants covered an average of 84%, compared to 18744 (94%) and 18748 (91%); these latter two, very

*Number of plants and plant height*. The information related to the number of plants and height of plants/m2 are shown in Table 3. The disking treatment showed, on average, higher values for number of plants and plant height. This last parameter represented a

Coverage. Table 4 shows the percentages of coverage, achieved five months after establish‐ ment. In all treatments the highest values were achieved with the higher plant densities and fertilization treatment, except for planting treatments with hoeing. Treatments involving the disking had values far above the other ones, regardless of the plant density and/or fertiliza‐ tion applied. Analyses of variance performed within each site preparation, indicated statisti‐ cally significant differences (P ≤ 0.05) considering the variables plant density and fe

Changes in the soil. In relation to changes in soil properties, increases were recorded for the content of nitrogen, phosphorus and potassium, although there was a decrease in organic

Economic considerations. Economic estimates indicated that establishment costs per hectare (in U.S. dollars) for the year in which the experiment was performed, varied according to the evaluated treatments, being lower for those without fertilization (US \$ 294, 410 and 396) in compared with those receiving fertilizer (US \$ 356, 472 and 473) for treatments with disk‐ ing, weeding and hoeing, respectively. Moreover, the expenses incurred to control weeds in one hectare included the purchase of a commercial herbicide (glyphosate), an adherent and

**Figure 2.** Dispersion data coverage and lines fixed to three-parameter sigmoid model, shown in Table 2.

13 and 26, for ecotypes 17434, 18744 and 18748, respectively;

close to the corresponding value of "a" (Table 2, Figure 2 ).

*2.4.2. Second experiment*

50 Soil Fertility

range of 3.5 to 12.2 cm.

application or not of fertilizer.

implementation of both. It imported US \$ 222.

matter content (Table 5).
