Productivity, Leaf Nutrient Content and Soil Carbon Stocked in Agroforestry and Traditional Management of Maize ( Zea mays L.)

The aim of the work was to evaluate the productivity, leaf nutrient content and soil nutrient concentration in maize ( Zea mays L.) grown in sequence with black oats ( Avena strigosa Schreb.) under Leucaena diversifolia alley cropping agroforestry system (AFS) and traditional management system/sole crop (without trees-TS), after two years of cultivation following a randomized block design. The experiment was carried out in the Brazilian Association of Biodynamic Agriculture, in Botucatu—São Paulo, Brazil. Treatments were: control (


Introduction
Agroforestry systems are agricultural practices with low energy demand, inputs and/or resources, as well as productive and sustainable systems and combine trees and shrubs (especially species of legumes) and food crops and/or forage [1]- [5].Nair (1985) [6] classified agroforestry systems as agrosilviculture, silvopastoral and agrosilvopastoral.
Alley-cropping agroforestry systems let to obtain a productive and sustainable use of land along with diversification of income sources for the small farmer (Kaya and Nair, 2001 [15]; Copijn, 1988 [16]) and have the following characteristics: the practices of cultivation and fallow are held simultaneously; with longer period of cultivation and more intensive use of land; gives a more effective regeneration of soil fertility with more efficient species and reduces the requirements of external inputs.Bertalot (1997) [17] and Bertalot and Mendoza (1998) [18] reported that one of the greatest potentials of alley cropping is its use in sloping areas, where the rows of trees can help reduce erosion by forming natural terraces.Haggar et al. (1993) [19] used two maize alley cropping treatments, with Erythrina poeppigiana and with Gliricidia sepium, and compared to sole-cropped maize (Zea mays L.) in an 8 yr old experiment at CATIE in Costa Rica.Maize biomass and maize N content, N released from mulch and residue decomposition, and N mineralization were all higher in the alley crop than the sole crop.Marin et al. (2006) [20] and Marin et al. (2007) [21] evaluated biomass productivity of maize, intercropped or not with gliricidia (Gliricidia sepium), and the effect of manure and gliricidia pruning fertilization on maize and spontaneous vegetation biomass productivity.The work was conducted within an area with gliricidia rows, and spaced six meters between each other and one meter between trees.Maize and spontaneous vegetation biomass productivity did not differ between plots fertilized with manure or gliricidia pruning, but these two organic fertilizers led to significantly greater biomass productivity compared to the control plots.
Bertalot et al. (2010) [12] evaluated the productivity of maize in sequence with black oat (Avena strigosa Schreb.)under Leucaena diversifolia alley cropping agroforestry system and traditional management (without trees) in Botucatu, Brazil, and concluded that both systems showed viability from the productive viewpoint and that the biomass use can substitute chemical fertilizer either partially or totally.Siqueira (1999) [22] shown maize in sequence with Raphanus raphanistrum as soil coverage obtaining similar production of biomass as winter crop.
Sharma (2011) [23] studied four ten-year-old land use systems.The systems include: a) agri-horticultural system (Psidium guajaba + Sorghum bicolor); b) agro-forestry system (Acacia auriculiformis + Sorghum bicolor); c) pastoral system (Stylosanthes hamata) and d) arable land system.From the viewpoint of chemical soil quality, agroforestry system proved most in terms of maintaining higher chemical soil quality index compared to other land use systems.Arable land, which is continuously under agriculture, maintained the lowest soil quality index.
The objective of the present study was to evaluate the productivity, leaf nutrient content soil fertility and carbon stocked in soil in an agroforestry system with Leucaena diversifolia and a traditional system (without trees), after two years of cultivation of maize (Zea mays) in rotation with black oats (Avena strigosa).

Material and Methods
The experiment was carried out from may 2000 to april 2002 at the Brazilian Association of Biodynamic Agri-culture (ABD) in Botucatu, São Paulo, Brazil (latitude 22˚ 57′ S, longitude 48˚ 25′ W), in the Cerrado area at an altitude of 900 meters above sea level.The local climate is classified as "cfa" (subtropical wet), according to Köppen.
The average annual temperature is 20.5˚C and average annual rainfall is 1.549 mm, occurring in greater quantities from November to March.The soil of the region is classified as red-yellow latosol (oxisol), medium textured (Jorge, 1986 [24]; Tomé Junior, 1997 [25]).
The experiment was carried out in two different areas, one of them managed under an agroforestry system of alleys of Leucaena diversifolia (AFS) and another area under traditional management system/sole crop (TS).The Leucaena diversifolia has already been planted with success in the Biodynamic Association area since 1995, due to its adaptability to Cerrado soils (Bertalot et al., 2002) [26].At the time of pruning, the material of L. diversifolia was cut, weighed and dried for chemical analysis of nutritional status according to methodology developed by Malavolta et al. (1997) [27] Figure 1.
Annual crops used to conduct the experiment in both areas were: black oats (Avena strigosa), grown as winter crop and used as green manure, in rotation with maize (Zea mays), grown as summer crop.
Before installing the experiment, soil samples representative of the area were collected at a depth of 0 -20 cm, to perform physical analysis by the hydrometer method (Embrapa, 1997) [30] and chemical analysis by the methodology described by Raij (1983) [31] and Raij et al. (2001) [32].Results are presented in Table 1.Table 1.Chemical and physical soil analysis before the installation of the trial (0 -20 cm depth) in agroforestry system (AFS) and traditional system (TS).In all treatments, including Control, crop residues were kept over the soil, beginning with black oat straw and maize stover in the first year of cultivation.The experimental design consisted of randomized blocks with four treatments and five replicates in both cropping systems.Each plot occupied an area of 20 m 2 (5 m wide × 4 m long), and 1 m border between plots.
Analysis of variance was performed by Estat D Program, developed by specialists of the University of the São Paulo State-UNESP, Jaboticabal-SP, Brazil.Tukey test was used to compare mean values and a joint analysis to compare systems was carried out, in accordance to Banzatto and Kronka, 1995 [33].
Soil Carbon Stock at 0 -20 cm depth Chemical and physical analysis of soil after two years of management were reported by Bertalot (2003) and Bertalot et al. (2013) [34].The determination of organic carbon and organic matter was performed by oxidation method of Walkley & Black, used by Luske and van der Kamp (2009) [35] and described by Cantarella, Quaggio and Raij (2001) [36].With the results was obtained the amount of carbon stocked in the soil using the following formula: Carbon stock in the soil = sampling depth x carbon content x bulk density Sowing of black oats.Black oats was planted at a spacing of 20 cm between rows.According to soil analysis (Table 1), it was not necessary to apply limestone because the base saturation was above 50%.Chemical fertilizer was applied at seeding expecting a grain yield of 2 -3 t•ha −1 as recommended by Camargo et al. (1997), and was as follows: 300 kg•ha −1 of 04-20-20 + 0.1% B plus 18 kg•ha −1 of N in treatments with application of fertilizer (2) and biomass + fertilizer (4), as related by Bertalot (2003) [28].
The chemical cover fertilization consisted of 40 kg•N•ha −1 in both years of planting.For treatments with application of biomass of L. diversifolia (3), 7.5 t•ha −1 of dry matter of L. diversifolia were added, in accordance with Copijn (1988) [16].Black oats were cut down at soft grain/dough stage, 120 days after seeding, as suggested by Derpsch and Calegari (1992) [37], and the cut straw was left as ground cover in all plots in both systems.
For chemical cover fertilization 40 kg•N ha −1 were applied in the first year of management.In order to raise the base saturation to 70% in the second year limestone was added to the soil (1 t•ha −1 ).Chemical fertilizer was applied in the seeding.For an expected productivity of 4 -6 t•ha −1 of grain, 250 kg ha of 08-28-16 + 0.4% Zn were added.Cover fertilization at 40 days was carried out with 40, in accordance with soil analysis.Green manure was added as 7.5 t•ha −1 of dry matter using prunings of L. diversifolia in Biomass and Biomass + fertilizer treatments in both systems, treatments 3 and 4, respectively (Bertalot, 2003).
No irrigation was applied during the study time.Temperature data and monthly rainfall during the experiment, from May 2000 to April 2002 are shown in Table 11.

Results and Discussion
Dry matter yield of black oats obtained in the first year of management was 6.00, 7.37, 6.19 and 8.13 t•ha −1 for treatments C, F, B and B + F, respectively in AFS.In TS yield was of 1.70, 6.74, 4.08 and 6.74 t•ha −1 , for treatments C, F, B and B + F, respectively, as reported by Bertalot (2003)  On the AFS, there was no difference in yield between treatments (B + F) and (F).However, the difference between treatments (B + F) and (F) was 760 kg•ha −1 of dry matter, provided only by the addition of biomass of  Leucaena diversifolia.In TS, treatments (B + F) and (F) were similar, with significance difference between them and other treatments.There was no significant difference between treatments (F) and (B) in AFS, demonstrating the ability of the tree in the farm system to recycle nutrients and put them at the disposal of cultures.Foliar analysis and nutrient content of black oat.The results of the analyses of black oat leaves the first year of management are shown in Table 2.As reported by Camargo et al. (1997) [39], the appropriate levels of nutrients (g•kg −1 ) in the leaves of black oats are as follows: 20 -30 g•kg −1 of N, 2.0 to 5.0 g•kg −1 P; 15 -30 g•kg −1 K; 2.5 to 5.0 g•kg −1 of Ca, 1.5 to 5.0 g•kg −1 of Mg, Comparing the values obtained in the AFS, it was observed that only P, Mg and S approached to appropriate levels.In traditional system-TS, only K approached these levels in treatments (F), (B) and (B + F).In terms of micronutrients, they all showed appropriate levels in both systems.
Using the values of nutrient concentration in the dry matter of black oats and biomass obtained it can be obtained the content of nutrients (Wendt, 1998) [40] and these results are shown in Table 3.It is observed a significant difference in the content of all nutrients in the treatment of both systems, and that in general the nutrients showed higher values in treatments (B + F) and (F) in both systems.Furthermore, with relation to biomass, nutrient values tended to be higher in the AFS.
Maize-first year of management.Productivity of maize.Productivity of maize in AFS and TS for first year of management is shown in Table 4 and Figure 3.In the AFS there was not significant difference in productivity between treatments (B + F), (F) and (B), but in relation to treatment (T), showing that an interaction may exist between the biomass of L. diversifolia and the presence of trees in this system towards higher yields similar to those obtained with the application of fertilizers, in the first year of management.
In traditional system there was no significant difference between treatments (B + F) and (F), and between treatments (B ) and (F), probably due to nutrients released by the remnants of the culture of oats and biomass of L. diversifolia that favor the production of treatment B.
Table 10.Soil carbon stocked at 0 -20 cm soil depth in agroforestry system (AFS) and traditional system (TS), after two years of management.

Trat.
Carbon stock at 0 -20 cm soil depth (Ton  On the system alleys, treatments (F), (B + F) and (B) provided significant increases in grain productivity of 44%, 42.29% and 39.34% respectively, in relation to treatment (T).

Maize leaf analysis.
The results of the analysis of maize leaf and nutrient concentration in both the systems are shown in Table 5.As Raij and Cantarella (1997) [41] stated, the appropriate nutrient levels in the leaves of maize are the following: Comparing the results obtained with the levels considered adequate, it was observed that the N contents were only suitable in treatment (B + F) of AFS.Values of N of treatments (F) and (B) tended to approach to ideal values.The TS any treatment showed appropriate levels of N, but treatment (B + F) tended to approach to ap-propriate levels.Due to initial soil chemical characteristics, only the joint application of biomass from L. diversifolia and fertilizers in AFS allowed to achieve the optimal N in foliar tissue of maize.
It is observed that in AFS there was significant difference between treatments in the concentration of N, K, Cu, and Zn.Differences in concentrations of N, P, K, Mg, S, B, Cu, Fe, Mn and Zn were observed in TS.
Comparing the results of the foliar tissue analysis in the AFS and TS, it is noted that the numerical values of the concentration of N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, were higher in treatmenst of AFS.This difference may be due to the influence of alley cropping system, but this fact should be further studied.Bertalot and Mendoza (2006) [42], based on the results of analyzes of leaf tissue samples of Brachiaria decumbens obtained from an alley cropping silvipastoril system with Acacia melanoxylon, in pastures with native trees and sole pastures-without trees, found that nutrient concentrations in B. decumbens grown in AFS were higher than in other systems.
Black oats-second year of management.
The results of the foliar analysis of the different treatments of black oats in the second year of management, for both systems, are shown in Tables 6 and 7.
Comparing these results with nutrients appropriate levels, it was observed that all treatments of agroforestry system are within the range of adequate levels of P; with respect to Ca, just the treatment (B + F) of the AF system was in accordance to recommended levels; Mg was adequate in treatments (B + F), (F) and (B) of AFS, probably due to the influence of alleys of L. diversifolia and nutrients availability.
It was observed that in the AFS there was a significant difference for N, K, Mg, S, Fe, Mn, Zn, with the highest values for the treatments (B + F) (F) and (B).Concentrations of N, K and Mg were higher in treatments where L. diversifolia biomass coverage was present.Regarding micronutrient concentrations of Mn and Zn followed the same behavior, not occurring the same fact with the Fe.In the TS, there was a significant difference for K, S, Fe, Mn.For both, macro and micro nutrients, treatments (B + F), (B) and (F) tended to have higher values.
The higher amounts of nutrients in general, were obtained in treatments (B + F) and (F), followed by treatment (B), in both systems, confirming the trend toward performance and yield of biomass dry matter.Greater values where obtained in the AFS system (alley cropping).Regarding these results, Borkert et al. (2003) [43] reported that black oat, although not being a leguminous species, absorbs and recycles reasonable amounts of N, large amounts of K, Ca and Mg, and among the micronutrients, Mn, Cu and Zn.
Maize-second year of management.
Maize production presented the second year of cultivation an increasing trend in all treatments in both production systems.This result may be due to the cumulative effect of mineralization and maize straw and oats, along the experiment.How productivity was higher in the AFS system, could also be occurring effect of biological nitrogen fixation, water retention and reduction of extreme microclimate through the rows of L. diversifolia.
It can be seen (Table 8 and Figure 4) that was significant difference between treatments and the behavior of these treatments in both systems followed the same pattern.Comparing the two systems, AFS produced significantly more grain maize (t•ha −1 ) than the TS, considering treatments T, B and F.
There was no significant difference between treatments B + F, B and F, in both systems, but in relation to treatment (T), and the decreasing productivity was B + F > B > F> C in AFS and B > B + F > F > C in TS.
Maize foliar analyses-second year of management.
The results of the leaf analysis in maize plant are shown in Table 9.The results showed significant differences between treatments in the concentrations of N, P, S, B, Cu, Fe and Mn in agroforestry system, and the concentrations of N, P, K, S, Cu, Fe, Mn and Zn in the traditional system.
Comparing the AFS and TS, it was observed that the concentration of N was higher in the AFS treatments, probably due to nitrogen fixation performed through the rows of L. diversifolia, the P concentration was higher in treatment (B + F) and (F) of the AFS because plants in AFS suffer less environmental stress (most suitable microclimate, less water stress and temperature.The same behavior was observed in relation to micronutrients, K concentration was highest in treatment (B + F) in both systems.Ca concentration was higher in treatment B of AFS and the concentrations of Mg, B and Fe were higher in all treatments of AFS.Mn concentration was higher in treatment (B + A), (B) and (F) of AFS.

Soil Carbon Stock
Carbon stock reached higher values in treatments B + F and B in both systems with significant difference among these treatments and other two treatments, showing that organic matter production and addition process contributes to increase the amount of carbon in the soil profile and it is related to organic matter process of degradation (Table 10).

Conclusion
The results showed that agroforestry systems contribute to improving naturally cultures productivity, as well as, stimulating increasing concentration of nutrients in leaf tissue.The presence of alley cropping systems and their management practices contribute to soil conservation, as well as for the maintenance of soil fertility and crop productivity.The addition of biomass from prunings of Leucaena diversifolia system in alley systems and successional management with black oats as green manure, associated or not with the addition of chemical fertilizers, helped to increase crop productivity.Traditional agricultural systems are benefited with the adoption of agroecological management techniques of farming.Nitrogen, phosphorus and potassium tended to have higher values in foliar tissue in AFS.It can also be concluded that agricultural production systems that successively in time, handle and/or add biomass allow the accumulation of soil carbon generating benefits for the physical, chemical and biological soil conditioning as well as helping to reduce the presence of carbon in the atmosphere and consequently its impact associated with the greenhouse effect.

Figure 1 .
Figure 1.Design of agroforestry and traditional systems.

Figure 4 .
Figure 4. Mean productivity of grains of corn in function of the treatments, both the systems-second year of management in t•ha −1 .

Table 2 .
Leaf nutrient concentration in black oats tissue in AFS and TS-first year of management.

Table 3 .
Nutrient content in dry matter of black oats-first year of management.

Table 4 .
Mean productivity of grains of Maize both the systems-first year of management (t•ha −1 ).* and * significant at 1% and 5%, respectively, by F test.Lowercase letters in the columns, comparison between treatments for each system.Capital letter in the lines comparison of systems for each treatment Means followed by the same letter do not differ among themselves, by Tukey Test (P > 0.05). *

Table 5 .
Leaf nutrient concentration in corn leaf tissue in AFS and TS-first year of management.

Table 6 .
Leaf nutrient concentration in black oats in AFS and TS-second year of management.
** and * significant at 1% and 5%, respectively, by F test.Means followed by the same letter do not differ among themselves, by Tukey Test (P > 0.05).

Table 7 .
Leaf nutrient content in black oats in AFS and TS-second year of management.
** and * significant at 1% and 5%, respectively, by F test.Means followed by the same letter do not differ among themselves, by Tukey Test (P > 0.05).

Table 8 .
Mean productivity of grains of corn in both the systems-second year of management (t•ha −1 ).

Table 9 .
Leaf nutrient concentration in corn in AFS and TS-second year of management.
** and * significant at 1% and 5%, respectively, by F test.Means followed by the same letter do not differ among themselves, by Tukey Test (P > 0.05).
Mean productivity of grains of Maize in function of the treatments, both the systems, first year of management in t•ha −1 .
** and * significant at 1% and 5%, respectively, by F test.Lowercase letters in the columns, comparison between treatments for each system.Means followed by the same letter do not differ among themselves, by Tukey Test (P > 0.05).Figure 3.

Table 11 .
Temperature data and monthly rainfall during the experiment, from May 2000 to April 2002.