Study area

The research was conducted at the California community, municipality of Villaflores, Chiapas, in the buffer zone of the Biosphere Reserve "La Sepultura" (REBISE) 15'40.7'' between 16 ° north latitude and 93° 36' 42.9'' west longitude, with rainy weather is tropical, average temperature of 24 ° C, annual rainfall of 1023 mm, topography and soil type Regosol + Foezem + Cambisol (^{INEGI, 2012}).

Production systems

Maize intercropped with beans (SPM-1), landrace maize (SPM-2), improved maize (SPM-3), whose characteristics are presented in Table 1: Three production systems were evaluated.

Table 1 Characteristics of maize production systems studied. 

Information analysis

An analysis on the systems approach, which involves the identification and characterization of system components maize production, inputs, outputs and relationships between components was performed (^{Guevara et al., 2011}). To describe the work of each system, the proposed methodology used was by ^{Geilfus (1997)}.

Energy balance

The analysis method described by ^{Meul et al. (2007)} was used, which considers the income of energy to the system, physical material flows and inputs used for production.

Based on the methodology by ^{Funes (2009)} energy efficiency was calculated using the variables: production system area, type and amount of food or products obtained direct or indirect energy costs of production, including human labour and animal, use of fuels, fertilizers and other inputs. Additionally the criteria set by ^{Márquez et al. (2011)} were used, who consider the direct and indirect energy used in production. The energy consumption was estimated using the methodology proposed by ^{Bowers (1992)}. With the values of inputs and outputs, energy efficiency and the number of people who can feed, based on energy equivalence shown in Table 2 was calculated.

Table 2 Energy Equivalence of inputs and outputs used in the analysis. 

Direct and indirect sources of energy

According to ^{Marquez et al. (2011)}, direct energy is that which is contained in the direct inputs such as fuel, electricity, fertilizer, pesticides, organic fertilizers and biological products, while indirect energy associated processes manufacturing, distribution and maintenance; for example, the need to obtain fuel from crude oil energy and required for the manufacture of pesticides and machinery, which is amortized over time.

Direct energy (Ed) ^{Marquez et al. (2011)}

a) Associated fuel consumption (E_dc) Energy (Mcal / ha)

Where: C_c= fuel consumption (L/ha) E_eg= energy equivalent of oil (41 MJ / L)

b) Energy associated with labour employed (E_dh) (MJ / ha)

Where: = energy equivalent of human labour (1.96 MJ/h for men and 1.57 MJ/h for women) (^{Mandal et al., 2002}); n_ob= number of workers involved in a given task

C_tob= capacity work of agricultural workers (ha/h).

c) Energy associated with animals used in work (E_da) (MJ/ha)

Where: E_a= energy equivalent of the animal work (5.05 MJ/h) = number of animals involved in a particular task; = working capacity of animals (ha/h).

Energy efficiency

The following equation (^{Funes et al., 2011}) was used to calculate the energy efficiency of production systems:

)4

Where: E_e= energy sufficiency; S=number of products; m= amount of product (kg); e= energy content of the product (MJ/kg); T= number of inputs; I= input quantity (kg); f= energy required to produce an input (MJ / kg).

To calculate the energy produced and consumed the following formulas were used:

Where: EP= energy produced; EC= energy consumed; Production = yield (kg ha^-1); Expenditure= spending inputs; EC= energy content as energy equivalence shown in Table 1 in Kcal/measurement unit.

Indicators on system productivity, as the amount of energy (MJ/ha/year) and protein (kg/ha/year) produced and further quantified correspondingly the number of people who could support the system according with average demand of one person per year of these nutrients (^{Funes et al., 2011}). The energy and protein content for the calculations were taken from ^{Gebhardt et al. (2007)}. Energy equivalence used for calculating the costs, direct and indirect inputs were those reported by ^{Garcia-Trujillo (1996)} and ^{Funes et al. (2011)}.

)7

Where: Pe = people who sustain themselves on the basis of the energy produced; mi = production of each product (kg); ei = energy content of each product (MJ); A = area of the farm (ha); Re = energy requirement of a person (kg/ha).

To calculate the number of people that can be fed given protein requirements the following formula (^{Funes et al., 2011}) was used:

)8

Where: Pe = people who sustain themselves on the basis of the protein produced; mi = production of each product (kg); pi = protein content of each product (MJ); A = area of the farm (ha); Rp = protein requirement of a person (kg ha^-1).

According to ^{Funes (2001)}, the average energy consumption of a person is 1022 Mcal/year, while consumption of vegetable protein is 15.3 kg/year.

Economic efficiency of the production system

To estimate the economic efficiency of the production systems of maize production costs and revenue from the sale of the harvest, in order to calculate the benefit/cost (RBC) ratio by the following formula is used:

Characteristics of maize production systems

At SPM-1 seeding of landrace maize variety known locally as "premature". We used 20 kg ha^-1, obtained from the harvest of the previous cycle. Producers who plant make an average of 2 ha, with average yield of 2 t ha^-1. The production is for home consumption, with 35% for household consumption and the rest for animal feed. The beans are grown during the period between the "bends" and the maize harvest, plant variety "white bean pod" at the rate of48 kg ha^-1 seeds, with an average yield of 700 kg ha^-1. Of the total production, 79% is sold and the rest is for consumption. The increased energy expenditure system from outside sources for the purchase of herbicides, insecticides, fungicides, fertilizers and fuel. The energy of human labour is provided by family labour and only in planting and fertilizer application as payment for the shelling of labour is required. The crop requires 125 ha^-1 wages, of which 35% is paid.

In the SPM-2 are uses the early variety and 20 kg ha^-1, also from the previous harvest. On average producers who use it, they sow 1 ha and produces about2250 kg ha^-1. 55.5% of the production is sold and the rest is for consumption. Approximately, 13.5% of the grain used to feed animals, preferably backyard birds, the rest is for family consumption. The largest proportion of energy used enters the system through herbicides, insecticides and fertilizers use 103 ha^-1 wages, of which 78 are covered with family work and the rest is hired.

In the SPM-3 is used on average 20 kg ha^-1 of improved maize seed (commercial hybrids) varieties. It has been observed that these materials are susceptible to ear rot season of heavy rains, causing losses up to 50% of the crop. The maize plots are on average 3 ha. The average yield was 2600 kg ha^-1. 100% of the production goes to marketing. Like the other two systems, the increased energy expenditure comes from external sources to acquire herbicides, fertilizers and fuel. Wages 104 ha^-1 of which 30 are covered with hired work force are required. Table 3 shows the amounts of inputs used in the systems evaluated are shown.

Table 3 Quantities of inputs used per crop cycle in each studied system. 

Description of the annual cycle of production systems

In general, the timing of agricultural activities in the three maize production systems is similar, except in the SPM-1, which has additional activities for bean management. During April and May the "rastrojeo" is performed (introduction of cattle on crop residues from the previous cycle), the construction of firebreaks gaps, burning and herbicide application is made. Maize planting takes place in June, when the rainy season starts. In all three systems, two applications of fertilizer are made during July and August. In systems monoculture maize herbicides applied during June and July and the SPM-1 system two additional applications for bean crops in August and September are made. The harvest takes place in December, but sometimes it is postponed until January or February next year (Table 4). ^{Aguilar (2010)}, makes a similar disclosure for these systems.

Table 4 Schedule of activities of the three systems studied maize production. 

R= rastrojeo; B= brecha corta fuegos; Q= quema; H= aplicación de herbicidas; S= siembra; F= fertilización; D= doblar; C= cosecha; E= desgrane; A= acarreo.

Management labour

The length of the day and its cost depends on the type of work and its origin, whether family or hired. For example, when labour is needed, the maximum working time is 6 h^-1 wages and wages paid $70^-1, shelling maize in only about 1 h works full wage is paid when it is family labour, the producer gets to work up to 10 h^-1 wages, and burning, the producer remains in the plot up to 24 hours to control the fire, according to the regulations of the National Commission of Natural Protected Areas (CONANP).

Energy balance

The SPM-1 and the SPM-2 had an energy efficiency higher than 1, indicating feasibility compared with SPM-3, which required more energy than that produced by the maize crop. In this regard, ^{Funes et al. (2011)} found that less diversified systems were less productive; therefore, although the production of a crop is smaller, diversification of the system makes energy more profitable. Moreover, energy efficiency SPM-3 (0.99) was very close to that obtained by ^{Alemán and Brito (2003)} in a system of maize in monoculture, with conventional methods of handling. However, if the results with studies ^{Pimentel (1980)} compared the three systems show low energy efficiency, since the average maize crop was 10 Mcal produced by Mcal inverted.

The energy balance is significantly affected by external inputs to maintain agricultural production (^{Valdés et al., 2009}). When analysing energy intensity in the SPM-1 and the SPM-2 shows that to produce 1 kg of maize used Mcal 3.18 and 3.40, respectively. Both are dependent on fossil fuels and chemicals, and inefficient in the use of this energy source and are not sustainable in the long term, according to the findings of ^{Pimentel and Pimentel (2005)}. The use of energy from chemicals, reported that more than 50% dependent on the contribution of the fertilizer ammonium sulfate (IDEA, 2007).

In production systems studied spend about 5377.5, 6453.0 and 8604.0 Mcal, contributing to obtain 0.37, 0.35 and 0.30 kg of maize, in each of the systems respectively. Moreover, the increased energy expenditure of inputs such as herbicides and insecticides in the SPM-1 is due to those required to control pests and diseases bean crop inputs. However, the energy contribution of this crop tends to offset these costs. For other inputs, such as the energy supply for fuel, there is little in the three systems, it only consumes shelling maize, by the use of machinery (tractor) and the sheller and in some cases, for moving crop.

Persons feasible for feeding

The increased production of energy and protein was for the SPM-1 (Table 5). From the energy point of view, the SPM-1 and SPM-3 systems produce enough energy to feed nine people ha^-1 year-1, while the SPM-3 has a potential to feed eight people ha^-1 year¹. These results agree with the points made by ^{Valdés et al. (2009)} who argued that in energy terms in the various systems more efficiently produce the protein from both animal and vegetable origin.

Table 5 Energy balance and energy production potential and protein maize production systems studied. 

Regarding the protein source, the higher capacity to meet the demands of human proteins was SPM-1 with 23 people ha^-1 year^-1, it includes beans, with which the system almost triple the protein content. For its part, the SPM-2 and SPM-3 systems have a capacity to feed 14 to 16 people ha^-1 year^-1, respectively. ^{Schiere et al. (2002)} reported that the number of people that can be fed with one hectare of monoculture (maize), is 10.4 on energy and protein sources 5.2 fountains.

Analysis of economic efficiency of production systems

The total cost of the production system of maize associated with beans (SPM-1) was superior to the others (Table 6), mainly due to high prices of labour, although less than 25% invest in fertilizers, second largest item of expenditure in the three systems. A detailed cost analysis shows that the concept agrochemicals are leading to higher maize production systems in the studied community, with 61.6, 40.6 and 44.25% of the total cost of each system, respectively.

Table 6 Structure of economic expenditures (Mexican pesos) and percent of total in the three systems studied maize production. 

From the percentage of the marketed crop yields and selling prices of the products, SPM-3 is the one that brings higher income (Table 7). These results agree with those obtained by ^{Miranda et al. (2008)} who claimed that diversified systems have improved both financial and energy performance, which is partly consistent with the results achieved in this study. Considering the market only 50% of the crop of the SPM-1, this system would prove to be the most efficient from the economic point of view as it would allow incomes up to $ 12,500 ha^-1, considering both crops.

Table 7 Income and income from maize production systems studied. 

The analysis of economic feasibility of the three production systems studied by calculating the cost benefit ratio (Table 8) shows that the SPM-3 is the most likely, with a profit of 41 cents for every peso invested.

Table 8 Analysis of economic feasibility from the cost/benefit ratio of the three systems studied maize production.