Introduction

The plastic films for quilting in agriculture, constitute the second application in importance after greenhouses. The world surface under this modality is 4 530 000 ha, with countries such as China with 2 000 000 ha, Japan with 150 000 ha, France and Spain with 100 000 ha each. In Latin America this application has been developed mainly in Central America and Mexico, surpassing the latter 9 000 ha. Its importance is very varied and consists of: increase and quality of production, precocity in the harvest, greater efficiency in the use of water, increase in soil temperature and control of weeds among others (^{Feng et al., 1999}; ^{Munguía et al., 2003}; ^{Kasirajan and Ngouajio, 2012}).

The techniques to modify the microclimate in crops such as plastic mulch favor greater profitability (^{Rodríguez et al., 2000}). They prevent the development of weeds by not allowing the photosynthetic light to pass through and they allow saving the water that they could consume, from the thermal point of view the padding behaves like a double effect filter, which accumulates heat in the soil during the day and leaves part of it during the night, this prevents or reduces the risk of frost due to low temperatures (^{Robledo and Martín, 1988}). In Mexico, over-exploitation of aquifers and low water productivity of only 1.6 kg of dry matter per cubic meter of water applied at the district level (^{CONAGUA, 2010}) and the low availability of water observed in some dams in the country in recent years, make urgent the establishment of strategies to make a rational and efficient use of this resource.

In the Comarca Lagunera that includes part of the states of Coahuila and Durango, the main dairy basin of the country is located; It is estimated that there is a cattle operation of 248 812 heads, with a daily demand of 3 732 tons of dry matter (^{El Siglo de Torreon, 2013}). To satisfy these needs are established mainly the crops of alfalfa (Medicago sativa L.), corn (Zea mays L.) and sorghum (Sorghum vulgare H.) these are established in the spring-summer cycle and oats (Avena sativa), mixtures of clover (Trifolium pratenese L.) and triticale (X. Triticosecale Wittmack) as winter fodder. The main factors that reduce the productivity and profitability of the agricultural production systems are: the limitation and high cost of irrigation water, the degradation of soils due to salinity problems and the low diversity of crops.

This causes problems of commercialization, increase of pests and diseases (^{Santamarina et al., 2006}). The forage maize in the Comarca Lagunera for the Spring-Summer cycle of 2012 represented an area of 33 215 ha and its average yield was 46 697 kg ha^-1 (^{El siglo de Torreon 2013}). However, this crop has been shown to have a potential of 70 000 kg ha^-1 of green forage (^{Montemayor et al., 2007}). The above has been achieved by incorporating new technologies derived from plastics such as sub-surface drip irrigation. The objective of the present investigation was to evaluate the effect of plastic mulch with different colors in the production of fodder maize, in a belt-type drip irrigation system.

Materials and methods

The Comarca Lagunera comprises part of the states of Coahuila and Durango, Mexico. It is located between the meridians 101° 41’ to 104° 61’ west longitude and between the parallels 24° 22’ and 26° 23’ north latitude, it has an area of 47 887 km² with an average altitude of 1 100 meters above sea level, with a mountainous extension and a flat surface where the agricultural area is located. Its climate is dry desert, with rain in summer and cool winter, the average annual rainfall is 258 mm and the annual average evaporation is 2 000 mm, for which the precipitation-evaporation ratio is 1:10; The average annual temperature is 21 °C with maximum of 33.7 °C and minimum 7.5 °C. The period of low temperatures or frosts of crops are presented from November to march, although in some cases they occur early in October and late in April (^{García, 1973}).

The investigation was carried out during the Spring-Summer cycle of 2012, in the small property Esmeralda located in the municipality of Gomez Palacio, Durango. The texture of the soil is sandy loam with a moisture retention capacity of 0.2 cm³ cm^-3. Planting was carried out in dry soil during the first days of May of the year, this was done manually with the Pioneer 30A60 hybrid, this hybrid is classified as intermediate cycle with a cut-off duration of 100 to 110 days for the production of forage.

Prior to sowing, plastic mulch was established on seed beds separated by 1.5 m, an irrigation tape was installed for each bed at an expense of 3 liters per hour per linear meter. The irrigation sheet applied throughout the crop cycle was 50 cm. The configuration of the sowing was of two rows of plants per each bed with a separation of 50 cm between rows and 13 cm between plants, the estimated population was 101 508 plants ha^-1. The plastic was perforated at the time of sowing and one seed was placed for each hole made. The padding evaluated was white, silver and black padding.

The soil without quilting was considered as a witness. The experimental design was in complete blocks with arrangement in strips and four repetitions. The response variables were: plant height (cm), stem diameter (mm), diameter and length of corn, fresh and dry weight of the plant and leaf area index (IAF), the variables of fresh and dry weight were measured in weekly form and the procedure was to take four plants of each experimental unit to obtain the fresh weight and later by drying in an oven, obtain the weight of dry matter.

Plant height, stem diameter, diameter and length of corn were measured 98 days after sowing (DDS). The leaf area index was measured every week during the period from 25 to 98 DDS, the readings were taken with the LAI 2000 Plant Canopy Analyzer (LI-COR, Inc. Lincoln, Nebraska, EE. UU). The behavior model of the leaf area index based on the days after sowing and the dry matter production model as a function of the IAF were obtained using the simple linear regression method.

Results and discussion

Leaf area index

The Figure 1 shows the behavior of the leaf area index with respect to the days after sowing, the models found in both production systems were of the second order polynomial type, that is, a linear effect and later a quadratic effect. ^{Jean-Claude et al. (2013)} mentions that IAF has a typical behavior, this starts with a slow growth, followed by a rapid growth (vegetative stage), until reaching a maximum value and later decreases by the senescence of the leaves, and because the crop reaches maturity physiological. Similar behaviors are reported by ^{Guevara et al. (2005)}; ^{Montemayor et al. (2012)}.

Figure 1 Behavior of the leaf area index with respect to the days after sowing of the forage maize grown with and without plastic mulch. 

In both production systems, the highest of IAF coincides with the stage of flowering of the crop, the estimated values of IAF were five for padding and four for the system without quilting. A good estimate of the IAF is important to estimate the interception of light by cultivation, transpiration and biomass accumulation; therefore, it has a great influence on the growth and production of the crop (^{Birch et al., 1988}; ^{Setiyono et al., 2007}). ^{Guevara et al. (2005)} reports maximum IAF values

of five for separate lines at 1.1 m and six for separate lines at 0.4 m at a planting density of 133 000 seeds ha^-1. ^{Andrew and Shashi (2009)} report maximum IAF values of 4.9 to 6.4 for a maize under irrigation conditions with an average evapotranspiration of 548 mm over a five-year study period.

In dry conditions the same authors report a maximum IAF of 3.1 to 4.4 with an evapotranspiration of 482 mm. ^{Giaveno et al. (2002)} reports IAF values of 4.4 to 5.5 for irrigated and fertilized maize and values below three under rainfed conditions. In the model found in the quilting system it has a daily linear growth of IAF of 0.294, while without quilting this value is 0.259, which represents 12% less growth with respect to the quilting system. ^{Montemayor et al. (2012)} found values of 0.251, 0.155 and 0.106 for irrigated maize with sub surface irrigation, central pivot and gravity.

It concludes that the decrease in the IAF is mainly due to a greater hydric stress in the plant, this induces a lower transpiration of the crop, less CO₂ absorption and reduction in the photosynthesis process; The above, is reflected in the phenological variables of the crop such as: plant height, dry matter weight and stem diameter.

Dry matter production and leaf area index

The Figure 2 shows the relationship between the IAF and the production of dry matter in the quilting system and without quilting. The models found were linear with coefficients of determination (R²) of 0.92 and 0.91 respectively. ^{Reta et al. (2007)} evaluated separations between rows of maize in two years and found linear models of dry matter production as a function of the IAF with R²= 0.86 and 0.79 respectively, it concludes that the increase in dry matter is due to the higher index of leaf area develops in the early stages of cultivation. ^{Zhang et al. (2011)} indicates that a higher leaf area index provided a larger accumulation of biomass and consequently higher grain production (7 251 kg ha^-1) and an efficiency of water use of 2.41 kg m^-3.

Figure 2 Production of dry matter based on the leaf area index of the forage maize grown with and without padding. 

^{Adekayode and Olojugba (2010)} report a correlation of 0.97 in grain production and leaf area index, mention that the IAF and the leaf distribution angle are important parameters for estimating the exchange of energy and gases in the canopies of the crop. The distribution and quantity of leaf area as well as the angle of the leaves are factors that control light interception within the maize canopy (^{Elings, 2000}; ^{Stewart et al., 2003}). ^{Subedi and Ma (2005)} reported that by removing all the leaves found in the lower part of the ear leaf after the anthesis, it reduced grain production from 17 to 25%.

The slope obtained in the models of the IAF and the dry matter produced by the plant was 86.29 g plant IAF^-1 in the system of padding and 65.76 g plant IAF^-1 in the system without quilting. The above represents an increase of 23.8% of dry matter produced in the quilting system with respect to the system without quilting. ^{Renquist and Martin (1982}) point out that, with polyethylene mulch during the summer, one third of the water is required compared to that needed when it is grown without padding, they conclude that padding improves the efficiency of water use and expresses in a higher fruit yield, this because of the better conservation of soil moisture and indirectly by the higher recorded soil temperatures. ^{Zribi et al. (2011)} indicates that the plastic mulch favors the structural stability and fertility of the soil, reduces the salinization of the soil that manifests itself in a greater production of dry matter.

Conclusions

No statistical differences were found in the production of dry matter between the quilting colors. However, the highest production was obtained in silver plastic, followed by black and then white. The use of plastic mulches to produce fodder maize increased the yields up to 25% more with respect to the system without quilting. The growth of the leaf area index as a function of the days after sowing was described by a linear quadratic model and the production of matter as a function of leaf area index was described by a linear model.