Introduction

Nitrogen is one of the primary crop nutrients required in higher amounts; however, its availability towards the plants is influenced by several processes including mineralization, immobilization by plants or microorganisms, nitrification and denitrification (^{Tisdale et al., 2005}). It also increases the size of the cells, leaf area and photosynthetic activity (^{Hashemi et al., 1994}). Furthermore, its importance lies in the environmental pollution caused by accumulating in the subsoil; and the generated due to denitrification (^{Beukema and Van Der Zaag, 1990}). In the past 30 years, the nitrate content in irrigation water has increased (^{Vahabzadeh et al., 2006}). For these reasons, studies show the interest of increasing nitrogen use efficiency potential to increase crop yields, increasing soil fertility and especially efficiently manage irrigation water and nitrogen fertilizer primarily reducing potential damage to the environment and the economy of the producer (^{llen et al., 2004}; ^{Muñoz and Hernández, 2004}).

In the United States, growing maize uses most fraction (3751%) of total nitrogen consumed annually, where 40-60% is taken up by the crop (^{Grassini and Casman, 2012}), it is in part ground and another is subject to potential losses to the environment through processes such as volatilization of NH3, NO3^- leaching, denitrification, runoff, emissions of N₂O (^{Snyder, CS 2012}). According to ^{Shicheng Zhao and Ping He (2012)}, the most logical strategy to increase the efficiency of nitrogen use is to combine applications basal nitrogen and coverage in the most important stages of growth and in turn match the growing demand and seasonal supply from the ground.

In Mexico, the efficient use of nitrogen fertilizer generally varies from 40-80% due to factors such as texture or compaction problems, land levelling, and characteristics incorporating crop residues, water application system, management irrigation, time of application and nitrogen source, amount of precipitation, depth of crop root systems and general management including phytosanitary issues (^{Castellanos, 2005}). In the north of Sinaloa, Mexico, the application of irrigation efficiencies in maize are on average 45%, being the biggest losses as a result of runoff and percolation (^{Gutiérrez, 2004}; ^{Sifuentes et al., 2010}), which suggests a similar loss of nitrogen impacts on production costs and pollution of surface and groundwater (^{Sifuentes, 2007}).

According to ^{Rimsky et al. (2002)} transportation of nitrates through the soil profile is influenced not only by its properties and fertilization but also by the type of the crop and, the implementation of major irrigation observed losses of nitrogen in soils with substantial contents of fine sand or silt under irrigation. Under the same criteria, ^{Spalding et al. (2001)} evaluated for six years, the impact of improved irrigation and nutrition practices (N-NO₃) in maize and alfalfa, using four production systems (conventional furrow irrigation, intermittent irrigation, sprinkler and centre pivot) significantly reducing N leaching with minor reductions in 6% of the yield.

Currently, the most serious problem facing farmers is to ensure that there is enough of each essential element for optimal use on the ground and in their developmental stages (^{Bowen and Bernard, 1990}) as the N naturally undergoes transformations from the atmosphere, soil and plant lost more accentuated with irrational practices such as over-irrigation and nitrogen over-fertilization; such is the case of N immobilized by microorganisms incorporating N organic of insoluble compounds and therefore unavailable for the plants (^{Tisdale, 2005}). However, this problem is aggravated in high soils in organic matter such as undergoing tillage (^{Bowen and Bernard, 1990}). Thus, nitrogen and water management are complementary, consequently, the plots with low irrigation efficiencies under high nitrogen supply may be deficient in this element reducing the yields (^{SIAP, 2010}; ^{INIFAP, 2005}).

Fields that have improved irrigation efficiency require less nitrogen, retaining profitable returns, for which it is important that the selection and management of irrigation are adequate (^{Bauder et al., 2007}). Because of this, the present work was to study different techniques of surface irrigation and its effect on the efficient use of nitrogen.

Materials and methods

The study was conducted during the autumn-winter crop cycles (OI) 2006-2007 and 2011-2012 in the Fort Valley Experimental Field (CEVAF) of the National Research Institute of Forestry, Agriculture and Livestock (INIFAP), located in "Juan Jose Rivers", "Guasave Sinaloa" Mexico in the 25° 46' 32" north latitude and 108° 48' 10" west longitude at an elevation of 20 meters, within the Irrigation District 075, "Rio Fuerte" the largest in Mexico. This area has an annual rainfall of 200-350 mm, clay loam soil (50% clay, 30% silt and 20% sand), low in organic matter (less than 1%) and bulk density of1.2 g cm^-3.

During the first cycle (2006-2007) a plot of three hectares was established in two irrigation low pressure (multi-gates), a PVC pipe (MCPVC) and the other Lay flat hose (MCLF), each with 6 inches in diameter and separation gates of 0.75 m. The system was installed according to the topographical conditions of the terrain and planting method. Adapting a piping system previously installed in the experimental plot which was powered by a diesel engine pump and supplied directly from an irrigation channel module pond Batequis. The control was a plot with conventional irrigation (RC) in rows with spacing of 0.76 m connected in open channels. The length of the grooves of the two low pressure systems was 120 m, while that of the control plot was 100 m.

In both plots with low pressure systems carried out a gravity irrigation design by the RIGRAV program (Rendon, 1995) to determine the optimal spending irrigation unit (Qo) and run time (Tr) that will generate high irrigation efficiencies for which it was necessary to calibrate soil hydraulic characteristics. In the control no design was made, only the single sheets were measured, which were applied by the sprinkler, selecting one groove in the center of each treatment and taking five equidistant points along the groove where a gravimetric sampling was performed (using auger) in three strata 0-30, 30-6- and 60-90 cm, then depositing the samples in aluminum containers which were dried and weighed.

In order to determine the effect of irrigation efficiency in the efficiency of N, a fertilization program was designed for each treatment. For both systems, the formula 360-60-60 was used for the control formula was used and also for the 430-6060, i.e., 20% of N units in the control than in the traditional system, with the assumption that by increasing the efficiency in the use of water will increase nitrogen efficiency. In the three treatment applying N and K, applied in instalments in four events (25% each) while the total of P units were applied at planting time (Table 1). The variety selected was DK 2020 and was planted on December 15, 2006.

Table 1 Management and fertilizer sources usage, fall-winter 2006-2007. 

For the second cycle (2011-2012), the treatments consisted of three techniques used surface irrigation (furrow): 1) alternate rows (SA) consisting of watering a groove and the other not, which may reduce the gross sheets implemented without affecting crop production (Webber et al., 2006); 2) beds (CAM) consisting of a furrow of 1.6 m wide and 0.20 m high; which enables a fast horizontal watering (Sifuentes, 2003); 3) reduction of expenditure (RG), reducing step by step the supplied water so that runoff losses at the end of the groove are eliminated and, the percolation losses at the start of the groove are minimized (Lal and Pandya, 1970) and the control (TES). The latter corresponds to conventional furrow irrigation. Each treatment was established on an area of 0.27 hectares (36 rows at 0.76 m with a length of 100 m). The variety selected was Pioneer P3245W, sown on December 2, 2011.

In the four treatments, we applied prior to the sowing, a basic fertilization of300 kg ha^-1 of the physical mixture 30-10-12; the supplementary fertilization, considering the contribution to the soil (108 kg ha^-1) and the projected irrigation efficiency (CAM 65, SA 70, RG 80 and TES 45%) for each treatment was performed based on urea resulting in a total of N applied of 329, 305, 268 and 475 kg ha^-1.

In order to determine the dose of nitrogen fertilization in both cycles was essential to know the nutrient requirements of the crop by stage of development and their productive potential, and the characteristics of their root system, content of nitrates in the soil organic matter content and all the irrigation management. For such reasons, in each growing season texture analysis, salinity and fertility were performed and thus proceed with adequate crop nutrition calculating doses of nutrients to the following equation.

Where: demand, represents the daily needs of each nutrient (kg ha^-1 day); supply refers to soil nutrient intake (kg ha^-1), estimated from the analysis of it and the degree of utilization efficiency of the nutrient which depends on irrigation, soil, fertilizer source, including squill value from 0 to 100%.

The crops were planted in dry, with a seeding density of 105 000 ha^-1 to 12.04 cm, applying immediately the germination irrigation. When the maize reached 40 cm height, we proceeded to grow and open a groove simultaneously.

Irrigation scheduling for all treatments was performed using the method of water balance through software irrimodel (Sifuentes et al., 2012) using an integrated model of locally calibrated irrigation scheduling for maize, which estimated the variation of soil moisture in the root zone integrating parameters of soil, plant and climate using the concept of growing degree days. Furthermore, the degree of use of nitrogen was also estimated by the following equation:

Where: EXT is the total nutrient removal by crop (kg ha^-1) and total nitrogen represents the contribution of soil and the amount of fertilizer added (kg ha^-1).

Results and discussion

The irrigation design (initial and aid) during the first cycle (2006-2007) was performed with the program RIGRAV, where the length of watering time (Tr), unit cost of irrigation (qu), Christiansen uniformity coefficient (CUC), raw sheet (Lb), application efficiency (Ea) and irrigation efficiency (Er), were simulated considering the parameters shown in Table 2. In practice, these values may differ from the actual values of a plot with the same texture. Because of this, the irrigation design obtained with direct or simplified method may be involve in practice irrigation is applied with lower than those obtained by the design efficiencies. For increasing these efficiencies, it is necessary to adjust the layout in the field during the first "start watering" timing. These values were generated with irrigation scheduling and the physical characteristics of the soil. It is noteworthy that for evaluation program recommendations were only applied in low pressure systems.

Table 2 Irrigation design parameters calibrated by gravity (RIGRAV). 

In addition to the data generated by the program RIGRAV, the times modeled irrigation run times and application efficiencies made which were within the recommended application with efficiencies ranging from 88 to 90% range were compared. Table 3 shows the efficiencies obtained for such treatments to increase considering that this would also increase the efficiency of nitrogen.

Table 3 Total watering sheets, and average irrigation application efficiencies for the treatments. 

The calendar used in this study consisted of four irrigation distributed germination irrigation (irrigation 1) and three aid sixth true leaf stage (V6), watery stage (R2) and milky (R3) (Table 4).

Table 4 Irrigation Calendar 2006-2007. 

In order to determine the degree of use of the main nutrients, the culture was subjected to analysis of growth to every part of the plant to observe the interaction and response to the addition of the nutrients added. It is noted that an interaction occurs when the response of one or more inputs added in combination, in this case water and fertilizer doses is uneven in comparison to the sum of their individual responses; therefore, before harvesting, the nutrient concentration in straw and grain was determined, for later estimate the total removals of nutrients and project productivity of these nutrients in grain production, since generally a significant difference was found in these extractions was determined, as shown in Tables 5 and ⁶.

Table 5 Nutrient extraction of maize under different irrigation methods (2006-2007). 

Table 6 Unitary nutrient extraction of maize under different irrigation methods (2006-2007). 

Nitrogen is linked to the movement of water in the soil, because as the irrigation application efficiency increases also increases nitrogen use efficiency (Figure 1 and Table 6) as pointed out by ^{Castellanos et al. (2005)}. The level of nitrogen used was estimated taking into account the contribution of the soil, which in this case was 70 kg and supplied by the fertilizer for 360 kg. With respect to the yield obtained for the three treatments, it was observed that was larger in the system of MC-lay flat with 10.5 t ha^-1, followed in the MCPVC system with 10 t ha^-1 and, the lowest yield was in the conventional system with 8.67 t ha^-1, which was mainly due to moisture conditions provided in the active root zone. These data further indicated that it may increase the productive potential of the crop and save on input costs and potentially reduce pollution of groundwater as N leaching losses become higher in the conventional irrigation as a result of increasing the raw sheet applied, widely adopted and resulting in a gradual increase in the concentration of nitrates in groundwater.

Figure 1 Efficiency of irrigation and nitrogen in two irrigation low pressure (MCLF and MCPVC) and conventional irrigation in maize (RC). 

For the second cycle, 2011-2012, the irrigation techniques were evaluated by the just established surface, using the same design criteria and irrigation scheduling of the previous study. Table 7 shows a summary of the risks applied for each irrigation technique used with their respective phenological stages coinciding with the critical stages of the crop and growing degree days to predict in advance, allowing water and nutrient requirements; while in Table 8 shows the sheets required for the cultivation and applied and efficiencies achieved.

Table 7 Calendar of the irrigation applied from 2011 to 2012. 

Table 8 Water requirements and application efficiencies. 

The Table 9 shows the total extraction of several nutrients at the end of the cycle, used to determine the degree of use of the fertilizer. Similarly in Figure 2, we can observe the grade efficiencies of nitrogen used considering a contribution of 108 kg soil and fertilizer in different supplies. The design beds with a dose of 329, alternate rows 305, 268 deficit conventional irrigation and475 kg ha^-1, respectively, and the final yield was 13.31, 13.11, 13.17 and 14.6 t ha^-1 in the same order.

Table 9 Maize nutrient extraction under different surface irrigation techniques 2011-2012. 

Figure 2 Efficiency of irrigation application and degree of use of nitrogen in three plot surface irrigation techniques. 

Conclusions

Using the low pressure irrigation systems with multi-gates MC-PVC and MC-Lay Flat, application efficiencies were obtained on average 80%. In addition, the results showed that, the excess of water dramatically decreased the efficiency of nitrogen, increasing losses due to percolation, which increase the degree of contamination of groundwater; these results were consistent with previous studies made by Pacheco (1998).

Low pressure irrigation systems proved to be a good alternative for technological irrigation at farm level, by allowing the transmission and distribution of irrigation water within the lot by lightweight, easy to carry and connect working at low pressure pipelines with less than a meter of elevation and valves for regulating the flow of delivery in the grooves and thereby improve irrigation efficiency. Besides, being available to the economy of the producers, since most crops established in areas larger than 10 hectares, from which the investment tends to be less than $5 000.00 pesos per hectare. Regarding the use of different techniques of surface irrigation, it is also showed increasing irrigation efficiency at farm level; however, significantly reducing nutrient losses outside the active root zone as nitrogen. It was also concluded that, the volume of water saved in the use of these techniques can be used in scenarios of low water availability.