Biomass and Harvest Index of Two Quality Protein Corn Varieties with Bio-Fertilization in Two Luvisols of Yucatan, Mexico ()
1. Introduction
In America, the United States produces an estimated (2016/2017) 382.47 million tons of maize followed by Brazil with 83.5, Argentina with 36.5 and Mexico with 24.5. Mexico is a country with the lowest yields of 3.2 t∙ha−1 in contrast to the yields of the USA and Argentina with 9.3, 8.0 t∙ha−1, respectively, but similar to Brazil with 3.5 t∙ha−1.
Even though the Mexican production is low, there is a tendency to increase since in 1993: it was 1.8 t∙ha−1 and currently it is 3.2 t∙ha−1; cultivating nowadays is approximately 7 million 157 thousand 586 hectares [1] ; it is mainly in sub-humid tropical, temperate humid and sub-humid zones [2] .
Most of the corn is produced under rainfed conditions [1] for self-consumption and it is grown by 2 million small producers [2] contributing to more than half of the national food security of the poorest rural strata [3] . These producers are still using native varieties with large genetic diversity [4] , but with very low yield potential and poor protein quality.
INIFAP has released improved Creole varieties converted to protein quality adapted to the stony soils of Yucatan, Mexico such as Sac Beh and Chichen Itza, which have more than 50% Lysine and Tryptophan than the common Creole maize. Average yields of 2.23 to 3.33 t∙ha−1 have been reported on rocky soils and can reach more than 5.0 t∙ha−1 on better deep soils such as the Luvisols (LV) [5] .
Using those improved varieties can be more profitable and environmentally friendly if cheaper in-puts such as biofertilizers (Mycorrhizae and Azospirillum) are to be incorporated into the traditional production systems with the idea of partially replacing the chemical fertilizers.
Rodríguez-Eugenio et al. (2019) [6] comment that soil contamination due to excessive applications of chemical fertilizers reduces food security; and nutrients such as nitrogen and phosphorus are transported to the surface and groundwater, contaminating the water.
Carcaño-Montiel et al. (2006) [7] argue that with biofertilizers the native phosphorus and potassium of the soil are exported to the plant and the acidifying effect of ammoniacal nitrogenous fertilizers is reduced.
On the other hand, as has been mentioned by Aguilar Carpio et al. (2015) [8] , crop growth is influenced mainly by climate and nutrients; so the influence of biofertilizers on productivity can be studied from the analysis of the dry matter accumulation and its relationship with other factors such as nitrogen, soil chemical characteristics and environmental conditions. One way to do it is by studying the Harvest Index (HI) defined as the ratio of grain to total shoot dry matter as a valuable parameter to measure reproductive efficiency. It is determined by interactions between genotypes (G), environment (E) and crop management (M) and can measure the physiological efficiency and ability of a crop for converting the total dry matter into economic yield [9] .
Even though general studies indicate that the inoculation with Azospirillum, Glomus and the use of nitrogen increases dry matter production and grain (as a result of higher growth indexes) in both native and hybrid maize, there is a lack of information on this subject in the tropical regions of Mexico.
Thus, the purpose of this work was to evaluate the total biomass production and the Harvest Index of two improved quality protein native corn varieties when biofertilizers in combination with chemical fertilizers were applied in two different Luvisols with low and high intensive agricultural use.
2. Materials and Methods
The work was carried out in the state of Yucatan, Mexico in the spring-summer 2017/2017 season under favorable rainfed conditions at the INIFAP-UXMAL Experimental Station located at 20˚29'08.1'' North Latitude and 89˚24'39'' West Longitude, in an altitude of 50 meters above sea level [10] .
The yellow grain Chichen Itza (Chich) and the white grain Sac Beh (Zac) were the corn varieties classified as Quality Protein ones, and used as phytometers in two different soils classified as Luvisols.
2.1. Selection of Experimental Plots
The first Lot 1 had a low intensive agricultural use and maize has been grown every 4 to 5 years with long fallow periods. In the second Lot 2 corn has been grown every year with intensive use of chemical fertilizers. Both Lots have contrasting chemical characteristics such as salinity, electrical conductivity and phosphorus contents.
The soil attributes, analyzed by Phytomonitor (2018) [11] , were compared with reference data from Nom-021-Semarnat-2000 [12] . Even when the pH’s are neutral, the electrical conductivity of Lot 1 is lower (EC = 0.66 mS/cm) than Lot 2 (1.53 mS/cm). Sodium (Na) is higher in Lot 2 (330 vs. 165 ppm). The organic matter (OM) is satisfactory in both lots, but it is higher in Lot 1 (2.78% vs. 2.11%).
According to the official Mexican standards [12] Phosphorus (P) in Lot 1 is in the optimal range (17 ppm) however, in Lot 2, with more intensive use, P is in excess with 80 ppm. Potassium (K) is in excess in both Lots with more than 1000 parts per million (ppm).
2.2. Treatments, Variables and Statistical Analysis
Eight treatments were studied in experimental units of 5 m × 4 m (20 m2) with four rows of 1 m wide and 5 m long. The corn population density was estimated in 50,000 plants ha−1 (Figure 1 and Figure 2). The treatments resulted when the two varieties (Figure 3 and Figure 4) named: Chichen Itza (Chich) and Sac Beh (Sac) were combined with the following four levels of fertilization: 1) chemical (Chem 1) fertilization (N-P2O5-K2O): (60-80-00), 2) chemical fertilization (Chem 1) with biofertilizers (Bio): (60-80-00 + Mycorrhizae + Azospirillum), 3) second dose of chemical fertilization (Chem 2) with biofertilizers (Bio): (30-80-00 + Mycorrzas + Azospirillum) and 4) The control (00-00-00). The treatments were distributed in a completely randomized block design with three repetitions in each Lot and were identified according to Table 1.
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Figure 1. Topological arrangement of corn plants.
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Figure 3. Chichen Itza yellow grain variety.
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Table 1. Treatments studied in Lot 1 and Lot 2 with Chichen Itza and Sac Beh.
Six plants with complete competence were selected, and at the end of the physiological cycle the Total Dry Biomass (TDB) production (stems, leaves, husk and grain) were measured and converted into t∙ha−1. The stems, leaves, and husk were considered as the Partial Biomass (PB) weighed under field conditions (Figure 5) and considered as the main variable influencing Grain Yield (GY) production. With the TDB and GY, all in dry base, the HARVEST INDEX (HI) was calculated with the formula: GY/TDB. An Analysis of Variance (ANOVA) with their Coefficients of Variation (CV) were performed to all variables.
2.3. Inoculation of Biofertilizers and Chemical Fertilization
The seeds were inoculated with a mixture (1:1 ratio) of both: 1) INIFAPTM brand biofertilizer with Rhizophagus intraradices (Mycorrhizae fungus) at a concentration of ≥60 spores and 2) Azospirillum brasilense (Bacterium) at a concentration of 1 × 10−6 Colony Forming Units (CFU) mL−1. After inoculation the seeds were dried at room temperature for 8 hours to be planted in the experimental plots. 15 days after sowing, the chemical fertilizer was applied to the corresponding treatments. The fertilizer was buried 10 cm from the corn stem in the form of Urea (N) and Triple Calcium Superphosphate (P2O5) in a single application.
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Figure 5. Weighing dry partial biomass under field conditions.
3. Results and Discussion
The variables to be discussed below are highly implicated in the efforts or capacity of plants, as biological machines, to convert most of their biomass into grain. The Harvest Index (HI) is a very important trait for plant breeding. The higher the capacity of corn plants to produce economic yields the higher the probability to be selected for breeding programs. In that way, the food self-sufficiency of a country can be ensured.
3.1. Statistic Analysis
Table 2 shows the Mean Squares and the statistical significance when submitting the grain yield and the other biomass components (t∙ha−1) to the corresponding Analysis of Variance (ANOVA). No statistical differences were found (p = 95%); therefore, applying chemical fertilizers (Chem), alone or combined with biofertilizers (Chem-Bio) and even not applying any treatment (Control) is statistically the same. However, the information will be discussed later on when considering the arithmetic data of the investigation. However, it seems that further research is needed since the variables studied, under the specific conditions of this work, did not implicate any substantial change.
The CV’s (%) ranged from 0.014 in Partial Biomass Lot 2 to 18.23 in Partial Biomass Lot 1. Authors such as Pimentel (1985) [13] comment that the CV’s can be different depending on the type of experiments. Other authors such as: [14] [15] [16] Gómez and Gómez (1984) [14] ; Martínez (1988) [15] ; Patel et al. (2001) [16] suggest that when the CVs are greater than 30%, the experiments have low precision.
Similar statistical results were reported by Uribe Valle and Dzib Echeverria (2006) [10] and Uribe-Valle et al. (2007) [17] . They did not find any statistical differences between yields when corn was treated with Mycorrhizae + Azospirillum, a chemical treatment (N-P2O5-K2O) (40-100-00) or a control (00-00-00) in a Luvisol of Yucatan, Mexico.
However, other authors in north Mexico like Díaz Franco et al. (2012) [18] have found important statistical differences suggesting that mycorrhizal inoculation alone was very competitive in relation to chemical fertilization. The
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Table 2. Mean squares and statistical significance between treatments evaluated for grain yield and partial biomass (t∙ha−1) through the analysis of variance.
ns =Statistically no significant at p = 95%; EE = Experimental Error, CV = Coefficient of Variation.
combined inoculation of G. intraradices and A. brasilense, did not present any additive effect on corn growth. In addition, of the ecological advantage, it is more profitable by reducing the cost production of corn as compared to the use of chemical fertilizers.
3.2. Biomass Production and Harvest Index (HI)
3.2.1. Lot 1 vs. Lot 2
The production of biomass (t∙ha−1) and the HI are observed in Table 3 and Table 4. Regardless of the treatments, the average partial biomass production in Lot 1 was 2.36 t∙ha−1 higher than that of Lot 2 and so was the grain yield with more than 0.76 t∙ha−1. This difference may be due to the high sodium (Na) content and higher Electrical Conductivity (EC) of Lot 2. The sensitivity of corn to salinity has been argued by Ayala-Contreras (2015) [19] . Despite the contrasting results with biomass, the HI was similar in each Lot, ranging from 0.41 and 0.42; indicating that of the total biomass, a little more than 40% refers to the grain in both experimental Lots. It seems that the extraction process of photo-assimilates, to form grain, is equally efficient in both Lots regardless of their contrasting chemical soil conditions. Studies on this subject have been reported by López-Castañeda (2011) [20] in barley crop growing in soils with different moisture conditions.
3.2.2. Chichen Itza and Sac Beh in Lot 1
The contrasting agronomic behavior between Chich and Sac, in Lot 1, are shown in Table 3. Sac produces more PB than Chich in all treatments including the Control. The maximum GY, in Lot 1 for both Chich and Sac varieties was found with the same formula Chem1-Bio where 60 kilos N ha−1, 80 kilos of phosphorus as P2O5 plus biofertilizers were applied as it is reflected in T5 (Chem 1-Bio-Chich) and T6 (Chem 1-Bio-Sac) with 5.88 and 5.83 t∙ha−1 respectevely. Even with practically the same GY, it was Sac which obtained the maximum HI (0.49) whilst Chich had 0.43 with the same abovementioned treatments. It was no found any effect on HI when applying Bio to Chich as it is observed when comparing T3 (0.44) vs. T5 (0.43). However, Sac showed better response to Bio as it is seen in T4 (0.41) vs. T6 (0.49).
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Table 3. Biomass, yield production and Harvest Index (HI) with biofertilizers in a low intensive agricultural use Luvisol (Lot 1) in the Experimental Field Station at Uxmal Yucatan, Mexico.
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Table 4. Biomass, grain yield and Harvest Index (HI) with biofertilizers in a low intensive agricultural use Luvisol (Lot 2) in the experimental field station at Uxmal Yucatan, Mexico.
The lowest HI’s of both varieties Chich and Sac were found in the Control T1 and T2 with 0.41 and 0.36 respectively, as well as those treatments (T7) and (T8) where N was reduced by half. The difference between treatments can be related to the root growth and the high exploring volume when biofertilizers are applied. By instance, works in the north of Mexico [18] have indicated that the root volume of corn can be 75% higher when Mycorrhizae fungus was applied as compared to the Control. The higher root volume of 155 cm3 was obtained with Mycorrhizae alone while the Control just had 40 cm3; and the total fresh fodder was exceeded by more than 60%.
3.2.3. Chichen Itza and Sac Beh in Lot 2
As it is observed in Table 4 of Lot 2, Sac continues with a general trend of having the highest PB with practically the same GY (4.63 t∙ha−1) as Chich (4.84 t∙ha−1). However, in this Lot 2, Chich, and no Sac, showed the best HI (0.46) performance. In these soils, of highly intensive agricultural use, the HI of Sac is practically the same (0.41 to 0.42) in all treatments referred to Chem alone or combined with Bio. However, the Control (T2) showed the lowest HI with 0.39. On the other hand, Chich obtained the highest HI (0.46) with T5 (Chem 1-Bio-Chi) and the lowest one (0.41) with T7 (Chem 2-Bio-Chi).
Similar works, but with a corn hybrid (H-526), have indicated higher HI’s, ranging from 0.49 to 0.63 [21] compared with the varieties Chich and Sac. The lower HI of 0.49 was related to the Control whilst the higher one was for a chemical fertilizer of (120 N-160 P2O5-000 K2O). However, when chemical fertilizer (120 N-80 P2O5-000 K2O) was complemented with chicken manure, the HI of the hybrid was similar (0.49) as the Control [21] . It seems that applying more fertilizers does not necessarily increase the GY, but it does increase the production of PB [21] . Studies related to the agronomic behavior of tropical corn hybrids, in the state of Veracruz, Mexico [22] have indicated that the HI’s can range from 0.2 to 0.5 depending on the corn material.
3.3. Correlations Coefficients (R2) between Grain Yield and Partial Biomass (t∙ha−1)
Table 5 shows the Determination Coefficients (R2) when the GY’s were compared with the PB. The highest R2 was obtained with Sac in both experimental lots with 0.75 and 0.84 for Lot 1 and Lot 2 respectively; while Chich showed very low Determination Coefficients of 0.19 and 0.27 in each lot. This indicates that the GY of Sac can be associated more intensely with the above ground PB than that of Chich.
The above analysis indicates that the GY may not always be highly associated with the production of PB but also depends on the genetic material and other factors that need further study. It has been found [23] that the dry matter and
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Table 5. Determination Coefficients (R2) for grain yield as dependent variable (Y) vs. partial biomass as independent variable (X) (t∙ha−1) for both Chichen Itza and Sac Beh varieties in lots with low (Lot 1) and high intensive agriculture use (Lot 2).
grain yield in the corn hybrid H-562 (applying 160 kg N ha−1) was mainly related to the size and duration of the photosynthetic biomolecular apparatus (Leaf Area and Duration of the Total Leaf Area) which induced a highest Growth and Assimilation Rate.
On the other hand, with the Vandeño corn variety, better response was obtained with biofertilizer and the application of nitrogen; but even when the dry matter increased this was not substantially reflected in the grain yield. This behavior is due to a higher expansion, duration and speed growth of the plant canopy [23] .
Referring to previous works of Ramirez et al. (2020) [24] related to the contents of amino acids Lysine and Tryptophan in both Chich and Sac, it would be very important to quantify the relationship between those amino acids and the variables studied in this work. But in a first glance, it seems that the HI’s of Sac, in both lots, are better associated to the amioacids than that of Chich. However, there is a trend for the aminoacids to decrease while the HI’s increase. This contrasting agronomic and biochemical behavior needs a further and deep understanding to improve the corn breeding programs.
4. Conclusions
No statistical differences were found between treatments in any Luvisol. However, regardless of the treatments, the general average of TDB, PB and GY of both varieties were higher in Lot 1 with the lower intensive agriculture use. Sac produces more PB than Chich in all treatments including the Control.
The maximum GY, in Lot 1 for both Chich and Sac varieties, was found with the same formula Chem 1-Bio as reflected by T5 (Chem 1-Bio-Chich) and T6 (Chem 1-Bio-Sac) with 5.88 and 5.83 t∙ha−1 respectively.
Even with practically the same GY, in Lot 1, it was Sac that obtained the maximum HI (0.49) whilst Chich had 0.43. No effect on HI was found when applying Bio to Chich as Sac showed. The lowest HI of both varieties was found in the Control and those treatments with half N.
In Lot 2, Sac continues with the general trend of having the highest PB (6.6 t∙ha−1 vs. 6.0 t∙ha−1) with practically the same GY (4.63 t∙ha−1) as Chich (4.84 t∙ha−1). However, Chich, and no Sac, showed the best HI (0.46) performance with T5 (Chem 1-Bio-Chich).
It seems that the GY of Sac can be more predictable if associated with the PB production due to the high Coefficient of Determination (R2) in both lots.
Acknowledgements
We thank the National Institute of Forestry, Agricultural and Livestock Research (INIFAP) of Mexico for financing this work as part of the project called: Eficiencia nutrimental con fertilizacion quimica y organica en Luvisoles rodicos de Yucatán (Nutrient efficiency with chemical and organic fertilization in rhodic Luvisols of Yucatan).