Potential Use of Aeration in Soybean and Corn Stored in the Northwest of Minas Gerais, Brazil

Abstract

Drying agricultural products is a crucial step in maintaining post-harvest quality. Understanding the use of equilibrium moisture content is essential in grain processing, as it is an inherent property of grains. The objective of this study was to assess the number of hours suitable for maintenance aeration, cooling, and low temperature drying, while also evaluating the risks of over-drying the product or the humidification of intergranular air. This study focused on soybeans and corn stored in Unaí, located in the Northwest Mesoregion of Minas Gerais, with a moisture content of 13.0 % (wet basis). Meteorological data were collected from January 1, 2020, to December 31, 2022, using weather stations operated by the Instituto Nacional de Meteorologia (INMET). The historical series from INMET provided daily meteorological data over the studied period, including collection hour, temperature, and relative humidity values. The results revealed that throughout the year, the air blown into the grain mass for both corn and soybeans-maintained conditions conducive to achieving a moisture content of 13% (on a wet basis). For corn, the months with the highest number of hours suitable for hygroscopic equilibrium were January, April, and June in 2020; May, June, and November in 2021; and April, May, and July in 2022. For soybeans, the months with the most hours suitable for hygroscopic equilibrium were May, June, and November in 2020; April, May, and November in 2021; and March, June, and December in 2022.

Keywords:
grains; psychrometry; hygroscopic equilibrium; storage.

HIGHLIGHTS

Aeration conditions of the largest grain producer in the Northwest of Minas Gerais.

Potential for low temperature drying operation.

Risk of risk of overdrying stored grain.

Hygroscopic equilibrium conditions with 13% moisture content for maintenance aeration.

INTRODUCTION

The Brazilian economy has shown a positive trade balance over the last few years, and one of the sectors that most contributes to this result is agribusiness [¹].

The most traded products in agribusiness are commodities, an example are soybeans and corn, which are products that do not have differentiation in terms of quality, which are traded on the stock exchanges of several countries around the world. Because they are products with a low profit margin for the producer and intermediaries, any loss during the process causes significant damage to those involved.

In Brazil, corn cultivation has been gaining space and is one of the main economic segments of Brazilian agribusiness, being the second most exported grain [²]. Furthermore, it is worth mentioning that in the 2022/2023 harvest, Brazil produced 131,838,600 metric tons of corn and 154,609,500 metric tons of soybeans, highlighting its potential for corn and soybean production and its importance in the economic scenario in the production chain of these crops [³].

The state of Minas Gerais should record another record in grain production during the 2022/2023 harvest, according to the first survey by the National Supply Company [³]. Soybean and corn are among the main products, which together make up a total of 91.5% of grain production in the state. Together, they should reach a volume of 16.6 million tons produced, reports the superintendent of Innovation and Agricultural Economy, of the Secretary of State for Agriculture, Livestock and Supply [⁴].

Storage is one of the processes that presents a great loss in post-harvest, both qualitatively and quantitatively. This process is fundamental to food production, as the harvest of a product often occurs once or twice a year and its consumption does not have this seasonality [¹].

The vast majority of grain storage facilities for bulk products have systems, such as thermometry and aeration, which allow measuring the temperature of the stored grain and homogenizing and/or cooling this stored product [¹].

Drying of agricultural products is a fundamental step for maintaining post-harvest quality [⁵]. Knowledge of the hygroscopic equilibrium is one of the main factors in grain drying, as this is a natural property of grains. However, the hygroscopic equilibrium, when not monitored before storage, can cause great damage to grain storage facilities.

In post-harvest, maintaining the moisture content of stored grains is of paramount importance to reduce product deterioration over time. In this sense, aeration is extremely important in maintaining the quality of stored grains. During the aeration process, the hygroscopic equilibrium between the grain mass and the insufflated air must be observed. Since soybean and corn grains are hygroscopic materials, they are capable of adsorbing, retaining or desorbing water vapour, causing the phenomenon called hygroscopic equilibrium to occur, which is when the moisture of the grain comes into balance with the drying air. The connection between the equilibrium relative humidity and the moisture of a given product can be presented through mathematical equations, called isotherms or hygroscopic equilibrium [⁶]. Knowledge of isothermal curves is of paramount importance for handling and storage under environmental conditions, as it serves to ensure that the moisture of the product remains at adequate levels under the conditions of temperature and relative humidity of storage, so that there is a reduction in the possibility of the development of pathogens and fungi in the grains [⁷].

Therefore, the present work aims to evaluate the number of hours with favorable conditions for conducting maintenance aeration, cooling, low temperature, risk of overdrying and risk of humidification of intergranular air in soybeans and corn stored in the municipality of Unaí located in the Mesoregion of the Northwest of Minas Gerais.

MATERIAL AND METHODS

Weather data

Meteorological data for the period from January 1, 2020 to December 31, 2022 were obtained from meteorological stations at the National Institute of Meteorology [⁸] for the Northwest region of Minas Gerais. The municipality of Unaí was chosen taking into account the social impact, the potential for agriculture and the potential for processing and storing grains.

Evaluated characteristics

Temperatures and relative humidity of the environment

Through the INMET historical series for the Northwest of Minas Gerais, daily meteorological data were obtained for the studied period, with the time of collection and their respective temperatures and relative humidity of the environment at that moment.

Air heating temperature

For all daily meteorological data recorded over a period of one year, an additional 2°C was added to the temperature of the ambient air, corresponding to its heating due to friction with the fan blades [⁹].

Then, using the psychrometric equations [¹⁰] the new psychrometric characteristics of the heated air were determined so that the humidity and equilibrium could be calculated.

Balance humidity

After determining the temperatures plus the heating from friction with the fan blades and their psychrometric characteristics, the equilibrium humidity was calculated using the Modified Henderson equation, illustrated below [¹⁰]:

$$U_e={[ln\frac{\left(1-U{R}_{ar}\right)}{\left(-a*\left(T+b\right)\right)}]}^{\frac{1}{c}}$$

Where:

U_e = Equilibrium moisture content, in % b.s.;

UR_ar = Relative humidity of heated air, in decimal;

T = Heated air temperature, in °C; and

a, b, c = parameters that depend on the nature of the product.

Criteria used to carry out maintenance aeration, cooling aeration and low temperature drying

Considering that the ideal moisture for stored soybean and corn grains is 13%, the following criteria were adopted to carry out the maintenance aeration, cooling aeration and drying aeration:

Maintenance aeration: when the equilibrium moisture content calculated by the Modified Henderson equation varies between 12.5% and 13.5%, aeration will be considered indicated.

Cooling aeration: when the equilibrium moisture content varies between 12.5% and 13.5% and the air temperature is equal to or less than 25°C, aeration will be considered feasible.

Low drying temperature drying: the air temperature should be between 26°C and 45°C and the Equilibrium moisture content should be in the range of 12.5% and 13.5%.

Risk of overdying: when the equilibrium humidity is less than 12.5%.

Risk of humidification of intergranular air: when the equilibrium moisture content is greater than 13.5%.

Statistical analysis

The data obtained were submitted to descriptive statistical analysis. To carry out this statistical procedure, an electronic spreadsheet was used.

RESULTS AND DISCUSSION

Table 1 represents the number of hours in which stored corn can reach hygroscopic equilibrium with climatic conditions observed in the municipality of Unaí-MG in the year 2020.

Table 1
Hours of hygroscopic equilibrium for corn in the municipality of Unaí, located in the Northwest of Minas Gerais for the year 2020.

Northwest Mineiro Mesoregion - Unaí
Corn - Year 2020
Air temperature
after	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
the fan
30	1	0	0	3	0	0	0	0	0	0	0	0	4
29	5	3	4	8	0	0	0	0	0	0	0	0	20
28	29	23	13	14	0	0	0	0	0	0	5	9	93
27	24	21	24	27	6	0	0	0	0	10	11	18	141
26	9	11	9	7	8	0	0	0	0	19	23	19	105
25	4	1	3	4	6	5	0	0	7	16	21	13	80
24	3	0	0	5	14	12	0	0	5	10	9	6	64
23	4	0	0	3	6	8	3	0	3	1	1	5	34
22	0	0	0	4	4	7	11	2	2	0	3	2	35
21	0	0	0	1	1	15	11	9	0	0	1	1	39
20	0	0	0	0	2	3	21	21	0	0	0	0	47
19	0	0	0	0	2	5	24	19	6	0	0	0	56
18	0	0	0	0	3	2	12	5	11	0	0	0	33
17	0	0	0	0	0	0	4	13	7	0	0	0	24
16	0	0	0	0	0	0	1	2	2	0	0	0	5
15	0	0	0	0	0	0	0	2	0	0	0	0	2
Total (h)	79	59	53	76	52	57	87	73	43	56	74	73	782

Table 2 represents the number of hours in which stored corn can reach hygroscopic equilibrium with climatic conditions observed in the municipality of Unaí-MG in the year 2021.

Table 2
Hours of hygroscopic equilibrium for corn in the municipality of Unaí, located in the Northwest of Minas Gerais for the year 2021.

Northwest Mineiro Mesoregion - Unaí
Corn - Year 2021
Air temperature
after	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
the fan
30	0	0	0	0	0	0	0	0	0	0	0	0	0
29	2	1	1	0	0	0	0	0	0	0	2	3	9
28	10	9	9	2	0	0	0	0	0	2	13	27	72
27	15	23	12	6	0	0	0	0	0	13	14	20	103
26	9	7	19	10	0	0	0	0	0	11	20	14	90
25	12	2	8	14	8	0	0	0	0	11	16	0	71
24	11	0	5	8	11	4	0	0	2	8	5	0	54
23	7	0	5	14	10	8	0	0	1	2	2	0	49
22	1	0	1	6	24	20	0	0	0	2	0	0	54
21	0	0	1	4	9	18	2	0	3	0	0	0	37
20	0	0	0	1	4	6	4	5	3	0	0	0	23
19	0	0	0	0	3	8	5	12	2	0	0	0	30
18	0	0	0	0	0	4	12	10	1	0	0	0	27
17	0	0	0	0	0	15	11	20	2	0	0	0	48
16	0	0	0	0	0	3	17	6	0	0	0	0	26
15	0	0	0	0	0	1	9	0	0	0	0	0	10
Total (h)	67	42	61	65	69	87	60	53	14	49	72	64	703

Table 3 represents the number of hours in which stored corn can reach hygroscopic equilibrium with climatic conditions observed in the municipality of Unaí-MG in the year 2022.

Table 3
Hours of hygroscopic equilibrium for corn in the municipality of Unaí, located in the Northwest of Minas Gerais for the year 2022.

Northwest Mineiro Mesoregion - Unaí
Corn - Year 2022
Air temperature
after	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
the fan
30	0	0	0	0	0	0	0	0	0	0	0	0	0
29	2	4	0	0	0	0	0	0	0	0	0	1	7
28	16	27	3	2	0	0	0	0	0	0	4	22	74
27	24	25	8	8	0	0	0	0	0	1	12	33	111
26	11	6	24	9	7	0	0	0	5	6	14	13	95
25	6	1	10	11	8	0	0	0	11	18	13	3	81
24	4	0	10	25	7	0	0	0	16	12	4	1	79
23	1	0	3	18	4	4	0	0	6	12	7	0	55
22	0	0	0	5	16	7	0	3	3	2	0	0	36
21	0	0	0	1	9	10	0	0	0	0	0	0	20
20	0	0	0	0	10	16	7	7	1	1	0	0	42
19	0	0	0	0	5	20	26	6	1	0	0	0	58
18	0	0	0	0	2	11	31	13	3	0	0	0	60
17	0	0	0	0	4	6	14	8	0	0	0	0	32
16	0	0	0	0	4	3	5	10	2	0	0	0	24
15	0	0	0	0	3	0	0	0	3	0	0	0	6
Total (h)	64	63	58	79	79	77	83	47	51	52	54	73	780

Table 4 represents the number of hours in which stored soybeans can reach hygroscopic equilibrium with climatic conditions observed in the municipality of Unaí-MG in the year 2020.

Table 4
Hours of hygroscopic equilibrium for soybeans in the municipality of Unaí, located in the Northwest of Minas Gerais for the year 2020.

Northwest Mineiro Mesoregion - Unaí
Soybean - Year 2020
Air temperature
after	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
the fan
30	0	0	0	0	0	0	0	0	0	0	0	0	0
29	0	0	0	0	0	0	0	0	0	0	0	0	0
28	0	0	0	0	0	0	0	0	0	0	0	0	0
27	6	7	3	5	0	0	0	0	0	0	0	0	21
26	20	18	15	10	1	0	0	0	0	1	3	3	71
25	13	20	20	15	3	0	0	0	0	7	20	24	122
24	8	11	14	7	8	0	0	0	0	22	28	20	118
23	1	2	4	3	5	0	0	0	2	8	8	6	39
22	2	0	0	2	12	7	0	0	5	1	7	4	40
21	1	0	1	2	12	12	1	0	0	0	3	2	34
20	1	0	0	1	10	13	1	0	0	0	1	1	28
19	0	0	0	5	6	14	7	4	0	0	2	0	38
18	0	0	0	0	3	6	12	7	0	0	0	0	28
17	0	0	0	0	2	9	12	9	0	0	0	0	32
16	0	0	0	0	1	1	11	8	0	0	0	0	21
15	0	0	0	0	4	1	12	2	1	0	0	0	20
Total (h)	52	58	57	50	67	63	56	30	8	39	72	60	612

Table 5 represents the number of hours in which stored soybeans can reach hygroscopic equilibrium with climatic conditions observed in the municipality of Unaí-MG in the year 2021.

Table 5
Hours of hygroscopic equilibrium for soybeans in the municipality of Unaí, located in the Northwest of Minas Gerais for the year 2021.

Northwest Mineiro Mesoregion - Unaí
Soybean - Year 2021
Air temperature
after	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
the fan
30	0	0	0	0	0	0	0	0	0	0	0	0	0
29	0	0	0	0	0	0	0	0	0	0	0	0	0
28	0	0	0	0	0	0	0	0	0	0	0	0	0
27	0	3	0	0	0	0	0	0	0	0	2	4	9
26	9	14	7	1	0	0	0	0	0	2	7	11	51
25	17	20	15	4	0	0	0	0	0	17	17	19	109
24	4	13	16	12	0	0	0	0	0	19	16	13	93
23	10	1	11	11	2	0	0	0	0	8	22	4	69
22	8	0	3	17	11	1	0	0	0	1	6	0	47
21	5	0	7	13	13	3	0	0	0	0	0	0	41
20	1	0	3	9	14	10	0	0	0	0	0	0	37
19	2	0	2	5	11	16	0	0	0	0	0	0	36
18	0	0	0	0	8	12	1	0	0	0	0	0	21
17	0	0	0	0	7	4	3	0	0	0	0	0	14
16	0	0	0	0	4	3	6	1	0	0	0	0	14
15	0	0	0	0	0	2	3	1	0	0	0	0	6
Total (h)	56	51	64	72	70	51	13	2	0	47	70	51	547

Table 6 represents the number of hours in which stored soybeans can reach hygroscopic equilibrium with climatic conditions observed in the municipality of Unaí-MG in the year 2022.

Table 6
Hours of hygroscopic equilibrium for soybeans in the municipality of Unaí, located in the Northwest of Minas Gerais for the year 2022.

Northwest Mineiro Mesoregion - Unaí
Soybean - Year 2022
Air temperature
after	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
the fan
30	0	0	0	0	0	0	0	0	0	0	0	0	0
29	0	0	0	0	0	0	0	0	0	0	0	0	0
28	0	0	0	0	0	0	0	0	0	0	0	0	0
27	0	1	0	0	0	0	0	0	0	0	0	2	3
26	6	15	3	5	0	0	0	0	0	0	3	18	50
25	17	19	7	8	0	0	0	0	1	2	11	21	86
24	13	5	17	12	3	0	0	0	3	11	12	15	91
23	4	3	20	5	8	0	0	0	5	6	14	4	69
22	5	0	12	17	4	0	0	0	2	13	13	3	69
21	2	0	7	12	5	0	0	0	2	0	4	2	34
20	0	0	0	3	11	10	0	0	1	1	2	0	28
19	0	0	0	2	5	7	0	0	0	0	0	0	14
18	0	0	0	0	6	7	0	0	0	0	0	0	13
17	0	0	0	0	6	20	4	2	0	0	0	0	32
16	0	0	0	0	4	16	11	0	0	0	0	0	31
15	0	0	0	0	2	8	19	0	0	0	0	0	29
Total (h)	47	43	66	64	54	68	34	2	14	33	59	65	549

For the municipality of Unaí-MG, located in the Mesoregion of Noroeste Mineiro, it was observed for corn over the years 2020, 2021 and 2022, it presented 782, 703 and 780 hours with hygroscopic equilibrium conditions, respectively (Table 1, 2 and 3). It was observed for soybean over the years 2020, 2021 and 2022, it presented 612, 547, and 549 hours with hygroscopic equilibrium conditions, respectively (Table 4, 5 and 6).

After analyzing all the tables, it could be observed that, over a year, both for corn and soybeans, the air blown into the grain mass presents psychometric conditions conducive to maintaining the product with a moisture of 13% b.u. It is worth noting that, for corn and soybeans in 2020, the months with the highest number of hours with hygroscopic equilibrium conditions were; corn (January, April and July) soybeans (May, June and November), for corn and soybeans in 2021, the months with the highest number of hours with hygroscopic equilibrium conditions were; corn (May, June and November) soybeans (April, May and November), the months of May and November had the same number of hours, for corn and soybeans in the year 2022 the months that had the highest number of hours with hygroscopic equilibrium conditions were; corn (April, May and July), with the months of April and May having the same number of hours, soybeans (March, June and December).

The variations of the months with the highest number of hours with hygroscopic equilibrium with the three years studied may have occurred due to climate changes that have occurred in recent years. These climate changes have also been linked to variations in grain production in the country due to the variation in precipitation volumes, temperature and relative humidity throughout the production period. More specifically in the Mesoregion of Noroeste Mineiro, where the Municipality of Unaí is located, there was also variation in climatic conditions, which may have resulted in oscillations of moments in which a greater or lesser number of hours occurred with hygroscopic balance over the last three years.

It is important to emphasize that for the municipality of Unaí-MG, the highest number of hours in which hygroscopic balance was obtained in the three years of study for corn and soybeans were concentrated in the temperature condition between 15°C and 32°C and the relative humidity of the air varying between 50% and 80%, showing that with these psychrometric conditions of the air, a greater period of hours of ideal conditions is obtained to maintain the hygroscopic balance in corn and soybeans at 13% b.u.

The ideal moisture for storing grain safely outdoors is in the range of 10% to 13%. From 14%, the grains show an increase in the respiratory rate, intensifying the heat release process, thus leaving the environment conducive to the development of microorganisms, mainly fungi, which cause bacterial deterioration [¹¹].

By segregating the hours with hygroscopic equilibrium found in the municipality of Unaí-MG under study by operation, it was possible to observe in tables 7, 8, 9, 10, 11 and 12 the number of hours suitable for maintenance aeration, cooling aeration, low temperature drying, risk of overdrying and risk of humidification of intergranular air.

Table 7
Number of hours suitable for maintenance aeration (1), cooling aeration (2), low temperature drying (3), risk of overdrying (4) and risk of humidification of intergranular air (5) throughout the year 2020 for corn stored in the municipality of Unaí, located in the Northwest of Minas Gerais.

Northwest Mineiro Mesoregion - Unaí
Corn - Year 2020
Operation	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
1	11	1	3	17	38	57	87	73	43	27	35	27	419
2	11*	1*	3*	17*	38*	57*	87*	73*	43*	27*	35*	27*	419*
3	68	58	50	59	14	0	0	0	0	29	39	46	363
4	231	176	170	163	229	289	409	550	635	466	274	284	3.876
5	433	461	521	481	462	374	248	119	42	222	372	374	4.109
Total (h)	743	696	744	720	743	720	744	742	720	744	720	731	8.767

• ^*
  It can be used for both maintenance aeration and cooling aeration.

Table 8
Number of hours suitable for maintenance aeration (1), cooling aeration (2), low temperature drying (3), risk of overdrying (4) and risk of humidification of intergranular air (5) throughout the year 2021 for corn stored in the municipality of Unaí, located in the Northwest of Minas Gerais.

Northwest Mineiro Mesoregion - Unaí
Corn - Year 2021
Operation	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
1	31	2	20	47	69	87	60	53	14	23	23	0	429
2	31*	2*	20*	47*	69*	87*	60*	53*	14*	23*	23*	0*	429*
3	36	40	41	18	0	0	0	0	0	26	49	64	274
4	281	159	282	264	338	383	554	648	698	442	177	160	4.386
5	309	461	389	391	337	250	128	43	8	230	442	482	3.470
Total (h)	657	662	732	720	744	720	742	744	720	721	691	706	8.559

• ^*
  It can be used for both maintenance aeration and cooling aeration.

Table 9
Number of hours suitable for maintenance aeration (1), cooling aeration (2), low temperature drying (3), risk of overdrying (4) and risk of humidification of intergranular air (5) throughout the year 2022 for corn stored in the municipality of Unaí, located in the Northwest of Minas Gerais.

Northwest Mineiro Mesoregion - Unaí
Corn - Year 2022
Operation	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
1	11	1	23	60	72	77	83	47	46	45	24	4	493
2	11*	1*	23*	60*	72*	77*	83*	47*	46*	45*	24*	4*	493*
3	53	62	35	19	7	0	0	0	5	7	30	69	287
4	203	151	308	372	368	396	498	665	559	495	220	129	4.364
5	447	424	349	266	292	244	157	25	96	145	393	490	3.328
Total (h)	714	638	715	717	739	717	738	737	706	692	667	692	8.472

• ^*
  It can be used for both maintenance aeration and cooling aeration.

Table 10
Number of hours suitable for maintenance aeration (1), cooling aeration (2), low temperature drying (3), risk of overdrying (4) and risk of humidification of intergranular air (5) throughout the year 2020 for soybeans stored in the municipality of Unaí, located in Northwest Mineiro.

Northwest Mineiro Mesoregion - Unaí
Soybean - Year 2020
Operation	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
1	26	33	39	35	66	63	56	30	8	38	69	57	520
2	26*	33*	39*	35*	66*	63*	56*	30*	8*	38*	69*	57*	520*
3	26	25	18	15	1	0	0	0	0	1	3	3	92
4	358	296	279	289	354	430	592	686	697	560	418	423	5.382
5	333	340	408	381	316	225	91	26	15	144	230	248	2.757
Total (h)	743	694	744	720	737	718	739	742	720	743	720	731	8.751

• ^*
  It can be used for both maintenance aeration and cooling aeration.

Table 11
Number of hours suitable for maintenance aeration (1), cooling aeration (2), low temperature drying (3), risk of overdrying (4) and risk of humidification of intergranular air (5) throughout the year 2021 for soybeans stored in the municipality of Unaí, located in Northwest Mineiro.

Northwest Mineiro Mesoregion - Unaí
Soybean - Year 2021
Operation	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
1	47	34	57	71	70	51	13	2	0	45	61	36	487
2	47*	34*	57*	71*	70*	51*	13*	2*	0*	45*	61*	36*	487*
3	9	17	7	1	0	0	0	0	0	2	9	15	60
4	411	255	404	405	493	576	690	737	716	522	310	310	5.829
5	192	357	265	243	181	88	22	0	0	152	314	388	2.202
Total (h)	659	663	733	720	744	715	725	739	716	721	694	749	8.578

• ^*
  It can be used for both maintenance aeration and cooling aeration.

Table 12
Number of hours suitable for maintenance aeration (1), cooling aeration (2), low temperature drying (3), risk of overdrying (4) and risk of humidification of intergranular air (5) throughout the year 2022 for soybean stored in the municipality of Unaí, located in Northwest Mineiro.

Northwest Mineiro Mesoregion - Unaí
Soybean - Year 2022
Operation	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec	Total (h)
1	41	27	63	59	54	68	34	2	14	33	56	45	496
2	41*	27*	63*	59*	54*	68*	34*	2*	14*	33*	56*	45*	496*
3	6	16	3	5	0	0	0	0	0	0	3	20	53
4	324	256	443	514	566	563	675	738	646	590	335	256	5.906
5	343	339	216	140	117	79	20	0	47	70	273	371	2.015
Total (h)	714	638	725	718	737	710	729	740	707	693	667	692	8.470

• ^*
  It can be used for both maintenance aeration and cooling aeration.

It was observed for corn over the years 2020, 2021 and 2022, it presented 419, 429 and 493 hours with favorable conditions for maintenance aeration and cooling aeration; 363, 274 and 287 hours for low temperature drying; 3,876, 4,386 and 4,364 hours for risk of overdrying; 4109, 3470 and 3328 hours for risk of humidification of intergranular air (Table 7, 8 and 9). It was observed for soybeans over the years 2020, 2021 and 2022, it presented 520, 487 and 496 hours with favorable conditions for maintenance aeration and cooling aeration; 92, 60 and 53 hours for low temperature drying; 5,382, 5,829 and 5,906 hours for risk of overdrying; 2757, 2202 and 2015 hours for risk of humidification of intergranular air (Table 10, 11 and 12).

The hours that represent super-drying, if conducted properly, can be used in operations to dehumidify grains in warehouses that have been accompanied by a risk of humidification of intergranular air process due to the action of pests and diseases or due to moisture migration.

In addition, they can be used for low temperature drying as long as there is strict monitoring to prevent the moisture of the grain from exceeding the ideal.

It was observed that corn has a smaller number of hours for risk of overdrying compared to soybean, which may be related to the physical, thermal and aerodynamic properties of the grain. It can also be linked with the composition of the grain. Soybean, because it has more oil in its composition, has less water retention than corn starch.

Therefore, it can be observed that in the municipality of Unaí-MG, it has great potential for risk of overdrying and risk of humidification of intergranular air corn and soybeans. Due to this high potential for risk of overdrying, it is necessary that some care be taken in the use of air in the drying and storage of grains, as risk of overdrying can cause various damages to the grains, such as mechanical damage, rupture of the husk and cracking, which causes economic loss of the product. Moistening is another risk factor for grains, causing the development of microorganisms, favoring the proliferation of fungi.

The occurrence of risk of overdrying implies that part of the stored product, or all of it, had the moisture reduced below that recommended for commercialization [¹²].

To avoid over-drying or over-risk of humidification of intergranular air during the aeration operation, it is extremely necessary for the operator to be aware of the psychrometric conditions of the ambient air, to have information on the storage conditions of the product, and to make use of the hygroscopic balance tables or equations for decision-making regarding the best time to conduct the operation [¹²]. Although there is a large amount of hours with risk of overdrying conditions, if conducted properly and with monitoring, this number of hours with favorable conditions for risk of overdrying can be used to conduct low temperature drying or dehumidification of stored products.

Through the hygroscopic equilibrium tables, it was possible to verify the hygroscopic equilibrium conditions for soybeans and corn stored in the Municipality of Unaí, indicating that there are conditions to carry out aeration and drying operations at low temperature so that the product maintains 13% of moisture. In addition to this, a high number of hours with hygroscopic equilibrium is also tolerated, which results in a moisture of less than 13% of moisture, which causes risk of overdrying, however, in this condition these hours can be used in a monitored way to dry at low temperature and significantly reduce the cost of the drying operation, in addition, this same condition can be used to remove flour spots in the lower part of the storage silo.

Finally, a high number of hours was also observed in which the hygroscopic balance generates risk of humidification of intergranular air of the stored product, which can result in physical, physiological and sanitary degradation of the stored product, requiring a lot of attention with the air insufflated in this condition.

CONCLUSION

The psychometric conditions of the atmospheric air that occurs in the municipality of Unaí-MG, present conditions of hygroscopic equilibrium ideal for maintenance aeration, cooling aeration and drying at low temperature.

The months with the highest number of hours with hygroscopic equilibrium for corn were January, April and June (2020); May, June and November (year 2021); and April, May and July (year 2022).

The months with the highest number of hours with hygroscopic equilibrium for soybeans were May, June and November (2020); April, May and November (year 2021); and March, June and December (year 2022).

The municipality of Unaí-MG experienced a significant number of hours in which the psychrometric conditions posed risks of overdrying or humidification of intergranular air considering corn and soybean storage.

• Funding:
  The authors received no financial support.

Acknowledgments:

We thank the Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM), Financiadora de Estudos e Projetos (FINEP) and Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) for supporting the research.

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• Editor-in-Chief: Bill Jorge Costa

• Associate Editor: Bill Jorge Costa

Publication Dates

• Publication in this collection
  24 Mar 2025
• Date of issue
  2025

History

• Received
  22 Jan 2024
• Accepted
  21 Nov 2024