How to ensure quality when sowing corn

Corn is one of the oldest cultivated crops and belongs to the group of cereals and is used for human and animal nutrition. For annual crops “a good harvest begins with a good sowing”. Therefore, implementing the crop appropriately, whether in terms of plant population, sowing depth or correct fertilization, are necessary items to ensure high productivity.

Corn is a crop sensitive to plant establishment, and it is necessary to adapt the correct population of plants per hectare as well as the spacing between them in the row. Because plants will compete for water, light and nutrients. Plants with poor distribution will harm their development, resulting in a decrease in crop productivity.

We treat the spacing between seeds as “longitudinal distance” and influence the quality of sowing. The longitudinal distribution of plants is evaluated as normal, faulty and double spacing. Normal spacings are within 0,5 to 1,5 times the average spacing, flawed plants are too far apart and double seeds are too close together. Therefore, the objective of good sowing is to have the plants equidistant from each other, with an adequate quantity per hectare, which will guarantee greater productive potential of the plants. Other factors such as seeding depth and speed can also affect seeding.

Regarding other factors that can affect sowing, we normally have horizontal perforated disc (mechanical) or pneumatic (vertical disc) dosing mechanisms in the seeder. These mechanisms present different quality conditions for sowing in which 60% normal spacing is expected in the mechanical system, while in the pneumatic system 90% regularity is expected. However, with good adjustment of the seeder it is possible to obtain high regularity values ​​in both types of mechanisms.

Therefore, understanding the seed distribution process throughout the area is essential, mainly due to new technologies such as precision agriculture. It is possible that in some places factors may occur that affect the quality of sowing. Therefore, understanding and verifying the spatial distribution can help to understand and allow localized investigation of factors extraneous to the seeding process.

In this context, the objective was to evaluate the quality of sowing through the stand and the longitudinal distribution of corn plants using precision agriculture techniques.

To meet this objective, an experiment was set up on a commercial farm, located in the municipality of Dourados, MS, with distroferric Red Latosol soil, with corn sowing carried out on March 05, 2020.

The contour was carried out using a GNSS application for a smartphone, resulting in approximately 35 ha and a sampling grid of 2 points per ha (Figure 1).

When sowing, a seeder with a pneumatic system and row spacing of 0,45 cm was used, with a total of 13 rows, coupled to a tractor with 301,5 kW of power at a working speed of 6 km h-¹, distributing the super early corn hybrid.

The stand was evaluated by directly counting plants in 2 m with 3 repetitions (rows) at each point, 10 days after corn sowing. The determination of normal, faulty and double spacings was carried out by direct measurement between plants, considering the spacings: "double" (D): < 0,5 times the Xref., "normal" (A): 0,5 1,5 o Xref.

The data were analyzed using descriptive statistics, geostatistics and interpolation. When spatial dependence was found between the data, kriging of the data was performed; when there was no spatial dependence, the inverse square of the distance (IDW) was used. The spatialization of stand variability and normal, faulty and double spacing was carried out through the construction of thematic maps.

After collecting the data in the field and processing the statistical analyses, a breadth of data and a high value of the coefficient of variation were observed, especially in the faulty and double spacing, clearly evident in some points. The stand and normal spacing data showed less variability, with an average of 2,51 plants/m and a regularity of 88,36%, slightly below the expected 90% for a pneumatic-type metering seeder.

In the spatial analysis of the longitudinal distribution of corn plants and the stand, through geostatistics (Table 2), it is observed that only the stand presents spatial dependence with an exponential semivariogram model with a spatial dependence index classified as moderate (25-75 %). Still for the stand variable, the range obtained was 94 m, which indicates that in the present work the distance considered for sampling (70,71 m) was satisfactory for achieving spatial dependence. The longitudinal distribution of the plan presented pure nugget effect graphs, showing that there is no spatial dependence between the fault, double and normal points, with the maps being generated by the inverse distance interpolator.

In the plant stand (Figure 2), more than 99% of the area had two to three plants per meter, which is considered acceptable. Only a small part of the area was below 2 plants/m located at the ends of the plot.

Normal spacing is important to avoid great variability in the stand, avoiding faulty and double spacing. For the pneumatic seeder used, it is stipulated that we have at least 90% of the normal spacing. Thus, we obtained only 38% of the area with spacing greater than or equal to 90% considered as normal (Figure 3), and the majority of the area, 61,52%, had spacing between 60% and 90% as normal. Low rainfall was observed during the establishment of crops, which may have hampered emergence.

The faulty spacing map (Figure 4a) shows that in 95,4% of the area there are less than 20% of faulty spacings, of which more than half are less than 10%. Relating to the plant stand per meter, it appears that there were missing plants, confirmed by the faulty spacing map. Double spacing (Figure 4b) has 98,7% of the total area less than 10% of double spacing. Which is a low percentage, affecting very little the equidistance of the plants.

In this way, it is evident that due to little rainfall at the time of sowing, some seedlings did not emerge, reducing the plant stand and increasing poor spacing.

Therefore, it appears that for corn sowing there is more pronounced spatial variability in the stand and in the normal spacing. Climate-related factors can affect seeding quality. There is greater variability in failed spacings than in double spacings.

By Gustavo Arantes Coelho, Jorge Wilson Cortez e Diandra Pinto Della Flora (UFGD)