Deficiencia De Nitrogeno En El Maiz

ABSTRACT

In order to evaluate the use of a chlorophyll meter (SPAD 502) as an indicator of leaf N content of maize (Zea mays), established a field trial in the National Agricultural Research Institute, Regional Research Center the Platina, Santiago, Chile. Four treatments were applied nitrogen fertilization using urea, 0, 100, 200 and 400 kg N ha-1, with four replicates in randomized blocks. Half of the dose was applied at planting and the rest was applied at the 6-7 leaf. Were sampled most recently mature leaves of corn in each treatment. At these levels were determined with SPAD chlorophyll. Ten measurements were made per sheet, in limbo, 5 on each side of the central vein in 3 plants per treatment. These same leaves were measured N content in the laboratory. Measurements were made in two stages, when the corn had 5-6 leaves and shortly after flowering. According to the results, the measurements made with the chlorophyll and analysis SPAD 502 N percentage are highly correlated. In the first and second date r2 was obtained 0.88 and 0.81, respectively. In this case and for the first time, SPAD values less than 35.3, equivalent to 1.84% of N in the leaves, would indicate that it is necessary to apply N

INTRODUCTION

It is a known fact for years, that maize (Zea mays L.) is a very demanding crop N and that N recovery fraction that is applied is low, typically less than 50% (Novoa and Loomis, 1981 ). In Chile the most recent estimates of the efficiency of use of N for corn range from 27-38% (Fernandez, 1995). Moreover, the increasing need to reduce costs, improve efficiency in the use of nitrogen fertilizers, and avoid nitrate pollution, requiring the use of new tools for measuring the nutritional status of crops and, even better, if this is accomplished by non-destructive measurements of plants.

In this sense, the ideal is to keep track of foliar levels of N during the crop development, it is still possible to correct deficiencies for positive effects on yields. United States (Wood et al. 1992; Peterson et al. 1993; Blackmer et al. 1994; Piekielek et al., 1997) and in other countries, it has been proposed to use a portable chlorophyll (SPAD 502) as an instrument that meets the measures deliver fast, accurate, inexpensive meter once acquired, easy to use, non-destructive sheet and highly correlated with the content of N from them. In Chile, Melinao et al. (1999) evaluated the wheat.

The main objective of this work was to evaluate the use of this meter in grain maize as a tool to measure the nitrogen content in the leaves of the crop, while progress in establishing a critical level to indicate whether deficiency or not N and guide the potential user of the instrument

MATERIALS AND METHODS

In order to evaluate the use of a portable chlorophyll meter, SPAD 502 (Minolta, Spectrun Technologies Inc., Illinois, USA), a trial was corn cultivar INIA 160, Regional Center La Platina Research Santiago, Chile (33 ° 34?? lat., 71 º 38?? long.). The floor where the trial was planted Mollisol, Maipo series. A soil test done before planting, showed that the soil had low levels of N (12.3 ppm) and means of P (11.4 ppm) and K (84 ppm) (Table 1). Furthermore, the pH was 7.9, organic matter 2.1%, and electrical conductivity 1.1 mS cm-1. To ensure a good level of P and K was applied at planting to the entire surface of the test, 169.78 kg ha-1 triple super phosphate and 100 kg ha-1 of potassium sulfate.

Block pH MOa

% CEb

mS cm-1 N

ppm P

ppm K

ppm

1

2

3

4 7,9

7,9

7,9

7,9 2,1

2,1

2,1

2,2 1,2

1,1

1,2

1,1 13,8

13,5

9,5

12,3 12,3

11,5

10,3

11,5 83,0

87,0

82,0

84,0

For variables of N content in the leaves is applied four nitrogen treatments in the form of urea: 0,100, 200 and 400 kg N ha-1, with four replications arranged in a randomized block design. Half of the dose was applied at planting and the rest at the 6-7 leaves.

On two dates, December 14, 1998 and January 21, 1999, leaf samples were taken. The first date was corn 6-leaf growth stage, usually state that decides the application of the second dose of N, and in the second period, shortly after flowering. These dates were chosen because the first is still time to correct a possible deficiency of N to reduce yields, and the second date because N applications could increase grain protein if desired, but not increase yields. Samples were taken from the most recently mature leaves of maize each treatment, this is the first sheet from the apex whose "collar" shows full. A sampled leaves were determined chlorophyll levels in SPAD 502 chlorophyll meter

Ten measurements were made with the SPAD, in the limbo of each leaf, five on each side of the central vein in 3 plants per treatment. Moreover, the same leaves were measured above the leaf content of N in laboratory by the Kjeldahl method (1883).

At harvest was done analysis of Zn, Cu, Fe, Mg and Mn in leaves, to check that there were no effects of other deficiencies in chlorophyll levels.

...