Agriculture Reference
In-Depth Information
were 4 comol
c
kg
−1
and 1.4 comol
c
kg
−1
. According to EMBRAPA (1995), base saturation for soy-
bean grain yield in the central region of Brazil should be near 70%. Variations in the results of acid-
ity indices for maximum and economic yields in the present study compared with those reported
earlier in the literature may be due to the use of different cultivars, variation in yield level, and other
soil and crop management practices.
3.8 CONCLUSIONS
There are four main criteria or techniques to diagnose nutrient deficiency, sufficiency, or toxicity in
soil and/or plants. These techniques are visual deficiency or toxicity symptoms, soil testing, plant
tissue testing, and plant or crop response to the applied nutrient. Among these techniques, visual
symptoms are the cheapest and a plant tissue test is the most expensive technique. However, care
should be taken in identifying N deficiency disorder through visual symptoms because sometimes
it may be confused with biotic and other abiotic stresses. Nitrogen deficiency is first observed in the
older leaves of plants. Because N is highly mobile in plants, when it is limited, it translocates from
the older to the younger part of the plants. Typical N deficiency symptoms are yellowing of the older
leaves and when deficiency persists for a longer period, the leaves become dry and almost dead.
Nitrogen toxicity rarely occurs in crop plants but it may create nutrient imbalance in plants when
present in excess. This nutrient imbalance may be detected by reducing the growth of plant organs
such as leaves, height and tillering in cereals, and branches in legumes.
A plant tissue test is an important N disorder diagnostic technique in crop plants. To compare
the tissue analysis results for N, preestablished critical or sufficiency level data are required for
each crop species under each agroclimatic region. In addition, the nutrient concentration in plant
tissue changes significantly with the advancement of plant age, and sufficiency level values should
be established at different growth stages during the crop growth cycle. Analytical results of plant
tissue should be compared with the same physiological age to obtain comparable results. Values of
tissue analysis of N are stable across a wide range of climatic conditions. There exist differences
among crop species for critical or sufficiency levels. However, varietal differences in an N critical
or adequate level are minimal for most crop species. There is no sound or authentic soil test for N
to make fertilizer recommendations, because N is absorbed mainly in the form of
NO
3
−
and
NH
4
+
by plants and their concentration changes significantly with time and space due to mineralization,
immobilization, and leaching from the soil-plant system.
Plant response to applied N in the soil is the most important diagnostic technique for N defi-
ciency and sufficiency. It can be done under greenhouse/controlled conditions and field conditions.
However, for making an N fertilizer recommendation to a given crop species, field experiments are
required. These experiments should be conducted at several locations. The ideal period to repeat
these experiments is 3 years but sometimes 2 year data can also be used to make N recommenda-
tions provided there is no significant variation from 1 year to another. Generally, average values
are used to make N recommendations for a crop species under an agroecological region. These N
disorder diagnostic techniques should be used in combination rather than in isolation to get good
results.
REFERENCES
Abbasi, M. K., M. M. Tahir, A. Sadiq, M. Iqbal, and M. Zafar. 2012. Yield and nitrogen use efficiency of rainfed
maize response to splitting and nitrogen rates in Kashmir, Pakistan.
Agron. J.
104:448-457.
Allen, V. G., C. P. Brown, R. Kellison, P. Green, C. J. Zilverberg, P. Johnson, J. Weinheimer et al. 2012.
Integrating cotton and beef production in the Texas southern high plains: I. Water use and measures of
productivity.
Agron. J.
104:1625-1642.
Aguilar, S. A. and van Diest, A. 1981. Root-phosphate mobilization induced by the alkaline uptake pattern of
legume utilizing symbiotically fixed nitrogen.
Plant Soil
61:27-42.
