Agriculture Reference
In-Depth Information
urea. Similarly, maximum panicle density was achieved with the addition of 278 mg N kg
−1
. Fageria
et al. (2011b) reported that maximum panicle density of upland rice was obtained with the addition
of 270 mg N kg
−1
by common urea in a Brazilian Oxisol. The results of the present study fall within
this range. Fageria et al. (2011b) also reported a significant increase in the panicle density of 20
upland rice with the addition of 400 mg N kg
−1
compared to the control treatment. Similarly, Fageria
(2009) also reported an increase in yield and yield components of upland rice with the application
of N in Brazilian Oxisols.
3.7.2 f
Ield
e
xperIments
The era of field experimentation, which began in 1834 when J.B. Boussingault, a French chemist, set
up the first field experiments at Bechelbonn, Alsace (France), was placed on a modern scientific basis
by Liebig's report of 1840 (Collis-George and Davey, 1960). The first field experiments in the form
used today were established by Lawes and Gilbert at Rothamsted in 1843. Since then, field experi-
ments have sought for and confirmed the importance of the essential elements in influencing the
production of field crops. However, a great deal of the evidence for the discovery of the essentiality of
nutrients has been in the laboratory experiments in nutrient solution and not from field experiments
(Collis-George and Davey, 1960).
Soil fertilizer tests are the oldest and most widely used method of determining fertilizer N
requirements and developing recommendations for crop plants. Yield response trials to develop
N fertilizer recommendations for crops were developed in the late 1950s (Kyveryga et al.,
2013). These tests indirectly account for the mineralization potential of soil, N leaching, deni-
trification, N immobilization, availability of fertilizer N, and climatic variability on N uptake
and yield (Gerik et al., 1998). They involve the measurement of yield response to increasing
levels of applied N fertilizer from experiments conducted at specific locations over several
years. Generally, a quadratic equation is used to calculate the N rate for maximum yield (Gerik
et al., 1998).
The application of field trial results led to a large increase in agricultural production around the
world. Research in agriculture is a complex process and demands constant efforts and experimen-
tation due to change in weather conditions, soil heterogeneity, and release of new cultivars (Barley,
1964). These changes are sometimes so significant that all management practices in use to produce
good yields of crops need reevaluation and adjustments to changed situations. For example, when a
new cultivar of a crop is released, its nutritional requirements are different from those under culti-
vation due to the difference in the yield potential, diseases, insect's resistance, and change in archi-
tecture. Therefore, field experiments are a basic need in modern agriculture to evaluate nutritional
requirements under different agroecological regions. It is very hard to transfer the experimental
results of one region to another due to the differences in soil properties, climatic differences, and
socioeconomic conditions of farmers (Fageria, 2007b). All these factors determine the techno-
logical development and its adaptation by farmers. In conducting field experimentation, certain
basic principles should be followed to arrive at meaningful conclusions. Some of these important
principles or considerations in field experimentation are discussed in this section. The principles
discussed here will help agricultural scientists in the planning and execution of their research tri-
als. Of course, the discussion is mainly concerned with the field of soil fertility and plant nutrition
but some basic principles are applicable to other disciplines of agricultural science too. These
principles are applicable everywhere with a slight modification according to the circumstances
of a particular situation. Most of the points discussed are the outcome of the author's practical
experience of more than 40 years in the field of agriculture, in general, and soil fertility and plant
nutrition, in particular.
Soil fertility is one of the important factors in determining crop yields. Further, maintaining soil
fertility at an appropriate level is also vital for sustainable agriculture and in reducing environmen-
tal pollution. To achieve these objectives, research data are required for different agroecological
