Combating phosphorus deficiency on alkaline calcareous soils by adsorption isotherm technique for legume crops in arid environments - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 285

Chapter 17

Combating phosphorus deficiency on alkaline
calcareous soils by adsorption isotherm
technique for legume crops in arid
environments

Muhammad Waqas 1 , Abdul Hannan 2 and Abdul Gaffar Sagoo 3
1 Directorate General of Agricultural Extension, Office of Agricultural Officer, Kahna Nau, Lahore, Pakistan
2 Office of Assistant Land Reclamation Officer - Factory area near Madni Masjid, Sargodha, Directorate of Land Reclamation, Irrigation Department,
Punjab, Pakistan
3 MLL Land Reclamation Research Station, Bhakkar, Punjab, Pakistan

17.1 Introduction

detailed experimentation has not been done. The major
purpose of testing soils for P is to determine the quantity
of supplemental P required to prevent economic crop
losses because of P deficiency; the second purpose is to
monitor the quantity of available P existing over time
(Fixen & Grove, 1990).
For predicting fertilizer requirements, the Freundlich
model has been used to monitor nutrient adsorption in
soil. This involves developing sorption isotherms
because these take into account intensity, quantity and
capacity factors, which are important for predicting the
amounts of soil nutrients required for maximum plant
growth. It can also help to predict how the nutrient
status of a soil will change with cropping over time. If
the critical solution level for plant growth can be identi-
fied, nutrient-sorption isotherms can be used to estimate
the fertilizer needed to adjust the soil solution to the
optimal level for maximum yield.
The amounts of nutrients required by a soil are affected
by the clay minerals, cation exchange capacity, organic
matter, CaCO 3 and other properties, but these need not
be calculated in order to determine soil requirements
using the sorption technique. The further important
benefit is that a relatively small amount of time and
laboratory work are needed to produce a sorption curve
for site-specific fertilizer recommendations for crops
(Solis & Torrent, 1989). Therefore, information about the

The major role of mineral fertilizers is to improve crop
yields, but the main constraint in achieving proven crop
potential is imbalanced use of fertilizers, particularly
low phosphorus (P) use as compared to nitrogen. P is an
essential element classified as a macronutrient because
of the relatively large amounts required by plants.
There is pervasive P deficiency for various agro-
nomic crops grown on alkaline calcareous soils. A large
proportion of applied P becomes immobile due to high
levels of P fixation by CaCO 3 in the soil (Rahmatullah
et al ., 1993). The fixation of P is of great importance in
making soil test interpretations and fertilizer recommen-
dations for different crops. Critical limits for P are not
based on soil physical and chemical characteristics, and
also are not crop specific, but are generalized and based
on scattered field trials for different areas, local
information and practical experiences (Nisar et al ., 1992).
Memon and Fox (1983) suggested that P sorption
curves can be used as a basis for transferring information
about P fertilizer requirements from one site to another
irrespective of variations in P-sorption capacity. A
P-sorption curve can be a useful tool for utilizing exist-
ing field trial data and for making predictions about
fertilizer P requirements for various crops in those areas
where a small amount of data are available or where