117losses which may be through soil erosion (wind and water), or through leaching or
volatilization. Moreover, the crop residues of the monocrop are mostly used by the
farmers as animal feed which also results in nutrient imbalances and nutrient min-
ing. The other reasons for nutrient mining includes the low fertilizer use in dryland
regions, and nutrient losses in the form of soil erosion and leaching (Henao and
Baanante 2006 ). For example, the nutrient losses due to soil erosion ranges from 10
to 45 kg NPK ha−^1 year−^1 in Africa. In Kenya, about 112, 2.5 and 70 kg ha−^1 of N, P
and K are lost every year (Smaling et al. 1993 ). In sub-Saharan Africa, the mining
of crop nutrients has been identified as severe yield limiting factor in dryland
agriculture. In 2002–2004, many African farmlands experienced a nutrient loss of
30 kg ha−^1 per year (IFDC 2006 ).
In India, the crops such as pearl millet (Pennisetum glaucum (L.) R. Br.), sor-
ghum, chickpea (Cicer arietinum L.), pigeonpea and groundnut (Arachis hypogaea
L.) remove 72 kg ha−^1 of N, P and K, while the actual annual addition to the soil is
only 10–11 kg ha−^1 (FAO 1988 ). Due to moisture deficiency in dryland soils, the
application method and the placement of fertilizer in relation to rhizosphere are very
critical. The top dressing or split application of fertilizer may not be a better choice
under dryland conditions. Likewise, placement of fertilizer away from the root zone
may also be less useful due to poor root development owing to deficiency of soil
moisture.
2.2 Low Fertilizer Use Efficiency and Low Fertilizer Input
In dryland regions, the fertilizer use efficiency is very low than that that in irrigated
agriculture (Saleem et al. 1996 ), owing to poor fertilizer and crop management
practices, water stress at critical growth stages, and high weed infestation in high
rainfall areas (FAO 1981 ). Imbalanced fertilizer application has been predicted as
one of the most important factors responsible for low fertilizer use efficiency and it
may cause a 20–50 % reduction in fertilizer use efficiency (Zia et al. 1997 , 1998 ;
Rashid et al. 2004 ), especially in dryland regions. In east Africa, depletion of soil
fertility in dry areas has been reported due to imbalance between the nutrient inputs,
their removal by crops and losses (Murage et al. 2000 ). Nambiar ( 1985 ) reported
that addition of N with P, may decrease P level within dry soil by 21–26, 64 and
68 % in Alfisols, Vertisols and Oxisols, respectively. They also reported depletion of
Zn, K and S in these soils when there was no external input from the artificial
sources. A survey by Singh and Venkateswarlu ( 1985 ) in India showed widespread
deficiency of Zn besides the deficiencies of N and P. In Bangladesh, N was found as
most limiting plant nutrient in rainfed rice (Oryza sativa L.) followed by P, S, and K
(BRRI 1984 ). In Nigeria, after growing maize (Zea mays L.) crop on an Alfisol, the
yield without P input was decreased by 98 % (Kang and Osiname 1979 ). According
to FAO, the fertilizer use in summer dryland crops was 201 % lower than irrigated
Nutrient Management in Dryland Agriculture Systems