Agriculture Reference
In-Depth Information
TABLE 8.10
Grain Yield of Upland Rice Cultivars Having Different Growth Cycles
at Two P Levels
Flowering Days
Growth Cycle (Days)
Grain Yield (kg ha
−
1
)
85 (25)
110
Low P (2.3 mg kg
−1
)
High P (4.9 mg kg
−1
)
95 (15)
120
1591
2093
106 (30)
130
1216
1320
111 (2)
135
1071
1164
Source:
From Fageria, N. K. 1992.
Maximizing Crop Yields
. New York: Marcel Dekker. With
permision.
Note:
Values in parentheses represent the number of cultivars tested. P was extracted by the
Mehlich 1 extracting solution.
compared to a low P level. The root dry weight varied from 0.21 to 0.54 g plant
−1
at a low P level.
Similarly, at a high P level, the root dry weight varied from 0.60 to 1.97 g plant
−1
, with an average
value of 1.27 g plant
−1
. The average increase in root weight with the addition of P was 234% com-
pared with control treatment. Figures 8.20 through 8.22 show that the root growth of three dry bean
genotypes was more vigorous at a high P level compared to a low P level. Improvement in the root
dry weight with the addition of P in dry bean is reported by Fageria (2009).
The traditional view is that a large vigorous root system through avoidance of plant water defi-
cit is a major feature of high yield in water-limited environments (Ludlow and Muchow, 1990)
and consequently higher N use efficiency in crop species or genotypes of the same species. Some
evidences suggest that vigorous and deep roots may have additional benefits for water extraction
and root function because water uptake continues at night, resulting in an increase in the soil
water content of upper soil layers and presumably of roots in these layers (Ludlow and Muchow,
1990).
In addition to several regular agricultural practices, WUE can be improved by growing crops in
soils enhanced with water-holding amendments such as polymers (Johnson and Leah, 1990). These
polymers are becoming more important in regions with insufficient water availability (Monnig,
2005). Applying superb-sorbent polymers can increase the water-holding capacity of soils and
reduce the detrimental effects of short-term drought in drought-prone arable areas (Karmini and
Naderi, 2007; Rostampour et al., 2013). Polymers absorb and store water and nutrients in gel form
and undergo cycles of hydration and dehydration according to moisture demand, increasing both
water and nutrient use efficiency in crop plants (Lentz and Sojka, 1994; Rostampour et al., 2013).
A superabsorbent polymer can hold 400-1500 times as much water as its dry hydrogel (Boman and
Evans, 1991). Polymers are safe and nontoxic, and decompose to CO
2
, water, NH
4
, and K
+
without
any residue (Mikkelsen, 1994). They have also been reported to improve soil physical properties
and reduce soil erosion, runoff, and nutrient loss (Shainberg et al., 1990, 1994; Rostampour et al.,
2013).
8.5 PLANT MANAGEMENT PRACTICES
Plant management practices such as the use of adequate seed rate and spacing, the use of efficient
crop species and genotypes within species, and the control of plant diseases, insects, and weeds are
important management practices to improve nitrogen use efficiency in crop plants. If these practices
are adopted properly at the right time, they have a significant impact on N use efficiency.
