Agriculture Reference
In-Depth Information
Generally, N has a positive interaction with potassium. Increasing the levels of N improved
K uptake if K was present in sufficient amounts in the growth medium. The influence of K on
the absorption of NO
3
-N by wheat plants was stronger than on the absorption of NH
4
-N (Ali
et al., 1987). These authors reported that the absorption of NO
3
-N increased with the addition
of K in the K-deficient plants while the absorption of NH
4
-N still remained at a lower rate in
spite of the addition of K (Ali et al., 1987). The influence of K was stronger on the translocation
of N from roots to shoots and the translocation of NO
3
-N was much higher compared to NH
4
-N
(Ali et al., 1987). Although K
+
is a cation, it does not compete in the absorption of the NH
+
ion;
rather, it increases NH
+
assimilation in plants and avoids possible NH
+
toxicity (Aulakh and
Malhi, 2005). Mengel et al. (1976) concluded that it was unlikely that K
+
competes with NH
+
for selective binding sites in the absorption process. Rice yield was significantly increased when
N, P, and K were added in adequate amounts in comparison to control as well as N and P alone
(Aulakh and Malhi, 2005).
Macleod (1969) reported that the optimum supply of K was important in promoting barley grain
and straw yield, as deficient K levels had a depressing effect, especially when N was supplied at
high rates. Johnson and Reetz (1975) observed that adequate soil test K levels are critical to realize
the full benefits of applied N for harnessing optimum corn yields and NUE in Ohio. Also, more of
the applied N was left in the soil after harvest, resulting in lower profitability and creating a greater
potential for a negative environmental impact.
Potassium is one of the most important nutrients affecting the nitrogen metabolism of rice plants
(Ali et al., 1985). Ali et al. (1985) reported that the N metabolism of rice plants was impaired by the
limited supply of K when plants were fed with NO
3
-N, but not when they were fed with NH
4
-N. Data
in Table 6.5 show the uptake of K at different N levels in the shoot of dry bean. There was a signifi-
cant quadratic uptake of K when N levels were in the range of 0-200 kg ha
−1
. Variation in K uptake
due to N application was 71%. The positive interaction of N with K was related to the improvement
in yield with the addition of N (Fageria and Baligar, 2005).
A positive interaction of N with K has been reported by Dibb and Thomson (1985). Dibb and
Welch (1976) reported that the increased K allowed for rapid assimilation of absorbed NH
+
ions in
the plant, as well as maintenance of a low, nontoxic level of NH
3
. The increased yield of crops with
the addition of N and P requires a higher level of K in the soil (Dibb and Thomson, 1985; Fageria
et al., 2011a). A positive interaction between N and K has been reported by Kemp (1983) in barley.
Barley yield was significantly increased with increasing N and K levels simultaneously.
Tropical soils such as Oxisols and Ultisols are poor in available P and K (Fageria and Baligar,
2008) and data of field experiments conducted on these soils show positive interactions among
N × P × K (Aulakh and Malhi, 2005). Data from Brazil show a positive N × K interaction in rice
TABLE 6.5
Influence of N on the Uptake of K in the Shoot
of 60-Day-Old Dry Bean Plants
N Rate (kg ha
−1
)
K Uptake (kg ha
−
1
)
0
4.4
40
9.4
80
17.2
120
16.7
160
28.6
200
33.2
R
2
0.71*
*Significant at the 1% probability level.
