Potassium fertilization and soil diagnostic criteria for forage corn (Zea mays L.) production contributing to lower potassium input in regional fertilizer recommendation

Figures & data

Table 1 Varietal differences in yield, potassium (K) concentration and K uptake for forage corn (Zea mays L.) at the yellow-ripe stage (Experiment 1).

Variety	Yield (Mg DW ha^–1)	K
		Concentration (g kg^–1 DW)	Uptake (kg ha^–1)
TS115	16.0 ^a	19.6 ^ab	316 ^a
NS80A	16.2 ^ab	20.1 ^ab	326 ^a
NS68A	18.0 ^abc	18.4 ^a	333 ^ab
FC113GP	19.2 ^abc	17.9 ^a	346 ^abc
DK708	18.3 ^abc	19.1 ^ab	355 ^abc
TX105	17.9 ^abc	19.9 ^ab	359 ^abc
Cecilia	20.7 ^abc	17.8 ^a	368 ^abcd
33G26	21.0 ^abc	17.6 ^a	371 ^abcd
DK727	18.8 ^abc	19.7 ^ab	372 ^abcd
KD620	18.5 ^abc	21.2 ^abc	394 ^abcde
NS68	21.7 ^abc	18.4 ^a	401 ^abcde
KD640	22.0 ^abc	18.2 ^a	403 ^abcde
KD720	18.8 ^abc	21.8 ^abc	410 ^abcde
DK567	19.7 ^abc	21.5 ^abc	426 ^bcde
33J24	19.7 ^abc	22.0 ^abc	433 ^cdef
Nasuhomare	24.2 ^c	17.9 ^a	440 ^cdef
DKC61-24	22.5 ^bc	19.7 ^ab	444 ^cdef
TX230	20.3 ^abc	22.8 ^bc	464 ^def
Yumechikara	20.1 ^abc	24.4 ^c	493 ^ef
KD670	23.2 ^c	22.9 ^bc	532 ^f
Mean	19.8	20.1	399
Median	19.7	19.7	398
Minimum	16.0	17.6	316
Maximum	24.2	24.4	532

DW, dry weight. Values represent mean of 2003 and 2004. Values followed by different letters are significantly different between the varieties by Tukey’s honestly significant difference (HSD) test at P < 0.05. K uptake is the amount of K in corn above ground harvested.

Table 2 Field management and soil chemical properties of five experimental fields in Experiment 2.

		Experimental fields
		A	B	C	D	E
Field management
Cultivation year		2005–2007	2006, 2007	2005–2007	2005, 2007	2005, 2006
CMC application rate (Mg FW ha^–1)		0	0	50	100	100
Soil chemical properties
pH		5.9	5.9	6.0	6.2	6.1
		(5.6–6.0)	(5.7–6.1)	(5.9–6.1)	(6.0–6.5)	(6.0–6.2)
Total C (g kg^–1)		54.2	48.9	60.4	61.7	73.4
		(53.1–56.1)	(48.3–49.5)	(58.0–62.3)	(54.6–68.7)	(71.4–75.4)
Total N (g kg^–1)		4.47	3.88	4.82	4.84	5.80
		(4.34–4.62)	(3.73–4.03)	(4.65–5.02)	(4.23–5.45)	(5.65–5.96)
C/N ratio		12.3	12.9	12.8	12.8	13.2
		(12.0–12.1)	(12.3–13.6)	(12.4–13.5)	(12.6–12.9)	(12.6–13.7)
Inorganic N (mg kg^–1)		37.2	21.8	48.1	51.2	28.7
		(22.0–54.1)	(19.8–23.8)	(38.8–57.5)	(34.9–67.5)	(25.4–34.7)
Available P (g kg^–1)		0.27	0.10	0.35	0.40	0.69
		(0.22–0.30)	(0.09–0.11)	(0.28–0.44)	(0.26–0.54)	(0.59–0.80)
Exchangeable cations (g kg^–1)	K	0.17	0.23	0.62	0.82	0.86
		(0.11–0.27)	(0.17–0.29)	(0.58–0.68)	(0.76–0.89)	(0.78–0.92)
	Ca	2.59	2.14	2.87	2.49	3.87
		(2.47–2.71)	(2.07–2.22)	(2.65–3.13)	(2.12–2.87)	(3.64–4.10)
	Mg	0.35	0.28	0.49	0.56	0.75
		(0.30–0.40)	(0.26–0.29)	(0.46–0.52)	(0.45–0.67)	(0.73–0.76)
CEC (cmolc kg^–1)		25.8	24.8	27.5	27.6	30.5
		(24.1–29.0)	(21.9–27.8)	(24.1–32.1)	(21.7–33.4)	(29.3–31.6)

CMC, cattle manure compost; FW, fresh weight; DW, dry weight; C, carbon; N, nitrogen; P, phosphorus; K, potassium; Ca, calcium; Mg, magnesium; CEC, cation exchange capacity. Values are mean of all cultivation years in each field. Ranges from minimum to maximum are shown in parentheses. All soil properties excluding pH are expressed on a dry soil weight basis. CMC had been biannually applied on field D since 2002 and on fields C and E for more than 10 years at each rate before each winter and summer forage crop cultivations. In fields A and B, CMC application had not been carried out since 2002.

Figure 1 Relationship between the potassium (K) uptake by corn (Zea mays L.) and the corn yield in Experiment 2. Results consist of the data in 2005 (n = 4), 2006 (n = 4) and 2007 (n = 4), and are expressed as means ± standard deviation. The varieties ‘Cecilia’ and ‘Yumechikara’ are shown as circles (○) and squares (□), respectively. The solid lines are expressed as a regression curve in common with both varieties. The regression curve with the coefficient of determination (R²) using the yield as an outcome variable (y) and the K uptake by corn as a predictor variable (x) was y = 3.581 ln(x) – 1.11 with R² = 0.623. The vertical and horizontal dashed lines indicate a K uptake of 200 kg ha⁻¹ and a target yield of 18 Mg dry weight (DW) ha⁻¹, respectively.

Figure 2 Relationship between the exchangeable potassium (K) content as an indicator for soil K fertility and the potassium uptake by corn (Zea mays L.) in Experiment 2. Results consist of the data in 2005 (n = 4), 2006 (n = 4) and 2007 (n = 4), and are expressed as means ± standard deviation. The varieties ‘Cecilia’ and ‘Yumechikara’ are shown as circles (○) with a lower solid line and squares (□) with an upper solid line, respectively. The regression curve with the coefficient of determination (R²) using the K uptake by corn as an outcome variable (y) and the exchangeable potassium (Ex-K) content in soil as a predictor variable (x) was y = 82.65 ln(x) + 298.4 with R² = 0.923 for cv. Cecilia and y = 114.2 ln(x) + 402.1 with R² = 0.941 for cv. Yumechikara. The vertical dashed lines indicate Ex-K contents of 0.17 and 0.30 g kg⁻¹. The horizontal dashed line shows a K uptake of 200 kg ha⁻¹. DW, dry weight.

Figure 3 Relationship between the exchangeable potassium (Ex-K) content in soil and the potassium (K) concentration in corn (Zea mays L.) in Experiment 2. Results consist of the data in 2005 (n = 4), 2006 (n = 4) and 2007 (n = 4), and are expressed as means ± standard deviation. The varieties ‘Cecilia’ and ‘Yumechikara’ are shown as circles (○) with a lower solid line and squares (□) with an upper solid line, respectively. The regression curve with the coefficient of determination (R²) using the K concentration in corn as an outcome variable (y) and the Ex-K content in soil as a predictor variable (x) was y = 3.804 ln(x) + 15.62 with R² = 0.969 for cv. Cecilia and y = 5.221 ln(x) + 20.24 with R² = 0.915 for cv. Yumechikara. The vertical dashed lines indicate Ex-K contents of 0.17 and 0.30 g kg⁻¹. The horizontal dashed line shows a K concentration of 11 g kg⁻¹ dry weight (DW).

Figure 4 Relationship between the exchangeable potassium (Ex-K) content in soil and the yield of corn (Zea mays L.) in Experiment 2. Results consist of the data in 2005 (n = 4), 2006 (n = 4) and 2007 (n = 4), and are expressed as means ± standard deviation. The varieties of ‘Cecilia’ and ‘Yumechikara’ are shown as circles (○) with a lower solid line and squares (□) with an upper solid line, respectively. The regression curve with the coefficient of determination (R²) using the yield as an outcome variable (y) and the Ex-K content in soil as a predictor variable (x) was y = − 7.843x² + 11.52x + 14.91 with R² = 0.389 for cv. Cecilia and y = − 11.64x² + 14.37x + 15.75 with R² = 0.561 for cv. Yumechikara. The vertical and horizontal dashed lines indicate an Ex-K content of 0.30 g kg⁻¹ and a yield of 18 Mg dry weight (DW) ha⁻¹, respectively. K, potassium.

Table 3 Soil chemical properties of fields A and F in Experiment 3.

		Field A 2008–2010	Field F 2009
pH		6.0 ± 0.1	5.9 ± 0.1
Total C (g kg^–1)		47.7 ± 2.0	56.9 ± 1.6
Total N (g kg^–1)		3.88 ± 0.20	3.77 ± 0.16
C/N ratio		12.4 ± 0.2	15.1 ± 0.2
Inorganic N (mg kg^–1)		25.5 ± 4.0	24.0 ± 2.5
Available P (g kg^–1)		0.44 ± 0.07	0.08 ± 0.02
Exchangeable cations (g kg^–1)	K	0.11 ± 0.03	0.37 ± 0.04
	Ca	2.66 ± 0.24	1.23 ± 0.10
	Mg	0.56 ± 0.12	0.26 ± 0.0
CEC (cmolc kg^–1)		29.3 ± 0.7	20.7 ± 0.4

C, carbon; N, nitrogen; P, phosphorus; K, potassium; Ca, calcium; Mg, magnesium; CEC, cation exchange capacity. Values are means ± standard deviation. All properties excluding pH are expressed on a dry soil weight basis.

Table 4 Response of corn (Zea mays L.) to potassium fertilizer application under low soil potassium fertility (Experiment 3).

	K application rate (kg ha^–1)
K basis	0	83	166	249
(K2O basis)	(0)	(100)	(200)	(300)
Yield (Mg DW ha^–1)
cv. Cecilia	16.9 ^A	18.5 ^B	20.4 ^C	19.9 ^BC
cv. Yumechikara	17.2 ^a	18.0 ^a	18.1 ^a	18.3 ^a
K concentration (g kg^–1 DW)
cv. Cecilia	6.3 ^A	8.9 ^B	11.2 ^C	11.7 ^C
cv. Yumechikara	7.9 ^a	10.7 ^b	14.2 ^c	14.6 ^c
K uptake (kg ha^–1)
cv. Cecilia	107 ^A	164 ^B	225 ^C	229 ^C
cv. Yumechikara	135 ^a	191 ^b	254 ^c	265 ^c
Apparent K recovery rate (%)
cv. Cecilia	–	69	71	49
cv. Yumechikara	–	67	72	52
K balance (kg ha^–1)
cv. Cecilia	–107	–81	–59	20
cv. Yumechikara	–135	–108	–88	–16

DW, dry weight; K, potassium; K₂O, potassium oxide. Corn varieties were grown at field A shown in Table 3. Data are means in 2008–2010. Values labeled with different uppercase and lowercase letters in rows differ significantly between K application rates for ‘Cecilia’ and ‘Yumechikara’, respectively [Tukey’s honestly significant difference (HSD) test, P < 0.05]. The apparent K recovery rate was calculated by the expression:

where R is the apparent K recovery rate (%), U_F is the K uptake by corn (kg K ha^–1) at each K fertilizer application rate and U₀ is the K uptake by corn (kg K ha^–1) at the K fertilizer application rate of 0 kg K ha^–1, F_R is the K fertilizer application rate (kg K ha^–1). K balance was calculated by subtracting the K uptake from the K fertilizer application rate.

Table 5 Response of corn (Zea mays L.) to potassium fertilizer application under high soil potassium fertility (Experiment 3).

	K application rate (kg ha^–1)
K basis	0	41.5	83	166	249
(K2O basis)	(0)	(50)	(100)	(200)	(300)
Yield (Mg DW ha^–1)
cv. Cecilia	22.2 ^A	23.2 ^A	22.5 ^A	22.4 ^A	22.6 ^A
cv. Yumechikara	22.2 ^a	21.7 ^a	21.5 ^a	21.3 ^a	21.1 ^a
K concentration (g kg^–1 DW)
cv. Cecilia	14.8 ^ABC	13.9 ^A	14.4 ^AB	15.1 ^BC	15.7 ^C
cv. Yumechikara	18.1 ^a	18.6 ^a	18.6 ^a	19.6 ^a	19.6 ^a
K uptake (kg ha^–1)
cv. Cecilia	327 ^A	321 ^A	322 ^A	338 ^A	354 ^A
cv. Yumechikara	401 ^a	404 ^a	399 ^a	413 ^a	413 ^a
Apparent K recovery rate (%)
cv. Cecilia	–	–15	–6	6	11
cv. Yumechikara	–	9	–2	7	5

DW, dry weight; K, potassium; K₂O, potassium oxide. Corn varieties were grown at field F shown in Table 3. Data are means of three replications. Values labeled with different uppercase and lowercase letters in rows differ significantly between K application rates for ‘Cecilia’ and ‘Yumechikara’, respectively [Tukey’s honestly significant difference (HSD) test, P < 0.05]. Apparent K recovery rate was calculated by the expression:

where R is the apparent K recovery rate (%), U_F is the K uptake by corn (kg K ha^–1) at each K fertilizer application rate and U₀ is the K uptake by corn (kg K ha^–1) at the K fertilizer application rate of 0 kg K ha^–1, and F_R is the K application rate (kg K ha^–1).

Table 6 Newly suggested potassium fertilization based on soil diagnosis of exchangeable potassium for low potassium input production of forage corn (Zea mays L).

Exchangeable K (g kg^–1 DW)		Management of K fertilizer application
K basis	K2O basis
< 0.15	< 0.18	Inorganic K fertilizer is applied at a rate of 83 kg K ha^–1 (100 kg K2O ha^–1). Additionally, cattle manure compost application at a rate of 20–30 Mg FW ha^–1 is needed to maintain soil K fertility because K removal by harvesting the corn plant exceeds the amount of K supplied as inorganic K fertilizer.
0.15–0.30	0.18–0.36	Inorganic K fertilizer application rate is reduced to 33 kg K ha^–1 (40 kg K2O ha^–1). However, inorganic K fertilizer is not essential in the use of cattle manure compost because of sufficient quantities of K in the compost.
≥ 0.30	≥ 0.36	Inorganic K fertilizer is not applied because of sufficient quantities of K in soil for forage corn production.

DW, dry weight; FW, fresh weight; K, potassium; K₂O, potassium oxide.

Table 7 Conventional soil diagnosis criteria of exchangeable potassium content and potassium fertilization for forage crops for Kanto and Tokai regions in Japan (NGRI 1988).

Exchangeable K (g kg^–1 DW)		Management of K fertilizer application
Non-volcanic ash soils	Volcanic ash soils
≤ 0.12	≤ 0.12	Inorganic K fertilizer is applied at a recommended rate or more in each prefecture.
0.12–0.25	0.12–0.42	Inorganic K fertilizer is applied at a recommended rate in each prefecture.
0.25–0.37	0.42–0.62	Inorganic K fertilizer application rate is decreased to 80% of a recommended rate in each prefecture.
0.37–0.50	0.62–0.83	Inorganic K fertilizer application rate is decreased to 20–50% of a recommended rate in each prefecture. Additionally, cattle manure application rate is also decreased.
≥ 0.50	≥ 0.83	Inorganic K fertilizer is not applied. Additionally, cattle manure application rate is decreased.

K, potassium; DW, dry weight. Exchangeable K contents are based on K equivalent, not K₂O. Non-volcanic ash soils consist of Sand-dune Regosol, Brown Forest soil, Gray Upland soil, Gley Upland soil, Red soil, Yellow soil, Dark Red soil, Brown Lowland soil, Gray Lowland soil and Gley soil with a cation exchange capacity (CEC) of 10–20 cmol_c kg^–1 DW. Volcanic ash soils consist of Andosol, Wet Andosol and Gleyed Andosol with a CEC of 20–35 cmol_c kg^–1 DW.

NGRI (National Grassland Research Institute) 1988: Report on the formulation of soil diagnostic criteria for forage field in the Kanto and Tokai region. Publication of the National Grassland Research Institute (Sôchi Shikenjyô Shiryô). 62–15, 30–37 (in Japanese).

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