Effect of balanced fertilization on yield and quality of potato in an acid soil in Chongqing, China

On an acid soil, not only optimal fertilizer application but neutralizing soil acidity is important to high yield and quality of potato production. Among the liming materials tested, quick lime was most effective in raising soil pH while Si-Ca fertilizer was most effective in improving soil P availability and potato yield.

1 Introduction

Soil acidification is a common problem in Chongqing, especially for upland soils. In the last two decades, soil acidification has even aggravated. In acid soils, a number of nutrient deficiencies such as P, K, Ca, Mg, B, etc., are encountered as constraints for crop production. Among these deficient nutrients, P deficiency is most commonly seen to limiting potato growth. Thus, the objectives of this study were to test effects of balanced fertilization and different lime materials on potato yield and quality.

2 Materials and Methods

The experiment was conducted at Xiaba village, Taiping town, Fengdu county, the potato production base in Chongqing. The soil was acidic with pH 4.9, organic matter 70.3 g/kg, NH₄-N 244 g/kg, available P 16.6 mg/kg and available K 109 mg/kg. The potato variety in study was Eshu No.5.
The experiment consisted of twelve treatments with three rates of N (90, 180 and 270 kg N/ha), four rates of P (0, 45, 90 and 135 kg P₂O₅/ha) and four rates of K (0, 75, 150 and 225 kg K₂O/ha) and replicated for three times. The optimal treatment (OPT) set for the experiment was 180-90-150 kg N-P₂O₅-K₂O. On the basis of OPT, silicon-calcium fertilizer ((Si-Ca, SiO₂ 22%%，CaO 41% and pH 8.2)) was used at 2250 kg/ha and quick lime at 1500 kg/ha. A single superphosphate (SSP, P₂O₅ 12%) treatment was set up as CK to compared with the OPT in which fused calcium-magnesium phosphate (Ca-Mg-P, P₂O₅ 15%, SiO₂ 20%，CaO45% and pH 8.5) was used. Urea was used for N and potassium chloride for K. In the treatments of Si-Ca and quick lime, mono-ammonium phosphate (N 11% and P₂O₅ 42%) was used as P sources.
The experiment plot was 20.93 m² (6.35 m ×3.3m) and prepared three days before seeding. The cutting potato seeds must have at least 2 eyes per piece. The seeds were planted on April 7^th with a population of 62115 hill/ha and harvest on August 29, 2013. All P, 60% N and 50% K fertilizers were used as basal application one day before seeding, and remaining N and K fertilizers were top-dressed at tuber swelling stage. The Ca-Mg-P, Si-Ca fertilizer and lime were broadcast on soil surface and then incorporated into soil by hoe.
At harvest, tuber yield of each plot was recorded separately.
3 Results and Discussion
Effects of different lime materials on P availability
Compared to SSP, different lime materials significantly increased amounts of available P in the acid soil (Fig. 1). Among them, Ca-Mg-P fertilizer and lime had better effects. This may be attributed to that the Ca-Mg-P fertilizer is both P source and basic material while lime is a strong basic material only.




Fig. 1 P efficiency as affected by different lime material
Effects of different treatments on potato yield
Different treatments had significant effects on potato tuber yield (Table 1). Potato yield increased with an increase in rates of N, P and K fertilizers and levelled off at 270 kg N /ha and 225 kg P₂O₅/ha. Based on quantity and percentage of the tuber yield increase, it indicates that the soil was most deficient in P and followed K and N.
Table 1 Potato tuber yield as affected by different treatments

Treatment	Potato tuber yield	Yield increase/decrease vs OPT
	kg/ha	kg/ha	%
180-90-150 (OPT)	19131 b	2482	14.91
90-90-150	16942 c	293	1.76
270-90-150	17321 c	672	4.03
180-45-150	17190 c	541	3.25
180-0-150	14070 d	-2579	-15.49
180-135-150	19715 b	3066	18.41
180-90-75	18405 b	1755	10.54
180-90-0	16476 c	-173	-1.04
180-90-225	16765 c	116	0.69
180-90-150+Si	22231 a	5582	33.53
180-90-150+lime	21668 a	5019	30.15
180-90-150 (SSP)	16649 c	-	-

As compared to the SSP treatment, use of Ca-Mg-P fertilizer (OPT) significantly increased potato yield. On the basis of OPT treatment, further addition of lime or Si-Ca fertilizer increased potato yield by 30.15% or 33.5%. This implies that though Ca-Mg-P fertilizer is a right source of P in acid soil, its basicity when used in normal fertilizer rates is not strong enough to neutralize the soil pH to the desired level. Thus, if the soil is very acid, extra amounts of lime is needed.
Effects of different treatments on soil pH prior to and after the field experiment
The three lime materials had different neutralizing effects on soil acidity (Fig. 2). The acidity neutralizing power of the three lime materials applied in the given rates were in an order of lime>Si-Ca>Ca-Mg-P. Though lime raised soil pH to a higher level than Si-Ca fertilizer, its effect on potato yield increase was slightly smaller than Si-Ca fertilizer. This may be due to the difference in enhanced availability of soil P besides the soil pH effect. As shown in Fig. 1, Si-Ca fertilizer raised soil available P more than lime, since P was shown as the most limiting nutrient on potato production in this soil (Table 1).Fig. 2 Effects of different treatments on soil pH before and after field experiment.

Effects of P and K fertilizers on potato quality
Potato starch and crude proteins were analyzed as quality indicators in this study. Results showed that both starch and crude protein contents in the potato tuber were well correlated with P and K rates (Fig. 3), indicating importance of P and K on potato yield and quality on this soil.

Fig.3 Potato quality as affected by different rates of P (left) and K(right)

4 Conclusions
Optimal fertilizer application is the key to high yield and quality of potato production. On the acid soil, neutralizing soil acidity with different liming materials can further increase potato yield on the basis of NPK fertilizers due to improved availability of soil P. Among the three liming materials, lime was most effective in raising soil pH while Si-Ca fertilizer was most effective in increasing soil P availability and potato yield.

References：
China Agricultural Techniques Extension and Service Center. 2006. Soil analysis specification. Chinese Agricultural Press, Beijing, China.
Yang, J.H. 2008. Soil and agricultural chemical analysis and environment monitoring. China Land Press, Beijing, China.
Xi, Z. B. 2003. Modern chemical fertilizers. Chinese Agricultural Press, Beijing, China.

The work was done by the IPNI collaborator in Chongqing, China. The project leader was Prof. Wei Li from the Chongqing Ag-ext Center.