Nutrient Management on Potato

Acid soils account for one-third of the total land area in Chongqing, southwest China. Soil acidity usually reduces the availability of plant nutrients and hinders crop growth. The objective of this experiment was to study the effects of different basic materials, P sources, and N and K rates on the availability of P and potato yield in an acid soil (pH 4.5) in Chongqing. Treatments included three types of basic materials (aglime, fused Si-Ca fertilizer, and fused Ca-Mg phosphate), two types of P fertilizers (fused Ca-Mg phosphate and single superphosphate), three rates of N (90, 180, 270 kg/ha), and four rates of K (0, 45, 90, and 135 kg/ha) in different combinations. The optimal fertilizer rate (OPT) was set as 180-90-150 kg N-P₂O₅-K₂O/ha plus either 1.5 t aglime/ha, 2.25 t fused Si-Ca fertilizer/ha, or fused Ca-Mg phosphate. Sixty percent of the fertilizer N and 50% of the fertilizer P were applied basally (at seeding) and the remaining amounts were applied at tuber swelling stage. All the other fertilizers and amendments were applied at seeding.

At the end of the cropping season, soil available P and K increased significantly with an increase in the rates of fertilizers applied. Soil available P content increased by 3 to 4 times with the addition of fused Si-Ca fertilizer and aglime, and by 4 times with the addition of fused Ca-Mg phosphate over the addition of single superphosphate. The soil available P in the singe superphosphate treatment after harvest was identical to that tested before the experiment. Potato tuber yield increased significantly with an increase in N, P and K rates and either leveled off or declined at each rate set for the OPT treatment. The addition of either fused Si-Ca fertilizer or aglime on the basis of OPT significantly increased tuber yield by 3,100 kg/ha (16%) or 2,537 kg/ha (13%), while the addition of fused Ca-Mg phosphate significantly reduced tuber yield by 2,482 kg/ha (-13%). Thus, the increase or decrease in yield by amendments was not attributed to additional Ca or Mg, but to the effects of increased pH and Si. Soil test values revealed that fused Si-Ca fertilizer and aglime raised soil pH 5 to 5.5, while fused Ca-Mg phosphate only increased pH by about 0.2 pH units. CHONGQING-BFDP-2011-02