Better crop development and higher yield in potatoes destined for processing industry

A Belgian research station shows early crop development, improved yield, tuber number and higher underwater weights of tubers with Qrop® fertilisers in potatoes destined for processing industry

A fertiliser programme for processing potatoes (cultivar Fontane), including Qrop® mix (20-10-16), Qrop® complex Top K (12-6-24) and Qrop® K PluS (12-0-46) was compared with two standard reference fertilisers urean + KCl, or calcium ammonium nitrate + KCl, in a randomised complete block design. In the SQM programme, the fertilisers were applied in split applications, compared to a full application of the standard references at planting. At the same rate of total N applied, use of Qrop® fertilisers improved early crop development and increased marketable tuber yield with 7%.

Using Qrop® fertilisers to compose the nutrient programme reduced the application of chloride from 193 to 0 kg Cl-/ha. This reduction of chloride is evidenced in the higher underwater weights of tubers as compared to the two standard references. Additionally, use of Qrop® fertilisers improved the NO3:NH4 ratio of the programmes from at best 1:1 in reference 2 to 2:1 or 3:1 in the SQM programmes. Combined with the ease of application of Qrop® fertilisers, allowing to side-dress the crop during tuber set, this supported tuber development and translated into higher yield.

The positive results of this trial have assisted in promotion of potassium nitrate in Qrop® fertilisers for potato production on the European continent. Currently trials with producers in other processing potato growing areas in Poland and Eastern Europe are ongoing or being discussed for next season. 

Figure 1. Trial area in Belgium inspected by Felipe Garziera, Global Market Development SQM International, planted with potato cultivar Fontane. This potato for processing covers 42% of the total potato area in Flanders.

Two reference treatments were included in the trial, both applying potassium as potassium chloride. For nitrogen supply, one reference treatment was based on urea, the other based on ammonium nitrate. Both reflect potato-growing economics in different potato-growing regions and the trial clearly shows -again- that the most economical option does not yield the highest rewards.

Potassium nitrate is not commonly used as a potassium source for rain-fed potatoes grown in North-West Europe. The aim of this trial was to show the benefit of potassium nitrate over potassium chloride for tuber quality in processing potatoes. SQM has ample experience in improving storage parameters and dry matter content in potatoes by reducing chloride application and improving the NO3:NH4 balance in a programme with split applications. This experience, based on trials with Qrop® fertilisers world-wide, was translated to Belgium, and tested by a renowned institute in Kruishoutem, Flanders: PCA, center for applied research and extension in potatoes (Figures 1, 2).

In Europe, processed potatoes (mainly as frozen chips and crisps) were worth 10 billion euro in 2017, or 1,5 % of the overall value of EU food industry output. Belgium and its neighboring country, the Netherlands, are important exporters of processed potato products, and a relatively high share of the total arable land is in use for processing potato production.

Figure 2. Koen d’Haeyer, Technical Service Support Manager SQM Europe with Jenny Heuvick and Pascal Dupont conducting the trial at PCA.

Trial details

The trial was conducted on a loam soil (pH 6,3 with 1% carbon), which was analysed for plant available nutrients to determine the recommended rate for cv. Fontane grown under optimal cultural practices. Recommended rates for macronutrients were determined as 150 kg N/ha, 50 kg P2O5/ha and 260 kg K2O/ha. 

Five treatments (Table 1) were compared in a randomised block design with 4 replicates. The treatments varied in K source (KNO3 vs KCl), application timing (total amount applied at planting or divided in two applications: at planting and at tuber setting), and application of nitrogen as urean or CAN (calcium ammonium nitrate). P was applied with the Qrop® treatments, but not in the standard references.
During the trial crop growth was monitored, and harvest was evaluated on 11,5 m2 per replicated plot, taken over the middle rows from the gross treated area of 54 m2 (8 rows of 9 m per plot). The total tuber yield, the tuber grading and the underwater weight of the tubers were determined.

Table 1. Treatments. Fertiliser specifications: Urean 30% N: liquid urea with ammonium nitrate. CAN 27%N: calcium ammonium nitrate. KCl: Potassium chloride. SQM’s virtually chloride-free NPK: Qrop® mix 20-10-16 and Qrop® complex Top K 12-6-24: both containing magnesium, phosphorus and calcium. Qrop® K PluS 12-0-46: prilled potassium nitrate.

Results Highlights

Shortly after emergence in June, the plants in all treatments that included Qrop® fertilisers were significantly taller compared to the plants in the reference treatments, indicating a faster initial growth (Figure 3). This is profitable for the tuber development since row closure is reached earlier. The highest total yields were achieved in the treatment including both Qrop® complex Top K and Qrop® K PluS (67 MT/ha), and the treatment including Qrop® mix and Qrop® K PluS (66 MT/ha). The increase in yield of these treatments compared to both reference treatments was statistically significant. 

The yield improvement could be explained by a statistically significant greater amount of tubers formed in size class 35-50 mm: 35 tubers/m2 in the reference treatment vs. 43-44 tubers/m2 in the SQM treatments. The negative effect of chloride-containing potassium fertilisers on processing potatoes is also reflected in the observed underwater weights. Tubers of plants fertilized with KCl showed significantly lower underwater weights than tubers of plants fertilized with SQM fertilisers. Underwater weight is important for production of fries: more frozen fries can be produced out of a kg of potatoes when the underwater weight is higher. An underwater weight of 419 g/5 kg is normal for the cultivar Fontana, and farmers contracts usually require a minimum between 370-400 g/5 kg.

Based on extra costs for the SQM programmes compared to the first reference (Urean+KCl), only 2,3 MT/ha extra needs to be produced to return the extra investment in these high quality fertilisers, at a theoretical price of 150 USD/MT of quality tubers suitable for frozen fries production. This yield increase is amply met with 3,4 MT/ha resp. 4,4 MT/ha extra production of the right size class in both SQM-treatments, even without considering the better underwater weigh of these tubers. 

Figure 3. Crop height development 12 and 26 days after emergence (DAE). Treatments including Qrop® fertilisers showed an improved early canopy development. * Significantly different from control Urean/KCl (Tukey p=0,05) 

Figure 4. Total tuber yield and marketable yield (tubers > 35 mm). Treatments including Qrop® fertilisers resulted in higher total and marketable yield. Extra investment in the treatments including Qrop® fertilisers compared to Urean/KCl, is returned with an extra marketable yield of 2,3 MT/ha at a received price for frites-quality of 150 USD/MT * Significantly different from control Urean/KCl (Tukey p=0,05).

Figure 5. Underwater weight of harvested tubers. * Significantly different from control Urean/KCl (Tukey p=0,05). 

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