1. Responsiveness of different potato (Solanum tuberosum) varieties to phosphorus fertilizer
Daoui K., R. Mrabet, A. Benbouaza, and E.H. Achbani
Institut National de la Recherche Agronomique (Maroc)

2. Introduction

3. In the Mediterranean Basin, potato is occupying an overall area of about one million ha and producing 18 million tons of tubers,
In Morocco, potato occupies an area of about to ha annually. The national production is about to tones so with a national main yield of about 23 t/ha which is below potential yield of about 40%.
Optimizing phosphorus fertilization is one way to reduce the gap between actual and potential yield.

4. Potato in the world
Table 1. Potato production and yield in different part of the world
(Source : FAO, 2008)
Harvested area (ha)
Production (t)
Yield (t/ha)
Afrique
10,8
Asie et Océanie
15,7
Europe
17,4
Amérique latine
16,3
Amérique du Nord
41,2
MONDE
16,8

5. Figure 1. Potato world production (1991 – 2007) (FAOSTAT)

6. Potato in Morocco Table 2. Production area of potato in Morocco
(Source: MAPM/ DDFP, 2010)
Zone d'office
Zone de DPA
Superficie (ha)
Production (T)
GHARB
4410
155660
SETTAT
6725
LOUKKOS
3650
92040
KHENIFRA
4835
97 000
MOULOUYA
3375
125670
EL HAJEB
4600
DOUKKALA
2475
74200
CASABLANCA
4170
73 030
SOUSS-MASSA
2170
60060
RABAT-SALE
3135
78 050
HAOUZ
2135
52825
CHEFCHAOUEN
2025
41 000
OUARZAZATE
700
22100
MEKNES
1955
71 430
TAFILALETE
430
11740
EL JADIDA
1900
49 600
TADLA
120
3970
KHEMISSET
1765
30 615
FES
1500
45 000
BEN SLIMANE
1220
18 740
TETOUAN
1010
18 855
AL HOCEIMA
1000
17 175

7. Labour charge is very important from planting till harvesting

8. Phosphorus in question

9. Phosphorus is one of major mineral nutrients required by Potato crop and its management in soil is critical. In fact, Potato requires a high amount of phosphorus for optimum growth and yield, However, P uptake and use is also dependant on genetic variability with the crops as well as the P fate in the environments including the soil.
Accordingly, a better understanding of mineral application and use by crops is one way for enhancing crop yields with a minimum impact on environment and reducing production costs. The use of genetically enhanced plants with improved P acquisition efficiency may represent a sustainable solution to increase crop yields.

10. In Morocco: Only 50 % of farmers use fertilizers

11. Soil phosphus content in Saïs Region
Source:
Fertilty Map of Morocco
Executed by the consortium:
INRA – IAV - ENA

12. Fez

13. MEKNES

14. ELHAJEB

15. Objectifs
The objective of this study is to assess, under field conditions, responsiveness of different potato varieties to mineral phosphorus application.

16. Materials & methods

17. A field trial was conducted at El Annaceur ((INRA, Morocco) situated 20 km far from Fès at latitude 33°41’, longitude 4°,50’ ; height 1345 m.
Soil characteristics are: clay (27%), silt (53%) and sand (20%). pH water (8,4). NO3-  (11,6 mg/kg). Organic Matter (2,80 %), P2O5 (Olsen) (67 mg/kg) and K2Oexangeable (520 mg/kg).

18. Seven potato varieties (Desirée, Nicola, Barna, Pamela, Daifla, Labella, Marguerita)
Combined with two phosphorus treatments:
P0 : without any P application and
P+ : 90 kg P2O5/ha as super triple phosphate (45%)).
The experimental design was a split plot with three replications, P on main plots and varieties on subplots.
Every subplot consisted on one line of 3m long of each variety separated on both sides by the check one (variety: Desirée) at distance of 0.70m. Ten tubers by variety were planted on each line.

19. Nitrogen was added at the rate of 50kg N/ha at planting and another 50 kg N/ha at tuber formation as ammonium nitrate
The trial was implemented on May and harvested on August. The crop was under drip irrigation system ,
Trial was well protected against parasites and weeds.

20. At maturity for every treatments (V
At maturity for every treatments (V*P) each ten plant have been harvested and tuber yield was estimated
The data were subjected to analysis of variance procedures (SPSS). Standard errors of the means were calculated. NKS test was applied to compare measured parameters from variety.  

21. The responsiveness of variety “i” was calculated on the basis of:
Vi: potato variety i
TY: tuber yield of potato (t/ha) of variety i
P+: treatment with added phosphorus as fertilizer.
P0: treatment with no added phosphorus as fertilizer.

22. Results

23. Effect of phosphorus and genotype on tuber yield of potatoes

24. Both variety (V) and phosphorus (P) have a significant effect on tuber yield of potato while interaction (V*P) had no significant effect on this parameter (figure 1).
Tuber yield varied between 16 t/ha for treatment (Barna (P0)) and 36 t/ha for treatment Pamella (P+). Phosphorus improves tuber yield by about 25%. .The variety Pamela gave the highest main tuber yield (34 t/ha) and performed well in both situations of P nutrition (P0 and P+). 

25. Responsiveness of potatoes varieties to phosphorus fertilizer

26. Figure 2. Responsiveness of different potatoes varieties to phosphorus fertilizer
Responsiveness of varieties to phosphorus application varied between 9% and 71% (figure 2). The variety Desirée showed the highest responsiveness to P application with 71% of improvement of tuber yield, while the varieties Daifla, Labella and Pamela responses to P application was on average only 10%. The varieties Nicola, Margarita and Barna responded to phosphorus application by respectively 18, 27 and 49%.

27. Phosphorus use efficiency
Hypothesis
Phosphorus use efficiency
Corresponds to grain yield per unit of P absorbed or phosphors utilization efficiency (PUZE) And
Is P absorbed per unit of available phosphorus or phosphorus uptake efficiency (PUPE).

29. Genetic adaptation of plants to low phosphorus supply
Mechanisms which improve P acquisition
Mechanisms which improve P utilisation
Root morphological characteristics
Root growth and distribution
Root diameter
Root-hair development
Mycorrhizal association
Root physiological characteristics
P uptake systm
P mobilization in the rhizosphere
Partitioning of P within the plant
Remobilization of P within the plant
P status of the harvested organ
Efficient utilization of P at the cellular level
Intracellular compartmentation of P
Metabolic requirements for P
Figure Mechanisms which improve genetic adaptation of plants to phosphorus-limited tropical soils. (Rao et al. (1999))

30. Conclusions
Within this experiment, even if just for one year, we do find genetic variability to phosphorus responsiveness among different potatoes varieties.
This indicates that choosing efficient variety may guarantee an improvement of tuber yield with less phosphorus fertilizer demand.
This work should be reconducted. More measures should be made to characterize genotypes and elucidate differences in performances among those genotypes

31. Acknowledgements
Workers and technical staff at the experiment station of El Annaceur (Morroco) are gratefully acknowledged