K. Manorama* and S.S. Lal 1. Key words: Intercrop, Potato, Potato cyst nematode, Stability index, Yield stability.

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1 Indian J. Agric. Res., 47 (3) : , 2013 AGRICULTURAL RESEARCH COMMUNICATION CENTRE / indianjournals.com YIELD STABILITY IN POTATO (SOLANUM TUBEROSUM L) UNDER VARYING SOIL MANAGEMENT PRACTICES K. Manorama* and S.S. Lal 1 Central Potato Research Station, Muthorai, The Nilgiris , India Received: Accepted: ABSTRACT Crop production potential can be maintained by managing the soil quality through different soil management strategies. In the present study, the data of four years has been used to investigate the effect of soil management, pest management, variety and cropping system/ rotation in a factorial RBD on the yield stability of potatoes grown in one year rotations. Potato yields in the recommended practice of growing PCN (Potato cyst nematode) resistant potato with French beans (Phaseolus vulgaris L.) as intercrop followed by cabbage (Brassica oleracea var. capitata L.) in rotation has recorded the maximum potato equivalent yield (PEY), which is 40 and 70% higher than the monocropping of potato with the same variety and susceptible variety respectively. The coefficient of variation was lower in this system indicating higher stability in yield. Stability analysis indicated that yields in this recommended system were less influenced by growing conditions as the PCN population was well under control in this treatment. The yields and yield stability were also influenced by cultivar and cropping system as they are the major role players in PCN management. The results indicate that management practices that improve soil quality and reduce the impact of pest (PCN) can enhance potato yield stability by mitigating the impact of adverse growing conditions. Key words: Intercrop, Potato, Potato cyst nematode, Stability index, Yield stability. INTRODUCTION Crops grown on soil that receives organic amendments have been shown to have access to greater soil moisture (Lotter et al., 2003) and are more resistant to weed (Gallandt et al., 1998) and insect pressures. Productivity increases in SOC (soil organic carbon) enriched soils, have improved in soil structure, water holding capacity (Johnston, 1991) and nutrient supply (Cassman, 1999). But, evidence is scarce that the amended systems reduce year to year variation in the yi elds. Broad generalizations on yield stability in relation to soil management practices can not be made with the available information. Potato (Solanum tuberosum L.) is a weather sensitive crop due to its shallower root system and also specific temperature requirement during tuberization. Periods of water deficit or excess severely limit potato yields though the total rainfall of the season is sufficient. The soils of potato * Corresponding author s kmano1000@yahoo.com 1 Central Potato Research Institute, Shimla , India cultivation are considered to be lower in SOC concentration and less in structural stability (Saini and Grant, 1980) due to high levels of soil disturbance and low levels of crop residue returns (Grandy et al., 2002). In Nilgiris, the average yields of potato remained almost constant for the last 15 years, despite improvement in varieties, application of fertilizers and pesticides. The present investigation was initiated during 2008 with four different soil management strategies using two different potato cultivars with the objectives of (i) assessing the impact of soil management on soil chemical and physical properties (b) investigating the influence of soil management, pest management, variety and cropping system on yield and yield stability of potatoes grown in Nilgiris region. Yield stability was estimated with the help of certain statistical measures using the data of four years on fixed plots.

2 MATERIALS AND METHODS The field trials were conducted from (2008 to 2011) at the Research Farm of Central Potato Research Station, Muthorai, The Nilgiris, Tamil Nadu, situated at an elevation of 2130 m above mean sea level at N latitude and E longitude and the soil is sandy clay loam in texture. The ph of the experimental site was 4.2, with 1.72% of organic carbon, 386,16.2 and 410 kg/ha of available N,P and K respectively. The experiment was repeated for four years in fixed plots. The experiment consisted of eight treatments which were replicated four times in a factorial RBD. The eggs of potato cyst nematode, Globodera sp present in the hard coated cysts hatch out only in the presence of root exudates of susceptible varieties of potatoes. Non-availability of host plant is expected to control this soil pest without much negative impact on the environment. Hence, the yield stability of potato is evaluated with both susceptible and resistant varieties to PCN. From the field trials, the observations on bio metric parameters, yield attributes and yields of potato, cabbage and frenchbeans were recorded. For the sake of convenient comparison, the yields of rotational crop and intercrop are converted into potato equivalent yield based on the market price of respective years. In addition, the data on potato cyst nematode population was also recorded after the completion of every crop, in order to find out its status and to check out whether there is any correlation between the PCN count and also the yield stability of the varieties tested under different treatments. Yield stability of different treatments was assessed by employing five parameters. In the first, the Coefficient of variance stability parameter is calculated with the following formula for total potato equivalent yield (PEY) of the rotation in each treatment. Vol. 47, No. 3, 2013? j 2 S 2 ti = (s-1) 233 Where Xij is the potato equivalent yield of ith treatment in jth year, is tge mean yield of ith treatment and s is the number of years. Superiority index (PI) is an estimate of treatment adaptability or suitability over a range of environments. It is calculated using the highest PEY treatment within each year as a reference point. The treatment with largest yield difference in comparison to the reference treatment would have highest Pi value (Lin and Binns 1988), but the stable treatment will have a lower Pi value.? j P i = Where Xij is the potato equivalent yield of ith treatment in jth year, Me is the PEY of the treatment with maximum yield in jth year and s is the number of years. The Geometric mean is used to calculate geometric adaptability index (GAI) for estimating the adaptability and suitability of the treatments (Mohammadi and Amri 2008) and the formula is Where Xij is the potato equivalent yield of ith treatment in jth year and s is the number of years. The treatments with high GAI are desirable. 2s The sustainability index was calculated by using the following formula (Gangwar et al. 2004). The treatment with high SI will be more sustainable. 2 The environmental variance is one of the major stability measures for the statistical stability concept (Lin et al. 1986) and it was calculated across the years. A treatment with minimum variance was considered to be stable. SI = X 100 M e

3 234 INDIAN JOURNAL OF AGRICULTURAL RESEARCH Where, is the average performance of i th treatment across the years, ó is the standard deviation and M e is the best performance of the i th treatment across the years. RESULTS AND DISCUSSION Soil Characteristics The treatment in which Farm Yard Manure was applied to 20 tonnes per hectare, increased the ph, SOC, CEC and total water stable aggregates substantially. This increase was more substantial when the resistant potato variety was grown in the rotation. The change in these soil characteristics was almost negligible when monocropping of potato was grown with susceptible variety (Kufri Jyoti). The improvement in soil organic carbon content and total water stable aggregates was more spectacular in the treatment where potato was grown as intercrop along with French beans in summer and cabbage was grown during autumn season (Table 2). The correlation between all the soil properties and mean yield was positive and higher values of positive correlation was observed with SOC and water stable aggregates. These two properties were more influenced positively by the treatment in which potato and french beans were grown together as intercrops in summer and cabbage was grown in autumn. Yield and yield variation The potato equivalent yield had shown an interesting trend over the last four years in different systems. In monocropping with susceptible variety, the PEY had shown decreasing trend with a very high CV of 15.6 per cent. Among the different combinations, growing of resistant potato variety as intercrop along with french beans followed by cabbage in autumn season has recorded the highest yield along with minimum variation in terms of CV value (1.6). The recommended practice of growing potato with french beans intercropping (3:2) in summer season followed by cabbage crop in autumn season had shown more stable yield levels in comparison with all other combinations of cropping (Table 3). Stability indices The environmental variance (Sti 2 ) and superiority index (Pi) should have minimal values against the stable treatments. The treatment in which resistant potato was intercropped with french beans and it was followed by cabbage in autumn season recorded nil values for these measures, indicating more stability in yield over the years. This was because of better control of PCN through ecofriendly management in this treatment which was possible both by growing resistant variety and also TABLE 1.Treatments (Crop rotation for one year) of the field experiment. Treatment Summ er Autum n Spring Monocropping of potato with PCN Susceptible variety Monocropping of potato with PCN Resistant Advance hybrid Potato (PCN Susceptible) Cabbage (Farmers practice) Potato (PCN Resistant) Cabbage (Farmers practice) Potato (PCN Susceptible) Cabbage (20t FYM / ha for potato) Amended soil Potato (PCN Resistant) Cabbage (20t FYM / ha for potato) Amended soil Potato (Kufri Giriraj) Potato (Kufri Giriraj) Fallow Potato (OS/93-D -204) Potato (OS/93-D -204) Fallow Potato (Kufri Giriraj) Cabbage (Quisto) Fallow Potato (OS/93-D -204) Cabbage (Quisto) Fallow Potato (Kufri Giriraj) w ith Cabbage (Quisto) Fallow 20t FYM/ha Potato (OS/93-D -204) Cabbage (Quisto) Fallow Potato (Kufri Giriraj) + French beans (3:2) intercropping Potato (OS/93-D-204) + French beans (3:2) intercropping Cabbage (Quisto) Cabbage (Quisto) Fallow Fallow

4 Vol. 47, No. 3, TABLE.2 Change in soil characteristics in different treatments over a period of six years. Treatm ent Per cent change in soil properties over four y ear period ph SOC CEC T otal Water stable aggregates Monocropping of potato with PC N Susceptible variety Monocropping of potato with PC N Resistant Advance hybrid Potato (PCN Susceptible) Cabbage (Farmers practice) Potato (PCN Resistant) Cabbage (Farmers practice) Potato (PCN Susceptible) Cabbage (20t FYM/ ha for potato) Am ended soil Potato (PCN Resistant) Cabbage (20t FYM/ ha for potato) Am ended soil intercropping - cabbage Initial Value Correlation with mean yield intercropping with non-host French beans and also soil enri chment through legume intercropping. The higher values for these two indices in monocropping of susceptible potato variety to PCN represent poor stability in yield over the years. In contrast to the above, the GAI (geometric adaptability index) and SI (Stability index) should have higher values for the stable treatments. The same treatment in which the CV, Sti 2 and Pi recorded lower values the GAI and SI recorded the highest values indicating that TABLE 3. Potato equivalent yield as influenced by different soil management strategies. Treatment PEY (t/ha) Mean Yield Monocropping of potato with PCN Susceptible variety Monocropping of potato with PCN Resistant Advance hybrid Potato (PCN Susceptible) Cabbage (Farmers practice) Potato (PCN Resistant) Cabbage (Farmers practice) Potato (PCN Susceptible) Cabbage (20t FYM/ ha for potato) Amended soil Potato (PCN Resistant) Cabbage (20t FYM/ ha for potato) Amended soil SEd Varieties Treatment Var x Trt CD5% Varieties Treatment Var x Trt NS 5.14

5 236 INDIAN JOURNAL OF AGRICULTURAL RESEARCH TABLE.4 Yield stability of different treatments with different statistical measures. Treatment CV S ti 2 PI GAI SI Mean PEY (t/ha) Monocropping of potato with PCN Susceptible variety Monocropping of potato with PCN Resistant Advance hybrid Potato (PCN Susceptible) Cabbage (Farmers practice) Potato (PCN Resistant) Cabbage (Farmers practice) Potato (PCN Susceptible) Cabbage (20t FYM/ ha for potato) amended soil Potato (PCN Resistant) Cabbage (20t FYM/ ha for potato) amended soil Correlation with mean yield the treatment is more stable in producing sustainable yields over the years (Table 4). Negative correlation existed between PCN population and the potential yield of different treatments and 66 per cent variation is mainly because of this only. So by adopting better strategies for managing potato cyst nematodes there is a possibility of increasing stability in potential yield of potato and potato based cropping systems in Nilgiris (Table 5). TABLE 5. Potato cyst nematode population as influenced by different soil management strategies. Treatment PCN Count after each rotation Rf value after 4 years Monocropping of potato with PCN Susceptible variety Monocropping of potato with PCN Resistant Advance hybrid Potato (PCN Susceptible) Cabbage (Farmers practice) Potato (PCN Resistant) Cabbage (Farm ers practice) Potato (PCN Susceptible) Cabbage (20t FYM / ha for potato) Amended soil Potato (PCN Resistant) Cabbage (20t FYM/ ha for potato) Amended soil Correlation w ith m ean yield

6 CONCLUSION Growing of PCN resistant potato and french beans in intercropping during summer and cabbage in autumn is the more stable potato-based cropping system for the southern hills. The yield stability of potato based cropping sequences over the years was influenced by soil characteristics especially, soil organic carbon and water stable aggregates as well as the PCN population. Improvement in SOC and total water stable aggregates improved the yield stability whereas, reduction in PCN population positively correlated with the yield stability. The soil Vol. 47, No. 3, management system designed to improve the soil characteristics through proper combination of crops and varieties in intercropping system and rotation provided the optimal combination of enhancement in potato equivalent yield and reducing year-to-year variability of those yields. Potato yield in continuous cultivation of potato was adversely affected year after year making the system more unstable. These results demonstrate that managing soil characteristics with proper selection of crops and varieties can be a viable strategy to buffer the effects of growing environment and stabilize the yield. REFERENCES Cassman, K G. (1999). Ecological intensification of cereal production systems: Yield potential, soil quality and precision agriculture. Proc. National Acad. Sci. USA 96: Gallandt, E R, Liebman M, Corson S, Porter G A and Ullrich S D. (1998). Effects of pest and soil management systems on weed dynamics in potato. Weed scie. 46: Gangwar B, Katyal, V and Anand KV. (2004). Stability and efficiency of cropping systems in Chhattisgarh and Madhya Pradesh. Indian J. Agric. Sci. 74 : Grandy A S, Porter G A and Erich M S. (2002). Organic amendment and rotation crop effects on the recovery of soil organic matter and aggregation in potato cropping systems. Soil Sci. Soc. Amer. J. 66 : Johnston A E.(1991). Soil fertility and organic matter. In W.S.Wilson (ed.) Advances in Soil Organic Matter Research : The impact on agriculture and the environment. The Royal Society of Chemistry, Melksham, Wiltshire. Pp: Lin C S, Binns M R and Lefkovitch L P.(1986). Stability analysis: Where do we stand? Crop Sci. 26 : Lin C S and Binns M R. (1988). A method for analyzing cultivar x location x year experiments: a new stability parameter. Theor. Appl. Genet. 76 : Lotter, D W, Seidel R and Liebhardt W.(2003). The performance of organic and conventional cropping systems in an extreme climate year. American Journal of Alternative Agriculture. 18 : Mohammadi Reza and Amri Ahmed.(2008). Comparison of parametric and non parametric methods for selecting stable and adapted durum wheat genotypes in variable environments. Euphytica 159 : Saini, G, and Grant W. (1980). Long term effects of intensive cultivation on soil quality in the potato growing areas of New Brunswick (Canada) and Maine (USA). Can. J. Soil Sci. 60 :