EFFECT OF SLOPES AND COMPOUND NPK FERTILIZER ON GROWTH AND YIELD OF MAIZE LOCAL VARIETIES, RELATIVE AGRONOMIC AND ECONOMIC FERTILIZER EFFECTIVENESS TO INCEPTISOL BUMELA, INDONESIA

Maize cultivation has been carried out on the mountainous slopes with high fertilizer inputs, but maize productivity is still low. This study investigates the effect of slope and NPK compound fertilization as well as the best combination of growth and yield of local maize, relative agronomic effectiveness (RAE) percentage and economic fertilizer effectiveness (EFE) ratio in Inceptisol Bumela Indonesia. Slope variations (0-8, 8-15, 15-35, >35%) are combined with compound NPK fertilizer levels (0, 50, 100, 150, 200 kg ha) with split plot design. Growth data was recorded for changes in plant height and leaves number from 7 DAP to 42 DAP, while yield and yield components are recorded at harvest. The results showed that slope and NPK compound fertilization can increase the growth and yield of maize plants. The combination of flat slopes and fertilizer level of 100 kg ha was the best combination in increasing plant height and the leaves number, accelerate the age of male and female flowering flowers, cob weight, grain yield and percentage of cob weight to grain yields. This combination was also able to increase the percentage of RAE, the ratio of EFE subsidized and non-subsidized. If farmers will continue to cultivate maize on the sloping land, it was recommended to arrive at hilly land with a fertilizer level of 100 kg ha only.

Maize cultivation in Gorontalo Province region was very massive and has carried out on upland with a slope of 0% (flat) to mountainous land (slope >35%) which was vulnerable to land degradation. In fact, soil erosion that occurred from the Agropolitan maize planting area reported by Husain et al., (2004) as many as 1,396 t ha -1 year -1 . If this condition was left, it will threaten the sustainability of maize farming. Upland for maize cultivation in Bumela Village was generally on Inceptisol (Indonesian Soil and Agroclimate Research Center Team, 1995). Inceptisol was a relatively young soil and its development was a level above of the Entisols (Rachim, 2007), including having a cambic horizons with a percentage of Na can be exchanged by 15% or more (Soil Survey Staff, 2014). Inceptisol has the potential to be developed (Nursyamsi et al., 2002;Hermawan et al., 2018) because it covers 70 million hectares in Indonesia (Kasno, 2009;Muyassir et al., 2012;Hermawan et al., 2018). However, these soils generally have low soil fertility and organic matter content (Abdurachman et al., 2008;Arviandi et al., 2015). Meanwhile, the high intensity of tillage for maize cultivation has led to a decrease in soil fertility (Lorenz et al., 2000;Husain et al., 2002;Pomalingo and Husain, 2003), so as the maize productivity is low, although fertilizer application exceeds recommendations.
A literature study on the results of the effect of slope and compound NPK fertilization combined with the specific growth and yield of maize local varieties has not been found. While information on the performance of growth and yield of maize local on various slopes combined with the level of NPK compound fertilization is very important for farmers and policy makers, especially in the Gorontalo Province. In fact, maize farmers continue to cultivate on sloping land of >25% with less fertilizer input or exceed the recommended fertilizer levels, so this research was important to done. This study aims to investigate the growth and yield of maize local variety of Motoro Kiki, the relative agronomic effectiveness (RAE) and economic fertilization effectiveness (EFE) on various slopes and NPK compound fertilization to Inceptisol Bumela, Indonesia.

MATERIALS AND METHODS OF RESEARCH
The study was conducted to four months (December 2019 to March 2020) on the toposequence of farmers maize land in Bumela Village, Bilato District, Gorontalo Regency, Gorontalo Province, Indonesia. Specifically geographical, the experimental field was rectangular located at 0 o 36'11.98"-0 o 36 '11.46  This soil is very dark gray brownish (10YR 3/2), granular of soil structure and sandy clay of texture, cation exchange capacity of 8.94 cmol kg -1 and base saturation 79.88%, Na saturation of 24.17% (Table 1). Annual average rainfall of 1,245.90 mm with annual average temperature of 28.02ºC (BWS Sulawesi II, 2019) and potential evapotranspiration of 152.95 mm, so the soil moisture regime was Ustic (106 dry days without humid days ) and the soil temperature regime was Isohyperthermic. Based on the morphology, soil physicochemical properties and other properties, the soil in the experimental field was classified as Oxic Humustepts (Soil Survey Staff, 2014).
Maize was planted with a distance of 20 x 40 cm in the planting hole of 2 maize seeds (December 26, 2019), so as to get 50 plant populations per plot. At the maize age of 7 day after planting (DAP), weed cleansing and thinning into 1 plant per holes. The first fertilization was done (1/2 level of fertilization per treatment) and plant embellishment was followed. Weed cleansing and embellishment was done when growing weeds manually with a hoe. At the maize age of 30 DAP, the second fertilization (the remaining 1/2 level of fertilization per treatment) was continued with plant embellishment. Maintenance continues until the harvest stage. Maize harvesting was done when the physical condition of the maize was dry and yellows (26 March 2020) or ± 90 DAP.
Observation of maize growth variables, including plant height (cm) and leaves number was carried out from plants aged 7 DAP to male flowers (± 42 DAP) on ten selected plants per plot. While the maize yield variables, including age of male and female flowering (DAP) were observed when maize flowers first appeared, the cob weight (t ha -1 ) was weighed after the maize seeds were separated from the cob, the grain yield (t ha -1 ) was weighed after the maize seeds were dried under 5 days sun exposure (± 15% moisture content) and the percentage of cob weight to grain yields (%).
NPK compound fertilizer applied, either singly or in combination was tested by relative agronomic effectiveness or RAE (Mackay et al., 1984;Chien, 1996) with the following equation: Where: Yt = maize yield on the tested fertilizer (t ha -1 ), Ys = maize yield standard (t ha -1 ), and Yo = maize yield on the control treatment (t ha -1 ). The greater the percentage of RAE, the better the effectiveness of fertilizer relative to agronomic traits. Meanwhile, to find out the fertilizer used has a good economic value, an economic fertilizer effectiveness (EFE) was carried out with the following equation: = Where: P = price of maize per kg (IDR Kg -1 ), Q = total yield (kg ha -1 ), and C = price of fertilizer (IDR Ha -1 ). If the EFE ratio was >1, the fertilizer tested has good economic value (Saeri and Suwono, 2012; Wijaya et al., 2015).
The price of maize per kg in the study area was IDR 3,500. While the price of Phonska compound NPK fertilizer consists of two, namely NPK Phonska was subsidized by the government at a price of IDR 2,300 and non-subsidized at a price of IDR 8,000. The two forms of NPK fertilizer were used as a comparison material as well as consideration in making the best agronomic and economical NPK compound fertilizer selection decisions. All data obtained were analyzed with ANOVA of split plot design divided into patterns 4 5 . If there was a treatment that has a significant effect, then it was continued with the Duncan Multiple Range Test (DMRT) at the test level P >0.05 with the tools of the Statistical Analysis System (SAS) program.

RESULTS AND DISCUSSION
Effect of slope and NPK compound fertilizer on maize growth. Slopes and NPK compound fertilization showed has significant effect on the plant height at the age of 14, 21, 28, 35, and 42 DAP, except at the age of 7 DAP in all treatments and at the age of 14 DAP in the treatment of compound NPK fertilizer that has not significantly affected ( Table 2). This was be fathomed because it was not directly related to the plant physiological aspects, but directly related to soil characteristics. Slopes were closely related to the quantity of soil organic carbon, total N, and enzyme activity by changing the rate of litter decomposition and soil microbial activity (Nahidan et al., 2015). The highest rate of plant height increase at the age of 28 DAP with an average percentage of plant height increase of 111.05% in all treatments and decreased until the age of 42 DAP. While, the highest rate of plant height increase with an average percentage of plant height increase of 70.56% was indicated by the slope 0% (flat) and NPK compound fertilizer as much as 50 kg ha -1 , while the rate of plant height increase was lowest with an average percentage of plant height increase of 58.12% only was shown by the slopes >35% (mountainous) and NPK compound fertilizer as much as 0 kg ha -1 .
Apparently, the effect of slopes began to be seen clearly in plant height from the age of 14 DAP to 42 DAP, where the flat slope had a significant effect on plant height and the peak effect of the slope was more pronounced at plant height aged of 35 and 42 DAP, followed by a undulating slope. The position of the slope has a significant effect on the maize growth (Changere and Lal, 1997). Hilly and mountainous slopes will receive more sunlight than undulating and flat slopes, so that decomposition of organic matter and nutrient cycling was better. Humidity is a basic environmental factor in a relatively dry area, so higher humidity at the shady slopes location can lead to better nutrition cycles and higher microbial community activity (Xue et al., 2018). The levels of C-organic, total N, P are available and K can be exchanged at the study site is relatively low (Table 1), so fertilizing action was needed. While the effect of NPK compound fertilizer began to be seen clearly in plant height later on from the age of 21 DAP to 42 DAP, where the fertilizing level of 100 kg ha -1 showed the highest plant height from the age of 28 DAP, 35 and 42 DAP, but it was not significantly different from the fertilizer level of 50 kg ha -1 and 200 kg ha -1 at the age of 21 DAP, 28, 35 and 42 DAP, except with fertilizer levels 0 kg ha -1 and 150 kg ha -1 were significantly different at the age of 28 DAP and 35 DAP. The NPK fertilization has a significant effect on the agronomic parameters of maize (Achiri et al., 2017). Nitrogen is another important soil nutrient that affects plant growth and water use efficiency (Sardans et al., 2008). The application of Phosphor fertilizer increases the efficient utilization of N fertilizer on the production of maize biomass (Mensah and Mensah, 2016). Potassium is needed for maize growth (Solihin et al., 2019).
The combination of slopes and NPK compound fertilizers began to showing a significant effect on plant height aged of 14 DAP to 42 DAP, while at age of 7 DAP had no significant effect ( Table 2). The combination of flat slope (0-8%) to undulating slope (8-15%) with NPK fertilizer compound level of 100 kg ha -1 shows the highest plant height at the age of 21 DAP to 42 DAP. While on a combination of hilly slopes (15-35%) and mountainous slopes ( 35%) with all levels of fertilization was relatively varied. However, if the lands with these slopes will still be used for maize cultivation, then it will be sought only to land with hilly slopes (15-35%) combined with NPK compound fertilizer levels of 100 kg ha -1 because plant height reaches of 174.45 cm at age of 42 DAP. At low fertilization rates, the amount of N and K absorbed by plants increases with the amount of fertilizer applied (Niu et al., 2013). Maize plants absorb large amounts of N from the soil at V6 and maximum absorption occurs before silking (Ma' et al., 2003).
The effect of the slope on the leaves number shows the significant effect from the age of 7 DAP to 42 DAP, while the effect of compound NPK fertilization shows the significant effect later starting at age of 21 DAP to 42 DAP (Table 3). The highest rate of leaves number increasing occurred at the age of 14 DAP with an average percentage of leaves number increase of 79.70% in all treatments and decreased until the age of 42 DAP. The rate of increasing the leaves number with an average percentage leaves number increase by 38.16% was indicated by the slopes >35% (mountainous) and NPK compound fertilizer as much as 150 kg ha -1 , while the rate of increasing the leaves number with an average the percentage of leaves number increase was 29.94% only, as indicated by the slopes 15-35% (hilly) and NPK compound fertilizer as much as 200 kg ha -1 . Leaves number of maize increased significantly as the plants aged with NPK fertilizing (Titah et al., 2016). Effect of slope on the leaves number at age of 7 DAP shows the highest leaves number on hilly slopes (15-35%) and not significantly different from flat slopes (0-8%) and undulating slopes (8-15%), but significantly different from slopes mountainous (>35%). At the age of 14 DAP, the effect of hilly slopes still shows the highest leaves number and was significantly different from flat slopes and undulating slopes, while those with mountainous slopes are not significantly different. At the age of 21 DAP and 28 DAP, the effect of flat slope has shown the highest leaves number and was significantly different from all slope classes, except at the age of 28 DAP which was only significantly different from hilly slopes. While at the age of 35 DAP and 42 DAP, the effect of mountainous slopes shows the highest leaves number and was not significantly different from flat slopes.
The effect of NPK compound fertilizer on the leaves number at the age of 7 DAP shows the highest leaves number at the fertilizer level of 200 kg ha -1 , while at the age of 14 DAP the highest leaves number at the fertilizer level of 50 kg ha -1 , although at the two ages it was not significantly different from all fertilization levels. At the age of 21 DAP, NPK compound fertilization shown has significant effect with the highest leaves number at the fertilizer level of 50 kg ha -1 and significantly different from the fertilizer level of 0 kg ha -1 only. While at the age of 28 DAP to 42 DAP, the effect of compound NPK fertilizer on the most leaves number was indicated by the fertilizer level of 100 kg ha -1 and significantly different from the fertilizer level of 0 kg ha -1 only, except at age of 35 DAP apart from being significantly different from the level 0 kg ha -1 also with a fertilizer level of 50 kg ha -1 . The combination of slope and compound NPK fertilizer shows a significant effect on the leaves number starting at age of 7 DAP to 42 DAP (Table 3). The combination of hilly slopes with NPK compound fertilizer of 200 kg ha -1 level shows the highest leaves number at the age of 7 DAP to 14 DAP and was significantly different with the combination of mountainous slopes with fertilizer levels of 50, 100 and 150 kg ha -1 at age of 7 DAP only, as well as a combination of flat slope and fertilizer level of 0 kg ha -1 to 200 kg ha -1 , a combination of undulating slopes with fertilizer levels of 0 kg ha -1 , 150 and 200 kg ha -1 , a combination of hilly and mountainous slopes with levels 100 kg ha -1 . While at the age of 21 DAP, the highest leaves number was indicated by a combination of flat slope and 50 kg ha -1 fertilizer level that was significantly different from all treatment combinations. The same pattern was also shown by the highest leaves number at the age of 28 DAP on a combination of flat slope and 50 kg ha -1 fertilizer level, but significantly different from the twelve other treatment combinations. At the age of 35 DAP, the effect of mountainous slopes with fertilizer level of 150 kga ha -1 combination showed the highest leaves number and was significantly different from nine other treatment combinations, whereas at age of 42 DAP the highest leaves number was indicated by a combination of mountainous slopes with a fertilizer level of 200 kg ha -1 and significantly different from thirteen other treatment combinations.
Effect of slopes and NPK compound fertilizer on maize yields. The effects of slopes and compound NKP fertilizers show a significant effect on all yield components (Table 4). On the flat slope (0-8%), the male flowers (42.21 DAP) and the female maize flowers (47.64 DAP) were the most significantly different from the other slopes, while on the hilly slopes (15-35%) the male flowers were the longest (45.84 DAP) and female flowers (49.31 DAP). The highest of cob weight and grain yields on the flat slope (0-8%) that it was significantly different from other slopes, except that the cob weight was not significantly different from other slopes. The highest of cob weight percentage ton grain yield was shown by mountainous slopes (>35%) and has not significantly different from flat slopes. The slope position also has a significant effect on maize yield (Changere and Lal, 1997), as the slope and organic fertilizer have a significant and very significant effect on potato yield (Wati et al., 2014). The 10-22% lower content of organic matter, nitrogen, and phosphorus on the lower middle slope is associated with a decrease in maize yield of 27% compared to the position of the upper middle slope (Wezel et al., 2002).
The effect of NPK compound fertilizer on the age of male and female maize flowers was the fastest out (44.87 DAP and 48.22 DAP respectively) and the highest cob weight was shown by the fertilizer level of 100 kg ha -1 which was significantly different with the level of fertilizer 0 kg ha -1 only. While the highest of grain yields hass shown by the fertilizer level of 200 kg ha -1 but not significantly different from the fertilizer level of 100 kg ha -1 , whereas the highest of cob weight percentage to grain yield was indicated by the level of 50 kg ha -1 and significantly different with the level of 0 kg ha -1 and 200 kg ha -1 only. The NPK fertilization has a significant effect on maize yield parameters (Achiri et al., 2017). Flowering time can often be accelerated 3-10 days by application of NPK fertilizer (Gumeleng, 2003). Female maize flowering were most quickly obtained at the fertilizer level of 250 kg ha -1 N, 100 kg ha -1 P and 75 kg ha -1 K whereas the latest were obtained at 0 kg ha -1 level (Nurdin et al., 2009). Phosphor is able to increase the photosynthesis process which will further influence the increase in dry weight of plants (Minardi, 2002). The combination of slope and NPK compound fertilizer shows a significant effect on all yield components ( Table 4). The combination of flat slope with NPK compound fertilizer level of 100 kg ha -1 shows the age of male and female maize flowering fastest and has significantly different from the ten slope combinations and fertilizer level at age of male maize flowering, and significantly different from the eight slope combinations and other fertilizer levels at age of female maize flowering. Meanwhile, the highest of cob weight was shown by a combination of hilly slopes and fertilizer level of 100 kg ha -1 which was significantly different from four other treatment combinations only. The highest of grain yiled was shown by the combination of flat slope and fertilizer level of 200 kg ha -1 , but it was significantly different from only eight other treatment combinations. Whereas the highest of cob weight percentage to grain yiled was shown by the combination of mountainous slopes with a fertilizer level of 100 kga ha -1 and significantly different from five other treatment combinations only. The best combination of slope and NPK compound fertilizer on maize yield parameters was flat slope with fertilizer level of 100 kg ha -1 . This was in line with the report of Ngosong et al., (2019) that N fertilizing between 50 and 100 kg N ha -1 was optimal for maize production in Cameroon's volcanic soil.
Relative agronomic and economic fertilization effectiveness. The highest of relative agronomic effectiveness (RAE) values, the ratio of economic fertilization effectiveness (EFE) with subsidized fertilizer and non-subsidized was shown by flat slopes (0-8%) which differ significantly by undulating slopes (8-15%) and mountainous slopes (>35%) on RAE, significantly different from all slopes in the EFE subsidized and non-subsidized ratio (Table  5), in other to the distribution was obtained following the RAE pattern S1> S3> S2> S4. Provision of standard or recommended of NPK Fertilizers (300 kg ha -1 NPK+250 kg ha -1 Urea) shows a higher RAE value (100) than other fertilizer doses to maize plants ( (Zulkarnain et al., 2017). Furthermore, the highest of the RAE value, EFE subsidized and non-subsidized ratio with NPK compound fertilization was shown by fertilizer level of 200 kg ha -1 which was not significantly different with fertilizer level of 50 kg ha -1 and 100 kg ha -1 at RAE, and has not significantly different only with the level of 100 kg ha -1 in the EFE subsidized and nonsubsidized ratio, so as the distribution was obtained following the pattern F4> F2> F3> F1> F0. The highest of RAE, the EFE subsidized and non-subsidized ratio in the combination of slope and NPK compound fertilization has shown by the combination of flat slope with fertilizer level 200 kg ha -1 which was significantly different from the ten other treatment combinations at RAE value and significantly different from eight other treatment combinations at the EFE subsidized and non-subsidized ratio (Table 5). While the lowest RAE value was indicated by the combination of flat slope with fertilizer level of 150 kg ha -1 which was significantly different from the combination of flat slope and fertilizer level of 50 kg ha -1 only, the EFE subsidized and non-subsidized ratio was indicated by the combination of mountainous slopes with fertilizer level of 0 kg ha -1 and significantly different from ten other treatment combinations. Thus, the combination of a flat slope with a fertilizer level of 100 kg ha -1 is the best combination that can be applied by maize farmers. This was in line with the report of Wijaya et al. (2015) that fertilizing urea at 100 kg ha -1 , SP-36 at 200 kg ha -1 and KCl at 100 kg ha -1 showed the highest EFE ratio in both subsidized and non-subsidized fertilizers. However, if farmers will continue to maize cultivating on sloping land, it was recommended to arrive at hilly slopes (15-35%) with fertilizer levels of 100 kg ha -1 only.

CONCLUSION
The slope and NPK compound fertilization can increase the maize growths. The best combination in increasing plant height and leaves number was the combination of flat slope and fertilizer level of 100 kg ha -1 . The slope and NPK compound fertilization can increase the maize yields. The best combination in accelerating the age of male and female maize flowering, increasing the grain yield was the combination of flat slope and fertilizer level of 100 kg ha -1 . While on cob weight was combination of hilly slope and fertilizer level of 100 kg ha -1 , whereas on the percentage of cob weight to grain yield was a combination of mountainous slope and fertilizer level of 100 kg ha -1 . The slope and NPK compound fertilization can increase the RAE percentage, the EFE subsidized and non-subsidized ratio. The best combination of flat slopes and compound NPK fertilization level of 200 kg ha -1 has significantly increase the percentage of RAE, the EFE subsidized and non-subsidized ratio, but relatively equal to the the level of 100 kg ha -1 . If farmers will continue to maize cultivating on the sloping land, it was recommended to arrive at hilly land with a fertilizer level of 100 kg ha -1 only.