DYNAMICS OF SOIL CARBON AND N, P, K NUTRIENTS ON CORN PLANTING PATTERN IN DRY LAND

A study was conducted during two planting seasons, namely planting season 1 (PS-1) 2017/2018 and (PS-2): 2018/2019, in Oelnasi Village, Central Kupang sub-district, Kupang District, East Nusa Tenggara, Indonesia. This study aimed to evaluate the rotation pattern of maize with legumes ground covers   towards the dynamics of soil carbon and nutrients N, P, K during the two growing seasons in a dryland farming system. The experiment was designed using a randomized block design with 3 (three) treatments replicated five times. The treatments evaluated were: crop rotation patterns consisting of: without rotation (farmer practice) and rotation pattern with Phaseolus lunatus; rotation pattern with Mucuna pruriens. Legume crops planted after harvesting the food crop and allowed to grow during the dry season. Approaching the rainy season, the biomass of the legume crop is returned to the land by immersing them it together with soil cultivation. Chemical fertilizers is given as an independent variables with a dose of 150 kg/ha of Urea; 100 kg/ha of SP36 and 100 kg/ha of KCL. The results showed that the rotation pattern of Mucuna pruriens significantly increased the soil organic C content by 50.56% and legume Phaseolus lunatus by 37.64% to PS-2. The rotation pattern of the legume covers / covered crop also significantly increased the efficiency of agronomic nutrients (N, P, and K nutrients) and maize yields during the two growing seasons. On the other hand, the farmer pattern (without rotation) showed a decrease in soil carbon to PS-2 which of course affect the efficiency of nutrient absorption.


INTRODUCTION
In general, the productivity of dry land farming in the district of Kupang, East Nusa Tenggara, Indonesia is relatively low compared to farming in wetlands. The main causes are the relatively low soil quality factor and relatively short (3)(4) wet months) rainfall distribution, (Matheus, 2014). Currently, many productive agricultural lands have been degraded due to intensive farming patterns of continuous planting patterns, besides erosion factors that cause a decrease in soil organic carbon (C) levels as an indicator of soil quality. It is reported that the soil organic carbon (C) contented of most agricultural land in Indonesia in the last three decades has reached a low level of <2% for wetlands, even for dry land <1.67% (Matheus et al., 2018).
The agricultural system can be sustainable if the soil organic C content is more than 2% (Handayanto, 1999). The solution to making dry land farming more productive requires an increase in soil organic carbon (C) as an important soil constituent component.
Soil organic carbon (C) is one of the main indicators of soil quality (Doran and Parkin 1994;Larson and Pierce 1994;Islam and Weil, 2000), because of its role in determining the physical, chemical, and biological properties of the soil (Olson et al. 2010;Liu et al. 2006). The soil has a high potential for carbon sequestration because it can contribute to agronomic, physiological efficiency, and is important in the recovery of nitrogen, phosphorus, and potassium (Rahman, 2013). In addition, carbon (C) soil, can increase the efficiency of fertilization.
Apart from organic C, macro nutrients of N, P, and K are essentially needed by plants in large quantities, so their availability in the soil must be considered. The fulfillment is through fertilization, but the level of fertilization efficiency is generally still low (Finck, 1992;Kasno and Rostaman, 2013 (Matheus, 2019). This rotation pattern is suitable for dry land farmers because it is easy and cheap, compared to using manure which is more expensive. The rotation pattern of the legume ground covers can contribute biomass as a source of carbon as well as that of natural nitrogen (Matheus, 2014). This study aims to determine the rotation pattern of the legume ground covers and their residual effects on the dynamics of soil organic carbon, N, P, K nutrients, and corn yields during the two growing seasons.

Study area
Field trials were carried out on land The experiment site was dry land that was cultivated continuously and previously planted with corn.

RESULT
The type of soil in the experimental location was belonged to the cambisol soil type, vertisol order, at an altitude of 440 m asl with flat topography (+ 5%). The results of the analysis of the soil used in the research area are presented in Table 1.
The results of preliminary soil analysis showed that the soils in the study location was belong to the ultisol order, with high (68.54%) clay content and the slope of 5%, could cause poorl drainage of the soil. Soil organic-C, available-P, potential and available-K were classified low, which probably due to farmers do not usually apply KCl fertilizer to plants and very little plant residues are returned to the soils.

Dynamics of N, P, and K nutrients.
In general, the rotation pattern treatment with legume ground covers significantly increased the macronutrients (N, P, and K) in the soil. The results of soil analysis that were carried out 3 (three) times, namely at planting time (after immersing the legume biomass); at the end of harvest PS-1, and at the end of harvest PS-2, which are presented in Table 2. Table 2 shows that there is a tendency to increase in soil macronutrients (N, P, and K) due to rotation patterns with legume ground covers. The rotation pattern with

Mucuna pruriens and Phaseolus lunatus
showed higher change in macronutrient content during the two growing seasons compared to those without rotation. The content of total N in the soil were also varied.

The highest total N content in rotation with
Mucuna pruriens was (0.35% N) at planting maize and decreased in PS-2 to 0.21%.

Agronomic nutrient efficiency
The agronomical efficiency of nutrients can be determined by comparing the number of nutrients transported by plants with the amount of nutrients from fertilizers added and in the soil (Jagadeeswaran et al., 2005 andMilkha et al., 2001). The results of the analysis of the nutrient uptake efficiency of N, P, and K are presented in Figure 2.   and 17% of P and 30% and 22% of K.

Rotation with the species Phaseolus lunatus
resulted in agronomic efficiency of 32% and 25% of N; 27% and 17% of P and 25% and 19% of K respectively, which were higher than the farmer practice (without rotation), with less agronomic efficiency in both PS1 and PS2.

Corn yields
The rotation pattern of the legume cover crop showed a significant effect on maize yields during the two growing seasons.
The yields of dry kernel corn in PS-1 (rainy season) and PS-2 (dry season) is presented in Figure 3.

The rotation pattern with legumes of
Mucuna prriens and Phaseolus lunatus significantly increased dry kernel corn yields, with 6.20 tonnes/ha and 5.52 tonnes / ha respectively in PS-1 but decreased to 5.24 tonnes/ha. and 4.68 tonnes/ha in PS-2 ( Figure   3). However, they were still higher than those without rotation (where the maize yield only   (Hairiah et al., 2006). The presence of organic carbon in the soil layer will would help increase aggregation, especially in soils with clay textures. Increasing soil aggregation had an effect on improving physical properties, which could lower bulk density and increase pore space and soil pore distribution (Stevenson, 1994;Wailiru and Lal, 2006). showed a decrease in soil carbon in PS-2, which resulted in reducing the efficiency of N, P and K absorption.