Effect of intercroping maize and soybean on soil fertility

This study was carried out to determine the effect of intercropping maize with soybean on soil fertility. The study was conducted at two sites and evaluated three soybean varieties (hybrid SB19, GAZELLE a local variety, hybrid TGX1990-5F) as sole crop and intercropped with maize, with maize pure stand as control. In the intercropped plots, one row of soybean was planted after every alternate row of maize. Data collected included soil nutrient status before planting and at harvest and nodulation in soybean. Variety TGX1990-5F had significantly more nodules followed by GAZELLE and SB19 was the last in sole crop and in intercrop at Embu during long rains and short rains (p ≤ 0.05). Mwea produced more nodules compared to Embu. Intercropping maize and soybean had no effect on the number of nodules per plant both seasons.However, TGX1990-5F fixed higher N of 0.39% compared to 0.29% for SB19 in sole crop respectively between sites for the first season after harvesting. TGX1990-5F showed higher N compared to GAZELLE in intercrops between sites for the second season after harvesting. Depending on the requirement of the plants nutrients, TGX1990-5F fixed moderate N for feeding plant. However, GAZELLE showed high Organic Carbon, Potassium and Phosphorus after harvesting than other varieties in both sites and rains seasons. Thus, variety TGX1990-5F can be recomended to smallscale farmers for intercropping with maize because it produced higher nodules and fixed higher N, hence reducing the cost for N fertilizers. * Corresponding Author: Habineza M. Jean Pierre  ir.jphaby@gmail.com International Journal of Agronomy and Agricultural Research (IJAAR) ISSN: 2223-7054 (Print) 2225-3610 (Online) http://www.innspub.net Vol. 12, No. 2, p. 87-100, 2018 Int. J. Agron. Agri. R. Pierre et al. Page 88 Introduction Low soil fertility is a important constraint in agricultural production in Sub Saharan Africa. Legume promise of being a cheap alternative soil fertility owing to their ability of fixing atmospheric nitrogen (Phiri et al., 2013). However, soil characteristics can be affected positively or negatively by growth conditions of crops. Intercropping is an agricultural practice of cultivating two or more crops in the same space at the same time (Lithourgidis et al., 2011). The authors also define intercropping as an old and commonly cropping system used which targets to match efficiently crop demands to the available growth resources and labor. Yield and nutrients acquisition advantages are frequently found in intercropping systems. However, there are few published reports on soil fertility in intercropping relative to monocropping (Wang et al., 2014). The stability under intercropping can be attributed to the partial restoration of diversity that is missed under sole crops. According to this statement, intercropping allows high insurance against crop failure, notably in environments known for heavy weather conditions like frost, flood, drought, and overall provides hight financial stability for farmers (Lithourgidis et al., 2011). Moreover, legumes enrich soil by fixing the atmospheric nitrogen transforming it and other mineral from an inorganic form to forms that are avaible for uptake by crops (Li et al., 2012). Biological fixation of atmospheric nitrogen can replace nitrogen fertilization fully or partially. When nitrogen fertilizer is limited, biological nitrogen fixation is the important source of nitrogen in intercropping systems (Fujita et al., 1992). In addition, because inorganic fertilizers contributed to ecosystem damage such as nitrate pollution, legumes grown in intercropping are taken as an alternative and sustainable path of bringing nitrogen in the soil into little input cost and without damage (Fustec et al., 2010). Furthermore, the green parts and roots of the legume component can decompose and provide nitrogen into the soil where it may be made available to subsequent crops. Specially, under low soil nitrogen conditions the advantages of legumes in an intercrop are greater (Fabio et al., 2017). Legumes broadly are more powerful in increasing the productivity of succeeding cereals. The carryover of nitrogen for succeeding crops may be 60-120kg in berseem (Trifolum alexadrium), 75kg in cluster bean (Cyamopsis tetragonolobus), 68kg in chickpea (Cicer arietinum), 54-58 kg in groundnut (Arachis hypogea) and 50-51kg in soybean (Glycina max) (Bandyopadhyay et al., 2007). In addition, apart from nitrogen, intercropping legume-cereal can allow acquisition of other nutrients such as phosphorus, potassium, sulphur and micro nutrients. Zhang et al., (2015) reported that, maize-soybean intercropping reduced use of N fertilizer per unit of area and enhanced relative biomass of intercropped maize, due to promoteded photosynthetic efficiency of bodder rows and N utilisation during symbiotic period. In addition, Ali at al., (2015) found that, maize-soybean intercropping increased soil organic carbon content, CEC, N, Ca, Mg and P level after harvesting than sole crops. Wang et al., (2014) reported that, globally, soil organic matter did not differ significantly from monocropping but did increase in maize-chickpea intercropping in two years. Soil total N did not differ between intercropping and monocropping in either year, except in maize-fababean intercropping in 2011. Intercropping reduced significantly soil Olsen-P, soil exchangeable K in both years, soil cation exchangeable capacity (CEC) in 2012 and soil p H in 2012. In the majority of cases soil enzyme activities did not differ across all the cropping systems at different P application rates compared to monocrops. However, Owusu & Sadick (2016) reported that before maize-soybean intercropping system, the soil was moderaterly slightly acid (p H=5.6), while the nitrogen was low (0.1%). They said also that, the available phosphorus was very low (4.95mg/kg). After the experiment the results showed that, some soil nutrients increased for exemple organic carbon (0.15%), phosphorus (5.25mg/kg), calcium (0.54cmol (+)/kg), sodium (0.06cmol(+)/kg) while others soil nutrients decreased like the total nitrogen (0.02%), magnesium (0.54 cmol (+)/kg) and potatium (0.12 cmol (+)/kg). In addition the same autors reported that, correlation analysis showed that, organic carbon and available phosphorus correlated positively with all parameters while nitrogen correlated positively with calcium, Int. J. Agron. Agri. R. Pierre et al. Page 89 potassium, magnesium, organic carbon, and phosphorus. Regehr (2014) reported that, soil quality improved significantily in maize-soybean intercropping than monocropping system. Intercropping resulted in higher rates of gross N mineralization than the sole crops, and the 2:3 intecrop resulted in higher rates of gross N immobilization than other treatments. Hence the research in this study for assessing the effect of intercropping maizesoybean on soil fertility at Embu and Mwea sites in Kenya. Materials and methods Description of the study sites The experiments were conducted in Embu and Mwea during two rain seasons of (2016 and 2017). KALROEmbu is located between latitudes 0゚08’35’’S and a longitude 37°27′02′′ E while KALRO-Mwea is located at a latitude of 00037’S and a longitude of 37o20’E in Kenya (kirinyaga county, 2014 and Embu county, 2014). During the experiment period the rainfall was 3.21 mm and 0.007 mm at Embu and Mwea, respectively. The mean temperature and relative humidity were respectively 21.42°C and 63.54% at Mwea and 20.3°c and 64.43% at Embu (KARLO Embu and Mwea agromet services). Land preparation was done by ploughing using ox-drawn equipment. Experimental treatment and design The treatments consisted of three soybean varieties planted as monocrop or intercropped with maize as follows: l.SB19 (Hybrid), GAZELLE (Local), TGX1990-5F (Hybrid), SB19 intercropped with maize, GAZELLE intercropped with MAIZE, TGX1990-5F intercropped with MAIZE, and maize sole crop as control. Maize variety used for intercropping was DUMA 43. The spacing used was: The monocrop soybean was planted at a spacing of 40cm x 15cm, Soybean intercropped with maize: (80cm x 15cm), Monocrop maize: (80cm x 25cm), Maize intercropped with soybean: (80cm x 25cm). The arrangement of intercropping was 1:1 with one row of maize intercepted by one row of soybean. The experiment was laid out as a randomized complete block design (RCBD) replicated three times The experiments received a basal application of DAP at the rate of 250kg ha-1 , (Roy et al., 2006). Because of insufficient rain fall, the trials received supplement by irrigation but the situation of rain fall was drastic and so bad in the second season. Soil sampling and nutrients analysis Soil samples were collected with auger tool using zigzag method at a depth of 0-30cm and then mix different samples of the same site in order to get one sample which is homogeneous in each site and taken for analysis at Soil Chemestry laboratory, University of Nairobi for macronutrients, micronutrients and some oligo elements like Zinc, Mn, cobalt and pH. Before planting and after harvesting soil analysis for each treatment was done also in order to ensure the amount of nutrient fixed after harvesting in each plot. The soil pH was measured by using pH meter as showed Van Reeuwijk (2002). Organic carbon was assessed following the model for Walkely and Black (1934). Total organic carbon = (Vblank − V sample) x 0.3 x N x 100 Weight x 100 77 V blank = Volume of blank, V sample = Volume of sample, 0.3 = Factor, N = Normality for FeSO4. The total nitrogen was measured using kjedal method as said by (Roberts et al., 1971). %N total = Titre x 14 x Normality of acid used x volume extracted x 100 Weight of sample x 1000 x Aliquote taken in (ml) However, the available phosphorus in the soil was quantified colorimetrically using spectrophotometer as said by (Roberts et al., 1971). P ppm = GR x volume extracted Weight x 50 3 GR: Absorption, 50: Volume devel