The effect of different tillage practices on soil erosion, water conservation and yield of maize in the semi-deciduous forest zone of Ghana

A study was carried out to assess the effects of different tillage practices on soil loss fertility erosion, runoff, in-situ moisture conservation, water use efficiency and crop growth and yield. The 3-season experiments (2000 major, 2000 minor and 2001 major seasons) were conducted on runoff plots at the Research Farm of the Department of Crop Science, Kwame Nkrumah University of Science and Technology (KNUST), Kumasi. Twelve (12) runoff plots (30m long and 4.0m wide constructed on an average slope of 6°h and fitted with measuring devices were used for the experiment. The area is within the semi-deciduous forest zone of Ghana with mean annual rainfall ranging from 1,300 to 1,400 mm. The treatments were: LT - Local Tillage by Hoe R-ALS - Ridging Along the Slope P-HACS - Ploughing and Harrowing Across the Slope T-RALS - Tied-Ridging Along the Slope R-ACS - Ridging Across the Slope BARE - Bare control plot ploughed and harrowed along the slope. All ridges were 50cm high and spaced at 80cm apart. Ties were 30cm high and spaced at 4 Om apart along the ridges. The treatments were studied in a randomized complete block design (RCBD) with two replications. The Results were analysed by ANOVA and the Duncan’s Multiple Range Test (DMRT) was used to test the significance of mean differences. Regression analysis was used to establish relationships between measured parameters. The test crop was maize (Zea mays) variety GIDABA. The soil was Akroso series classified as Haplic Acrisol (FAO/UNESCO). It is a sandy loam (top soil) to sandy clay loam (subsoil). The parameters measured included bulk density, particle size analysis; runoff and soil loss; nutrient and organic matter losses; crop height, stover, above ground dry matter and grain yields; harvest index and water use efficiency. The mean bulk density at the 0 - 20 cm depth immediately after land preparation ranged from 1.20 to 1.40 gcm-3 with a rank LT (1.4)>BARE (1.31)>P-HACS (1.30)>R-ACS (1.22)> T-RALS (1.20) = R-ALS (1.20). Bulk density at the 20 - 45 cm depth was 1.60gcm-3 for all treatments. At harvest, bulk density increased almost to the initial values (1.55 — 1.60 gcm3) recorded before land preparation. The respective range of runoff for the three seasons 2000 major, 2000 minor and 2001 major were 39.4 - 142.0 mm, 5.6 - 39.6mm and 28.3 - 78.7 mm for the R-ACS - BARE. The magnitude of runoff was in the order of BARE>LT>R-ALS>P-HACS>T-RALS>R-ACS. The differences in the first four treatments were not significant but were highly significant (P>0.01) for TRALS and R-ACS. Rain water storage ranged from 321.7 to 409.7mm and 119.3 to 200.9mm for the 2000 and 2001 major seasons respectively with treatments ranking as R-ACS>T-RALS>BARE>P-HACS>R-ALS>LT. In the 2000 minor season, all the treatments except R-ACS (4.7mm) recorded negative moisture storage. R-ACS and T-RALS recorded significantly (p>.0.01) lower soil loss than the other treatments for all the three seasons. Soil loss over the three seasons followed a decreasing order of BARE>LT>RALS>P-HACS>T- > Cumulative soil loss over the three seasons resulted in top soil depth loss of 10.8, 8.5, 7.4, 4.6, 2.0 and 1.4 mm for BARE, LT, R-ALCS, P-HACS, T-R.ALS and R-ACS respectively. Tillage practices significantly influenced nutrient loss. The concentration of nutrient tended to be higher with smaller soil losses. Total nutrient loss however increased with increasing soil loss. The total amount of organic matter loss during the three seasons ranged from 356.7 — 2314.5 kgha-1 with trend of BARE>LT>R-ALS>P-HACS>T-ALS>RACS. The total nitrogen loss in both the eroded sediment and runoff for the entire experimental period was in the order of LT>BARE>R-ALS>P-HACS>TRALS>R-ACS and ranged from 25.0 to 277.7 kg ha-1. In all the three seasons nitrate concentration and amounts in runoff was significantly higher than ammonium. Total available phosphorus (P) losses for the three seasons of experimentation ranged between 0.41 and 2.0 kg ha-1 with a trend of BARE> LT> R-ALS> P-HACS>T-RALS> R-ACS. Potassium losses range between 0.56 and 2.33, 0.03 and 0.34 and 0.38 and 3.36 kg ha-1 for the 2000 major and minor and 2001 major wet seasons respectively. The order of losses for the major seasons was LT>BARE>RALS> P-HACS>T-RALS> R-ACS. Apart from P and K, the differences in the enrichment ratios under the various tillage treatments were not significant. R-ACS and TRALS tended to record significantly (P>0.05) greater plant heights whilst R-ALS recorded the least. Maize grain yield in the 2000 major and minor and 2001 major wet seasons was in the range 1.7 — 2.8, 0.99 — 1.97 and 1.1 - 2.6 t ha-1 respectively. With a trend R-ACS>T-RALS>P-HACS>LT>R-ALS, the R-ACS and T-RALS consistently out yielded the remaining treatments. Relationships established between measured parameters showed soil loss to positively correlated with runoff (r2 = 0.81 - 0.89). Soil loss per ha-mm of runoff was 1.1 t ha-1. Soil loss and runoff were negatively correlated with their nutrient concentrations. The magnitudes of the correlation co-efficients were generally low. The total nutrient loss of each treatment (kg ha-1) was however positively correlated with runoff (r2 = 0.40 - 0.97) and soil loss (r2 = 0.63 - 0.99). Plant height was highly significantly (P>0.01) and negatively correlated with runoff (r2 = 0.92 - 0.96), cumulative soil loss (r2 = 0.99) and cumulative total nutrient loss (r2 = 0.87). Maize grain, stover and above ground dry matter yields were negatively correlated with runoff, soil loss and nutrient loss. Yield loss per kg ha1 against cumulative soil loss were 13.9 kg-ha-1 for grain (r2 = 0.89), 353.3 kg ha-1 stover (r2 = 0.80) and 49.3 kg ha-1 above ground dry matter (r2 = 0.88). A kg ha1 of cumulative total nutrient loss decreased grain yield by 4.6 kg ha1 (r2 = 0.62), 13 kg ha’1 stover (r2 = 0.71) and 17.6 kg ha-1 above ground dry matter (r2 = 0.73). There was a significant positive correlation between crop height and grain yield (P>0.05) and stover yield (P>0.01). A cm loss in crop height reduced grain (r2 = 0.89) and stover (r2 = 0.92) yields by 46.3 and 99.2 kg ha-1 respectively. The recommended choice of tillage practice for soil, water and nutrient conservation, improved biomass production and grain yield is in a decreasing order of R-ACS>T-RALS>P-HACS>LT>R-ALS. LT, as a prevalent tillage practice in smallholder farming systems should always be complemented by proper residue management and nutrient replenishment strategies.

Source: KNUST