Influence of agroecological intensification techniques on soil moisture, nutrient status and yields of sorghum (sorghum bicolor (l.) moench) and cassava (manihot esculanta crantz) in Yatta sub-county, Kenya
Despite agriculture being the principle source of livelihood for majority of households in the arid and Semi-Arid Lands (ASALs), agricultural productivity has continued to decline mainly due to, among others, declining soil fertility, poor crop production practices and erratic and unreliable rainfall. Food security is further threatened by adoption of crop varieties not adapted to the ASALs at the expense of more drought tolerant varieties. A study was conducted to contribute towards enhancing soil fertility and food availability in the ASALs through use of selected Agro-ecological intensification techniques. The study examined the effect of different cropping systems and organic inputs on soil moisture, nutrient status and yield of cassava and sorghum. The ecological sustainability of the treatments was also assessed by calculating nutrient balances. On farm field experiments were conducted for two Short Rain seasons (SRS) and two Long Rain seasons (LRS), making a total of four seasons (SRS of 2010, LRS of 2011, SRS of 2011 and LRS of 2012). The experimental design was a randomized complete block design with a split plot arrangement. The main plots were three cropping systems: (i) Intercropping (Dolichos [Lablab purpureus]/Cassava, Dolichos/Sorghum, Pigeon pea [Cajanus cajan (L.) Millsp.]/Sorghum, Pigeon pea/Cassava); (ii) Rotation (Dolichos-Cassava, Dolichos-Sorghum, Pigeon pea-Cassava, Pigeon pea-Sorghum); (iii) Monocrop (pure cassava and sorghum). The split plots were; Farm Yard Manure (FYM), compost and control. All crops had above ground biomass incorporated after harvest in the same plot they were harvested from. Soil moisture, Organic Carbon (OC), Nitrogen (N), Phosphrous (P) and Pottasium (K) levels were determined at the end of every rainy season. NPK content of sorghum grain and cassava tuber was also dertemined at harvest. Soil NPK, tissue NPK as well as yields of various crops were used to as data input into the NUTMON toolbox for the calculation of nutrient balances as a basis of assessing the sustainability of the of the imposed treatments. The results showed that the highest moisture levels were observed under sorghum/pigeon pea intercrop (9.81% in Katangi and 12.30% at Ikombe) and cassava/dolichos intercrop (8.10 at Katangi and 10.30% at Ikombe) with FYM application. Sorghum grain and tuber yields were highest under sorghum/dolichos (2.23 tha-1 at Katangi and 2.0 t ha-1 at Ikombe respectively) and cassava/pigeon pea intercrop (23.53 tha-1 at Katangi and 37.80 tha-1 at Ikombe) respectively with FYM application. In the sorghum cropping systems, high soil Organic carbon were observed under sorghum/dolichos inetcrop with FYM (1.86% at Katangi and 1.95% at Ikombe during the LRS 2011). High soil N levels were under sorghum/doliochos intercrop with application of FYM (0.27% during SRS 2011 at Katangi and 0.21% during the LRS of 2011 at Ikombe). High P levels were observed under sorghum/dolichos intercrop with FYM (37.28 ppm during LRS of 2012 at Katangi and 39.78 ppm SRS of 2011) while K levels were similarly high under sorghum/dolichos intercrop with FYM (1.21 cmol/kg at Katangi and 1.10 cmol/kg at Ikombe during the SRS 2010). In the cassava cropping systems, soil OC was highest under cassava/dolichos intercrop with FYM during the LRS of 2012 (2.90% at Katangi and 2.12% at Ikombe). High N levels were observed under cassava/dolichos intecrop with FYM (0.14% at Katangi and 0.11% at Ikombe during the SRS of 2011), while soil P values were high under the same cropping system and organic input combination (38.80 ppm at Katangi during the SRS of 2010 and 39.61 ppm at Ikombe during the LRS 2011). Soil K levels were similarly higher under cassava/dolichos intercrop with FYM (0.73 cmol/kg at both sites during the SRS 2010). Sorghum grain N was highest under sorghum monocrop (1.52% during of SRS 2011 at Katangi and 2.62% LRS of 2011 at Ikombe) except in LR 2012 at Katangi where it was highest under dolichos-sorghum rotation with FYM (1.86%). Tuber N was highest under cassava/pigeon pea intercrop rotation with FYM (1.71% and 1.65% during SRS 2011-LRS 2012 at Katangi and Ikombe respectively) except in SR 2010-LR 2011 at Katangi where higher tuber N was under pigeon pea-cassavarotation monocrop with FYM (1.59%). Sorghum grain P was not influenced by cropping systems in SR 2010, LR 2011 at both sites as well as SR 2011 and LR 2012 in Katangi and Ikombe respectively. FYM application resulted in higher grain P than compost and control respectively. Grain P concentration was highest under sorghum/dolichos intercrop with FYM in LR 2012 (1281.69 ppm) but this was not significantly different to sorghum/pigeon pea intercrop with FYM applied at Katangi. In SR 2011 at Ikombe, grain P was highest under sorghum monocrop with FYM (119.80 ppm) but this was not different to sorghum/pigeon pea and sorghum/dolichos intercrop with FYM. Sorghum grain K was affected by cropping systems only in LR 2012 at both sites and SR 2011 in Katangi only. At Katangi in SR 2011 (0.25 cmol/kg) and LR 2012 (0.24cmol/kg), sorghum/pigeon pea intercrop produced the highest grain K but this was not different to sorghum/dolichos intercrop and pigeon pea-sorghum rotation. At Ikombe in LR 2012, sorghum/dolichos intercrop (0.24 cmol/kg) produced higher grain K though not different to monocrop, sorghum/pigeon pea intercrop and dolichos-sorghum rotation. Organic inputs also did not affect grain K in Ikombe in all the seasons and in SR 2010 at Katangi. Where organic inputs‘ effects were significant, FYM application resulted in higher K compared to compost and control. NPK balances under cassava based cropping systems were significantly lower than sorghum based cropping systems. N balances were significantly higher when cassavaor sorghumwas rotated with dolichos and compost applied. For dolichos-cassava rotation with compost applied, the balances were 21.00 Kg/ha/yr at Katangi and 14.90 Kg/ha/yr at Ikombe during SRS 2010-LRS 2011. Dolichossorghum rotation and compost applied had balances of 61.00 Kg/ha/yr and 61.87 Kg/ha/yr during SRS 2010-LRS 2011, and 25.03 Kg/ha/yr and 23.30 Kg/ha/yr during SRS 2011-LRS 2012 at Katangi and Ikombe respectivelyP losses were less negative under pigeon pea-sorghum with FYM applied during SRS 2010-LRS 2011 (0.13 Kg/ha/yr at Katangi and -0.07 Kg/ha/yr at Ikombe) and SRS 2011-LRS 2012 (-2.00 Kg/ha/yr at Ikombe and -0.63Kg/ha/yr at Ikombe). Pigeon pea-cassava rotation with compost applied had less negative P balances (-8.40 Kg/ha/yr at Katangi and _-8.96Kg/ha/yr at Ikombe) during SRS 2010-LRS 2011 . Pigeon pea rotation with sorghum and FYM applied during SRS 2010-LRS 2011 (13.60 Kg/ha/yr at Katangi and -28.20 Kg/ha/yr at Ikombe) and SRS 2011-LRS 2012 (13.5 Kg/ha/yr at Katangi and 14.53 Kg/ha/yr at Ikombe) resulted in reduced K losses while with cassava the same cropping system was superior with application of FYM during SRS 2010-LRS 2011 (27.53 Kg/ha/yr at Katangi and 60.20 Kg/ha/yr at Ikombe). Cassava/pigeon pea and sorghum/dolichos intercrop produced higher yields and would be appropriate in addressing food insecurity in the short run. However, since long-term sustainability is important for food availability to be enhanced, then farmers should be encouraged to adopt practices that would reduce losses of nutrients especially N and P. Therefore, rotation sorghum or cassava with dolichos would reduce N losses while P losses would reduce under rotation with pigeon pea with FYM and compost applied in sorghum and cassava respectively. Appropriate strategies should be sought in order to improve the productivity of the latter technology. Alternatively, strategies that would reduce nutrient losses under cassava/pigeon pea and sorghum/dolichos with FYM should be investigated in order to make them sustainable.