Effects of nitrogen and phosphorus micro-dosing on maize-pigeon pea intercrops grown under different soil moisture management practices

Declining soil fertility and moisture stress arc among the serious constraints facing agriculture in most developing countries in the world. Tanzania inclusive. Continuous farming with none or low use of fertilizer accelerates nutrient mining in the soil. Average fertilizer use under smallholder farming systems is 16 - 19 kg/ha in sub Saharan Africa. Low fertilizer adoption by smallholder farmers arc mainly due to inadequate knowledge on fertilizer usage, untimely availability of inorganic fertilizers and low affordability. Declining soil fertility may cause yield reduction of up to 50% when not addressed resulting into low food availability and poor income generation. Inadequate rainfall and uneven distribution results into prolonged dry spells. Low rainwater and poor runoff management practices under the flat cultivation increases water loss, moisture stress and soil erosion that affects plant nutrient availability and uptake. In both semi-arid and sub-humid areas. maize production is also limited by inadequate soil moisture due to fluctuation of rainfall regimes. A prolonged dry spell and change in rainfall pattern results into low crop yield and shrinkage of grazing land which increase conflicts between crop producers and pastoralist. Recommended N and P fertilizer rates have been developed in maize as the most limiting in different agro-ccological zones. However, only 12% of smallholder farmers use inorganic fertilizers due to poor capital and unavailability of fertilizer in their areas. Use of a fertilizer micro-dosing technology which is about 25% of the rate recommended, would enable farmers to start with the lowest-cost effective technology and gradually move to higher capital-intensive technologies as their resources increase. Il is an entry point for resource poor farmers to use fertilizers. Intcr-row rainwater harvesting practicesii have been reported to increase crop yield in rain-fed farming and minimizes risks of crop failure in drought prone areas. The influence of micro-dosing fertilizer and soil moisture conservation through inter-row rainwater harvesting on maize and pigeon-pea cropping systems would increase crop productivity, maximize land use efficiency, increase financial return and nutritional quality. Most recommendations of technologies arc from agronomic analysis with emphasis on maximum yield without economic analysis. As farmers do the economic analysis at farm level. profitability analysis is therefore important in recommending fertilizer micro­ dosing rate along with rainwater harvesting practices and cropping system. Therefore, the objectives of this study were: i) To determine micro-dose rates of phosphorus and nitrogen for maize crop, ii) To evaluate the effect of nitrogen and phosphorus fertilizer micro-dosing on yields, resource utilization and nutritional quality of maize and pigeonpea cropping systems as influenced by soil moisture management through rainwater harvesting technique, and iii) To determine the profitability of the micro-dose rates in maize production, as well as profitability of inter-row rainwater harvesting and fertilizer use on maize and pigeonpea cropping systems. To achieve the objectives of this study, two field experiments were conducted in Ilakala and Changarawc villages of Kilosa District in Morogoro Region Tanzania. The first experiment was laid out in split-plot involving three phosphate fertilizer types (Diammonium phosphate, Minjingu mazao and triple super phosphate), and micro-dose rates (12.5, 25, 50 and 75% of recommended N and P) with control and recommended rate (80 kg N and 40 kg P/ha). The second experiment was laid outiii in split-split plot design. It involved rainwater harvesting practices (tic ridge, open ridge and flat cultivation), cropping systems (maize sole, pigeonpea sole and 1:1 maizc-pigconpea intercrop), and fertilizer use (control, micro-dosing and recommended rate). Results indicated that Minjingu mazao fertilizer had significantly higher maize yield than DAP by 6.63% and TSP by 9.55%. Fertilizer micro dose rates at 12.5% (10 kg N and 5 kg P/ha) and 25% (20 kg N and 10 kg P/ha) increased the yield from 1012 kg/ha in control to 1928 kg/ha (90.5%) and 2394 kg/ha (137%). respectively. Tied ridges conserved soil moisture by 13.33% more than flat cultivation at 30 cm depth after ten days of rainfall. Ridges increased maize yield by 8 - 15% than Hat cultivation, but decreased pigeon pea yield by 23% than Hat cultivation. Fertilizer use increased maize yield by 93% at micro-dosing rates and 132% at recommended rate compared to control plot, l ie ridges and fertilizer use increased maize yield by 90% and pigeon pea yield by 20% than flat cultivation without fertilizer. Land use efficiency was ranging from 28 to 100% higher in intercropping than sole crop. Financial return was high ranging from 2 to 4 million shillings from maize­ pigeonpea intercrop applied with micro-dose and recommended fertilizer in both tied ridges and fiat cultivation. Maize sole had more energy than pigeonpea under tied ridges, however the highest energy was between 60.000 and 70.000 kJ/ha from intercrops and recommended fertilizer. The highest protein ranging between 400 and 500 kg/ha was from intercropping applied with micro-dose and recommended fertilizer in both tied ridges and flat. Micro-dosing rale at 12.5% was more profitable than no fertilizer application and the profitability increased towards 25%iv and 50% of recommended fertilizer rates and thereafter, decreased at recommended rate. Tied ridges and fertilizer micro-dose had higher gross margin than open ridges and flat cultivation in maize sole cropping. Pigeonpea sole cropping had higher gross margin in flat cultivation than tie and open ridges. Maize and pigeonpea intercropping under fertilizer micro-dosing had the highest gross margin above 4.5 million Tanzanian shillings. Intercropping maize and pigeonpea had high B/C ratio ranging from 6.1 to 15.6 in commercial farming and from 12 to 32 in subsistence farming. Adoption of micro-dosing fertilizer at 12.5% could be an entry point to fertilizer use and later on advance to 25% and 50% micro-dosing rates which arc more profitable with better yield under smallholder farming systems in sub-humid tropics. Inter-row rainwater harvesting and fertilizer micro-dosing would increase food and nutritional security and optimize profit in both sole and intercropping systems of sub-humid tropical farming.